AC Magnetic properties of fluxed and sintered iron alloys

PM

LITERATURE

PARTICLE SIZE P R E D I C T I O N IN A N ATOMIZATION SYSTEM

transform into morphology.

C. Tornberg (Soderfors Powder AB, Soderfops, Sweden). A model for d e t e r m i n a t i o n of particle size in a t o m i z a t i o n using surface tension a n d viscosity of t h e alloy a n d forces acting on t h e m o l t e n metal, was described. It was r e p o r t e d t h a t ff t h e m a t e r i a l properties a n d t h e atomization conditions are known t h e n t h e particle size can be deduced. Effects of some alloy e l e m e n t s on surface tension a n d viscosity were discussed. Some predicted a n d e x p e r i m e n t a l results for Fe, Ni a n d Co alloys were presented.

MICROSTRUCTURAL EVOLUTION O F PLASMA SPRAYED MOLYBDENUM SILICIDE

APPLICATION OF POWDERS WITH OPTIMIZED E Q U I A X E D GRAINS W.A. Kaysser et al (Max Planck Inst. ffir Metallforschung, Stuttgart, Germany). The fine grain size needed for s u p e r plasticity was discussed with reference to t h e grain sizes in w a t e r a n d i n e r t gas atomized powders a n d it was s h o w n t h a t t h e grain size can be controlled in t h e r a n g e 0.5 to 0.01 of t h e particle size. Effects of p r o c e s s v a r i a b l e s o n g r a i n size w e r e considered. Results for high alloy steels a n d intermetallic compounds, w i t h regard to a n a r r o w d i s t r i b u t i o n of grain sizes independent of particle sizes were presented. PLASMA MELT GAS ATOMIZATION ( P M G A ) OF NIOBIUM A L U M I N I D E H, Kohmoto et al (Mitsubishi Materials Corporation, J a p a n ) . The use of PMGA for p r o d u c t i o n of Nb~2d by a new process was described. Mean particle d i a m e t e r was r e p o r t e d to be 100 p m a n d t h e 0 c o n t e n t to be 700 ppm. Microstructural e x a m i n a t i o n showed t h e s t r u c t u r e to consist of a body c e n t r e d cubic s u p e r s a t u r a t e d solid solution of A1 in Nb for t h e rapidly solidified p o w d e r c o m p a r e d with a n ordered A15 s t r u c t u r e for a cast ingot.

Spray forming DENDRITIC/EQUIAXED T R A N S F O R M A T I O N D U R I N G SPRAY ATOMIZATION A N D D E P O S I T I O N X. Liang et al (University of California, California, USA). The s t r u c t u r e s of atomized a n d s p r a y deposited Ni3AI were investigated. Three types of s t r u c t u r e were reported, a) fine rapidly solidified (RS) d e n d r i t e s with a slate like morphology, b) a n h o m o g e n e o u s densely c o m p a c t e d e q u i a x e d s t r u c t u r e a n d c) a m i x e d zone containing d e n d r i t e s a n d e q u i a x e d structures. The s t r u c t u r e s were discussed with respect to t h e r m a l energy considerations. S u b s e q u e n t h e a t t r e a t m e n t was s h o w n to c a u s e t h e d e n d r i t e s to

42 MPR January 1993

an

REVIEW

equiaxed

grain

I~G. Shaw et al (Rensselaer Polytechnic Inst, Troy, New York, USA). It was n o t e d t h a t r a p i d l y solidified sprayed structures frequently contain defects. The m e c h a n i s m by w h i c h t h e sprayed n o n - e q u i l i b r i u m MoSi2 t r a n s f o r m s on h e a t t r e a t m e n t to a fully d e n s e s t a t e was investigated by a n n e a l i n g a t 700 to 1500 °C. The a s - s p r a y e d m a t e r i a l was s h o w n to consist of segregated Si a n d h e x a g o n a l MosSi3 p h a s e s a n d pores. On a n n e a l i n g a b o v e 800 °C t h i s t r a n s f o r m s t o t h e equilibrium body centred t e t r a g o n a l p h a s e w i t h increases in density a n d hardness. Residual stresses require higher t e m p e r a t u r e s for relief. The p l a s m a spray/ v a c u u m a n n e a l is shown to be a viable m e t h o d for p r o d u c i n g fully d e n s e h i g h t e m p e r a t u r e MoSi2.

