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Migration of grain boundaries on heating of assemblies of small particles of molybdenum
PM
s t r e n g t h was found to be related to n u m b e r a n d s h a p e of pores a n d improved with i n c r e a s e d density. The prealloyed steel showed improved fatigue and tensile properties after h e a t t r e a t m e n t b u t t h e reverse was found in t h e case of t h e partially alloyed materials. E F F E C T S OF HIGH TEMPERATURE SINTERING ON USE OF PM ALLOY STEEL PARTS
LITERATURE
REVIEW
MIGRATION OF GRAIN BOUNDARIES ON HEATING OF A S S E M B L I E S OF SMALL PARTICLES OF MOLYBDENUM
Y.A. V o s k r e n e n s k y et al, Poroshkovaya Metallurgiya, No 6, 1992, 83-89. (In Russian). A study of p h e n o m e n a occurring during the a n n e a l i n g of Mo at t e m p e r a t u r e s up to 13O0°C is described. Recrystallization, grain b o u n d a r y migration a n d defect formation were investigated. The results are discussed in terms of models of structural transformations specified by grain boundary rearrangement.
H.I. Sanderow ( M a n a g e m e n t a n d Engineering Technologies, Dayton, Ohio, USA), Industrial tteating, Vol 59, No 6, 1992, 41-45. It is reported t h a t high t e m p e r a t u r e sintering, at 1120 to ll5O°C, resulted in improved physical and mechanical properties o f a l l o y s t e e l s . T h i s is a t t r i b u t e d to the formation of a liquid phase. Application to the production of vehicle p a r t s is emphasized.
P R O P E R T I E S OF COMPOSITE NICKELALUMINIUM POWDERS PRODUCED BY MECHANOFUSION AND PLASMA SPRAYED COATINGS
Magnesium
M. U m a k o s h i et al ( K u r u m e N a t i o n a l College of Technology, Kurume, J a p a n ) , J
Nickel
Japan Soc Powder and Powder Metallurgy, PM MATERIALS FROM RAPIDLY SOLIDIFIED FLAKES OF AZ91 MAGNESIUM ALLOY FLAKE
T. Sato et al, J Japan Inst Light Metals, Vol 42, No 6, 1992, 345-351. (In J a p a nese). Flaky Mg alloy AZ91 powders, with or w i t h o u t a d d i t i o n s of Si, Ni or Ce, were produced by atomization a n d splat cooling on a r o t a t i n g w a t e r cooled Cu roll. The powders were cold pressed and hot extruded. The as-extruded Si alloy h a d a t e n s i l e s t r e n g t h of 371 MPa. Loss of s t r e n g t h with increased t e m p e r a t u r e is reported. At 3 0 0 C superplastic elongation up to 415% was found. It is suggested t h a t Mg alloys with high specific s t r e n g t h at room t e m p e r a t u r e c o m b i n e d w i t h high ductility at elevated t e m p e r a t u r e s can be produced by the use of rapid solidification techniques.
Molybdenum E F F E C T OF BORON CARBIDE ADDITIONS ON PROPERTIES OF SINTERED MOLYBDENUM COMPACTS
T. Sakamoto, (Yatsushiro National College of Technology, Tatsushiro, J a p a n ) , J Japan
Soe Powder and Powder Metallurgy, Vol 40, No l, 1993, 112-117. (In J a p a nese), The use of B4C as a sintering aid for Mo powder was studied. The effect of B4C of densification, was small a n d with increase in t e m p e r a t u r e MoB a n d MoC were formed during sintering. Use of Ni as well as B4C results in liquid p h a s e sintering, the liquid p h a s e being a eutectic. Vicker's h a r d n e s s up to 2390 is reported for the Mo-Ni-B4 alloy.
