Structure and thermal stability of nanocrystalline silver

Structure and thermal stability of nanocrystalline silver

high t e m p e r a t u r e a n d in n u c l e a r reactors. An outline is given of t h e p r o d u c t i o n of c o m p o n e n t s m a d e from Re a ...

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high t e m p e r a t u r e a n d in n u c l e a r reactors. An outline is given of t h e p r o d u c t i o n of c o m p o n e n t s m a d e from Re a n d it's alloys in which PM h a s a significant role.

a n d elongation were found to d i m i n i s h in t h e range 90 to 98%W.

At low t e m p e r a t u r e s Nd oxidizes b u t above 400 ° C t h e p o w d e r behaves as p u r e Fe.

T U N G S T E N HEAVY ALLOYS

Hard materials and tool steels

Silver STRUCTURE A N D THERMAL STABILITY O F NANOCRYSTALLINE SILVER T.Kizuka et al. (Univ of Tokyo, Tokyo, J a p a n ) . J. Japan Inst, o f Metals, Vol 55, No 3, 1991, 233-240, (In J a p a n e s e ) . Electron microscopy was used to investigate t h e grain b o u n d a r y s t r u c t u r e in n a n o c r y t a l l i n e Ag. S p e c i m e n s w e r e p r e p a r e d by compacting ultrafine p o w d e r a t p r e s s u r e s of 250 MPa to 2 GPa in v a c u u m followed by isochronal a n n e a l i n g up to 800°C The d o m i n a n t features of t h e asc o m p a c t e d specimens were c o h e r e n t twins a n d voids 2 to 5 n m in size a n d t h e r e were high values of hardness. An a n n e a l i n g t h e h a r d n e s s was lowered, t h e r e was grain coarsening although the grain size r e m a i n e d small.

Titanium n.

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VOLUME C H A N G E S D U R I N G S I N T E R I N G O F M I X T U R E S OF TITANIUM A N D NICKEL POWDERS M.M.Antonova et ai, Poroshkovaya Metallurgiay, No 4, 1991, 34-39, (In Russian). Interactions in Ti-33%Ni powder m i x t u r e s on h e a t i n g in H or v a c u u m at 700 to 940 ° C were studied. It was found t h a t t h e i n t e r a c t i o n m e c h a n i s m changes a t 900°C, Below 900°C solid s t a t e m e c h a n i s m s are d o m i n a n t b u t c o n t a c t melting occurs above 900°C. Volume changes a n d p h a s e composition of s i n t e r e d specimens suggest that equilibrium is more closely a p p r o a c h e d o n s i n t e r i n g in H. This is attributed to hydrogenation and dehydrogenation o f t h e Ti d u r i n g isothermal heat treatment.

L.B.Ekbom, ( N a t i o n a l Defence R e s e a r c h Establishment, Sundbyberg, Sweden). Scandinavian J. Metallurgy, Vol 20, No 3, 1991, 190-197. Production, properties a n d applications of W-Ni-Fe heavy alloys are reviewed. An outline of t h e p r o d u c t i o n process is given and the structural changes occurring d u r i n g liquid p h a s e sintering a t 1470°C are described. During sintering t h e Fe a n d Ni powders m e l t a n d t u n g s t e n grains grow by a s o l u t i o n / p r e c i p i t a t i o n m e c h a n i s m . A t t e n t i o n is drawn to t h e need for a full u n d e r s t a n d i n g of s i n t e r i n g in o r d e r to optimise process conditions relative to t h e p r o p e r t i e s , P r o c e s s i n g of m a t e r i a l s in microgravity conditions is discussed.

Electrical and magnetic materials ~nnrnl

STRUCTURE PROPERTY R E L A T I O N S H I P S IN S I N T E R E D HEAVY ALLOYS D.V.Edmonds (Univ of Oxford, Oxford, UK).

Int. J, Refractory Metals and Hard Materials, Vol 10, No 1, 1991, 15-26. The s t r u c t u r e of W heavy alloys was investigated. Participation in t h e binder, t h e W grains a n d at interfaces is considered because this is t h o u g h t to influence t h e s t r e n g t h a n d t o u g h n e s s . The effects of impurities are discussed. Tensile s t r e n g t h

