Manufacture of powder compacts

POWER P R O D U C T I O N 1,

FRICTIONAL L O S S E S IN ULTRASONIC GAS ATOMIZATION ( U S G A ) NOZZLES

A. lJnal. Imperial College, London, UK, Powder Metallurgy, Vol 33, No 3, 1990, 327-333. Attention was drawn to a recent observation t h a t gas flow rates in USGA are less t h a n t h o s e predicted, by a factor as m u c h as 50%, a n d t h a t t h i s was due to a self-adjusting effect in t h e nozzles. It was shown that this explanation was inappropriate. Calculations are p r e s e n t e d in w h i c h t h e nozzle is t r e a t e d as a n adiabatic pipeline with frictionless losses a n d it is shown t h a t operating conditions correspond to subsonic flowwith choking at t h e exit. A p r e s s u r e loss of 36% was c a l c u l a t e d . S u g g e s t i o n s a r e m a d e for minimization of t h e p r e s s u r e loss.

PRODUCTION AND P R O P E R T I E S OF ATOMIZED ALUMINIUM-CHROMIUM ALLOY POWDERS

L ~ P o z n y a k et al. Poroshkovaya Metallurgiya, No 4, 1991, 7-10. (In Russian). A u n i t for the p r o d u c t i o n of No-Cr-A1 alloy p o w d e r s by m e t a l m e l t i n e r t gas a t o m i z a t i o n i n d e s c r i b e d . R e s u l t s of characterization, composition, particle size a n d size d i s t r i b u t i o n a n d m i c r o s t r u c t u r e are p r e s e n t e d a n d discussed.

PRODUCTION OF ULTRAFINE CARBONYL IRON POWDER BY PLASMA-CHEMICAL DECOMPOSITION

V.D.Parkhomenko et al. Poroshkovaya Metallurgiya, No 4, 1991, 10-14. (In Russian). An analysis of Fe p o w d e r m a d e by decomposition of Fe(CO)5 in a plasmachemical reactor, with respect to s t r u c t u r e a n d particle size a n d size distribution, is presented. Kinetics of p o w d e r nucleation a n d growth are described a n d discussed. It was found t h a t t h e initial particle growth was rapid and that the growth rate d i m i n i s h e d with position in t h e reactor. Applications of t h e d a t a o b t a i n e d were demonstrated. OPTIMIZATION OF COPPER ALLOY MELTING FOR POWDER PRODUCTION BY ATOMIZATION

N.S.Sarkisyan et al. Poroshkovaya Metal-

46 MPR December 1991

lurgiya, No 4, 1991, 64-69. (In Russian). Process v a r i a n t s for t h e melting of Cu a n d its alloys p r i o r to a t o m i z a t i o n are discussed. The effects of t i m e of holding t h e melt on homogeneity were investigated as was t h e o p t i m u m use of d e o x i d a t i o n by a B addition. The effects of i m p u r i t y levels in t h e m e l t were d e t e r m i n e d for a wide r a n g e of e l e m e n t s a n d r e l a t e d t o i m p u r i t y d i s t r i b u t i o n a n d diffusion in t h e m o l t e n metal. ATOMIZATION AS A CHEMICAL E N G I N E E R I N G UNIT P R O C E S S

K.Bauckhage. (Univ of Bremen, Germany). Chem. Ing. Tech. Vol 62, No 8, 1990, 613625. (In G e r m a n ) . The m e c h a n i s m s of liquid a t o m i z a t i o n , d i s i n t e g r a t i o n , flow in t h e s p r a y a n d i m p a c t of t h e droplet on to t h e s u b s t r a t e are discussed w i t h regard to particle size distribution. Size d i s t r i b u t i o n is, said to be a d y n a m i c p a r a m e t e r i n w h i c h local changes occur a n d t h e i m p o r t a n c e of t h e s e local effects is emphasized. The effects are a t t r i b u t e d to coalescence, evaporation or chemical reactions. Use of improved instrum e n t a t i o n for m e a s u r e m e n t of particle size d i s t r i b u t i o n m a k e s it possible to use a differential a p p r o a c h to particle size analysis r a t h e r t h a n a n integral one. PRODUCTION OF POWDER BY ATOMIZATION OF MOLTEN METAL WITH LOW TEMPERATURE LIQUID GAS

