The Effect of Vibrations (Sonic and Subsonic Frequencies) during the Period of Solidification on the Mechanical Properties of Castings of Gas Turbine Materials with Special Reference to H. R. Crown Max and Nimonic C. 75

TECHNISCHE HOGESCHOOL

K! U • rtÖjIEfiïUIGBOUWKUNDM ^ S o a i f r a a t 10 - DELFT

1 h AUG. 1956

THE COLLEGE OF AERONAUTICS

CRANFIELD

THÉ EFFECT OF VIBRATIONS ON THÉ

MECHANICAL PROPERTIES OF H. R.

CROWN MAX AND NIMONIC C. 75

by

VLIEGTUIGBOUWKUNDE Kanaalstraat 10 - DELFT Report No. 91 September, 1955

T H E C O L L E G E OF A E R O N A U T I C S

C R A N F I E L D

The Effect of Vibrations (Sonic and Subsonic Frequencies) during the Period of Solidification on the Mechanical P r o p e r t i e s of Castings of Gas Turbine Materials with Special Reference to H. R. Crown Max and Nimonic C. 75

by

J e r z y Jagaciak, D. C. A e . , and

Josiah W. Jones, M. Sc. , F. I. M. , A. F. R. Ae. S.

S U M M A R Y

Test castings were designed to produce data which would help in the production of gas turbine blades as castings. For castings in H, R, Crown Max the investigation is limited to the effect of sub-sonic frequencies and range of amplitudes; but in the experiments conducted on Nimonic C. 75, both sub-sonic and sonic ranges of frequency were investigated.

It can be concluded that certain frequencies notably improve the quality and properties of castings. This effect is attributed to the formation of more uniform and smaller crystals during this p r o -cess, and to an increase in density.

CONTENTS INTRODUCTION

P A R T I. E F F E C T O F SUBSONIC VIBRATIONS DURING SOLIDIFICA-TION ON THE MECHANICAL P R O P E R T I E S O F H. R. CROWN MAX.

1. F o u n d r y equipment and technique 1. 1, Vibrating t a b l e

1. 2. Melting furnace

1. 3. M e a s u r e m e n t of t e m p e r a t u r e 1. 4. Shell moulding technique 1. 5. Choice of p a t t e r n

1. 6. C l a m p s and fixtures for v i b r a t i n g the mould 2. F o u n d r y p r a c t i c e

2. 1. Casting of H. R. Crown Max 2. 2. Methods of t e s t i n g

2. 2. 1. V i c k e r s P y r a m i d H a r d n e s s T e s t 2. 2. 2. M a c r o s t r u c t u r e s

2. 2. 3. Selection of t e s t p i e c e s f r o m c a s t i n g 2. 2, 4. Mechanical t e s t s

2. 3. Conclusions from t e s t s of ten t r i a l c a s t i n g s

3. Effect of frequency on c a s t H. R, Crown Max with fixed a m p l i t u d e of 2 m m .

3. 1. Method of c a s t i n g

3. 2. T e s t i n g specific g r a v i t y of c a s t i n g s to e x p l o r e changes in p o r o s i t y

3. 3. P r e s e n t a t i o n of r e s u l t s

4. Effect of v a r y i n g amplitude with fixed frequency 4,000 v. p. m. 4. 1. Exanaination of m i c r o s t r u c t u r e s

5. Conclusions.

P A R T II. E F F E C T O F VIBRATIONS, SUB-SONIC AND SONIC, DURING SOLIDIFICATION ON THE MECHANICAL P R O P E R T I E S O F NIMONIC C. 75.

Introduction

1. D e s c r i p t i o n of a p p a r a t u s 1. 1. E l e c t r o m a g n e t i c v i b r a t o r 1. 2. Development of new furnace 1. 3. M e a s u r e m e n t of t e m p e r a t u r e 1. 4. Choice of p a t t e r n for c a s t i n g

1. 5. E l a s t i c s u s p e n s i o n and f i x t u r e s for s h e l l mould 2. F o u n d r y p r a c t i c e

2. 1. Method of c a s t i n g 2. 2. Conditions of v i b r a t i o n 2. 3. Methods of t e s t i n g

4. Conclusions from experiments v/ith Nimonic C. 75 PART IIL GENERAL SUMMARY

1. Theoretical discussion 2. General conclusions

APPENDIX Survey of literature Tables 1 - 5

Graphs 1 - 2 1

Fig. 1. Vibrating table

Fig. 2. Arc furnace, electromechanical vibrator and foundry equipment

Fig. 3. Effect of casting temperature on mechanical properties of H. R. Crown Max (diagram)

Fig. 4. Photograph and design data of pattern for test casting Fig. 5. Distribution of hardness tests

Fig. 6. Macrostructures of castings etched in acqua regia Fig. 7. Position of test pieces in test casting

Fig. 8. Microstructures of non vibrated and vibrated castings etched in acqua regia, magnification x 100

Fig. 9. As Fig. 8 but x 200 Fig. 10. As Fig. 8 but x 600

Fig. 11. Surface effect of castings as polished but not etched x 100 Fig. 12. Graph of rate of cooling of furnace used to estimate

temperature of casting

Fig. 13. Control of thickness of shell mould

Fig. 14. Arrangement of vibrator, arc furnace and mould

Fig. 15. Arrangement of furnace and mould for vibrating during casting

Fig. 16. Rate of cooling of furnace to control temperature of operation

Fig. 17. Position of test pieces in casting

Fig. 18. Attachment of mould bottom to vibrator Fig. 20. Microstructure of Nimonic C. 75 x 100 Fig. 21. Nimonic C. 75 as polished x 100

INTRODUCTION

The production of turbine blades for modern aircraft is a lengthy and complicated process. The rotor blades, for example, a r e forged and then machined to the required contours, both being expensive operations. The object of the investigation outlined in this report was to develop a new method for producing the turbine blades which would save time, reduce the cost and give improved mechanical properties.

The proposed method was to cast suitable test castings, and overcome the non- uniformity of the cast structure by vibrating the casting during the solidification period. It was anticipated that the choice of a suitable casting technique would reduce the machining to a minimum, and that the method of vibrating would give the blades the desired strength.

Hinchliff and Jones (1) carried out some work on test wedge type castings of H. R. Crown Max, vibrating them, while solidification was taking place, at sub-sonic frequencies of 23 and 48 v. p. s. They showed that while mechanical properties were dependent on casting temperatures in the non-vibrated condition, there was some improvement as a result of the vibration at all frequencies. There were critical conditions of frequency and ampli-tude for the maximum effect but frequency was by far the more important factor. They reported an absence of literature on the phenomena but a later survey is now concluded. F r o m the work on H, R. Crown Max, with new equipment which made possible greater control of conditions, the conclusions of Hinchliff and Jones a r e confirmed. The work is extended to include Nimonic C75 at sub-sonic and sonic frequencies.

H. R. CROWN MAX Composition - %

C. 0.20 Si. 1.60 Mn. 0.40 Cr. 23.00 Ni. 11.50 W. 3.00 P r o p e r t i e s

This steel possesses good strength at elevated temperatures, has specific gravity of 8.0, and in the heat-treated condition a yield s t r e s s of 30 tons per sq. in. It is usually produced in bar form. Both welding and casting properties a r e good, and the best casting temperature is about 1550°C.

NIMONIC C. 75 Composition - % C a r b o n 0.08 - 0.15 Si. 0.30 - 0.80 Mag. 1.00 m a x m . P r o p e r t i e s I r o n Sulph, Cu. 2.00 m a x m . 0.015 " 0.50 " Cr. Al. Ti. Ni. 19-21 0.40 m a x m 0,25 Balance

T e n s i l e s t r e n g t h 46 tons p e r sq. in. Rolled o r c a s t condition 0.1 P r o o f s t r e s s 30 tons p e r sq. in.

20-30% elongation

20-307o r e d u c t i o n of a r e a

Nimonic C. 75 tends to l o s e titanium due to oxidation during m e l t i n g and the o p e r a t i o n r e q u i r e s e x p e r i e n c e d c o n t r o l .