Vol 40, No 2, 1993, 241-246. (In J a p a nese). Ni-(5 to 20) at% A1 p o w d e r s were p r e p a r e d by m e c h a n o f u s i o n a n d p l a s m a sprayed on to mild steel s u b s t r a t e s in air. The properties of t h e powders a n d coatings w e r e e x a m i n e d , t h e fine Al p a r t i c l e s a d h e r e d well to t h e Ni powders b u t did n o t c o a t uniformly. The p o w d e r s a r e r e p o r t e d to differ f r o m c o m m e r c i a l l y o b t a i n e d p o w d e r in m o r p h o l o g y a n d microstructure. Partial oxidation and s h o r t reaction times were found to inhibit t h e f o r m a t i o n of Ni a l u m i n i d e s . T h e s t r u c t u r e a n d properties of t h e coatings m a d e with t h e m e c h a n o f u s e d powders were similar to those m a d e with the commercial powders.
Silver SINTERED SILVER-TIN OXIDE CONTACT MATERIALS
S. Hofmann et al MetaU, Vol 46, No 7, 1992, 686-689. (In G e r m a n ) . It is n o t e d t h a t Ag-SnO 2 c o n t a c t materials have good switching properties b u t are difficult to sinter. It is reported t h a t by t h e m e a n s of 7 ~m A g a n d 1 p m SnO2 powders a n d Cu as a sintering aid improved sintering characteristics can be obtained.
Tungsten E F F E C T OF WIRE HISTORY ON SUBSTRUCTURE AND SECONDARY RECRYSTALLIZATION OF D O P E D TUNGSTEN
C.L. Briant et al (GEC, Schenectady, new
York, U S A ) , Metallurgical Trans A, Vol 24A, No 4, 1993, 843-851. A s t u d y of p r i m a r y a n d s e c o n d a r y recrystallization in W wire, with regard to process history, is described. Use was m a d e of annealing in situ in an electron emission microscope. The fibres, produced by wire drawing initially showed lateral growth a n d s h o r t e n i n g . At i n c r e a s e d t e m p e r a t u r e s stepwise secondary recrystallization occured. The t e m p e r a t u r e for secondary recrystallization was found to be d e p e n d e n t on heating rate a n d was higher for slower rates. This is a t t r i b u t e d to g r e a t e r r e l i e f of i n t e r n a l s t r a i n a n d reduction of t h e d r i v i n g f o r c e . No correlation between secondary recrystallization and primary grain structure is reported. POTASSIUM B U B B L E S IN T U N G S T E N WIRE
C.L. Briant (GEC, Schenectady, New York, USA), Metallurgical Trans A, Vol 24A, No 5, 1993, 1073-1084. The presence, a n d t h e need for, K bubbles in W lamp filaments is noted. The m e c h a n i s m s of formation of b u b b l e s is discussed, deformation of ellipsoids of K v a p o u r a n d growth as a result of internal pressure, sometimes with quite large sizes. A model is p r e s e n t e d for the process a n d nucleation theory is used to describe the overall process of bubble growth.
Ceramics PHASE FORMATION MICROSTRUCTURE AND HIGH TEMPERATURE STRENGTH OF ALUMINIUM NITRIDE-SILICA CERAMICS
V.A. Izhevsky et al, Poroshkovaya metallurgiya, No 6, 1992, 36-39. (In Russian). Phase formation during sintering of A1NSiO 2 m a t e r i a l s w a s i n v e s t i g a t e d a s functions of composition a n d particle size. The s t r e n g t h of t h e ceramic is r e t a i n e d on heating to 1600c'C a n d this is a t t r i b u t e d to s t r u c t u r a l s t a t e a n d o p t i m u m sintering conditions.
Electrical and magnetic materials PREPARATION OF SAMARIUM-IRONNITROGEN PERMANENT MAGNET ALLOYS
W. Lei et al (Academica Sinica, Shenyang, China), Acta MetaUurgica Sinica, Vol 29, No 3, 1993, B126-B129. (In Chinese). It is reported t h a t a p e r m a n e n t m a g n e t material, b a s e d on Sm-Fe-N, h a s been p r e p a r e d by MA, h e a t t r e a t m e n t a n d n i t r i d i n g u s i n g e l e m e n t a l Sm a n d Fe powders.
