- Email: [email protected]
Review of powder extrusion technology
was r e p o r t e d to have good mechanical p r o p e r t i e s a n d w e a r r e s i s t a n c e , in comparison with c e m e n t e d carbides, was described. The hard p h a s e was Mo2NiB2 and the matrix was an Ni base alloy with Cr and Mo both p h a s e s being formed during liquid p h a s e sintering. The effects of Cr were described. Phase formation and structural evolution were described.
Measurement COMPARISON OF DENSITY M E A S U R E M E N T T E C H N I Q U E S IN PORE F R E E STRUCTURAL S T E E L S P.M. Machmeier, D.W. Smith (Michigan State University, Michigan, USA). A study of t h e m e t h o d s used for the determination of the density of fully d e n s e plain C and low alloy steels was described. Mass/volume, w a t e r displacement and He pycnometry were the m e t h o d s used and the results of density m e a s u r e m e n t s in two l a b o r a t o r i e s were analysed statistically. Measured and calculated densities were compared. FACTORS A F F E C T I N G DIMENSIONAL TOLERANCES OF HIGH STRENGTH PM STEELS C. Engstrom, C. Lindberg (HSgan~is, Sweden). The ability of PM to p r o d u c e high strength steel components, in a range of c o m p o s i t i o n s , to close d i m e n s i o n a l t o l e r a n c e s w a s d i s c u s s e d . S c a t t e r in dimensions was considered with respect to v a r i a t i o n s in p o w d e r p r o p e r t i e s . The importance of d a t a concerning the effects of composition and process p a r a m e t e r s on final d i m e n s i o n s was e m p h a s i z e d . A summary of these on dimensional scatter was presented. It was shown t h a t for some c o m p o n e n t s t h e d i m e n s i o n a l variability d e p e n d s on the powder and in o t h e r cases on the process conditions. CRACKS IN PM PARTS AND A STUDY OF THEIR GENERATION H. Tsuru, T. Nakagawa (University of Tokyo, Japan). The causes of cracking in PM components were discussed with p a r t i c u l a r r e f e r e n c e to c o m p a c t i n g conditions, powder characteristics and part s h a p e complexity. Using an electric drive CNC p r e s s w i t h six s e p a r a t e l y c o n t r o l l e d tool m o t i o n s a s t u d y of cracking in compacting was undertaken. Factors investigated included tool position, speed and applied pressure. Typical crack forming m e c h a n i s m s were identified. Press control p r o c e d u r e s for crack avoidance were suggested.
Extrusion REVIEW OF POWDER EXTRUSION TECHNOLOGY W.T. Nachtrab, P.R. Roberts (Nuclear Metals Inc, Concord, Massachusetts, USA). Hot direct extrusion was discussed with r e f e r e n c e to t h e large r e d u c t i o n s a n d t e x t u r e s which can be a t t a i n e d and t h e ability to produce long lengths of material. In application to the consolidation of metal powders to fully d e n s e rods and sections, where cast ingots would not be a m e n a b l e to e x t r u s i o n , c a n be m a d e . T o o l i n g f o r extrusion and thermomechanical capability of materials were discussed. A N ALTERNATIVE P R O C E S S ROUTE FOR PRODUCING E X T R U D E D ALUMINIUM ALLOYS M. Goncalves (Inst de Pesquisas Tecnologicas SA, Brazil). An alternative route for processing air atomized A1 alloy/SiC particle, containing s o m e larger t h a n usual particles, a n d without degassing was described. It was r e p o r t e d t h a t the e x t r u d e d materials had p r o p e r t i e s equivalent to t h o s e of ingot alloys. From the results of e x p e r i m e n t s it was shown t h a t there is a possibility of p r o d u c i n g A1 alloys w i t h o u t e x p e n s i v e process steps.
solving of process problems. The objective was s t a t e d to be improved performance of PM p a r t s at minimal cost. E x a m p l e s were driven at the use of SPC and SDE. A 15% increase in performance was r e p o r t e d with a reduction in costs caused by lowered rejection rate. E F F E C T S OF COOLING RATE ON THE DUCTILITY OF T U N G S T E N HEAVY ALLOYS M. Nakai et al (Nippon Yakin Kogyo Co, Japan). An investigation of the effects of cooling rate on the ductility of W heavy alloys was r e p o r t e d . It w a s e s t a b l i s h e d t h a t t h e n u m b e r of pores formed during cooling from liquid p h a s e sintering t e m p e r a t u r e increased with the cooling rate with resultant reduction in d u c t i l i t y . Experiments were carried out on s p e c i m e n s s u b j e c t e d to d i f f e r e n t i a l cooling. F a s t e r cooling gave smaller W grains out greater W-W contiguity which increased the brittle neck area and reduced d u c t i l i t y giving a c o r r e l a t i o n b e t w e e n structure and properties. P R E S S I N G AND SINTERING D E F E C T S IN POWDER MIXTURES
J. Zasadzinski et al (University of Mining and Metallurgy, Poland). An investigation of method for consolidation of PM materials with high density without sintering was described. The p r o c e s s u s e s s i m u l t a n e o u s cyclic e x t r u s i o n and upsetting. The effects of p r o c e s s v a r i a b l e s on s t r u c t u r e a n d p r o p e r t i e s of A1 a n d Cu alloys w e r e studied and it was r e p o r t e d t h a t t h e s e were similar to t h o s e of c a s t / w r o u g h t materials.
