Mechanical properties of magnesium alloy produced from machined chips

P R O P E R T I E S OF LIQUID PHASE S I N T E R E D LOW ALLOY S T E E L CONTAINING BORON

E. Dudrova et al ( U s t a v Materialoveho Vyskumu SAV, Kosice, Slovakia), Pokroky Psaskove Metalurgie, No 3, 1993, 63-74. (In Czech). Studies of a steel, 0.7% Mn-1.65% Cr0.2% Mo-0.7% graphite, with a n d w i t h o u t 0.2% B, are described. B is s h o w n to e n h a n c e d e n s i f i c a t i o n u p t o 94%, to increase Vicker's h a r d n e s s from 190 to 290 a n d to reduce b e n d s t r e n g t h . The e n h a n c e m e n t is a t t r i b u t e d to liquid p h a s e sintering. The m i c r o s t r u c t u r e is s h o w n to have evolved 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 n d consists of r o u n d e d grains in a eutectic matrix. It is considered t h a t wear p r o p e r t i e s will also be improved.

Magnesium MECHANICAL P R O P E R T I E S OF MAGNESIUM ALLOY P R O D U C E D FROM MACHINED CHIPS

M. Mabuchi et al (Industrial Research Inst., Nagoya, J a p a n ) , J J a p a n Soc Powder a n d Powder Metallurgy, Vol 40, No 4, 1993, 397-400. (In J a p a n e s e ) . A c o m p a r i s o n is m a d e b e t w e e n cast AZ91 Mg alloy a n d m a t e r i a l s m a d e from sintered or e x t r u d e d chips. Sintering was a t 370°C a n d t h e e x t r u s i o n ratio was 10:1. Sintered m a t e r i a l h a d a low tensile s t r e n g t h of 90 MPa a n d 1% elongation. The e x t r u d e d alloy gave 340 MPa with 10% a n d e x h i b i t e d superplasticity at 300°C a n d s t r a i n rate of lxl0-4/sec. As cast AZ91 h a d a tensile s t r e n g t h of 130 MPa a n d 10% elongation after extrusion.

Nickel S I N T E R I N G CHARACTERISTICS AND SURFACE CHEMISTRY OF ULTRAFINE NICKEL POWDERS

Y. Sakka, T. Uchikoshi (National Research Inst. for Metals, Tokyo, J a p a n ) , P o w d e r Metallurgy, Vol 36, No 3, 1993, 179-185. S t u d i e s of t e m p e r a t u r e p r o g r a m m e d d e s o r p t i o n of ultrafine Ni p o w d e r s are described. Ni powders exposed to air are c o n t a m i n a t e d by Ni oxide a n d hydroxide. Sintering characteristics of t h r e e s a m p l e s of u l t r a f i n e Ni p o w d e r s were i n v e s t i g a t e d sintering being in flowing H or vacuum. Dimensional a n d structural changes were studied. The m e c h a n i s m s of sintering of clean Ni powders in v a c u u m is by neck growth a n d densification by m a s s t r a n s f e r which s t a r t s at 125°C. The air e x p o s e d Ni s h o w s t h r e e s t a g e s in s i n t e r i n g , g a s desorption, growth of surface oxides a n d sintering of t h e Ni a n d oxide. In H two m a x i m a in t h e shrinkage rate curves are n o t e d one being due to reduction of surface oxide a n d t h e o t h e r to mass t r a n s p o r t .

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Titanium SINTERING BEHAVIOUR OF TITANIUM COMPACTS WITH TITANIUM HYDRIDE MADE BY INJECTION MOULDING

H. Kyogoku et al (Industrial Research Inst. of Hiroshima Prefecture, Fukuyama, J a p a n ) J Japan Soc Powder and Powder Metallurgy, Vol 40, No 4, 1993, 439-443. (In Japanese). A n i n v e s t i g a t i o n of d e b i n d i n g a n d sintering of Ti compacts, w i t h a d d i t i o n of Till, m a d e b y i n j e c t i o n m o u l d i n g is d e s c r i b e d . A f t e r d e b i n d i n g a t 150°C s p e c i m e n s h a d m i c r o s t r u c t u r e s of Ti grains with pores. Debinding a t 250 a n d 320°C gave precipitates of TiC. Increase in s i n t e r i n g t e m p e r a t u r e gave i n c r e a s e d density regardless of debinding t e m p e r a t u r e . It is r e p o r t e d t h a t t h e a d d i t i o n of Till e n h a n c e d densification.