P A R T I . E F F E C T O F SUB-SQNjC VIBRATIONS DURING SOLIDIFICA-TION ON THE MECHANICAL P R O P E R T I E S O F H. R. CROWN

MAX

1- FOUNDRY EQUIPMENT AND TECHx^JIQUE

Since it was d e s i r e d to develop a technique which would be a v a i l a b l e in n o r m a l foundry p r a c t i c e , such m e t h o d s w e r e used a s far a s p o s s i b l e , but the a c t u a l equipment was i m p r o v i s e d . It was n e c e s s a r y to design and c o n s t r u c t an e l e c t r i c a r c furnace of the r e q u i r e d s m a l l c a p a c i t y and the v i b r a t i n g table had to be s t r o n g and d i m e n s i o n a l l y s u i t a b l e for a f r a m e w o r k a l r e a d y built. The o t h e r m a i n r e q u i r e m e n t s w e r e l a r g e r a n g e of f r e q u e n c i e s and a m p l i t u d e s , t o g e t h e r with c o n s i d e r a b l e load c a r r y i n g capacity. The e a s e , s i m p l i c i t y and s p e e d of o p e r a t i o n had to be c o n s i d e r e d . Such r e q u i r e m e n t s w e r e p a r t l y satisfied by the choice of a m e c h a n i c a l v i b r a t o r o p e r a t e d by an out of b a l a n c e cam.

1. 1. Vibrating table

The v i b r a t i n g table (Fig. 1) of G e r m a n design was installed. The V i b r a t o r o p e r a t e d d i r e c t l y from the m a i n s , and worked on the p r i n c i p l e of an

offset weight r o t a t i n g on a shaft d r i v e n by a s m a l l e l e c t r i c m o t o r . The t a b l e was capable of v i b r a t i n g up to 10 l b s . v/eight at 8, 000 v i b r a t i o n s p e r minute and amplitude 0.4 m m . The frequency was v a r i e d by m e a n s of a v a r i a b l e r e s i s t o r for fine a d j u s t m e n t and by a l t e r i n g the position of the l e a v e s s u p p o r t i n g the vibrating t a b l e for c o a r s e adjustment.

The apparatus was calibrated by the makers, but for the purpose of this investigation, frequency was measured for each casting, at first using a stroboscope and later a tachometer. The amplitude was measured using a microscope fitted with a m i r r o r at 45° and a scale calibrated in 1/10 mm. The microscope was located with a m i r r o r facing a 1 in. X I in. dark plate with a white thin line and mounted on a side of the vibrating table. During the test runs, the source of light was projected on a plate, and a white line appeared in a microscope as a measurable band.

1. 2. Melting furnace

A carbon a r c furnace (Fig. 2) was used for the melting of H. R. Crown Max. The current of 120-140 amps, and 80 volts was supplied by a transformer and passed through -f in. diameter carbon rods. The

capacity of the furnace was 3 lbs. and the time of heating to the required melting temperature varied between three and four hours.

Besides the slow r a t e of heating, a disadvantage of this furnace was an open spout, which, in spite of all the efforts of preheating it by blow-lamps, never reached a temperature higher than 300 to 400°C. Thus, on pouring, the spout was chilling the metal and this was a reason why the quality of some castings was not satisfactory.

1. 3, Measurement of temperature

It had been established by previous experiments that H. R. Crown Max has a wide range of temperatures where the properties of castings a r e not affected by pouring temperature (Fig, 3), For this purpose a Platinum and Pt/13%Rh. Thermocouple was used to keep the casting temperature within this range. Later, the cooling rate of the furnace was also found. (Fig, 12).

During the casting process, the temperature of the furnace was raised to 1650OC, the a r c then switched off, the temperature checked and when it reached leOO^C the carbons were withdrav/n and the melt poured into an already vibrating shell. This operation, from the withdrawal of the carbons to pouring, took five to six seconds. Therefore, the temperature in the furnace, on pouring, must always have been within the p e r

-missible range. (Fig. 12).

1, 4. Shell moulding technique

There a r e a few available types of moulds that could be used for this work, but the latest shell moulding technique seemed to be most suitable. For example, Sillimanite base moulds were used in previous work, but

b e c a u s e of t h e i r h e a v i n e s s , expense and the difficult method of p r o -duction, they w e r e not c o n s i d e r e d to be ideal for the p u r p o s e of t h i s investigation. The s m o o t h n e s s of c a s t i n g s and the p r e c i s i o n of shell moulding i n d i c a t e s that the method m a y be c o n s i d e r e d for casting of t u r b i n e b l a d e s . T o l e r a n c e s on c a s t i n g s can be r e d u c e d to a s little a s 0.002 in. to 0.005 in. The method is a l s o s u i t a b l e for m e c h a n i s a t i o n . Briefly, shell moulding i s the production of foundry moulds from r e s i n - b o u n d e d s a n d s , i n s t e a d of the t r a d i t i o n a l clay bond. A l r e a d y c o n s i d e r a b l e information and e x p e r i e n c e e x i s t s of this method. The moulding m a t e r i a l c o n s i s t s of a dry blend of s i l i c a sand and five to eight p e r cent of r e s i n . T h i s r e s i n , known a s ' t h e r m o - s e t t i n g ' r e s i n , m a y be of the phenolic, c r e s y l i c o r u r e a type, which i s produced by condensing phenol, c r e s o l or u r e a r e s p e c t i v e l y with aqueous f o r m aldehyde in the p r e s e n c e of a c a t a l y s t . The r e s u l t i n g product i s d e -h y d r a t e d , cooled and ground to a fine powder. It is i m p o r t a n t t-hat t-he sand i s quite dry and that the sand and r e s i n a r e thoroughly mixed. The method of application of shell moulding technique for the p r o d u c -tion of s h e l l moulds is e x t r e m e l y s i m p l e and fast. It i n c o r p o r a t e s the u s e of a m e t a l p a t t e r n , p r e h e a t e d to the r e q u i r e d t e m p e r a t u r e , which is allowed to be in contact with the m i x for the t i m e r e q u i r e d to m e l t the r e s i n to conform to the c o n t o u r s of the p a t t e r n . T h i c k n e s s of the s e m i m o l t e n l a y e r depends upon the t i m e of contact and the t e m p e r a -t u r e of -the p a -t -t e r n . Nex-t, -the p a -t -t e r n and -the c r u s -t a d h e r i n g a r e t r a n s f e r r e d to an oven to c o m p l e t e the baking of a shell. This r e -action t a k e s p l a c e p a r t l y by heat t r a n s f e r from the p l a t e and p a r t l y f r o m the h e a t of the oven.

A brief s u m m a r y of the p r o c e d u r e for producing s h e l l mouldings is a s follows:

* (a) Thorough mixing of sand and r e s i n in the following p r o p o r t i o n s 80 p a r t s of s a n d H (Redhill)

20 p a r t s of s a n d F (Redhill)

. 05 p a r t s of Bakelite wetting r e a g e n t (Z. 11502) 7 p a r t s of Bakelite R e s i n (R0222)

(b) Heating of p a t t e r n at 250*^0. for two m i n u t e s and application of Bakelite P a r t i n g Agent (Z11501)

(c) P a t t e r n allowed to r e m a i n in contact with m i x for about 100

s e c o n d s , in o r d e r to f o r m about f i n , thick s e m i - m o l t e n l a y e r ( F i g . 13)

(d) Curing of p a t t e r n and a d h e r i n g c r u s t in an oven at 350°C for about t h r e e m i n u t e s . At this s t a g e , it is b e s t to judge visually the quality of the s h e l l , a brownish colour indicating the c o m p l e -tion of t h i s p r o c e s s . Overbaking or burning r e s u l t s in a weak p a t t e r n .

(e) Ejection by gentle tapping. 1. 5, Choice of p a t t e r n

The object of t h i s investigation was to c a s t an a v e r a g e shape of t u r b i n e blade in p r e s e n t - d a y u s e , and a m i l d s t e e l p a t t e r n was m a d e to comply with the specification u s e d by Hinchliff and J o n e s (Ref, 1), i. e. a

s i m p l e wedge type s h a p e without c u r v a t u r e .

1. 6. F i x t u r e s and c l a m p s for v i b r a t i n g the mould

In o r d e r to hold the mould in position while vibrating, it was n e c e s s a r y to d e s i g n s p e c i a l f i x t u r e s and c l a m p s . The c l a m p s had to be e a s y to o p e r a t e and able to withstand ' b u r n i n g ' by split m e t a l . To t e s t the rigidity of the c l a m p s , the v i b r a t i o n s of the table w e r e c o m p a r e d with a n u m b e r of v i b r a t i o n s of s h e l l mould and c a s t i n g by m e a n s of a

S t r o b o s c o p e . It was found that t h e r e w e r e no differences in v i b r a t i o n s p e r m i n u t e ; the c l a m p s w e r e t h e r e f o r e c o n s i d e r e d s a t i s f a c t o r y .