Magnetic properties AC M A G N E T I C P R O P E R T I E S OF FLUXED A N D S I N T E R E D IRON ALLOYS D. Rodrigues et al (Inst. de P e q u i s a s Tecnologicas, Brazil). The use of Na c a r b o n a t e as a sintering aid (or flux) was investigated in respect of Fe, Fe-Si, Fe-P a n d Fe-Si-P alloys a n d its role in promoting microstructural h o m o g e n e i t y was discussed. Sintering was at 880 to 1180°C, lower t h a t is required to p r o m o t e i n t e r diffusion of t h e e l e m e n t s in t h e alloys. The AC m a g n e t i c p r o p e r t i e s of t h e fluxed alloys sintered a t 1120°C were r e p o r t e d to be s u p e r i o r to t h o s e of t h e nonfluxed allows s i n t e r e d a t 1300°C. E F F E C T S OF P R O C E S S I N G A N D MATERIALS ON S O F T M A G N E T I C P E R F O R M A N C E O F PM PARTS FJ. Hanejko et al (Hoeganaes Corporation, Riverton, New Jersey, USA). The m a g n e t i c p r o p e r t i e s of Fe b a s e PM m a g n e t alloys were reviewed w i t h reference to possible i m p r o v e m e n t s in p e r f o r m a n c e arising from process optimization. In a n e x p e r i m e n t a l study a t t e n t i o n was given to t h e effects of sintering conditions. Materials studied included p u r e Fe a n d Fe alloys with P, Si a n d Ni. CHARACTERIZATION OF GAS A T O M I Z E D MANGANESE-ALUMINIUMCARBON-NICKEL POWDERS A. Yanagitani et al (Sanyo Special Steel Co, Ltd, J a p a n ) . A s t u d y of PM Mn-AI-C-Ni alloys for magnetic applications was described. Powders were made by inert gas

a t o m i z a t i o n a n d s t r u c t u r e was e x a m i n e d by electron microscopy and phase t r a n s f o r m a t i o n s by d i f f e r e n t i a l t h e r m a l analysis. It was found t h a t T p h a s e could be o b t a i n e d by h e a t t r e a t m e n t of t h e E p h a s e g e n e r a t e d by r a p i d solidification. The transformation took place in two e x o t h e r m i c stages. It was considered t h a t two types of t h e E p h a s e exist in t h e atomized powders in Ni rich a n d Ni lean zones, respectively.

Surface treatment D E V E L O P M E N T A N D CONTROL OF SURFACE POROSITY IN S I N T E R E D 316L S T A I N L E S S S T E E L B.S. Becker, J.D. B o l t o n ( U n i v e r s i t y of Bradford, Bradford, UK). The use of stainless steel femural s t e m s a n d polymeric cups in r e p l a c e m e n t hip j o i n t s was discussed in t e r m s of t h e service life of t h e prosthesis, 10 to 15 years, failure being a t t r i b u t e d to lack of lubrication. The use of p o r o u s m a t e r i a l s to bring a b o u t i m p r o v e m e n t s in lubrication was outlined. The experimental work described e s t a b l i s h e d t h e process conditions n e e d e d to c o n t r o l t h e surface p o r o s i t y of t h e s i n t e r e d 316L stainless steel. LASER S H O C K P R O C E S S I N G FOR SUPERFICIAL D E N S I F I C A T I O N O F PM MATERIALS B. D u b r u j e a u d et al (Ecole des Mines de Paris, Paris, France). The use of laser shock t r e a t m e n t to preferentially densify the surfaces of a u t o m o b i l e parts, w h e r e t h e bulk of t h e m a t e r i a l does n o t require full densification, was discussed. The i n f l u e n c e s of l a s e r p a r a m e t e r s , such a n d pulse d u r a t i o n a n d energy, were investigated for Distaloy AE with initial porosities of 8 a n d 20%. The laser densification was assessed by quantitative microscopy and high resolution microtomography. A m a t h e m a t i c a l model e n a b l e d prediction of the densification. The experimental m e a s u r e m e n t s were r e p o r t e d to agree with t h e model. Pin-on-disc t e s t s were used to d e t e r m i n e w e a r properties.

Sintering P R E D I C A T I O N O F PACKING A N D S I N T E R E D DENSITY FOR BIMODAL POWDER M I X T U R E S R.M. G e r m a n (Pennsylvania State Universit-y,USA). The use of bimodal powder mixtures, as a means of increasing green and sintered densities was discussed with regard to the data required for the predication of composition effects on density. A model for the behaviour of the mixture was