J.Backer. (Krupp Pulvermetall GmbH, Essen, Germany). Metall, Vol 25, No 8, 1991, 764-771, (In G e r m a n ) . Atomization of Fe a n d Ni using A at 200 ° C is described. The d e v e l o p m e n t s have c o n c e n t r a t e d on nozzle design a n d liquid gas technology a n d on t h e effects of process parameters on characteristics of the powders. The process uses conventional gas a t o m i z a t i o n w i t h a d d i t i o n a l liquid i n e r t gas supply. The p o w d e r is r e p o r t e d to be of high purity, spherical s h a p e a n d to be in t h e size r a n g e 60 to 150 pm. PREPARATION OF TITANIUM CARBIDE POWDER BY S E L F PROPAGATING HIGH TEMPERATURE SYNTHESIS

D-G.Chang et al, (National Univ, Taejon, Korea). J. Korean Inst. of Metals, Vol 29, No 6, 1991,626-630. (In Korean). The high temperature combustion synthesis of TiC from e l e m e n t a l powders was investigated. It was found t h a t t h e purity of t h e TiC was high. Lattice c o n s t a n t s

were m e a s u r e d a n d were found to increase with C content. Particle sizes were in t h e range 2 to 40 ~m. CHANGES IN PHYSICAL P R O P E R T I E S OF ULTRAFINE NICKEL CARBONYL POWDER ON LONG TERM STORAGE

R.Teng, a n d C.Lu. (Central Iron a n d Steel Research Inst, China). J. Iron and Steel Research, Vol 1, No 1, 1989, 49-54. (In Chinese). C h a n g e s in p a r t i c l e size a n d size d i s t r i b u t i o n i n u l t r a f i n e c a r b o n y l Ni powder on long term storage are described a n d discussed. It was found t h a t small particles ( s m a l l e r t h a n 15 n m ) t e n d to d i s a p p e a r a n d t h a t t h e p r o p o r t i o n of mid-size range particles (30 to 80 n m ) increases. This t e n d e n c y was found to be less for increased m e a n particle size. Thus t h e m e a n particle size increases on long t e r m storage. CHANGES IN SPECIFIC SURFACE OF ULTRAFINE CARBONYL NICKEL POWDER ON LONG TERM STORAGE

R.Teng, (Central Iron a n d Steel Research Inst, China). J. Iron and Steel Research, Vol 1, No 2, 1989, 55-60. (In Chinese). The causes of c h a n g e in t h e specific surface of ultrafine Ni p o w d e r on long t e r m s t o r a g e a r e d i s c u s s e d w i t h r e g a r d to changes in m e a n particle size a n d size distribution. Migration of a t o m s is said to be t h e d o m i n a n t m e c h a n i s m in causing changes in t h e particle surface state.

PRESSING MANUFACTURE OF POWDER COMPACTS

A.D.Rosato et al, (New J e r s e y I n s t of Technology, Newark, New Jersey USA). Int, Materials Reviews, Vol 36, No 2, 1991, 4561. The relationships between powder c o m p a c t quality a n d uniformity of particle size d i s t r i b u t i o n within t h e c o m p a c t a n d r e t e n t i o n of refined m i c r o s t r u c t u r e are critically reviewed. The p a p e r deals with t h e creation of uniform green c o m p a c t s from powders and dynamics of the c o n s o l i d a t i o n process w i t h reference to p a r t i c l e size s e g r e g a t i o n i n d u c e d by vibrations and occuring during powder flows. The implications of segregation on t h e f o r m a t i o n of g r e e n c o m p a c t s a r e considered and the formation of

segregation induced by ultrasonic v i b r a t i o n s is discussed. The a p p l i c a t i o n of dynamic ( i m p a c t ) consolidation to form dense c o m p a c t s is described. The kinetics a n d energetics of t h e i m p a c t consolidation process are discussed a n d particle b o n d i n g a n d shock energy d i s t r i b u t i o n reviewed. EXTRUSION OF METAL POWDERS