2. FOUNDRY P R A C T I C E

2. 1. Casting of H. R. Crown Max

One of the m o s t i m p o r t a n t facts e s t a b l i s h e d f r o m p r e v i o u s work i s that the frequency, not the a m p l i t u d e , h a s the g r e a t e r effect on the m e c h a n i c a l p r o p e r t i e s of c a s t i n g s . The i n v e s t i g a t o r s b e l i e v e d that t h e r e may be s o m e c r i t i c a l v a l u e s of f r e q u e n c i e s and a m p l i t u d e s r e s u l t i n g in m a x i m u m i m p r o v e m e n t in m e c h a n i c a l p r o p e r t i e s of c a s t -ings. T h e r e f o r e , it was f i r s t n e c e s s a r y to find the r a n g e of f r e q u e n c i e s and a m p l i t u d e s showing m a x i m u m i m p r o v e m e n t in m e c h a n i c a l p r o p e r -t i e s .

F o r t h i s , t e n p r e l i m i n a r y c a s t i n g s w e r e m a d e , with frequency and amplitude being v a r i e d s i m u l t a n e o u s l y . By cutting s p e c i m e n s from t h e s e c a s t i n g s , and t e s t i n g them, for p r o p e r t i e s , the effect of frequency and a m p l i t u d e was d e t e r m i n e d . T h e r e s u l t s of m e c h a n i c a l t e s t s a r e found in T a b l e s 1 and 2 and plotted in G r a p h s 1 to 5. Hence, by t h i s p r o c e d u r e , it was p o s s i b l e to fix the a m p l i t u d e at the point of m a x i

2. 2. Method of testing the castings for properti^es 2 . 2 . 1 . Vickers Pyramid Hardness Test

The ten preliminary castings were tested for hardness by using a Vickers Pyramid Hardness Machine at 30 kg. load. Readings were taken every half-inch along the length of the section of casting (Fig. 5). Table 2 shows the data obtained. From this the average Vickers

Pyramid Hardness number was found for each casting. It is evident that although there is no marked increase of hardness in the case of vibrated castings, yet the values a r e more uniform throughout the whole section of blades, thus indicating a more uniform arrangement of crystals.

2. 2. 2. Macrostructures

The castings were polished and macro-etched, the etching reagent being Aqua Regia. It was found that the reagent was most efficient at about 30^^ to 35°C. Macroetchings of the castings showed the change from the columnar structure to the small and uniform equi-axed structure of the vibrated castings. The change was quite clear to visual examination but owing to the surface of the casting photographs were not very satisfactory. Examples a r e shown in Fig. 6.

2. 2. 3. Selection of test pieces from casting

The 'sampling' of the test pieces from the representative castings was considered carefully, and the best positions specified. (Fig. 7). It was decided to cut two No. 11 tensile test pieces, one 'vertical' and the other 'horizontal', together with one 'horizontal' impact test piece.

2. 2. 4. Mechanical tests

The tensile test pieces were tested on Hounsfield Testing Machines. The impact specimens were notched and tested using Hounsfield Impact Testing Machines. The values obtained are shown in Table 1. It should be pointed out that the fractures of the tensile and impact test pieces were examined for inclusions and porosity before accepting any data as satisfactory. There were no false fractures due to the machining of the test pieces.

2. 3. Conclusions from tests of ten trial castings

The data obtained from the first ten preliminary castings revealed the general effect of vibrations on mechanical properties of castings

and the following conclusions can be d r a w n from G r a p h s 1 and 2 -(a) the s u b - s o n i c v i b r a t i o n s c a u s e an i m p r o v e m e n t in m e c h a n i c a l

p r o p e r t i e s of c a s t i n g s

(b) the m o s t beneficial frequency i s about 2,500 v. p. m. and a m p l i t u d e of about 2 m m .

3, E F F E C T O F FREQUENCY ON CAST a R. CROWN MAX, AMPLITUDE BEING F T X E D AT 2 MM.

3. 1. Method of c a s t i n g

It was now decided to fix an a m p l i t u d e at 2 m m . i. e. the point of m a x i m u m i m p r o v e m e n t in m e c h a n i c a l p r o p e r t i e s , and v a r y the frequency throughout the a v a i l a b l e r a n g e . A s it was not p o s s i b l e to v a r y the frequency without a l t e r i n g the am.plitude on the e x i s t i n g v i b r a t o r , a s p e c i a l c a n t i l e v e r was designed by m e a n s of which it was p o s s i b l e to load the t a b l e m e c h a n i c a l l y , s u p p r e s s i n g the a m p l i t u d e with-out a l t e r i n g the n u m b e r of v i b r a t i o n s of the table. (Damping c o n t r o l l e v e r Fig. 2)

The c a s t i n g technique during t h i s s t a g e was exactly the s a m e a s in the c a s e of the t e n p r e l i m i n a r y c a s t i n g s d e s c r i b e d in P a r t II. To c o v e r the whole r a n g e of f r e q u e n c i e s , fifteen c a s t i n g s w e r e m a d e .

^" ^' T e s t i n g specific g r a v i t y of c a s t i n g s to e x p l o r e changes in p o r o s i t y

In o r d e r to e x p l o r e the effect of v i b r a t i o n s on c a s t i n g s a s the m e a n s of i m p r o v i n g the m e c h a n i c a l p r o p e r t i e s , it was decided to t e s t the c a s t i n g s for density. F o r t h i s p u r p o s e , s p e c i a l equipment was used, and the data i s shown in Table 3 and plotted in G r a p h 11. T h e a p p a r a t u s con-s i con-s t e d of a p r e c i con-s i o n b a l a n c e and a vacuum flacon-sk. The con-s p e c i m e n con-s w e r e d e g r e a s e d , d r i e d and weighed in a i r . The A r c h i m e d e s p r i n c i p l e was u s e d in the d e t e r m i n a t i o n of v a l u e s of d e n s i t i e s , and it was t h e r e -fore n e c e s s a r y to weight the t e s t p i e c e s again in w a t e r at 4°C. T h i s low t e m p e r a t u r e v/as m a i n t a i n e d by adding s m a l l p a r t i c l e s of i c e to the contents of the flask.

3. 3. P r e s e n t a t i o n of r e s u l t s

T h e r e s u l t s obtained in P a r t I a r e p r e s e n t e d in Table 3 and G r a p h s 6 -11, and T a b l e 4 and G r a p h s 12 - 17, and s u m m a r i s e d in the following table.

Effect on m e c h a n i c a l p r o p e r t i e s of v a r i a t i o n of frequency from

2, 000 to 6, 0Öcrv~p7m! ~~ ~~"^ ^~~""

Non v i b r a t e d 5^.QP_Q_y:P:^^- 4,000 v.p.m. T e n s i l e s t r e n g t h ~ "^ ' 40 45. 5 ~~~^ 45^ 4 tons sq. in. 0. 1% P r o o f s t r e s s 22 23 24 tons sq. in. _ _ „ _ - _ _ _ _ _ _ _ _ _ _ _ _ —A ..

Elongation "30"" 36 ' ' 38

% on 2 in, ____________,„._ Balanced i m p a c t 9 13, 3

ft. l b s .

•4

T h e i m p a c t t e s t was not a v a i l a b l e from the c a s t i n g s at 4,000 v. p. m. but t h e r e would a p p e a r to be l i t t l e difference between the effect of t h e s e f r e q u e n c i e s . It should be noted that s t r e n g t h , elongation and i m p a c t s h a r e in the i m p r o v e m e n t .

4. E F F E C T O F VARYING AMPLITUDE WITH FIXED FREQUENCIES O F 4,000 V. P. M.

To find the influence of v a r i a t i o n of a m p l i t u d e on the m e c h a n i c a l p r o p e r -t i e s of c a s -t i n g s , i-t was n e c e s s a r y -to fix -the frequency a-t 4,000 v. p. m. and v a r y the a m p l i t u d e . The c a n t i l e v e r d e s c r i b e d p r e v i o u s l y (Fig. 2) was u s e d to control the r i g h t a m p l i t u d e s . Ten c a s t i n g s w e r e made c o v e r i n g the whole r a n g e of a m p l i t u d e s . The c a s t i n g s w e r e cut and t e s t e d in the u s u a l m a n n e r . The data i s given in Table 4, and shown in G r a p h s 12 16. T h e r e i s a m a x i m u m value of amplitude to given the b e s t i m p r o v e -m e n t for both e l a s t i c and p l a s t i c p r o p e r t i e s . F r o -m the g r a p h s it could be deduced a s Maximum value P r o p e r t y of a m p l i t u d e T e n s i l e s t r e n g t h 1 to 1. 5 m m . P r o o f s t r e s s 0. 75 to 1. 25 Elongation p e r cent 0. 5 to 1. 0 Reduction in A r e a 0. 5 to 1. 0 Impact 0. 75 to 1. 25

A c o m m o n value would be about 1. 0 m m , but it s u g g e s t s that the p l a s t i c p r o p e r t i e s r e s p o n d m o r e quickly to the effect of the vibration,

4. 1, E x a m i n a t i o n of m i c r o s t r u c t u r e s

The m i c r o s t r u c t u r e c o n f i r m s the m e c h a n i c a l t e s t i n g a s the c h a r a c t e r i s t i c l a r g e d e n d r i t e in the s t a t i c c a s t i n g (Fig. 8) h a s completely d i s -a p p e -a r e d under the influence of v i b r -a t i n g -at 4, 500 v. p. m.