Tungsten DENSIFICATION MECHANISMS AND MECHANICAL P R O P E R T I E S OF A T U N G S T E N ALLOY

C. Chausse, F. N a r d o u ( L a b o r a t o r y for Ceramic Materials and Surface Treatments, Limoges, France) Revue de Metall., Vol 90, No 5, 1993, 624-628. (In French). A study of t h e sintering of W-2.1wt% Ni0.54% Fe-0.34% Co, u n d e r a wide range of conditions, is described. In p a r t i c u l a r t h e stage before liquation was investigated by dilatometry and microstructural characterization. Up to 900°C e x p a n s i o n occurs prior to t h e onset of sintering w h i c h is d e n o t e d by contraction. The shrinkage is expressed in mathematical form. Densification a n d m e c h a n i c a l p r o p e r t i e s i n t h e s o l i d s t a t e s i n t e r e d alloy a r e described. Liquid p h a s e forms a t 1400°C a n d above. Diffusion of W into t h e liquid p h a s e was detached. Liquid p h a s e sintering results in greater densification a n d h i g h e r mechanical p r o p e r t y values.

Ceramic materials BONDING STRUCTURE AND PROPERTIES OF METAL/CERAMIC INTERFACES

J.M. Howe (University of Virginia, Chariottesville, Virginia, USA), Int. Materials Reviews, Vol 38, No 5, 1993, 233-256. Bonding, reactions and interface s t r u c t u r e in m e t a l a n d ceramic interfaces are critically r e v i e w e d w i t h p a r t i c u l a r e m p h a s i s o n A1 a n d Ti alloys b o n d e d to AI2O3 a n d SiC. It is s h o w n t h a t some properties, including metal/ceramic w e t t i n g a n d w o r k of a d h e s i o n c a n b e p r e d i c t e d from s i m p l e b o n d i n g models. T h e r m o d y n a m i c s a n d kinetics of interface reactions are of significance. Reactions are shown to follow parabolic rate laws a n d

thick layers, above 1 ~ m are shown weaken interfaces. Process variations r e p o r t e d to have s u b s t a n t i a l influence t h e properties of interfaces a n d t h e s e discussed.

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Bearing alloys E F F E C T OF CALCIUM FLUORIDE ON COPPER AND SILVER BASE BEARING ALLOYS

V.N. Paderno et al, Poroshkovaya Metallurgiya, No 9, 1992, 84-88. (In Russian). The effects of a d d i t i o n of CaF2 o n properties of Ag a n d Cu base b e a r i n g / electrical contact materials was investigated. It is r e p o r t e d t h a t t h e CaF2 s t r e n g t h e n s t h e m a t r i x of t h e alloy a n d reduces t h e coefficient of friction.

Composites A N INVESTIGATION OF S I N T E R E D GLASS-METAL COMPOSITES

Y. Kun et al ( S o u t h E a s t University, Nanjing, China), PM Technology, Vol 11, No 1, 1993, 47-52. (In Chinese). I t is r e p o r t e d that metal/glass c o m p o s i t e s h a d b e e n p r o d u c e d by PM m e t h o d s . Fe, A1 a n d o t h e r m e t a l s a n d alloys were used. Properties, m i c r o s t r u c t u r e s a n d possible applications are discussed. FABRICATION OF POROUS NICKELCOPPER TAPE REINFORCED WITH ALUMINA PARTICLES

I~ Hoshino, T. Kohno (Mitsubishi Materials Corp, Omiya, J a p a n ) , J Japan Soc Powder and Powder Metallurgy, Vol 40, No 4, 1993, 417-420 a n d 421-425. (In J a p a n e s e ) . Studies of fabrication of a porous Ni-Cu tape, reinforced w i t h A1203 particles a n d of i n t e r n a l o x i d a t i o n in t h e a l l o y s a r e described. The t a p e was fabricated from e l e m e n t a l Ni-Cu-Al powders a n d sintered by a o x i d a t i o n - r e d u c t i o n route. Sintered a n d green d e n s i t i e s were similar. It is suggested t h a t t h e sintered density can be predicted from t h e t a p density.

Electrical and magnetic materials E F F E C T OF HEAT TREATMENT CONDITIONS ON PROPERTIES OF MANGANESE-ZINC F E R R I T E S

J. Miklik, V. C h r o u s t (Vyzkumny, U s t a v Praskove Metal., Sumperk, Czechoslovakia), Pokroky Psaskove Metalurgie, No 3, 1993, 5-9. (In Czech). O p t i m u m sintering conditions for Mn-Zn ferrite rings with high permeability were determined. I t is s h o w n t h a t o p t i m u m properties can be a t t a i n e d by control of furnace conditions and