P.R.Roberts a n d B.L.Ferguson, (Deformation Control Technology Inc, Cleveland, Ohio, USA). Int,Materials Reviews Vol 36, No 2, 1991, 62-79). T h e t e c h n o l o g y of m e t a l p o w d e r e x t r u s i o n a n d t h e m e c h a n i c s of e x t r u s i o n are critically reviewed. E m p h a s i s is placed on direct extrusion are introduced. Treatment is g i v e n t o d i s p e r s i o n s t r e n g t h e n e d metals, superalloys, rapidly solidified powders, toxic m a t e r i a l s a n d composites. E x a m p l e s are given w h i c h highlight the advantages of powder extrusion. DYNAMIC CONSOLIDATION OF RAPIDLY SOLIDIFIED TITANIUM ALLOY POWDERS

H.L.Coker et al, (New Mexico Inst of Mining a n d T e c h n o l o g y , New, Mexico, U S A ) , J.Materia£v Science, Vol 26, No 5, 1991, 1277-1286. The paper describes the explosive c o n s o l i d a t i o n of Ti alloy powders. The t e c h n i q u e used was cylindrical explosive compaction using a double tube m e t h o d a n d densities of 97 to 100% were attained. I m p r o v e d c o m p a c t i o n was n o t e d w h e r e t h e r e h a d b e e n fusion a t i n t e r p a r t i c l e contact zones. Optical and electron microscopy were used to study the c o m p a c t s a n d details of t h e s t r u c t u r e are described a n d discussed. Planar arrays of dislocations and deformation twinlike details were observed. The s t r u c t u r e s were correlated with mechanical properties. Ti was shown t h a t t h e results from small specimens could be scaled u p to 50, 75 a n d 100 m m specimens. INSTANTANEOUS AND RESIDUAL S T R E S S E S DEVELOPED DURING HIP OF METALS AND CERAMICS

W-B, Li et al, (Univ of Lule,h~ LuleA~ Sweden). Metallurgical Transactions A, Vol 22A~ No 5, 1991, 1071-1078. HIP densification of metallic or ceramic p r e f o r m s is d i s c u s s e d . D e n s i f i c a t i o n commences at t h e outside of t h e preform creating a shell which thickens until the whole compact is d e n s i f i e d . The d e v e l o p m e n t of t h e d e n s e shell effectively reduces the p r e s s u r e on t h e core of the c o m p a c t a n d t h e p r e s s u r e differences may lead to anisotropic creep of t h e shell a n d this c o n t r i b u t e s to s h a p e changes. Cooling a n d residual stresses were calculated as a function of process and material p a r a m e t e r s . It is f o u n d t h a t c o o l i n g

stresses, which are tensile at t h e surface, may cause cracking in brittle m a t e r i a l s including ceramics.

SlNTERING RELATIONSHIPS B E T W E E N SINTERING SHRINKAGE AND PHASE DIAGRAMS

A.P.Savcitskii, (Siberian B r a n c h USSR Academy of Sciences, Tomsk, USSR). Science of Sintering, Vol 23, No 1, 1991, 3-17, S h r i n k a g e d u r i n g t h e s i n t e r i n g of powder c o m p a c t s h a s been investigated with respect to c o m p o s i t i o n a n d p h a s e equilibria. A model for a c o m p a c t e d two c o m p o n e n t m i x t u r e ; w h i c h provides a n insight into t h e m e c h a n i s m responsible for volume changes, h a s been developed a n d is related to alloy f o r m a t i o n resulting from diffusion, INFLUENCE OF MAGNESIUM OXIDE ON THE MICROSTRUCTURE OF FINE GRAINED ALUMINA AND ALUMINAZIRCONIA COMPOSITES

A.Bos et al, (Univ of Twente, Enschede, The N e t h e r l a n d s ) . Science of Sintering, Vol 23, No 1, 1991, 19-24, The effect of MgO on t h e sintering of fine grained A1203 a n d A1203-ZrO powders was investigated, MgO was f o u n d to be a n e f f e c t i v e s i n t e r i n g aid, l o w e r i n g t h e t e m p e r a t u r e required to initiate sintering and the temperature for maximum d e n s i f i c a t i o n . High d e n s i t y a n d a fine grain size were a t t a i n e d on sintering MgOAl20a-ZrO a t 1450°C. DENSIFICATION A N D SHRINKAGE DURING LIQUID PHASE SINTERING