It i s difficult to decide if this refining effect continues at 6, 000 v. p . m. at t h i s magnification but at x 600 (Fig. 10) the i n c r e a s e d r e s o l u t i o n s u g g e s t s that the a r e a s of p r i m a r y d e p o s i t s and the coring effect i s l e s s a s a r e s u l t of vibration. The effect i s s i m i l a r to a slight annealing of c a s t s t r u c t u r e and it m a y be that the v i b r a t i o n and m i x i n g effect p r o m o t e diffucsion and s o b r i n g the s t r u c t u r e n e a r e r to equilibrium, It i s difficult to s a y that the g r a i n s i z e of the m a t r i x i s s m a l l e r but the l a r g e r n u m b e r of p r i m a r y d e p o s i t s s u g g e s t t h i s effect and in fact would p r o m o t e it.

The e x a m i n a t i o n of the ' a s p o l i s h e d ' condition s u g g e s t s that v i b r a t i o n d i s t r i b u t e s i n c l u s i o n s finely and m o r e uniformly, and the d e t e r m i n a -tion of d e n s i t y h a s s u g g e s t e d that p o r o s i t y i s r e d u c e d .

P r e s e n t t h e o r i e s of the influence of m i c r o s t r u c t u r e on m e c h a n i c a l p r o p e r t i e s would confirm that the changes i n m i c r o s t r u c t u r e between the s t a t i c and v i b r a t e d c a s t i n g would be a s s o c i a t e d with the i m p r o v e -m e n t s in e l a s t i c and p l a s t i c p r o p e r t i e s which h a v e been found,

5. CONCLUSIONS

T h e e x p e r i m e n t a l data i s p r e s e n t e d in G r a p h s 6 - 1 6 f r o m which it is concluded:

-(a) That for H. R. C r o w n Max t h e r e i s a s i m u l t a n e o u s i n c r e a s e in the value of a l l t e n s i l e p r o p e r t i e s in the v i b r a t e d c o m p a r e d with the non v i b r a t e d c a s t i n g s . Non v i b r a t e d 4,000 v.p. m. T e n s i l e s t r e n g t h t o n s . sq. in. 0. 1% proof s t r e s s t o n s . sq. in. Elongation % on 2in. Reduction in a r e a I m p a c t ft. l b s , Hounsfield 7. 4 10. 0 The i m p r o v e m e n t in e l a s t i c and p l a s t i c p r o p e r t i e s s u g g e s t h o m o -g e n i s a t i o n of the s t r u c t u r e and an a p p r o a c h to i t s m a x i m u m p o s s i b l e p r o p e r t i e s .

(b) M i c r o s c o p i c and m a c r o s c o p i c examination r e v e a l a refining of the s t r u c t u r e , and a s u b s t i t u t i o n of the t r a d i t i o n a l s t r u c t u r e

39.6 2 2 , 5 29 2 8 . 5 45 2 5 . 0 39 3 4 . 5

of elongated c r y s t a l g r a i n s for a uniform equiaxed s t r u c t u r e which confirm the i m p r o v e d m e c h a n i c a l p r o p e r t i e s r e c o r d e d above.

(c) The i m p r o v e d i m p a c t value m e e t s a m a j o r need for c a s t i n g s . (d) The r e s u l t s a r e f u r t h e r c o n f i r m e d by the i n c r e a s e in density

v/hich i s quite definite a s the effect of i n c r e a s e d frequency r e a c h e s a m a x i m u m , but f u r t h e r work to m e a s u r e density at h i g h e r f r e q u e n c i e s wouid be of t h e o r e t i c a l value.

P A R T I I E F F E C T O F VIBRATIONS, SUBSONIC AND SONIC, DUI'ING SOLIDIFICA!ION ON THE MECHANICAL PKOr-ERTIES O F NIMONIC C. 75

INTRODUCTION

It h a s been p r o v e d f r o m the e x p e r i m e n t s conducted on H, R. Crown Max that the effect of frequency on the m e c h a n i c a l p r o p e r t i e s of c a s t i n g s i s beneficial up to 67 - 83 v. p. s . , and that beyond t h i s point the effect g r a d u a l l y d i m i n i s h e s . It w a s , t h e r e f o r e , of g r e a t i n t e r e s t to find the effect of frequency h i g h e r than 116 v. p. s.

Due to the type of v i b r a t o r used, it was not p o s s i b l e to i n c r e a s e the frequency above t h i s value during the i n v e s t i g a t i o n s on H. R. Crown Max s o effort was d i r e c t e d to developing suitable a p p a r a t u s that would enable t h i s e x p e r i m e n t to be p e r f o r m e d . The expectations from such e x p e r i m e n t s w e r e a l s o i n c r e a s e d by the r e p o r t w r i t t e n by R u s s i a n w o r k e r s i n v e s t i g a t i n g a s i m i l a r p r o b l e m (Ref. 2). T h e i r a p p r o a c h was s o m e w h a t different, a s they w e r e introducing the changes in s t r u c t u r e of s t e e l s by using high-frequency c u r r e n t s . One of t h e i r m o s t r e l e v a n t c o n c l u s i o n s was that the p r o p e r t i e s of s t e e l s d u r i n g t h e s e e x p e r i m e n t s w e r e r i s i n g to a c e r t a i n m a x i m u m , falling to n o r m a l a g a i n and r i s i n g infinitely a f t e r w a r d s . I m p r e s s e d by t h i s evidence, it v/as decided to i n v e s t i g a t e the effect of h i g h e r f r e q u e n c i e s on m e c h a n i c a l p r o p e r t i e s of Nimonc C. 75 and this p a r t of the r e p o r t d e s c r i b e s the development of s u i t a b l e a p p a r a t u s , the method of c a s t i n g and the r e s u l t s obtained. The r a n g e of f r e q u e n c i e s was between 0 and 10,000 v. p. s. (Note change of units to v i b r a t i o n s p e r second for Nimonic C. 75 only).

1. DESCRIPTION OF APPARATUS 1, 1. Electromagnetic vibrator (Fig. 14)

An electric vibrator built at the College was used . The apparatus consists of a pov/er unit, an amplifier and an exciter. The associated units will vibrate mechanical structures linearly within the

fre-quency range 0-10,000 v. p. s . , and maximum thrust of 2 lbs, and maximum amplitude of 1 in, with a power requirement of 120 watts. The frequencies at which the castings were made were read from the oscillator dial. The dial was carefully calibrated during the building period of the vibrator against a cathode tube.

The amplitudes were measured by using a travelling microscope calibrated in 1/100th,mm. and focussed on perspex mounted to the exciter rod. The perspex vas coated with tinfoil except for a very thin horizontal line cut with a razor blade t> permit the light to pass from behind. This process of measuring the amplitudes v/as rather complicated, requiring great accuracy and concentration, The method was still further complicated when it was found, during the test

runs, that the wave pattern of the vibrating system was non-linear. In spite of all the efforts to eliminate a superimposed frequency by means of cushioning the vibrator, the ideal conditions were never reached, as these oscillations a r e contributed by the vibrations of the building foundations.

It was necessary to make about twenty castings to cover the whole range of available frequencies. It was thought advisable to specify these and carry out the experiments in accordance with this schedule. Realising the difficulties met while measuring the amplitudes, it was decided to obtain them at the specified frequencies prior to the casting process.

It v/as necessary to simulate the conditions met during the test runs. For this purpose, a static casting was made, placed back in a shell mould and fixed in a position 'ready for pouring'. At the selected frequencies, the amplitudes were measured and tabulated (Table 5).

1. 2. Development of new furnace

For this set of experiments, a new furnace had to be designed and built. Although similar in shape to that used in the first part of the report it had many modifications and improvements.