50 MPR December 1991

I.Urrutibeaskoa et al, (Univ of Navarra, San Sebastian, Spain). Powder Metallurgy, Vol 33, No 3, 1990, 305-311. Structural changes in four high speed steel (HSS) compositions were investigated by electron microscopy after sintering in v a c u u m or N-based i n d u s t r i a l a t m o s p h e r e s . C a r b i d e s MC a n d MsC were f o u n d o n s i n t e r i n g in v a c u u m b u t c a r b o n i t r i d e s were found in a d d i t i o n on sintering in t h e N-based gas. O p t i m u m sintering conditions gave rise to a small a m o u n t of eutectic a n d over-sintering resulted in t h e f o r m a t i o n of different types of eutectic carbides. D E S I G N OF S I N T E R E D H S S POWDERS FOR WEAR A P P L I C A T I O N S

Hrrnr

P R O D U C T I O N A N D P R O P E R T I E S OF SILVER-NICKEL A N D SILVER-NICKELCARBON CONTACT MATERIALS FOR LOW VOLTAGE ELECTRICAL ENGINEERING W.Haufe (Siemens AG, Erlangen, Germany). Metall, Vol 45, No 7, 1991, 674-679, (In German). The p r o d u c t i o n of Ag-Ni a n d Ag-Ni-C contacts containing 10 to 30%Ni a n d 0.5 to 4%C using a press-sinter-press r o u t e is described. Information concerning properties is given and reviewed concerning t h e use of t h e s e m a t e r i a l s for low voltage switching. The c o m p o n e n t s w e r e t e s t e d i n a h i g h s p e e d switch. Symmetrical, Ag-Ni/Ag-Ni, and assymetrical, Ag-Ni/A~-Ni-C, c o n t a c t p a i r s were tested. Structure a n d porosity values are reported.

M.Igharo a n d J.V.Wood, (Univ of Nottingham, UK). Powder Metallurgy, Vol 33, No 3, 1990, 313-320. Structure, m e c h a n i c a l p r o p e r t i e s a n d d i m e n s i o n a l s t a b i l i t y of s i n t e r e d h i g h speed steel (HSS), some diluted w i t h Fe, were investigated, after different processing routes, w i t h respect to a s s e s s m e n t of value for wear resistant applications. Dimensional stability is i m p a i r e d if a n y liquid p h a s e forms d u r i n g s i n t e r i n g a t t e m p e r a t u r e s above 1200°C, w h i c h also gives r i s e t o c a r b i d e n e t w o r k s . Over sintering results in a s h a r p r e d u c t i o n in b e n d strength. The observed p h e n o m e n a are e x p l a i n e d in t e r m s of t h e resistance of carbides to dissolution. S I N T E R I N G OF COBALT C E M E N T E D T U N G S T E N CARBIDE WITH VANADIUM CARBONITRIDE A D D I T I O N S R.Hulyal a n d G.S. U p a d h y a y ~ ( I n d i a n Inst of Technology, Kanpur, I n d i a ) . Int, J.

OXIDATION SIZING OF IRON A N D IRON-NEODYMIUM-BORON POWDERS

Tungsten

STRUCTURAL C H A N G E S IN M GRADE HSS DURING SINTERING

B.Stewart et al. (National Physical Laboratory, Teddington, UK). J.Mater~als Science, Vol 26, No 5, 1991, 1401-1408. Development of a particle sizing t e s t w h i c h was a p p l i e d to Fe a n d Fe-Nd-B powders was described. The m e t h o d is b a s e d on o x i d a t i o n of t h e powders, small particles oxidizing faster t h a n coarse one. Particle sizes are deduced from t h e rate constants in the Ahrenius law by comparison of experimental and t h e o r e t i c a l curves. For Fe p o w d e r s t h e process compared favourably with s c a n n i n g electron microscopy. There were difficulties with t h e alloy powders due to preferential oxidation of t h e constituents.

Refractory Metals and Hard Materials, No 1 10, No 1, 1991, 1-7. The a d d i t i o n of V(C,N) in s u b s t i t u t i o n for WC in WC-10%Co was found to result in p o o r d e n s i f i c a t i o n a n d a r e d u c t i o n in m e c h a n i c a l properties. The a p h a s e was observed in t h e m i c r o s t r u c t u r e a n d this as a t t r i b u t e d to t h e h i g h e r affinity of C O V t h a n W. M a x i m u m h a r d n e s s was n o t e d a t 20%V(C,N) in t h e carbide phase. S I N T E R I N G O F COBALT C E M E N T E D T U N G S T E N CARBIDE WITH RHENIUM ADDITIONS R.Hulyal a n d G.S.Upadhyaya, ( I n d i a n I n s t of Technology, Kanpur, India). Int, J. Refractory Metals and Hard Materials, No 1 10, No 1 1991, 9-13.