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The reduction of doped tungsten blue oxide (TBO) to non-sag tungsten — mechanistic considerations
i~
The structures of atomised white cast iron powders containing 2.5 to 4.5%C and solidified at 10 to 105°C/sec were studied. The structures were very different from those of normal white cast iron. Increased cooling rate reduced the vol fraction of eutectic but at 3.9%C the structure was wholly eutectic. The structure was refined by i n c r e a s e d cooling rate. The r a p i d l y cooled Austenite was s a t u r a t e d with C. E F F E C T S OF H E A T I N G M E T H O D D U R I N G S I N T E R I N G ON S T R U C T U R E A N D P R O P E R T I E S OF IRON-BASE MATERIALS
N.A. Nikishov et al, Metalloved
Term. Obrab. Met, No 1, 1991, 35-37. In Russian.
The structure, p h a s e composition and mechanical p r o p e r t i e s of s i n t e r e d rings made from Fe-l.8%C-2.9%Cr-l.9%Cu or an alloy containing a special Cr carbide in addition to 0.6%C were described. Process conditions are stated. Induction sintering was r e p o r t e d to yield a p r o d u c t of better quality. E F F E C T S OF A D D I T I O N S OF ALKALI METAL C O M P O U N D S O N S T R U C T U R E A N D P R O P E R T I E S OF PM CARBON STEEL
L.N. D'yachkov et al, Metalloved
Term Obrab met, No 1, 1991, 37-39. In Russian.
The addition of bicarbonates of Na, K or Li to a PM steel with 0.5 to 0.55%C was found to accelerate diffusion of C in the steel, increase the a m o u n t of C retained and yield a m o r e h o m o g e n e o u s s t r u c t u r e , particularly at low sintering temperatures. Improved mechanical properties were reported when alkali bicarbonate additions in the range 0.2 to 0.5% were made. Sintering of the compacted powders was in the range 950 to 1250°C for 2 hours. E F F E C T OF S I N T E R I N G C O N D I T I O N S ON T H E M E C H A N I C A L P R O P E R T I E S OF M E T A L I N J E C T I O N M O U L D E D (MIM) STAINLESS STEEL
M. Tsuda, H. Kyogoju, J. J a p a n Soe Powder
and Powder Metallurgy, Vol 38, No 4, 1991, 523-528. In Japanese. The effects of sintering conditions on the density and mechanical properties of MIM 304L s t a i n l e s s steel w e r e investigated. Density was increased by increased time and/or temperature. Specimens were cooled e i t h e r in N or vacuum. The N cooled specimens had higher h a r d n e s s an s t r e n g t h which were a t t r i b u t e d to nitride formation at the surface. E F F E C T S OF B O R I D E A D D I T I O N S ON S I N T E R I N G OF A U S T E N T I T I C STAINLESS STEEL POWDER COMPACTS M. Kamada et al, J. J a p a n Soc Powder and
Powder Metallurgy, Vol 38, NO 2, 1991, 529-534. In Japanese. 58
MPR
February
1992
PMLITERATURE
REVIEW
The effects of b o r i d e a d d i t i o n s on d e n s i f i c a t i o n o f 304L s t a i n l e s s s t e e l powder were studies with respect to liquid p h a s e sintering. CrB t r a n s f o r m s the Cr3B d u r i n g s i n t e r i n g a n d a e u t e c t i c liquid between this and the m a t r i x p h a s e forms. Small pores were found to d i s a p p e a r but large ones remained and t h e s e were said to be located at the site of the original CrB particles. The liquid p h a s e is r e p o r t e d to aid in densification and solidifies to Cr2B plus Austenite. Similar results are reported for FeB and NiB additions. E F F E C T S OF CARBON C O N T E N T O N S I N T E R I N G BEHAVIOUR A N D T E N S I L E P R O P E R T I E S OF S I N T E R E D MARTENSITIC STAINLESS STEELS
M. Kamada, Y. Tokunaga, J. J a p a n
Soc Powder and Powder Metallurgy, Vol 38, No 2, 1991, 535-539. In Japanese. The effects of carbon content, sintering t e m p e r a t u r e and heat t r e a t m e n t conditions on the p r o p e r t i e s on sintered martensitic 410L stainless steel were investigated. It was reported t h a t the vol fraction of ferrite at the s i n t e r i n g t e m p e r a t u r e d e c r e a s e s w i t h i n c r e a s e in %C a n d decrease in sintering temperature, aferrite is said to aid d e n s i f i c a t i o n a n d p o r e r o u n d i n g due to high self diffusion. A m i n i m u m of 0.1%C is required to produce a martensitic structure. Strength increases with %C due to e n h a n c e d densiflcation.