(a) Suitable a i r gaps w e r e i n t r o d u c e d between c r u c i b l e and furnace wall

(b) The top of the furnace was r e i n f o r c e d with mild s t e e l b a r s (c) An e l e c t r i c a l l y p r e h e a t e d spout was introduced a s a m e a n s

of i m p r o v i n g the quality of c a s t i n g s . It c o n s i s t e d of an e l e c t r i c e l e m e n t wrapped round a heat r e s i s t i n g tube. The c u r r e n t of 4. 5 a m p s , was p a s s e d from the m a i n s through a v a r i a c and t r a n s f o r m e r . The spout t e m p e r a t u r e j u s t before the pouring was about 800-900°C,

(d) The m a t e r i a l used for the building of the furnace lining was c r u s h e d s i l l i m a n i t e and s i l l i m a n i t e s i l e s t e r m i x t u r e . The c a p a c i t y of the melting pot, a s b e f o r e , was about 3 l b s . The t i m e r e q u i r e d to r a i s e the furnace to the d e s i r e d t e m p e r a t u r e v a r i e d from 1 to l | h o u r s .

1. 3. M e a s u r e m e n t of t e m p e r a t u r e

The b e s t casting t e m p e r a t u r e of Nimonic C. 75 i s about 1530 C. During the casting p r o c e s s , the t e m p e r a t u r e of m e l t was r a i s e d to about 1620°C., a r c switched off, t e m p e r a t u r e m e a s u r e d and the m e t a l p o u r e d into the a l r e a d y v i b r a t i n g shell. Fig. 16 gives the r a t e of cooling of the furnace and the o p e r a t i n g s e q u e n c e . It can e a s i l y be a s s e s s e d that the c a s t i n g t e m p e r a t u r e was always within the p e r m i s s i b l e r a n g e .

1. 4. Choice of p a t t e r n for c a s t i n g

It was decided to c a s t a r o d ^ i n . d i a m e t e r and about 6 in. long. Fig. 17 gives a detailed sketch, and the position of the test p i e c e s . Two p r e -l i m i n a r y c a s t i n g s w e r e made to s e e whether, due to e x c e s s i v e -length of rod, the c a s t i n g would not be p o r o u s at the bottom. It was found that the c a s t i n g s w e r e p e r f e c t l y sound and it was decided to u s e t h i s p a t t e r n , except for the v e r y local pipe at top of f e e d e r head.

1. 5. E l a s t i c s u s p e n s i o n s and f i x t u r e s for s h e l l mould

An e x c i t e r was capable of v i b r a t i n g safely two pounds through the r e q u i r e d r a n g e of f r e q u e n c i e s . The weight of s h e l l and casting was n e a r l y t h i s amount. It was c o n s i d e r e d n e c e s s a r y then to suspend a shell in a ' n e u t r a l p o s i t i o n ' s o that the load on the e x c i t e r would be r e d u c e d p r a c t i c a l l y to nothing. F o r t h i s p u r p o s e , a s p e c i a l c l a m p was designed to which a s h e l l could be e a s i l y fastened and a s p e c i a l f r a m e built to facilitate t h i s s u s p e n s i o n . (Fig. 15). A s d e s c r i b e d before, the

e x c i t e r rod was tapped 5BA, and in o r d e r to fasten the s h e l l p e r -manently to the rod, the s h e l l was made with a s c r e w at the bottom (Fig. 18).

2. FOUNDRY P R A C T I C E

^' ^- Method of c a s t i n g

It was decided to m a k e about twenty c a s t i n g s c o v e r i n g the whole r a n g e of f r e q u e n c i e s and a m p l i t u d e s .

The nriethod of casting, although s i m i l a r in p r o c e d u r e to that d e s c r i b e d when dealing v/ith H. R. Crown Max, involved the addition of two p e r cent Ni. Ti. o r F e . Ti. s i n c e at high t e m p e r a t u r e s Titanium tends to oxidise. The c o m p o s i t i o n s of t h o s e a r e a s follov/s

-F e . Ti. 30 p e r cent Ti. 10 p e r cent AL Balance -F e . N i . Ti. 20 p e r cent TL 10 p e r cent Al.ïSalance Ni.

In the c a s e of the c a s t s d e s c r i b e d in t h i s section, F e . Ti. was added on the c o m p l e t i o n of the m e l t i n g p r o c e s s . Obviously, t h i s m e a n t that the b a r s r e a d y for melting had to be weighed v e r y carefully. A l s o , j u s t before pouring into the s h e l l , a deoxidising r e a g e n t . Magnesium, was added in the following p r o p o r t i o n and composition

-0. 05 p e r cent Magnesium - a s 5 p e r cent Mg.- Ni. alloy

The s e q u e n c e of o p e r a t i o n s when c a s t i n g , can be s u m m a r i s e d a s follows:-(a) F u r n a c e r a i s e d to the r e q u i r e d t e m p e r a t u r e

(b) B a r weighed and fed into furnace

(c) When at the r e q u i r e d t e m p e r a t u r e , checked by optical p y r o m e t e r , additions of F e . T i . , and about h a l f - a - m i n u t e l a t e r Mg. w e r e m a d e

(d) V i b r a t o r for mould switched on and s e t at the r e q u i r e d frequency

(e) A r c switched off and t e m p e r a t u r e checked by m e a n s of Platinunn + 1 3 p e r cent Rhodiam T h e r m o c o u p l e

(f) When at about 1600°C. c a r b o n s withdrawn and m e l t p o u r e d into the a l r e a d y v i b r a t i n g shell.

This l a s t p r o c e s s took f r o m 5 to 6 s e c o n d s , t h e r e f o r e it can be

concluded that the p o u r i n g t e m p e r a t u r e m u s t a l w a y s have been at about 1530°C.

2. 2, Conditions of vibration

Owing to the limitations of power there is a tendency for amplitude to vary and decrease with increase of frequency. Above 100 v. p. s, however, the variation was only between 0. 2 and 0. 1 mm. and so frequency was considered the only variant above 100 v. p. s.

The major improvement in properties for this material was however found in the frequency range below 100 v. p. s. and there was a large variation in amplitude. Experience with H. R. Crown Max showed that the effect of amplitude was a minor one but it will be necessary to explore this effect for this alloy v/ith other apparatus when available. Also unlike H, R. Crown Max, which showed a maximum improve-ment and a critical frequency, the improved mecharjcal properties increased due to vibration to a maximum at 80 v. p. s. , decreased to a low value at 1000 v. p. s. and then gradually increased to a new maximum from 5000 to 10, OOO v. p. s. which was the limiting condi-tions of the v/ork. These effects a r e summarised in Table 5.

2. 3. Method of testing

The test pieces were cut as specified in Fig. 17 and tested for mechani-cal properties using a Hounsfield Tensometer-test specimen No. 11 and a Hounsfield Balanced Impact Test. The test data is tabulated in Table 5 and Graphs 17 - 21,

3. EFFECT OF CASTING TECHNIQUE ON MICROSTRUCTURE It was found that the best etching reagent consisted of 16 parts of saturated ferric chloride, 1 part of sulphuric acid, 3 parts of hydro-chloric acid, 16 parts of water and the best etching time was about 30 seconds,

Similar effects were found in the microstructure as with H. R.

Crown Max and examples a r e shown in Figs. 20 and 21. The typical cored dendrites of the cast structure a r e changed to the equivalent of an annealed condition with suggestions of a small grain size and uniform distribution of fine constituents.

The surface in the 'as polished' condition shows the reduction in porosity v/hich is confirmed by the determination of specific gravity. The fact that the maximum mechanical properties coincide with

maximum density is of considerable theoretical interest and justifies further experiment,

4. CONCLUSIONS FROM EXPERIMENTS WITH NIMONIC 0.75 The material showed improved mechanical properties as a result of the vibration. Unlike the H. R, Crown Max it not only showed a critical effect at subsonic frequency 80 v. p, s. but after falling to a low value similar to the non vibrated condition at 800 v, p. s. continued to r i s e again to the limiting conditions of the vibrator 10, 000 v. p. s.

The following values a r e extracted from the full data in Table 5.

Non vibrated 80 v. p. s. 10, 000 v. p. s. Tensile strength tons, sq. in. 0. 1% proof s t r e s s tons sq. in. Elongation % on 2 in. Balanced impact ft. lbs. 45 30 24 16 50 34 31 25 48 32 27 19

This alloy confirms a most attractive feature of this method, in that not only a r e the ultimate and proof strength improved but so also are the elongation and impact values.

The valve operated electromagnetic vibrator is an expensive piece of equipment both in cost and maintenance, especially if provided with enough power to overcome the limitations experienced in this work and control both frequency and amplitude for a casting of practical size. Further it is not of a suitable robust character for use on a foundry floor. The improvements associated with the lower subsonic frequency, as available from an electromechanical device, will justify the practical use of the method,

PART III. GENERAL SUMMARY 1. THEORETICAL DISCUSSION

The theoretical possibilities and mechanism of vibration on the cast structure are discussed by Hinchliff and Jones (Ref. 1). It is suggested that high mechanical properties of a material, in particu-lar a combination of strength, elongation and impact value, a r e associated with the microstructure found in forgings but the r e v e r s e of these conditions is always found with the structure formed by the ordinary mechaniom of cooling associated with castings.