W.A. Kaysser et al (Max Plank Inst ffir Metallforschung, Stuttgart, Germany). It was n o t e d t h a t in p r e s s i n g and s i n t e r i n g o f m e t a l p o w d e r s t h e r e is differential densification which results in reduced m e a n density and increased defect formation and e x a m p l e s were given. An e x p e r i m e n t a l study of Mo-20 vol% fine c e r a m i c p a r t i c l e p o w d e r m i x t u r e s was described. The p r o c e s s i n g , by i s o s t a t i c compaction and sintering was monitored at all stages. Measured a n d calculated densities were c o m p a r e d and it was shown t h a t the development of severe porosity defects was related to the initial green density. Increase in green density reduced the incidence of defects. The findings were correlated with the microstructure. The e f f e c t o f g r e e n d e n s i t y on s i n t e r i n g potential, creep rate and solid state particle r e a r r a n g e m e n t was shown.
Defect control
Ferrous wear
STRUCTURE AND P R O P E R T I E S OF PM MATERIALS F O R M E D BY A NEW METHOD WITHOUT SINTERING
APPLICATION OF STATISTICS TO PROBLEM SOLVING IN SINTERING A.B. Davala (MG Industries, Valley Forge, Pennsylvania, USA). The p a p e r discussed the use of statistics in process control (SPD) and design of experiments ( S D E ) f o r PM. It w a s c o n s i d e r e d t h a t t h e u s e of t h e s e is essential for the p r o p e r development for PM and t h a t SDE can be used in the routine
SINTERED IRON-COPPER-TIN-LEAD ANTIFRICTION MATERIALS M.C. Sekeran, P. Singh (Indian Inst of Technology, Kanpur, India). The development of F e - C u - P b - M o S 2 antifriction materials was described. Optimum composition and processing conditions were established and the wear properties d e t e r m i n e d . I n c r e a s e in % M o S 2 w a s r e p o r t e d to give improved friction and wear properties.
MPR December 1992 57
Measurement COMPARISON OF DENSITY M E A S U R E M E N T T E C H N I Q U E S IN PORE F R E E STRUCTURAL S T E E L S P.M. Machmeier, D.W. Smith (Michigan State University, Michigan, USA). A study of t h e m e t h o d s used for the determination of the density of fully d e n s e plain C and low alloy steels was described. Mass/volume, w a t e r displacement and He pycnometry were the m e t h o d s used and the results of density m e a s u r e m e n t s in two l a b o r a t o r i e s were analysed statistically. Measured and calculated densities were compared. FACTORS A F F E C T I N G DIMENSIONAL TOLERANCES OF HIGH STRENGTH PM STEELS C. Engstrom, C. Lindberg (HSgan~is, Sweden). The ability of PM to p r o d u c e high strength steel components, in a range of c o m p o s i t i o n s , to close d i m e n s i o n a l t o l e r a n c e s w a s d i s c u s s e d . S c a t t e r in dimensions was considered with respect to v a r i a t i o n s in p o w d e r p r o p e r t i e s . The importance of d a t a concerning the effects of composition and process p a r a m e t e r s on final d i m e n s i o n s was e m p h a s i z e d . A summary of these on dimensional scatter was presented. It was shown t h a t for some c o m p o n e n t s t h e d i m e n s i o n a l variability d e p e n d s on the powder and in o t h e r cases on the process conditions. CRACKS IN PM PARTS AND A STUDY OF THEIR GENERATION H. Tsuru, T. Nakagawa (University of Tokyo, Japan). The causes of cracking in PM components were discussed with p a r t i c u l a r r e f e r e n c e to c o m p a c t i n g conditions, powder characteristics and part s h a p e complexity. Using an electric drive CNC p r e s s w i t h six s e p a r a t e l y c o n t r o l l e d tool m o t i o n s a s t u d y of cracking in compacting was undertaken. Factors investigated included tool position, speed and applied pressure. Typical crack forming m e c h a n i s m s were identified. Press control p r o c e d u r e s for crack avoidance were suggested.