Molybdenum B O R O N I S I N G T R E A T M E N T FOR SINTERED MOLYBDENUM-NICKEL POWDER COMPACTS
T. Sakamoto. J. J a p a n Soe Powder and
Powder Metallurgy, Vol 38, No 4, 1991, 492-498. In Japanese. Boronising using BoB, NiB and B4C in an a c t i v a t o r c o n t a i n i n g NH4C1, BaF3 or Na2CO3, of sintered Mo and Mo-38% was investigated. The b o r o n i s e d alloys were e x a m i n e d by X-ray diffraction and electron probe micro analysis (EPMA). It was found t h a t the thickness of the boronised layers increased with time a n d / o r temperature. The layers c o n t a i n e d MoB, Mo2B a n d Mo2B5. The c h l o r i d e or f l u o r i d e w e r e identified w h e n p r e s e n t in the activator. NiB powder was not found to increase the boride layer thickness.
Titanium P R O D U C T I O N OF T I T A N I U M BASE M E T A L MATRIX C O M P O S I T E S ( M M C ) BY VACUUM PLASMA SPRAYING
P.A. Dearnley, K.A. Roberts, (University of Cambridge, Cambridge, England), Powder Metallurgy, Vol 34, No 2, 1991, 112-118.
~
The p r o d u c t i o n of Ti-base MMC by vacuum p l a s m a spraying has been studied by high s p e e d cinematography. The p l a s m a was found to show fluctuations in length. The m e c h a n i s m of co-spray deposition has been elucidated by use of a wipe test and is d e s c r i b e d as e m b e d d i n g of c e r a m i c p a r t i c l e s into t h e s u b s t r a t e f o l l o w e d by covering w i t h Ti splats. M e t a l / c e r a m i c collisions in flight are r e p o r t e d to be of small significance. MICROSTRUCTURE AND MECHANICAL P R O P E R T I E S OF R E S I S T A N C E SINTERED TITANIUM
C.H. Lui, P.W. Kao, Scripta MetaU Mater,
Vol 24 No 12, 1990, 2279-2284. An i n v e s t i g a t i o n into t h e r e s i s t a n c e s i n t e r i n g o f Ti, w h i c h s h o w e d r a p i d d e n s i f i c a t i o n to d e n s i t y above 96% in a b o u t 2 s e c o n d s , is d e s c r i b e d . T h e r e s i s t a n c e s i n t e r e d Ti was r e p o r t e d to have higher s t r e n g t h t h a n conventional PM Ti. T h e r a p i d d e n s i f i c a t i o n is attributed to the formation of a liquid p h a s e at p a r t i c l e b o u n d a r i e s w h i c h is squeezed into adjacent cavities by applied pressure.
Tungsten T H E R E D U C T I O N OF D O P E D T U N G S T E N BLUE O X I D E ( T B O ) TO NON-SAG T U N G S T E N - A L I T E R A T U R E REVIEW
B. Zeiler et al, (Technical University, Vienna, Austria), Int J. Refractory Metals and
Hard Materials, Vol 10 No 2, 1991, 83-90. A review of the literature concerning the doping of TBO with I~ A1 or Si and the s u b s e q u e n t H r e d u c t i o n to metal, was presented. The effects of the p r o p e r t i e s of the blue oxide with respect to doping reactions, the formation of intermediate W o x i d e s a n d ~W a n d t h e r e d u c t i o n of dopants containing compounds on reduction kinetics were discussed. Conclusions on t h e t h e o r i e s of d o p a n t i n c o r p o r a t i o n , a review of r e d u c t i o n p a r a m e t e r s and p o w d e r properties were presented. T H E R E D U C T I O N OF D O P E D T U N G S T E N B L U E O X I D E ( T B O ) TO NON-SAG T U N G S T E N - M E C H A N I S T I C CONSIDERATIONS
B. Zeiler et al, (Technical University, Vienna, Austria), Int J. Refractory Metals a n d
Hard Materials, Vol 10, No 2, 1991, 91105. Experimental observations of the reduction of d o p e d TBO are described. Differences were noted between the sub oxides formed on reduction of d o p e d and u n - d o p e d TBO. A m e c h a n i s m for t h e i n c o r p o r a t i o n of t h e d o p a n t s , chemical vapour transfer and overgrowth phases, in
z
~ Jam mIII i~ =1 a~'a~ iI.111]lql = J all ::kval | ~ ' , •
tire reduction is discussed. I[ w a s found t h a t d o p a n t p h a s e particle size i n c r e a s e s with r e d u c t i o n t e m p e r a t u r e .
is s h o w n to s e g r e g a t e at grain b o u n d a r i e s a n d pores in W billets or crack facets in rods a n d wires.
