Densification of sintered iron preforms in indirect cold extrusion

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stressed vessel can be used to attain high pressure and give rapid re-cycle times. DENSIFICATION OF S I N T E R E D IRON PREFORMS IN INDIRECT COLD EXTRUSION W.Z. Misiolek, J. Lokowski ( R e n s s e l a e r Polytechnic Inst., Troy, New York, USA). The use of indirect cold extrusion of Fe preforms was described. Deformation and densification of the preforms was analysed by finite element methods• High densities were attained and this was attributed to effects of re-pressing and plastic deformation. Distribution of porosity was m e a s u r e d in s a m p l e s before and after extrusion. E x p e r i m e n t a l a n d n u m e r i c a l d a t a were compared and reported to be in good agreement. MULTI-LAYER COMPACTION OF IRON POWDERS

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ROLE OF INITIAL POWDER CHARACTERISTICS IN S U P E R S O L I D U S LIQUID PHASE SINTERING R. Tardon, R.M. German ( P e n n s y l v a n i a State University, Pennsylvania, USA). Supersolidus liquid p h a s e sintering was discussed with regard to the p r o d u c t i o n of high p e r f o r m a n c e net s h a p e p a r t s and e f f e c t s of p o w d e r c h a r a c t e r i s t i c s a n d p r o c e s s c o n d i t i o n s . S u p e r s o l i d u s liquid p h a s e s i n t e r i n g w a s i n v e s t i g a t e d for bronze, p h o s p h o r - b r o n z e and Cu-Ni alloys. The study enabled isolation of mierostructural evolution and the influence of process parameters. R e c o m m e n d a t i o n s for t h e processing of high alloy materials were made. MICROSTRUCTURAL C H A N G E S IN LIQUID PHASE SINTERING TUNGSTEN-NICKEL ALLOYS

N.D. Sopchak, W.Z. Misiolek (Rensselaer Polytechnic Inst., Troy, New York, USA). Multi-layer c o m p a c t i o n in w h i c h a c o m p a c t is built, u p by c o m p a c t i o n of successive layers of powder in the die, was described. Use of the technology was said to allow p a r t s with a high aspect ratio to be made, free from large density gradients. properties of multi-layer compacted p a r t s were investigated as functions of powder characteristics, of two Fe powders, layer thickness and density distribution.

S. Kohara (Science University of Tokyo, Tokyo, J a p a n ) . A study of microstructural changes in WNi alloys, liquid p h a s e sintered at 1500°C for various times, was described. It was reported t h a t the grain size of W increases w i t h r e d u c t i o n in %Ni a n d t h i s w a s attributed to agglomeration of W particles. The grain size is influenced by gravity with a larger W grain size at the b o t t o m of the compact. The gravity effect increased with increase in %Ni and decreased with increase in sintering time.

Sintering

Modelling

APPLIED THERMODYNAMICS ICA. Thorsen (Technical University of Denmark, Copenhagen, Denmark). The application of chemical principles, particularly thermodynamics, to sintering was d i s c u s s e d , The p r a c t i c a l u s e of thermodynamics in a n u m b e r of applications was outlined using e x a m p l e s s u c h as n o n - w e t t a b i l i t y of c e m e n t e d c a r b i d e s in b r a z i n g a n d g a s - m e t a l reactions. A gas analysis technique, linked to a c o m p u t e r p r o g r a m for performing thermodynamic calculations was described. The application to liquid p h a s e sintering of stainless steel was discussed.

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MODELLING OF HOT ISOSTATIC P R E S S I N G OF TITANIUM PARTS TO NEAR-NET SHAPE M.E. Canga et al (Carnegie-Mellon University, Pittsburg, Pennsylvania, USA). The p a p e r described a t e c h n i q u e of modelling of HIP based on visco-plastic constitutive representation of t h e r m o m e c h a n i c a l b e h a v i o u r of m e t a l powders with equations being r e p r e s e n t e d in rate form. An algorithm, using finite element m e t h o d s was used to solve the differential equations. The technique was applied to manufacture of Ti parts.