The vibration, by introducing mixing effects, should r e d u c e the g r a d i e n t of t e m p e r a t u r e which p r o d u c e s the long n a r r o w d e n d r i t e of the c a s t s t r u c t u r e and by p r o m o t i n g m o r e uniform conditions of t e m p e r a t u r e and c h e m i c a l c o m p o s i t i o n p r o d u c e a m o r e uniform equiaxed c r y s t a l g r a i n s t r u c t u r e analogous to that found in a forging. It i s a l s o s u g g e s t e d that t h e s e conditions waild r e m o v e , by m o r e uniform distribution, the weakening defects always found in the con-dition of the g r a i n boundary of c a s t s t r u c t u r e s .

It i s of c o n s i d e r a b l e s u p p o r t to t h e s e t h e o r e t i c a l s u g g e s t i o n s that two quite different alloys r e s p o n d in the s a m e fundamental way to changes in m i c r o s t r u c t u r e and the a s s o c i a t e d improvem.ents in a l l m e c h a n i c a l p r o p e r t i e s . It i s a n t i c i p a t e d that s i m i l a r i m p r o v e m e n t

will t a k e p l a c e in fatigue s t r e n g t h ,

2. GENERAL CONCLUSIONS

F r o m the e x p e r i m e n t s conducted on H. R, Crown Max and Nimonic C. 75 the follov/ing conclusions can be d r a w n

-(1) T h e r e i s a m a r k e d i m p r o v e m e n t in m e c h a n i c a l p r o p e r t i e s of c a s t i n g s due to effect of v i b r a t i o n s in s u b s o n i c r a n g e . T h e m a x i -m u -m i -m p r o v e -m e n t s o c c u r at about 4, 000 to 5, 000 v, p, -m, for H. R. Crown Max and about 75 to 85 v, p. s. for Nimonic C. 75. T h e s e a r e tabulated below.

% I m p r o v e m e n t in % I m p r o v e m e n t in H. R. Crown Max Nim.onic C, 75 U l t i m a t e t e n s i l e s t r e n g t h I m p a c t % Elongation % Reduction of a r e a . 1% proof s t r e s s 14 62 30 40 10 11 61 25 28 13 (2) T h e i m p r o v e m e n t s in m e c h a n i c a l p r o p e r t i e s w e r e c o n f i r m -ed by the «changes in m i c r o s t r u c t u r e which w e r e common to both m a t e r i a l s . L a r g e c o r e d d e n d r i t e s d i s a p p e a r e d and in p l a c e of t h e m t h e r e was a finer s t r u c t u r e a p p r o a c h i n g an annealed condition. T h e r e was an i n c r e a s e in density a s s o c i a t e d with the highest t e s t r e s u l t s .

(3) It i s to be expected that g e n e r a l c a s t i n g p r o p e r t i e s would i m p r o v e in the v i b r a t i n g mould and it i s of i n t e r e s t to note t h e r e was no cold shut with the H. R. Crown Max even in the thin end of the mould r e p r e s e n t i n g the t r a i l i n g edge of a b l a d e , in spite of the fact that the

u n d e r p r e s e n t p r a c t i c e m a y be p o s s i b l e by t h i s method.

(4) T h e e l e c t r o m e c h a n i c a l v i b r a t o r i s not an expensive p i e c e of equipment and i s r o b u s t enough for u s e on a foundry floor.

(5) F u r t h e r work will be n e c e s s a r y to i n v e s t i g a t e whcfher p a r t s of a c a s t i n g of v a r y i n g t h i c k n e s s would s h a r e equally in the refining effect but with the H. R. Crown Max the c a s t i n g d e c r e a s e d f r o m ^ i n . t h i c k n e s s to a v e r y thin s e c t i o n while the Nimonic alloy was of uniform section.

(6) Both a l l o y s show the a t t r a c t i v e effect that both s t r e n g t h and p l a s t i c p r o p e r t i e s a r e i m p r o v e d ,as a l s o i s the i m p a c t value which i s often the p a r t i c u l a r l i m i t i n g factor in the u s e of c a s t i n g s . F r o m t h e s e effects t h e r e i s good hope that even fatigue p r o p e r t i e s m a y be i n c r e a s e d . ACKNOWLEDGEMENTS

The a u t h o r s a r e grateful to P r o f e s s o r J. V. Connolly, B. S . , F. R. Ae. S. for o r i g i n a l l y suggesting the work and continued i n t e r e s t . T h e Appendix was w r i t t e n by Mr. J. J a g a c i a k while a student at M a s s a c h u s e t t s

I n s t i t u t e of Technology.

REFERENCES

1. Hinchliff and J o n e s Effect on s u b - s o n i c v i b r a t i o n s during t h e p e r i o d of solidification of c a s t i n g s ,

College of A e r o n a u t i c s R e p o r t No. 89 2. Sokoloff, S. Va, Influence of u l t r a s o n i c waves on t h e

solidification of m o l t e n m e t a l . Acta P h y s i c o c h e m i c a , U. S. S. R. 3 (1935), p. 939. 3. Crav/ford, A, E. Some m e t a l l u r g i c a l a p p l i c a t i o n s of u l t r a s o n i c s . M e t a l l u r g i a , Vol. 47. No. 2 3 1 , 1953.

APPENDIX

——= __— ^ ,

SURVEY OF LITERATURE

The first known attempts to improve the properties of cast metals by means of vibrations were to irradiate ultra-sonic waves into molten metal. F i r s t Boyle and Taylor (1) found that ultrasonic

vibrations could efficiently degas light metals. Patents along similar lines were issued to Kruger and Kosman (2) and to Kerth (3) in 1934, Yahu and Reisenger (4) patented a process for treating molten metal with high frequency mechanical vibrations of 100, 000 to 200, 000 v. p. s. produced by a piezo-electric source at a low energy level and coupled into the melt by means of vibrating metal probe or through an oil bath. It was claimed that gas inclusions,- dross and slag v/ere brought to the surface by the process, producing uniform, fine grained castings, and increasing the toughness, ult.'mate tensile strength and yield strength of metal.

In the same year (1935) Sokolof (5) studied the effect of supersonic vibrations on the solidification of zinc. Frequencies in the range

600-500 k c s / s e c , were used, Sokolof reported that the vibrated metals had a different grain structure from those solidified without vibration. The grain structure showed a pronounced dendritic formation giving the appearance of coarser grain size, although close examination revealed that the actual grain size was finer.

Schmid and Ehret (6) used a magnetostrictive vibrator fixed to the crucible holding the melt. They found that, in general, the vibrated metals solidified to a finer grain size than those untreated but that the grain size was often refined non-uniformly throughout the ingot cross section. Antimony, cadmium and duralumin were used in these experi-ments, Antimony and cadmium exiiibited marked grain refinement when vibrated. Duralumin behaved peculiarly, the dispersed phase was no longer present as a grain boundary netv/ork. Coring was absent after vibration and the hardness increased from 78 to 96 VPHN,

Schmid and Roll (7) attempted to isolate the effects of frequency and intensity of vibration on grain refining. Using frequencies of 50, 9, 000 and 200, 000 v. p. s. respectively and intensities of 2 - 39 watts/ cm^, they conducted experiments on several low melting Wood's metal alloys containing various combinations of bismuth, cadmium, lead, tin and zinc. All of these alloys showed a needle-like structure when

solidified without vibration. Specimens solidified under vibration showed a disintegration of the needle structure, the effect becoming more

have g r e a t e s t effect.

T h e s e i n v e s t i g a t i o n s developed a t h e o r y that g r a i n r e f i n e m e n t is c a u s e d by frictional effects between the m e t a l l i c m e l t and the solidifying c r y s t a l s . F r o m a p p r o x i m a t e c a l c u l a t i o n s they p r o d u c e d evidence that f r a g m e n t a t i o n was p o s s i b l e u n d e r the i m p o s e d e x p e r i -m e n t a l conditions of vibration. Hiederaann (8) endeavoured to refine the g r a i n s i z e of s t e e l c a s t i n g s by high frequency v i b r a t i o n s but was u n s u c c e s s f u l .

V i b r a t i o n h a s been u s e d to d i s p e r s e l e a d in a l u m i n i u m (9) and cad-m i u cad-m in s i l u cad-m i n (6).