SOLUTION SOFTENING OF IRIDIUM AND RHENIUM IN TUNGSTEN AT ROOM TEMPERATURE
AN INVESTIGATION OF COMPACTION I N P R E S S I N G O F T U N G S T E N HEAVY ALLOYS
A. Lui el al, (Arizona State University, Tempe, Arizona, USA), h~,t J. Refractory
A.L. Lobov et al, (Central Scientific Res e a r c h I n s t i t u t e for F e r r o u s Metallurgy, USSR), Stal', No 10, 1990, 94-97. I n
Metals a n d H a r d Materials, Vol 10, No 2, 1991, 1 0 7 1 1 4 .
Russian.
A t t e n t i o n w a s d r a w n to t h e l o w t e m p e r a t u r e b r i t t l e n e s s of W a n d to a l l e m p t s lo overcome t h i s hy alhrying a n d t h e use of high p u r i t y W. It was s h o w n t h a t the addition of RE to W results in i n c r e a s e s in room t e m p e r a t m e ductility a n d h i g h t e m p e r a t u r e s t r e n g t h . The possible use of Ir was discussed. An investigation of t h e room temperature structure and properties, which h a d theob.jective of e l u c i d a t i n g t h e m e c h a n i s m of sold s o l u t i o n s o f t e n i n g in WIr a n d Ir in t h o r i a t e d W, w a s described.
A s t u d y of c o m p a c t i o n p r o c e s s e s in W-Ni a n d W-Ni-Fe heavy alloys is described. The p o w d e r s used, t h e r e l a t i o n s h i p s b e t w e e n compact density and compressive strength a n d t h e c o m p a c t i n g p r e s s u r e a n d alloy c o m p o s i t i o n are considered.
EFFECTS OF NICKEL:IRON RATIO ON MECHANICAL PROPERTIES OF T U N G S T E N HEAVY ALLOYS
PRODUCTION OF SILVER-TIN OXIDE ELECTRICAL CONTACTS FROM ELECTROLESSLY PLATED COMPOSITE POWDERS
Electrical a n d m a g n e t i c materials
Soc P o w d e r a n d Powder Metallurgy, ~7~1 38, No 4, 1991, 540-547. In Japanese.
H. C h a n g et al, (University of Utah, USA),
"Fire influences of Ni:Fe ratio a n d t h e a d ( l i t i o n o f Co (:,n t h e m e c h a n i c a l properties of W-based heavy alloys have been studied. The Ni:Fe ratio varied in t h e range one p a r t of Ni to one to ten p a ~ s of Fe a n d t h e Co a d d i t i o n s were e i t h e r 0.5 of 1.Owl~?a. M a x i m u m values for s t r e n g t h a n d ductility were l o u n d at Ni:Fe - 1:4 a n d 0.5%Co. The r e s u l t s were d i s c u s s e d in t e r m s of m i c r o s t r u c t u r e , sizes of fracture s o u r c e s and matrix toughness.
Sintered electrical c o n t a c t m a t e r i a l were p r e p a r e d from SnO 2 p o w d e r s w h i c h h a d been p l a t e d with Ag by a novel m e t h o d . The m e c h a n i s m of e l e c t r o l e s s p l a t i n g w a s investigated u s i n g m i x e d p o t e n t i a l theory. The p o w d e r s a n d s i n t e r e d c o n t a c t s w e r e e x a m i n e d by s c a n n i n g electron m i c r o s c o p y and the electrical and mechanical p r o p e r t i e s were m e a s u r e d .
:
strengths obtained.
above
5 0 0 K g l . ' m m ~ we re
MICROSTRUCTURAL CHARACTERISATION OF CEMENTED CARBIDES USING SCANNING ELECTRON MICROSCOPY (SEM) WITH AUTOMATIC IMAGE ANALYIS (AIA) A. Nordgren, (Swedish I n s t i t u t e for Metals R e s e a r c h , S t o c k h o l m , S w e d e n ) , I n t J.
Refractory Metals a n d t l a r d MateriaLs, Vol 10, No 2, 1991, 61-81. The s t r u c t u r e s of WC-Co a n d WC 07-Co (7 - cubic p h a s e s o t h e r t h a n WC) were s t u d i e d by SEM w i t h AIA. The s t u d y was a i m e d at developing t h e use of AIA with c e m e n t e d c a r b i d e s w i t h r e g a r d to t h e d e t e r m i n a t i o n ofcarbide grain size, v o l u m e fraction and contiguity. Optimised specimen preparation, high resolution m i c r o s c o p y a n d i m a g e p r o c e s s i n g were f o u n d to be required. Two m e t h o d s of o b t a i n i n g back s c a t t e r e d electron e o n t r a s t , a t o m i c n u m b e r a n d channelling, were used. The r e s u l t s were r e p o r t e d to be sufficient accuracy for t h e m e t h o d to be u s e d for t h e c h a r a c t e r i s a t i o n of a wide range of h a r d materials.