Extrusion REVIEW OF POWDER EXTRUSION TECHNOLOGY W.T. Nachtrab, P.R. Roberts (Nuclear Metals Inc, Concord, Massachusetts, USA). Hot direct extrusion was discussed with r e f e r e n c e to t h e large r e d u c t i o n s a n d t e x t u r e s which can be a t t a i n e d and t h e ability to produce long lengths of material. In application to the consolidation of metal powders to fully d e n s e rods and sections, where cast ingots would not be a m e n a b l e to e x t r u s i o n , c a n be m a d e . T o o l i n g f o r extrusion and thermomechanical capability of materials were discussed. A N ALTERNATIVE P R O C E S S ROUTE FOR PRODUCING E X T R U D E D ALUMINIUM ALLOYS M. Goncalves (Inst de Pesquisas Tecnologicas SA, Brazil). An alternative route for processing air atomized A1 alloy/SiC particle, containing s o m e larger t h a n usual particles, a n d without degassing was described. It was r e p o r t e d t h a t the e x t r u d e d materials had p r o p e r t i e s equivalent to t h o s e of ingot alloys. From the results of e x p e r i m e n t s it was shown t h a t there is a possibility of p r o d u c i n g A1 alloys w i t h o u t e x p e n s i v e process steps.
solving of process problems. The objective was s t a t e d to be improved performance of PM p a r t s at minimal cost. E x a m p l e s were driven at the use of SPC and SDE. A 15% increase in performance was r e p o r t e d with a reduction in costs caused by lowered rejection rate. E F F E C T S OF COOLING RATE ON THE DUCTILITY OF T U N G S T E N HEAVY ALLOYS M. Nakai et al (Nippon Yakin Kogyo Co, Japan). An investigation of the effects of cooling rate on the ductility of W heavy alloys was r e p o r t e d . It w a s e s t a b l i s h e d t h a t t h e n u m b e r of pores formed during cooling from liquid p h a s e sintering t e m p e r a t u r e increased with the cooling rate with resultant reduction in d u c t i l i t y . Experiments were carried out on s p e c i m e n s s u b j e c t e d to d i f f e r e n t i a l cooling. F a s t e r cooling gave smaller W grains out greater W-W contiguity which increased the brittle neck area and reduced d u c t i l i t y giving a c o r r e l a t i o n b e t w e e n structure and properties. P R E S S I N G AND SINTERING D E F E C T S IN POWDER MIXTURES
J. Zasadzinski et al (University of Mining and Metallurgy, Poland). An investigation of method for consolidation of PM materials with high density without sintering was described. The p r o c e s s u s e s s i m u l t a n e o u s cyclic e x t r u s i o n and upsetting. The effects of p r o c e s s v a r i a b l e s on s t r u c t u r e a n d p r o p e r t i e s of A1 a n d Cu alloys w e r e studied and it was r e p o r t e d t h a t t h e s e were similar to t h o s e of c a s t / w r o u g h t materials.
W.A. Kaysser et al (Max Plank Inst ffir Metallforschung, Stuttgart, Germany). It was n o t e d t h a t in p r e s s i n g and s i n t e r i n g o f m e t a l p o w d e r s t h e r e is differential densification which results in reduced m e a n density and increased defect formation and e x a m p l e s were given. An e x p e r i m e n t a l study of Mo-20 vol% fine c e r a m i c p a r t i c l e p o w d e r m i x t u r e s was described. The p r o c e s s i n g , by i s o s t a t i c compaction and sintering was monitored at all stages. Measured a n d calculated densities were c o m p a r e d and it was shown t h a t the development of severe porosity defects was related to the initial green density. Increase in green density reduced the incidence of defects. The findings were correlated with the microstructure. The e f f e c t o f g r e e n d e n s i t y on s i n t e r i n g potential, creep rate and solid state particle r e a r r a n g e m e n t was shown.
Defect control
Ferrous wear
STRUCTURE AND P R O P E R T I E S OF PM MATERIALS F O R M E D BY A NEW METHOD WITHOUT SINTERING
APPLICATION OF STATISTICS TO PROBLEM SOLVING IN SINTERING A.B. Davala (MG Industries, Valley Forge, Pennsylvania, USA). The p a p e r discussed the use of statistics in process control (SPD) and design of experiments ( S D E ) f o r PM. It w a s c o n s i d e r e d t h a t t h e u s e of t h e s e is essential for the p r o p e r development for PM and t h a t SDE can be used in the routine
SINTERED IRON-COPPER-TIN-LEAD ANTIFRICTION MATERIALS M.C. Sekeran, P. Singh (Indian Inst of Technology, Kanpur, India). The development of F e - C u - P b - M o S 2 antifriction materials was described. Optimum composition and processing conditions were established and the wear properties d e t e r m i n e d . I n c r e a s e in % M o S 2 w a s r e p o r t e d to give improved friction and wear properties.
MPR December 1992 57