Of s p e c i a l i n t e r e s t i s the work done r e c e n t l y by A r m o u r R e s e a r c h Foundation, whose r e s u l t s confirm the conclusions in this R e p o r t . The i n v e s t i g a t i o n continued f:.'om 1951 to 1954. It was found that the m o s t beneficial f r e q u e n c i e s w e r e f r o m 50 - 100 v, p. s,, and the c o n c l u s i o n s d r a w n f r o m t h e i r e x p e r i m e n t s a r e quoted

-(1) The i m p a c t v i b r a t i o n u t i l i s e d in this work (about 60 v. p. s . ) p r o d u c e d a refinem.ent of the a s - c a s t g r a i n s i z e .

T h e d e g r e e of r e f i n e m e n t i s subject to the following c o n d i t i o n s : -(a) In any one alloy s y s t e m , g r a i n r e f i n e m e n t i s m o s t effective at

low alloy c o n t e n t s . That i s the n o r m a l g r a i n refining i n c r e a s i n g alloy content to r e d u c e differential effects.

(b) Refinement i s m o s t effective when the r a t e of solidification i s slow. Again, s i n c e r a p i d cooling i s itself a r e c o g n i s e d method of g r a i n refining, the s i m u l t a n e o u s use of v i b r a t i o n s can only be expected to e x e r t c o m p a r a t i v e l y little e x t r a benefit.

(c) T h e ability of v i b r a t i o n to induce g r a i n r e f i n e m e n t i s not s t r o n g l y i m p a i r e d a s the c r o s s s e c t i o n a l a r e a of the solidifying m e l t i s reduced,

(d) T h e r e l a t i o n s h i p b e t w e e n v i b r a t i o n a l i n t e n s i t y and g r a i n r e f i n e -ment m a y be r e g a r d e d a s a p p r o x i m a t e l y p a r a b o l i c in f o r m , that i s , above a c e r t a i n i n t e n s i t y l e v e l little added g r a i n r e f i n e m e n t s e e m s p o s s i b l e .

(2) T h e application of v i b r a t i o n during solidification r e s u l t e d in a pronounced r e d u c t i o n in the depth of c o l u m n a r g r a i n growth.

BIBLIOGRAPHY

R. W. Boyle and C, B. T a y l o r . T r a n s . Royal Soc. Canada, 20, (1926), 245.

F . K r u g e r and W. Koosman. G e r m a n P a t e n t No. 604, 486 (1934). V. H e r t l . A u s t r i a n P a t e n t No. 142, 886 (1934)

R. J a h n and C. R e i s e n g e r . B r i t i s h P a t e n t No. 456, 657 (1935) S. va Sokoloff. Acta P h y s i c o c h e m i c a , U. S. S. R . , 3, (1935), 939. C. Schmidt and L. E h r e t . Z. E l e c t r o c h e m . 4 3 , (1937), 869

C. Schmidt and A. Roll, Z. E l e c t r o c h e m , 45, (1939), 769 B. L O. S. F i n a l R e p o r t No. 1679.

C. M a r i n g and C. Ritzan, Z. Metallkunde. (1936), 293.

W. Bosnack and O. Tichy. A m e r i c a n F o u n d r y m a n Soc. P r e p r i n t No. 4 9 - 3 5 , (1949).

A. Cibula and R. W. Ruddle. J. Inst, M e t a l s . 76, (1949), 361. K. F. A l d e r . A r m a m e n t R e s . E s t . Metal R e p o r t No. 7/50.

P r o g r e s s R e p o r t No. 1, C o n t r a c t No. A. F. 33(038)-11208, July 1950. A r m o u r R e s e a r c h Foundation of Illinois, Institute of Technology,

P r o j e c t No. 95-1059B, C o n t r a c t No, DA. 11-022-ORD-355 (1952).

U^ C71 0 5 _{cn v\} c^ _{* .} t 4 ^ to to INS 1 0^ CO 00 1 ^3 00 to CO en • 4^ CO rf^ CO • _en 00 O 00 CO to (-* en 00 • _o 00 o C/3 o CO o • en 00 00 o to »-• co 00 -a 00 00 en co 00 00 00 C35 00 CO C A 3 00 1 1 .»f^ 00 en co 00 oo o o o o •-• en o o o • _eo o o o • o a> en o o o co o o o 1-» o en o o co o o o o 00 en o o o 00 • _o en o o o CD to 00 00 co en to t-» o to 00 C D en 00 o 00 en ^3 1 * ^ o to co CD O 00 o co en to h-« CJ5 F r e q u e n c y V. p. m. Amplitude - m m . U. T. S. t o n s / s q . in. 0 . 1 % proof s t r e s s t o n s / s q . in. Hounsfield I m p a c t Value ft. l b s . % Elongation % Reduction of a r e a V. P . H a r d n e s s No. a t 30KG load o cr r+ P (-•• a O CO 3 P o p CQ r+ D CTQ cu >

r

TABLE 2.

Table giving V. P. h a r d n e s s n u m b e r s for the f i r s t ten p r e l i m i n a r y c a s t i n g s . T e s t i n g P o s -ition 1 2 3 4 5 6 7 8 9 10 Casting No. and F r e q u e n c y 0 2500 3000 4000 4500 5000 5500 6000 6500 7009 1 2 3 4 5 6 7 235 222 220 211 209 201 _ 225 221 212 205 211 213 .. 223 220 210 213 210 -^ • • -^ 236 206 207 210 201 204 ^ 231 219 207 207 207 -_ 233 220 220 210 215 214 _ 224 219 216 208 211 200 208 227 214 213 213 208 -— i v e x a y y 216 214 215 - - 211 214 218 214 216 values

NOTE that v a l u e s given in t h i s Table a r e a l r e a d y a v e r a g e values obtained from t h r e e r e a d i n g s a c r o s s the s e c t i o n of the casting. To get a l l the ' a v e r a g e s ' 210 V. P . H a r d n e s s n u m b e r s w e r e taken.

T A B L E 3

Data obtained when i n v e s t i g a t i n g the effect of frequency, a m p l i t u d e being constant at 2 m m . • o iz; 0) ^ 4^ CO

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1 2 3 4 5 6 7 8 2, 3, 3, 4, 4, 5, 6,

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C a r b o n A r c Optical P y r o m e t e r V i b r a t i n g T a b l e C a n t i l e v e r to c o n t r o l a m p l i t u d e T a c h o m e t e r Blowlamp Shell moulds Clamp and s p r i n g to c o n t r o l a m p l i t u d e

FIG. 2 - ARC FURNACE. ELECTROMECHANICAL VIBRATOR AND FOUNDRY E Q U I P M E N T

VLIEGTÜIGBOUWKUNDE Kanaalstraat 10 - DELFT

Range of 100 C. where there i s no

change in mechanical properties,

^ X

1400 1450 1500 1550 1600 Pouring Temperature

FIG. 3 - E F F E C T OF CASTING TEMPERATURE ON MECHANICAL PROPERTIES OF H. R. CROWN MAX (DIAGRAM)

<

a

o

THREAD

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FIG. 4 - PHOTOGRAPH AND DESIGN DATA OF PATTERN FOR TEST CASTING

^ ^

1.0 m m . a m p l i t u d e

FIG, 6 - MACROSTRUCTURES O F CASTINGS E T C H E D IN AQUA REGIA a 1 '^

1 *

1 • 1

^1

( [

^ t

V i b r a t e d at 75 v . p . s . & 2 m m . 100 v . p . s . & 2 m m . H . R. CROWN MAX

MICROSTRUCTURES O F NON VIBRATED AND VIBRATED CASTINGS E T C H E D IN AQUA REGIA

Static V i b r a t e d at 75 v . p . s . & 2 m m . 100 v . p . s . & 2 m m . Static V i b r a t e d at 75 v . p . s . • ] / - <>.•

J^-

^•, -."'A^' •*' ?« 100 v . p . s . ' . ^ ^ - j S J k ^ H. R. CROWN MAX FIG. 10 - MICROSTRUCTURES O F NON

VIBRATED AND VIBRATED CASTINGS E T C H E D IN AQUA REGIA, MAGNIFICATION X 600

FIG. 11 - SURFACE E F F E C T O F CASTINGS AS POLISHED BUT NOT E T C H E D X 100

TIME IN SECONDS

FIG. 12. GRAPH OF RATE OF COOLING OF

FURNACE USED TO ESTIMATE TEMPERATURE OF CASTING.