T. Kaneko, J. Japat~
CONTROL OF PARTICLE SIZE OF TUNGSTEN POWDER
Materials Science a n d E n g i n e e r i n g B, Vol BS, No 2 1991, 99-105.
H a r d m a t e r i a l s a n d tool steels
I). S u e t al, E n g a n d Chcm Metallurgy, Vol
10, No 4, 1989, 67-7"0. I'n Chinese. The eflbcts of p r o c e s s variables on t h e particle size of W powder m a d e by t h e r e d u c t i o n of W blue oxide were investigated in i n d u s t r i a l s c a l e e x p e r i m e n t s . T h e optimum process conditions were e s t a b l i s h e d a n d a n e q u a t i o n for t h e prediction of particle size w a s deduced.
BEHAVIOUR OF TRACE ELEMENT POTASSIUM IN DOPED TUNGSTEN M. Zhou et al, J. Central South l n s t i t u t e o f
M i n i n g a n d Metallurgy (China, Vo120, No 4, 1989, 390-397. In Chinese. The d i s t r i b u t i o n a n d b e h a v i o u r of K in W p o w d e r have been e x a m i n e d as a f u n c t i o n of powder particle size. K c o n t e n t w a s f o u n d to increase with d e c r e a s e in particle size. K
HIGH STRENGTH MICROGRAINED CEMENTED CARBIDES T. F u k a t s u et al, (Toshiba Tungaloy Co Ltd, Kawasaki, J a p a n ) , I n t J. Refractory Metals
a n d H a r d Materials, Vol 10, No 2, 1991, 61-81. An i n v e s t i g a t i o n i n t e n d e d to give i m p r o v e d p r o p e r t i e s to MC-Co m a t e r i a l s is described. C a u s e s of p r o p e r t y reduction, p o r e s , Co p o o l s c o a r s e W g r a i n s a n d i m p u r i t i e s are d i s c u s s e d . The effects of carbide grain growth, inhibitors a n d t h e purity of the raw materials were i n v e s t i g a t e d w i t h respect to d e f e c t s a p p e a r i n g on t h e f r a c t u r e s u r f a c e o f t r a n s v e r s e r u p t u r e d s p e c i m e n s . The r e s u l t s were s h o w n to d e m o n s t r a t e t h a t p o w d e r p u r i t y w a s m o s t significant a n d by u s i n g high p u r i t y WC p o w d e r t r a n s v e r s e r u p t u r e
OPTIMISATION OF PROCESSING PARAMETERS FOR DIRECT VACUUM SINTERING OF A T15 HIGH SPEED STEEL (HSS) M. S a n t o s et al, (LNETI, Lisbon Portugal),
P o w d e r Metallurgy, Vol 34. No 2, 1991, 93100. A s t u d y of t h e v a c u u m s i n t e r i n g of w a t e r a t o m i s e d T15 HSS is described. Effects of p r o c e s s variables, c o m p a c t i n g p r e s s u r e and s i n t e r i n g t e m p e r a t u r e and t h e t i m e were investigated, metallographic and f r a c t o g r a p h i c s t u d i e s w e r e c a r r i e d out. H i g h e s t s t r e n g t h s were a s s o c i a t e d with low p o r o s i t y , t h e a b s e n c e of g r a i n b o u n d a r y films a n d a fine h o m o g e n e o u s m i c r o s t r u c t u r e . It is s u g g e s t e d t h a t cracks e x i s t i n g in fine carbide particles are s u b critical in a f r a c t u r e m e c h a n i c s s e n s e S t u d i e s of g r o u n d a n d g r o u n d p l u s polished specimens showed that grinding a l o n e w a s a d e q u a t e for p r e p a r a t i o n of quality control s p e c i m e n s .
TUNGSTEN CARBIDE HARD METALS CEMENTED WITH FERRO-ALLOYS T. Farooq, T2. Davies, (UMIST/University of Manchester, Manchester, E n g l a n d ) , I n t J.