MPR September 1993 43
s t r e n g t h was found to be related to n u m b e r a n d s h a p e of pores a n d improved with i n c r e a s e d density. The prealloyed steel showed improved fatigue and tensile properties after h e a t t r e a t m e n t b u t t h e reverse was found in t h e case of t h e partially alloyed materials. E F F E C T S OF HIGH TEMPERATURE SINTERING ON USE OF PM ALLOY STEEL PARTS
LITERATURE
REVIEW
MIGRATION OF GRAIN BOUNDARIES ON HEATING OF A S S E M B L I E S OF SMALL PARTICLES OF MOLYBDENUM
Y.A. V o s k r e n e n s k y et al, Poroshkovaya Metallurgiya, No 6, 1992, 83-89. (In Russian). A study of p h e n o m e n a occurring during the a n n e a l i n g of Mo at t e m p e r a t u r e s up to 13O0°C is described. Recrystallization, grain b o u n d a r y migration a n d defect formation were investigated. The results are discussed in terms of models of structural transformations specified by grain boundary rearrangement.
H.I. Sanderow ( M a n a g e m e n t a n d Engineering Technologies, Dayton, Ohio, USA), Industrial tteating, Vol 59, No 6, 1992, 41-45. It is reported t h a t high t e m p e r a t u r e sintering, at 1120 to ll5O°C, resulted in improved physical and mechanical properties o f a l l o y s t e e l s . T h i s is a t t r i b u t e d to the formation of a liquid phase. Application to the production of vehicle p a r t s is emphasized.
P R O P E R T I E S OF COMPOSITE NICKELALUMINIUM POWDERS PRODUCED BY MECHANOFUSION AND PLASMA SPRAYED COATINGS
Magnesium
M. U m a k o s h i et al ( K u r u m e N a t i o n a l College of Technology, Kurume, J a p a n ) , J
Nickel
Japan Soc Powder and Powder Metallurgy, PM MATERIALS FROM RAPIDLY SOLIDIFIED FLAKES OF AZ91 MAGNESIUM ALLOY FLAKE
T. Sato et al, J Japan Inst Light Metals, Vol 42, No 6, 1992, 345-351. (In J a p a nese). Flaky Mg alloy AZ91 powders, with or w i t h o u t a d d i t i o n s of Si, Ni or Ce, were produced by atomization a n d splat cooling on a r o t a t i n g w a t e r cooled Cu roll. The powders were cold pressed and hot extruded. The as-extruded Si alloy h a d a t e n s i l e s t r e n g t h of 371 MPa. Loss of s t r e n g t h with increased t e m p e r a t u r e is reported. At 3 0 0 C superplastic elongation up to 415% was found. It is suggested t h a t Mg alloys with high specific s t r e n g t h at room t e m p e r a t u r e c o m b i n e d w i t h high ductility at elevated t e m p e r a t u r e s can be produced by the use of rapid solidification techniques.
Molybdenum E F F E C T OF BORON CARBIDE ADDITIONS ON PROPERTIES OF SINTERED MOLYBDENUM COMPACTS
T. Sakamoto, (Yatsushiro National College of Technology, Tatsushiro, J a p a n ) , J Japan
Soe Powder and Powder Metallurgy, Vol 40, No l, 1993, 112-117. (In J a p a nese), The use of B4C as a sintering aid for Mo powder was studied. The effect of B4C of densification, was small a n d with increase in t e m p e r a t u r e MoB a n d MoC were formed during sintering. Use of Ni as well as B4C results in liquid p h a s e sintering, the liquid p h a s e being a eutectic. Vicker's h a r d n e s s up to 2390 is reported for the Mo-Ni-B4 alloy.