NEW GRAIN GROWTH CONCEPTS IN LIQUID PHASE SINTERING

A CONTINUUM MODEL OF POROUS STRUCTURALLY I N H O M O G E N E O U S BODY

D.F. Heaney, R.M. German (Pennsylvania State University, Pennsylvania, USA). An i n v e s t i g a t i o n o f l i q u i d p h a s e sintering in Cu-Co alloys was described. Compositions were chosen to give volume fractions of liquid p h a s e in the range 0.02 to 0.98 and Cu-Co was used because t h e r e is little difference between the densities of liquid and solid. Grain sizes were d e t e r m i n e d after sintering for 4 hours. The results were considered to link grain coarsening theory with t h e p r a c t i c e of liquid p h a s e sintering.

B. Etros et al (Donetsk Physico-Teehnical Inst., Ukraine). A m a t h e m a t i c a l m o d e l of p l a s t i c deformation of i n h o m o g e n e o u s materials was presented. Constitutive equations were developed empirically. The model was used as t h e basis of an investigation of viscous fracture and localized deformation during p r e s s u r e t r e a t m e n t of d e n s e and porous materials. The model was c o m p a r e d with experiment. Hydro-extrusion was given as a potential application of the model.

MODELLING COMPACTION OF S T E E L POWDER PARTS J.R.L. Trasorras et al (Concurrent Technologies Corp, USA). A model for the compaction of ductile metal powders was presented. The model takes into account the relationship between elasticity and deformation and the effects of plastic flow and work hardening. The model was t e s t e d experiraentally using a steel powder and details of the e x p e r i m e n t s were provided. The model was i m p l e m e n t e d in a finite element m e t h o d program. The model predictions of density fields and c o m p a c t i o n l o a d s were c o m p a r e d with experiment. Result,~ from multi-level part compaction were p r e s e n t e d to illustrate the critical influence of tooling compliance on stresses during compaction. FINITE E L E M E N T MODELLING OF MULTI-LEVEL COMPACTION OF METAL POWDERS D.T. Gethin et al (University College of Swansea, Swansea, UK). The a p p l i c a t i o n of f i n i t e e l e m e n t m e t h o d s in simulation of compaction of multi-level p a r t s was described• A n u m b e r of p a r t s h a p e s was considered to illustrate how different histories result in different p r e d i c t i o n s of d e n s i t y f i e l d s in t h e compacts. Load release and ejection modelling were also considered. C o m p a r i s o n s were m a d e with e x p e r i m e n t s to illustrate the validity of the approach. CONSTITUTIVE EQUATIONS FOR GRANULAR MATERIALS COMPACTED WITH INTERNAL FRICTION H. Shima, H. KoLera (Kyoto University, Kyoto, J a p a n ) . The p a p e r d e s c r i b e d e x p e r i m e n t a l m e a s u r e m e n t and numerical prediction o! elastic properties of sintered Fe-Ni and Fe Cu alloys as a function of density. Elastic moduli were m e a s u r e d using a resonant frequency technique. Sources of discrepancy between e x p e r i m e n t a l and predicted values were discussed, i \ semi-empirical model based on best-fit analysis was developed.

Metal injection moulding BATCH AND CONTINUOUS MIXING OF METAL INJECTION MOULDING FEEDSTOCK R. Raman, R.M. German (Pennsylvania State University, Pennsylvania, USA). The mixing of feedstocks for MIM by batch and continuous methods was described and dis;cussed. The hierarchy of process conditions influencing homogeneity and quality was identified and an insight of the f u n d a m e n t a l s needed for modelling of m i x i n g w a s given. E v i d e n c e f o r d e agglomeration and air e n t r a p m e n t during mixing was presented. The key factor in

MPR October 1994 41