P o w d e r Metallurgy, Vol 27, No 4, 1991, 34 7-355. WC c e m e n t e d with ferro-alloys ( s t a i n l e s s steel or Fe-Co-NiMoB m a t r i x ) were c h a r a c t e r i s e d for s t r u c t u r e , h a r d n e s s . s t r e n g t h a n d t o u g h n e s s . It w a s f o u n d t h a t high d e n s i t y w a s a t t a i n e d , t h e r e w a s good bonding and high hardness when a s t a i n l e s s steel m a t r i x w a s used. The Fe-
MPR February 1992 59
The structures of atomised white cast iron powders containing 2.5 to 4.5%C and solidified at 10 to 105°C/sec were studied. The structures were very different from those of normal white cast iron. Increased cooling rate reduced the vol fraction of eutectic but at 3.9%C the structure was wholly eutectic. The structure was refined by i n c r e a s e d cooling rate. The r a p i d l y cooled Austenite was s a t u r a t e d with C. E F F E C T S OF H E A T I N G M E T H O D D U R I N G S I N T E R I N G ON S T R U C T U R E A N D P R O P E R T I E S OF IRON-BASE MATERIALS
N.A. Nikishov et al, Metalloved
Term. Obrab. Met, No 1, 1991, 35-37. In Russian.
The structure, p h a s e composition and mechanical p r o p e r t i e s of s i n t e r e d rings made from Fe-l.8%C-2.9%Cr-l.9%Cu or an alloy containing a special Cr carbide in addition to 0.6%C were described. Process conditions are stated. Induction sintering was r e p o r t e d to yield a p r o d u c t of better quality. E F F E C T S OF A D D I T I O N S OF ALKALI METAL C O M P O U N D S O N S T R U C T U R E A N D P R O P E R T I E S OF PM CARBON STEEL
L.N. D'yachkov et al, Metalloved
Term Obrab met, No 1, 1991, 37-39. In Russian.
The addition of bicarbonates of Na, K or Li to a PM steel with 0.5 to 0.55%C was found to accelerate diffusion of C in the steel, increase the a m o u n t of C retained and yield a m o r e h o m o g e n e o u s s t r u c t u r e , particularly at low sintering temperatures. Improved mechanical properties were reported when alkali bicarbonate additions in the range 0.2 to 0.5% were made. Sintering of the compacted powders was in the range 950 to 1250°C for 2 hours. E F F E C T OF S I N T E R I N G C O N D I T I O N S ON T H E M E C H A N I C A L P R O P E R T I E S OF M E T A L I N J E C T I O N M O U L D E D (MIM) STAINLESS STEEL
M. Tsuda, H. Kyogoju, J. J a p a n Soe Powder
and Powder Metallurgy, Vol 38, No 4, 1991, 523-528. In Japanese. The effects of sintering conditions on the density and mechanical properties of MIM 304L s t a i n l e s s steel w e r e investigated. Density was increased by increased time and/or temperature. Specimens were cooled e i t h e r in N or vacuum. The N cooled specimens had higher h a r d n e s s an s t r e n g t h which were a t t r i b u t e d to nitride formation at the surface. E F F E C T S OF B O R I D E A D D I T I O N S ON S I N T E R I N G OF A U S T E N T I T I C STAINLESS STEEL POWDER COMPACTS M. Kamada et al, J. J a p a n Soc Powder and
Powder Metallurgy, Vol 38, NO 2, 1991, 529-534. In Japanese. 58
MPR
February
1992
PMLITERATURE
REVIEW
The effects of b o r i d e a d d i t i o n s on d e n s i f i c a t i o n o f 304L s t a i n l e s s s t e e l powder were studies with respect to liquid p h a s e sintering. CrB t r a n s f o r m s the Cr3B d u r i n g s i n t e r i n g a n d a e u t e c t i c liquid between this and the m a t r i x p h a s e forms. Small pores were found to d i s a p p e a r but large ones remained and t h e s e were said to be located at the site of the original CrB particles. The liquid p h a s e is r e p o r t e d to aid in densification and solidifies to Cr2B plus Austenite. Similar results are reported for FeB and NiB additions. E F F E C T S OF CARBON C O N T E N T O N S I N T E R I N G BEHAVIOUR A N D T E N S I L E P R O P E R T I E S OF S I N T E R E D MARTENSITIC STAINLESS STEELS
M. Kamada, Y. Tokunaga, J. J a p a n
Soc Powder and Powder Metallurgy, Vol 38, No 2, 1991, 535-539. In Japanese. The effects of carbon content, sintering t e m p e r a t u r e and heat t r e a t m e n t conditions on the p r o p e r t i e s on sintered martensitic 410L stainless steel were investigated. It was reported t h a t the vol fraction of ferrite at the s i n t e r i n g t e m p e r a t u r e d e c r e a s e s w i t h i n c r e a s e in %C a n d decrease in sintering temperature, aferrite is said to aid d e n s i f i c a t i o n a n d p o r e r o u n d i n g due to high self diffusion. A m i n i m u m of 0.1%C is required to produce a martensitic structure. Strength increases with %C due to e n h a n c e d densiflcation.