Vol 40, No 2, 1993, 241-246. (In J a p a nese). Ni-(5 to 20) at% A1 p o w d e r s were p r e p a r e d by m e c h a n o f u s i o n a n d p l a s m a sprayed on to mild steel s u b s t r a t e s in air. The properties of t h e powders a n d coatings w e r e e x a m i n e d , t h e fine Al p a r t i c l e s a d h e r e d well to t h e Ni powders b u t did n o t c o a t uniformly. The p o w d e r s a r e r e p o r t e d to differ f r o m c o m m e r c i a l l y o b t a i n e d p o w d e r in m o r p h o l o g y a n d microstructure. Partial oxidation and s h o r t reaction times were found to inhibit t h e f o r m a t i o n of Ni a l u m i n i d e s . T h e s t r u c t u r e a n d properties of t h e coatings m a d e with t h e m e c h a n o f u s e d powders were similar to those m a d e with the commercial powders.
Silver SINTERED SILVER-TIN OXIDE CONTACT MATERIALS
S. Hofmann et al MetaU, Vol 46, No 7, 1992, 686-689. (In G e r m a n ) . It is n o t e d t h a t Ag-SnO 2 c o n t a c t materials have good switching properties b u t are difficult to sinter. It is reported t h a t by t h e m e a n s of 7 ~m A g a n d 1 p m SnO2 powders a n d Cu as a sintering aid improved sintering characteristics can be obtained.
Tungsten E F F E C T OF WIRE HISTORY ON SUBSTRUCTURE AND SECONDARY RECRYSTALLIZATION OF D O P E D TUNGSTEN
C.L. Briant et al (GEC, Schenectady, new
York, U S A ) , Metallurgical Trans A, Vol 24A, No 4, 1993, 843-851. A s t u d y of p r i m a r y a n d s e c o n d a r y recrystallization in W wire, with regard to process history, is described. Use was m a d e of annealing in situ in an electron emission microscope. The fibres, produced by wire drawing initially showed lateral growth a n d s h o r t e n i n g . At i n c r e a s e d t e m p e r a t u r e s stepwise secondary recrystallization occured. The t e m p e r a t u r e for secondary recrystallization was found to be d e p e n d e n t on heating rate a n d was higher for slower rates. This is a t t r i b u t e d to g r e a t e r r e l i e f of i n t e r n a l s t r a i n a n d reduction of t h e d r i v i n g f o r c e . No correlation between secondary recrystallization and primary grain structure is reported. POTASSIUM B U B B L E S IN T U N G S T E N WIRE
C.L. Briant (GEC, Schenectady, New York, USA), Metallurgical Trans A, Vol 24A, No 5, 1993, 1073-1084. The presence, a n d t h e need for, K bubbles in W lamp filaments is noted. The m e c h a n i s m s of formation of b u b b l e s is discussed, deformation of ellipsoids of K v a p o u r a n d growth as a result of internal pressure, sometimes with quite large sizes. A model is p r e s e n t e d for the process a n d nucleation theory is used to describe the overall process of bubble growth.
Ceramics PHASE FORMATION MICROSTRUCTURE AND HIGH TEMPERATURE STRENGTH OF ALUMINIUM NITRIDE-SILICA CERAMICS
V.A. Izhevsky et al, Poroshkovaya metallurgiya, No 6, 1992, 36-39. (In Russian). Phase formation during sintering of A1NSiO 2 m a t e r i a l s w a s i n v e s t i g a t e d a s functions of composition a n d particle size. The s t r e n g t h of t h e ceramic is r e t a i n e d on heating to 1600c'C a n d this is a t t r i b u t e d to s t r u c t u r a l s t a t e a n d o p t i m u m sintering conditions.
Electrical and magnetic materials PREPARATION OF SAMARIUM-IRONNITROGEN PERMANENT MAGNET ALLOYS
W. Lei et al (Academica Sinica, Shenyang, China), Acta MetaUurgica Sinica, Vol 29, No 3, 1993, B126-B129. (In Chinese). It is reported t h a t a p e r m a n e n t m a g n e t material, b a s e d on Sm-Fe-N, h a s been p r e p a r e d by MA, h e a t t r e a t m e n t a n d n i t r i d i n g u s i n g e l e m e n t a l Sm a n d Fe powders.
MPR September 1993 43