S-J.L.Kang et al, (Korea Advance Inst of Science a n d Technology). J. American Ceramic Soc., Vol 74, No 2, 1991, 425-427. Densification and shrinkage during l i q u i d p h a s e s i n t e r i n g of Mo-4Ni a r e described, Densification is a t t r i b u t e d to p o r e filling a n d g r a i n g r o w t h . Liquid pressure falls as t h e pores fill a n d allows grain s h a p e a c c o m m o d a t i o n with r e s u l t a n t shrinkage. The grains tend to spheroidize and the microstructure becomes more homogeneous. Grain growth is said to be a d e t e r m i n i n g factor in densification.

FUNDAMENTALS KINETICS OF GAS POROSITY DEVELOPMENT IN THE P R O C E S S OF GRANULE CRYSTALLISATION

V.V.Soboley, Poroshkovaya MetaUurgiya, No 4, 1991, 1-6, (In Russian). Mathematical e q u a t i o n s describing t h e d e v e l o p m e n t of g a s p o r o s i t y d u r i n g

solidification of powders are discussed in relation to steel a n d A1 each containing H. C h a n g e s in pore density are considered. Predicted a n d e x p e r i m e n t a l r e s u l t s are r e p o r t e d to be in good agreement. Use of t h e results for t h e prediction of t h e kinetics of porosity f o r m a t i o n is d e m o n s t r a t e d . ELASTIC DEFORMATION OF TOOLS DURING COMPACTION OF POWDERS

A.V.Stepanenko et al. Poroshkovaya Metallurgiya, No 4, 1991, 15-19, (In Russian). Finite e l e m e n t m e t h o d s (FEM) have been used for t h e analysis of t h e elastic d e f o r m a t i o n of thick wall shells used in t h e c o m p a c t i o n of powders. The calculation is b a s e d on d e t e r m i n a t i o n of t h e s t r a i n e d state of t h e shell a n d t h e m e a s u r e m e n t of t h e elastic deformation. Effects o n t h e q u a l i t y of t h e c o m p a c t e d part are considered a n d a l t e r a t i o n s to t h e process of optimization are suggested. INTERPARTICLE D E S T R U C T I O N OF IRON POWDER MATERIALS

S.A~Firstov et al. Poroshkovaya MetaUurgiya, No 4, 1991, 78-85, (In Russian). The p a p e r suggests t h a t a p a r a m e t e r , xm, t h e degree of interparticle destruction, is used as a m e a s u r e of t h e quality of s i n t e r i n g a n d t h a t t h i s is r e l a t e d to measured mechanical properties. A characteristic temperature, Tbo, which is reduced by increased compaction pressure, Sintering of Fe powders of different grades was shown to give h i g h e r Tbo for atomized powders than for reduced powders, Sintering a t Tb0 gives material with crack r e s i s t a n t of t h e order of 20 MPa.. ANALYSIS OF THE SELECTION FUNCTION FOR MILL USING BALLS AS GRINDING MEDIA

S.Nomura et al, ( B a b c o c k Hitachi KK, Hiroshima, J a p a n ) . Powder Technology, Vol 68, No 1, 1991, 1-12. The use of bails as grinding media is analysed. The premise is made that at least one crack must be generated or made to extend if a particle is to be broken by ball impact. The results are compared with experimental observations. The effects of powder and ball properties and mill charge and capacity are taken into consideration. E F F E C T S OF M E A S U R E M E N T M E T H O D S ON THE P R O P E R T I E S OF MATERIALS

J.M.Geoffroy a n d J.T.Carstensen, (Univ of Wisconsin, Madison, Wisconsin, USA). Powder Technology, Vol 68, No 1, 1991, 91-96. A s t u d y is r e p o r t e d of t h e effects of m e a s u r e m e n t m e t h o d s on the p r o p e r t i e s of m a t e r i a l s in compression. The Heckel e q u a t i o n is used a n d it is considered t h a t t h e m e a s u r e m e n t m e t h o d a n d t h e deformation m e c h a n i s m s influence the s h a p e of t h e Heckel plot, M a t e r i a l s w h i c h u n d e r g o plastic d e f o r m a t i o n show different s h a p e s

MPR December 1991 47