Molybdenum B O R O N I S I N G T R E A T M E N T FOR SINTERED MOLYBDENUM-NICKEL POWDER COMPACTS
T. Sakamoto. J. J a p a n Soe Powder and
Powder Metallurgy, Vol 38, No 4, 1991, 492-498. In Japanese. Boronising using BoB, NiB and B4C in an a c t i v a t o r c o n t a i n i n g NH4C1, BaF3 or Na2CO3, of sintered Mo and Mo-38% was investigated. The b o r o n i s e d alloys were e x a m i n e d by X-ray diffraction and electron probe micro analysis (EPMA). It was found t h a t the thickness of the boronised layers increased with time a n d / o r temperature. The layers c o n t a i n e d MoB, Mo2B a n d Mo2B5. The c h l o r i d e or f l u o r i d e w e r e identified w h e n p r e s e n t in the activator. NiB powder was not found to increase the boride layer thickness.
Titanium P R O D U C T I O N OF T I T A N I U M BASE M E T A L MATRIX C O M P O S I T E S ( M M C ) BY VACUUM PLASMA SPRAYING
P.A. Dearnley, K.A. Roberts, (University of Cambridge, Cambridge, England), Powder Metallurgy, Vol 34, No 2, 1991, 112-118.
~
The p r o d u c t i o n of Ti-base MMC by vacuum p l a s m a spraying has been studied by high s p e e d cinematography. The p l a s m a was found to show fluctuations in length. The m e c h a n i s m of co-spray deposition has been elucidated by use of a wipe test and is d e s c r i b e d as e m b e d d i n g of c e r a m i c p a r t i c l e s into t h e s u b s t r a t e f o l l o w e d by covering w i t h Ti splats. M e t a l / c e r a m i c collisions in flight are r e p o r t e d to be of small significance. MICROSTRUCTURE AND MECHANICAL P R O P E R T I E S OF R E S I S T A N C E SINTERED TITANIUM
C.H. Lui, P.W. Kao, Scripta MetaU Mater,
Vol 24 No 12, 1990, 2279-2284. An i n v e s t i g a t i o n into t h e r e s i s t a n c e s i n t e r i n g o f Ti, w h i c h s h o w e d r a p i d d e n s i f i c a t i o n to d e n s i t y above 96% in a b o u t 2 s e c o n d s , is d e s c r i b e d . T h e r e s i s t a n c e s i n t e r e d Ti was r e p o r t e d to have higher s t r e n g t h t h a n conventional PM Ti. T h e r a p i d d e n s i f i c a t i o n is attributed to the formation of a liquid p h a s e at p a r t i c l e b o u n d a r i e s w h i c h is squeezed into adjacent cavities by applied pressure.
Tungsten T H E R E D U C T I O N OF D O P E D T U N G S T E N BLUE O X I D E ( T B O ) TO NON-SAG T U N G S T E N - A L I T E R A T U R E REVIEW
B. Zeiler et al, (Technical University, Vienna, Austria), Int J. Refractory Metals and
Hard Materials, Vol 10 No 2, 1991, 83-90. A review of the literature concerning the doping of TBO with I~ A1 or Si and the s u b s e q u e n t H r e d u c t i o n to metal, was presented. The effects of the p r o p e r t i e s of the blue oxide with respect to doping reactions, the formation of intermediate W o x i d e s a n d ~W a n d t h e r e d u c t i o n of dopants containing compounds on reduction kinetics were discussed. Conclusions on t h e t h e o r i e s of d o p a n t i n c o r p o r a t i o n , a review of r e d u c t i o n p a r a m e t e r s and p o w d e r properties were presented. T H E R E D U C T I O N OF D O P E D T U N G S T E N B L U E O X I D E ( T B O ) TO NON-SAG T U N G S T E N - M E C H A N I S T I C CONSIDERATIONS
B. Zeiler et al, (Technical University, Vienna, Austria), Int J. Refractory Metals a n d
Hard Materials, Vol 10, No 2, 1991, 91105. Experimental observations of the reduction of d o p e d TBO are described. Differences were noted between the sub oxides formed on reduction of d o p e d and u n - d o p e d TBO. A m e c h a n i s m for t h e i n c o r p o r a t i o n of t h e d o p a n t s , chemical vapour transfer and overgrowth phases, in
z
~ Jam mIII i~ =1 a~'a~ iI.111]lql = J all ::kval | ~ ' , •
tire reduction is discussed. I[ w a s found t h a t d o p a n t p h a s e particle size i n c r e a s e s with r e d u c t i o n t e m p e r a t u r e .
is s h o w n to s e g r e g a t e at grain b o u n d a r i e s a n d pores in W billets or crack facets in rods a n d wires.