•/2 \

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w ki 0) '4 \ii z S£ •- 6 1/ 'w I / / / / / /

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t

- " " ^ ^ ^ 2 0 4 0 6 0 BO lOO I 2 0 I 4 0 I 6 0 I 8 0

"DWELL TIME IN SECONDS

T r a n s f o r m e r Shell Mould in P o s i t i o n P r e h e a t e d Spout A m p l i f i e r P o w e r Unit A s s o c i a t e d P o w e r Units M o v i n g - C o i l E x c i t e r Unit I n s u l a t i n g Wood

FIG. 14 - ARRANGEMENT O F VIBRATOR, ARC FURNACE AND MOULD

A r c F u r n a c e E l a s t i c S u s p e n s i o n s

C l a m p

Shell mould

S o u r c e of Light for m i c r o s c o p e

Moving Coil E x c i t e r Unit

' — M i c r o s c o p e

P e r s p e x S c r e e n

FIG. 15 - ARRANGEMENT O F FURNACE AND MOULD FOR VIBRATING DURING CASTING

PIG. 16 - R A T E O F COOLING O F F U R N A C E T O C O N T R O L T E M P E R A T U R E O F O P E R A T I O N MILD S T E E L P A T T E R T .

S0mM

— 5 B. A. T h r e a d .'Special Nut E x c i t e r Rod hiH FIG. 17 - P O S I T I O N O F T E S T P I E C E S IN CA.STING F I G . l a - A T T A C H M E N T O F MOULD B O T T O M T O V I I R A T O R

static

^.:.:' •

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... V • ' . ? ^ » • * NIMONIC C. 75

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V i b r a t e d 8000 C. P . S. > * • - - . • • • • , • . . . • • * • V ' • • • . / ^ z • • • • / • . ^ - • • , • • • , - • • • . ' ^ * - • - » . • - • / ' •. ~ v v * • •-• •,.'*••.'' •• • •• • .-. 7 FIG. 20 - MICROSTRUCTURE O F NIMONIC C. 75 X 100 FIG. 21 - NIMONIC C. 75 AS POLISHED X 100 AS E T C H E D .

0 42 g D ^ 1 4 %

"N

1000 2000 3000 4000 5000 6000 (3.0) (2.0) (1.0) (0.6)

FREQUENCY VIBRATIONS PER MINUTE AMPLITUDE IN MM. (shown in brackets)

7000 (0.15)

GRAPH.!. ULTIMATE TENSILE STRESS

1000 2000 3000 4000 5000 6000 7000 8000 (3.0) (2.0) (1.0) (0.6) (0.15) FftEQUENCY VIBRATIONS PER MINUTE

AMPLITUDE IN MM. (shown in brackets)

GRAPH 2 IMPACT PROPERTIES

1000 2000 3000 4000 5000 6000 7000 (3.0) (2.0) (1.0) (0.6) (0.15) FREQUENCY VIBRATIONS PER MINUTE

AMPLITUDE IN MM. (shown in brackets)

GRAPH. 3. ELONGATION

MAXMJM IMPROVEMENl

-^ O V ,

1000 2000 3000 4000 5000 6000 7000 (3.0) (2.0) (1.0) (0.6) (0.15) FREQUENCY VIBRATIONS PER MINUTE

AMPLITUDE IN MM. (shown in brackets)

GRAPH.4. REDUCTION OF AREA

3 0 \ \ . MAXM. R S E O F o y . 000 2000 3000 4000 5000 6000| 7000 (3.0) (2.0) (1.0) (0.6) (0.15) FREQUENCY VIBRATIONS PER MINUTE

AMPLITUDE IN MM. (shown in brackets)

GRAPH.5. - I ^ P R O O F STRESS

MECHANICAL PROPERTIES O F TEST CASTINGS WITH V A R I A T I O N O F

4 ^ M ^ M«

1 •

XIMUM 1» 14'/. ilPROVEI wtFNT 2000 3000 4000 5000 6000 NUMBER O F VIBRATIONS P E R MINUTE

GRAPH. 6. ULTIMATE TENSILE STRESS.

w

<

D « MAXIMUM IMPRGVEMEN

iJ'2V._

lOQO 2000 3000 4000 5000 6000 7000 NUMBER O F VIBRATIONS P E R MINUTE

GRAPH. 7. IMPACT PROPERTIES.

1000 2000 3000 4000 5000 6000 7000 NUMBER O P VIBRATIONS P E R MINUTE

GRAPH. 8. ELONGATION PROPERTIES.

Ü « s *^ < < s. 3 0 0 f1 no g i n . ^ ^ X «

r

^ - . ^ ^ ^ IN/WM IMPROVEMENT O F 4 0 ' / 4 I , 1 ^

NUMBER O F VIBRATIONS P E R MINUTE

GRAPH. 9. REDUCTION OF AREA.

i O

IB

14

^ MAXM. RISE OF IC _{JvT^^" - .}

NUMBER O F VIBRATIONS P E R MINUTE

GRAPH. IO. • 1 % 8'^ 8 0 7-fl ^ " ( '^^^^ ) 7000 PROOF STRESS. 1000 2000 3000 4000 5000 6000

NUMBER OF VIBRATIONS P E R MINUTE ' GRAPH. II. DENSITY OF H.R. CROWN MAX

EFFECT ON MECHANICAL PROPERTIES AND DENSITY OF VIBRATION AT FIXED AMPLITUDE AND VARYING FREQUENCY.

I O I S 2 0 2-5 AMPLITUDE IN MM.

3 0 3 5 4 0

-.STATIC

VALUES MAXIMUM IMPROVEMENT 6 0 %

O-S 1 0 IS 2 0 2-5 3 0 3 5 4 0 AMPLITUDE IN MM

GRAPH. 12. ULTIMATE TENSILE STRESS _{GRAPH.I 3. IMPACT VALUES}

1 0 I S 2 - 0 2-5 3 0 3 5 AMPLITUDE IN MM. 50 < ft Ar\ k ^ _Z Ö , ^ 1 u ;.; 20 0 I / / > "~~~ r—-—, •^--STATIC VALUE 1 1 MAXIKJ "-^--^^ "[^"^""^-...^ * 1 1 HJM IMPROVEMENT 4 0 " . 1 0 I S 2 0 2S AMPLrTUDL IN MM. 3 0 4 0

GRAPH. 14. ELONGATION GRAPH.15. REDUCTION OF AREA

3 0 26 UJ w 22 u. 14 10 Mfl.XM RISE 13' '. S 1 0 IS 2 0 2 S 3 0 3-5 4 0 AMPLITUDE IN MM.

GRAPH 16 •I'jf^ PROOF STRESS

EFFECT ON MECHANICAL PROPERTIES OF VIBRATION AT FIXED FREQUENCY OF 4pOO VIBRATIONS PER MINUTE AND

4 0 x-^ MAXM. IMPBDVEM KNT 1 1% _{- - « - ^} • 4 0 6 0 lOO 120 140 160 MAXM IMPROVEMENT 5%

IPOO 2pOO 3pOO 4 P 0 0 5(00O 6pOO FREQUENCY IN V.P.S.

7 0 0 0 epOO 9IDOO IQOOO

GRAPH. 17. ULTIMATE TENSILE STRENGTH.

3POO 4 p o O 5,000 61OOO FREQUENCY IN V.P.S. — w -MAXM. IMPROVEMENT 18% 7jooo e p o o ? i 0 0 0 10,000

GRAPH. 18. IMPACT VALUES.

' ^ ^ X ^ ^ f _ _ , y — AAXM. IMPP 28% OVEMENT^ ₎ ""^x 4 0 6 0 8 0 100 I 8 0 140 I 6 0 ->--MAXM IMPROVEMENT I 10% I

1,000 2pOO ¥ > 0 0 4pOO ^ 0 0 0 epOO 7 0 0 0 « p o o 9,000 IQOOO FREQUENCY IN V.RS.

1 2 0 4 0 lOO I20 J -_!_ .X. I 6 0 MAXM RISE OF 77o. 2 , 0 0 0 3ipOO 4 p O O SPOO 6,000 FREQUENCY IN V.PS. 7 , 0 0 0 8 , 0 0 0 9 . 0 0 0 IQOOO

GRAPH. 2 0 . PROOF STRESS.

1 8 - 4 8 - 3 fl-? ^ ^ ^ " «-^ 1 2 0 4 0 6 0 8 0 lOO I 2 0 140 I 6 0 - 1 . _{. J .}

O ipOO S p O O 3 p O O 4 P O O S p O O 6,00O 7 p O O BpOO 9 , 0 0 0 l O p O O

FREQUENCY IN V.P.S.

GRAPH. 21. DENSITY.

EFFECT OF VARIATION OF FREQUENCY OF VIBRATION OF MOULD DURING SOLIDIFICATION OF CASTING ON TENSILE PROPERTIES & DENSITY OF NIMONIC C.75.