SOLUTION SOFTENING OF IRIDIUM AND RHENIUM IN TUNGSTEN AT ROOM TEMPERATURE
AN INVESTIGATION OF COMPACTION I N P R E S S I N G O F T U N G S T E N HEAVY ALLOYS
A. Lui el al, (Arizona State University, Tempe, Arizona, USA), h~,t J. Refractory
A.L. Lobov et al, (Central Scientific Res e a r c h I n s t i t u t e for F e r r o u s Metallurgy, USSR), Stal', No 10, 1990, 94-97. I n
Metals a n d H a r d Materials, Vol 10, No 2, 1991, 1 0 7 1 1 4 .
Russian.
A t t e n t i o n w a s d r a w n to t h e l o w t e m p e r a t u r e b r i t t l e n e s s of W a n d to a l l e m p t s lo overcome t h i s hy alhrying a n d t h e use of high p u r i t y W. It was s h o w n t h a t the addition of RE to W results in i n c r e a s e s in room t e m p e r a t m e ductility a n d h i g h t e m p e r a t u r e s t r e n g t h . The possible use of Ir was discussed. An investigation of t h e room temperature structure and properties, which h a d theob.jective of e l u c i d a t i n g t h e m e c h a n i s m of sold s o l u t i o n s o f t e n i n g in WIr a n d Ir in t h o r i a t e d W, w a s described.
A s t u d y of c o m p a c t i o n p r o c e s s e s in W-Ni a n d W-Ni-Fe heavy alloys is described. The p o w d e r s used, t h e r e l a t i o n s h i p s b e t w e e n compact density and compressive strength a n d t h e c o m p a c t i n g p r e s s u r e a n d alloy c o m p o s i t i o n are considered.
EFFECTS OF NICKEL:IRON RATIO ON MECHANICAL PROPERTIES OF T U N G S T E N HEAVY ALLOYS
PRODUCTION OF SILVER-TIN OXIDE ELECTRICAL CONTACTS FROM ELECTROLESSLY PLATED COMPOSITE POWDERS
Electrical a n d m a g n e t i c materials
Soc P o w d e r a n d Powder Metallurgy, ~7~1 38, No 4, 1991, 540-547. In Japanese.
H. C h a n g et al, (University of Utah, USA),
"Fire influences of Ni:Fe ratio a n d t h e a d ( l i t i o n o f Co (:,n t h e m e c h a n i c a l properties of W-based heavy alloys have been studied. The Ni:Fe ratio varied in t h e range one p a r t of Ni to one to ten p a ~ s of Fe a n d t h e Co a d d i t i o n s were e i t h e r 0.5 of 1.Owl~?a. M a x i m u m values for s t r e n g t h a n d ductility were l o u n d at Ni:Fe - 1:4 a n d 0.5%Co. The r e s u l t s were d i s c u s s e d in t e r m s of m i c r o s t r u c t u r e , sizes of fracture s o u r c e s and matrix toughness.
Sintered electrical c o n t a c t m a t e r i a l were p r e p a r e d from SnO 2 p o w d e r s w h i c h h a d been p l a t e d with Ag by a novel m e t h o d . The m e c h a n i s m of e l e c t r o l e s s p l a t i n g w a s investigated u s i n g m i x e d p o t e n t i a l theory. The p o w d e r s a n d s i n t e r e d c o n t a c t s w e r e e x a m i n e d by s c a n n i n g electron m i c r o s c o p y and the electrical and mechanical p r o p e r t i e s were m e a s u r e d .
:
strengths obtained.
above
5 0 0 K g l . ' m m ~ we re
MICROSTRUCTURAL CHARACTERISATION OF CEMENTED CARBIDES USING SCANNING ELECTRON MICROSCOPY (SEM) WITH AUTOMATIC IMAGE ANALYIS (AIA) A. Nordgren, (Swedish I n s t i t u t e for Metals R e s e a r c h , S t o c k h o l m , S w e d e n ) , I n t J.
Refractory Metals a n d t l a r d MateriaLs, Vol 10, No 2, 1991, 61-81. The s t r u c t u r e s of WC-Co a n d WC 07-Co (7 - cubic p h a s e s o t h e r t h a n WC) were s t u d i e d by SEM w i t h AIA. The s t u d y was a i m e d at developing t h e use of AIA with c e m e n t e d c a r b i d e s w i t h r e g a r d to t h e d e t e r m i n a t i o n ofcarbide grain size, v o l u m e fraction and contiguity. Optimised specimen preparation, high resolution m i c r o s c o p y a n d i m a g e p r o c e s s i n g were f o u n d to be required. Two m e t h o d s of o b t a i n i n g back s c a t t e r e d electron e o n t r a s t , a t o m i c n u m b e r a n d channelling, were used. The r e s u l t s were r e p o r t e d to be sufficient accuracy for t h e m e t h o d to be u s e d for t h e c h a r a c t e r i s a t i o n of a wide range of h a r d materials.
T. Kaneko, J. Japat~
CONTROL OF PARTICLE SIZE OF TUNGSTEN POWDER
Materials Science a n d E n g i n e e r i n g B, Vol BS, No 2 1991, 99-105.
H a r d m a t e r i a l s a n d tool steels
I). S u e t al, E n g a n d Chcm Metallurgy, Vol
10, No 4, 1989, 67-7"0. I'n Chinese. The eflbcts of p r o c e s s variables on t h e particle size of W powder m a d e by t h e r e d u c t i o n of W blue oxide were investigated in i n d u s t r i a l s c a l e e x p e r i m e n t s . T h e optimum process conditions were e s t a b l i s h e d a n d a n e q u a t i o n for t h e prediction of particle size w a s deduced.
BEHAVIOUR OF TRACE ELEMENT POTASSIUM IN DOPED TUNGSTEN M. Zhou et al, J. Central South l n s t i t u t e o f
M i n i n g a n d Metallurgy (China, Vo120, No 4, 1989, 390-397. In Chinese. The d i s t r i b u t i o n a n d b e h a v i o u r of K in W p o w d e r have been e x a m i n e d as a f u n c t i o n of powder particle size. K c o n t e n t w a s f o u n d to increase with d e c r e a s e in particle size. K
HIGH STRENGTH MICROGRAINED CEMENTED CARBIDES T. F u k a t s u et al, (Toshiba Tungaloy Co Ltd, Kawasaki, J a p a n ) , I n t J. Refractory Metals
a n d H a r d Materials, Vol 10, No 2, 1991, 61-81. An i n v e s t i g a t i o n i n t e n d e d to give i m p r o v e d p r o p e r t i e s to MC-Co m a t e r i a l s is described. C a u s e s of p r o p e r t y reduction, p o r e s , Co p o o l s c o a r s e W g r a i n s a n d i m p u r i t i e s are d i s c u s s e d . The effects of carbide grain growth, inhibitors a n d t h e purity of the raw materials were i n v e s t i g a t e d w i t h respect to d e f e c t s a p p e a r i n g on t h e f r a c t u r e s u r f a c e o f t r a n s v e r s e r u p t u r e d s p e c i m e n s . The r e s u l t s were s h o w n to d e m o n s t r a t e t h a t p o w d e r p u r i t y w a s m o s t significant a n d by u s i n g high p u r i t y WC p o w d e r t r a n s v e r s e r u p t u r e
OPTIMISATION OF PROCESSING PARAMETERS FOR DIRECT VACUUM SINTERING OF A T15 HIGH SPEED STEEL (HSS) M. S a n t o s et al, (LNETI, Lisbon Portugal),
P o w d e r Metallurgy, Vol 34. No 2, 1991, 93100. A s t u d y of t h e v a c u u m s i n t e r i n g of w a t e r a t o m i s e d T15 HSS is described. Effects of p r o c e s s variables, c o m p a c t i n g p r e s s u r e and s i n t e r i n g t e m p e r a t u r e and t h e t i m e were investigated, metallographic and f r a c t o g r a p h i c s t u d i e s w e r e c a r r i e d out. H i g h e s t s t r e n g t h s were a s s o c i a t e d with low p o r o s i t y , t h e a b s e n c e of g r a i n b o u n d a r y films a n d a fine h o m o g e n e o u s m i c r o s t r u c t u r e . It is s u g g e s t e d t h a t cracks e x i s t i n g in fine carbide particles are s u b critical in a f r a c t u r e m e c h a n i c s s e n s e S t u d i e s of g r o u n d a n d g r o u n d p l u s polished specimens showed that grinding a l o n e w a s a d e q u a t e for p r e p a r a t i o n of quality control s p e c i m e n s .
TUNGSTEN CARBIDE HARD METALS CEMENTED WITH FERRO-ALLOYS T. Farooq, T2. Davies, (UMIST/University of Manchester, Manchester, E n g l a n d ) , I n t J.
P o w d e r Metallurgy, Vol 27, No 4, 1991, 34 7-355. WC c e m e n t e d with ferro-alloys ( s t a i n l e s s steel or Fe-Co-NiMoB m a t r i x ) were c h a r a c t e r i s e d for s t r u c t u r e , h a r d n e s s . s t r e n g t h a n d t o u g h n e s s . It w a s f o u n d t h a t high d e n s i t y w a s a t t a i n e d , t h e r e w a s good bonding and high hardness when a s t a i n l e s s steel m a t r i x w a s used. The Fe-
MPR February 1992 59