superalloy composites

superalloy composites

nia, Irvine, California, USA.) The s o l i d i c a t i o n m i c r o s t r u c t u r e s of spray a t o m i s e d A1-Si alloy powders were investigate...

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nia, Irvine, California, USA.) The s o l i d i c a t i o n m i c r o s t r u c t u r e s of spray a t o m i s e d A1-Si alloy powders were investigated, using quantitative image analysis, as a function of cooling rates a n d alloy compositions. It was r e p o r t e d t h a t t h e s t r u c t u r e of t h e powders could be cellular, degraded d e n d r i t e s or fully dendritic. The secondary dendrite spacing and morphology c h a n g e d with Si content. The s t r u c t u r e s were discussed with regard to solidification history and interfacial stability.

I N T E R F A C E S IN NICKEL A L U M I N I D E C O M P O S I T E S AND NICKEL A L U M I N I D E / S U P E RALLOY COMPOSITES M.Ke, W.W. Milligan. (Michigan Technological University, Houghton, Michigan USA.) The p r o d u c t i o n of NiA1/Ni3Al a n d NiA1/ IN718 composites from powders a n d sheet m e t a l was described. The composites were reported to be lighter t h a n t h e superalloys to be t o u g h a n d to retain t o u g h n e s s after t h e r m a l e x p o s u r e . The s t r u c t u r e s a n d stabilities of t h e p h a s e s d e t e c t e d were discussed.

STEREOLOGICAL M E T H O D S FOR QUANTIFICATION OF PORE-GRAIN BOUNDARY CONTACT AND MODELLING OF PORE INHIBITED GRAIN GROWTH DURING SINTERING

Y.Lin, R.B.Patterson. (University of Alabama, Birmingham, Alabama, USA.) The use of stereology for t h e study of sintering was discussed. In p a r t i c u l a r p o r e / grain b o u n d a r y contact, Zener drag forces a n d pore mobility were calculated. A model f o r p o r e i n h i b i t e d g r a i n g r o w t h for quantifying microstructural evolution during sintering was described. An inverse relationship between m e a n grain size a n d pore surface area/unit volume was reported. E x p e r i m e n t a l work on Cu, W, VO2 a n d A120 a powders was reported to show s u p p o r t for the model.

58 MPR June 1992

MICROSTRUCTURAL EXAMINATION O F PARTICLE-PARTICLE COORDINATION AND CONTACT AREA DURING HIP CONSOLIDATION OF SPHERICAL AND NON-SPHERICAL POWDERS B.K. Lograsso, ( I o w a S t a t e University, Ames, Iowa, USA.) The paper reported a study of quantitative microscopy of HIP of spherical a n d non-spherical powders from t a p to full density. Differences were n o t e d b e t w e e n t h e two p o w d e r s in p a r t i c l e particle coordination density a n d particleparticle area density-path. The results were discussed with reference to the densification of t h e two powder types.

MICROSTRUCTURE-PROCESSINGPROPERTY RELATIONS IN HIGH PERFORMANCE T U N G S T E N HEAVY ALLOYS

A . B e l l h a d j h a m i d a , R.M. G e r m a n , ( P e n n State University, Pennsylvania, USA.) Investigations of the effects of composition a n d process variables on t h e m i c r o s t r u c t u r e a n d properties of W heavy alloys were d e s c r i b e d . The k i n e t i c s of mierostructural coarsening as influenced by refractory additions a n d t h e effects on mechanical properties a n d sintered grain size were discussed. Variation in grain composition, which correlated with growth k i n e t i c s were r e p o r t e d . The s t u d y was reported to provide a n u n d e r s t a n d i n g of p r o c e s s e s for t h e p r o d u c t i o n of h i g h p e r f o r m a n c e W heavy alloys.

QUANTITATIVE CHARACTERIZATION OF M I C R O S T R U C T U R E O F T U N G S T E N HEAVY ALLOYS Z.Fang, R.B. Patterson. (University of Alabama, Birmingham, Alabama, USA.) Quantitative microscopy was applied to t h e c h a r a c t e r i z a t i o n of l i q u i d p h a s e s i n t e r e d W-Ni-Fe h e a v y alloys. M e a n p a r t i c l e size, m e a n free p a t h b e t w e e n particles, m e a n curvature a n d contiguity were included in the parameters considered. Two- a n d t h r e e - d i m e n s i o n a l

modelling of m i c r o s t r u c t u r e was outlined. The use of a growth p a t h envelope m e t h o d for t h e study of kinetics of m i c r o s t r u c t u r a l evolution was reported.

COMPUTER CONTROLLED SCANNING ELECTRON MICROSCOPY FOR SIZE ANALYSIS O F IRREGULAR P A R T I C L E S

N.Y.C. Yang e t al. ( S c a n d i a N a t i o n a l Laboratory, Livermore, California, USA-) C o m p u t e r controlled s c a n n i n g electron microscopy for analysis of small, irregular p o w d e r particles was described. The effects of sample p r e p a r a t i o n a n d i n s t r u m e n t a l conditiofns on particle size analysis were considered for different particle morphologies. The results were discussed with regard to u n c e r t a i n t i e s in t h e d a t a a n d r e c o m m e n d a t i o n were m a d e concerning t h e uncertainties. METAL POWDER PRODUCTION BY CENTRIFUGAL ATOMIZATION INTO A ROTATING Q U E N C H BATH

K~S. Funke et al. (Iowa State University, Ames, Iowa, USA.) The p a p e r described a process v a r i a t i o n in centrifugal atomization into a r o t a t i n g q u e n c h b a t h (RQB) i n t e n d e d to produce large size powder particles in the range 0.2 to 2.0 ram. Ag a n d Ag-15wt%Cu alloy powders of m e a n particle size 0.45 to 0.65 mm were produced with a standard deviation of 1.41 to 1.57. It was suggested t h a t a smaller size range could be a t t a i n e d by changes in process variables. The large powder size was a t t r i b u t e d to absence of s e c o n d a r y d i s i n t e g r a t i o n of d r o p l e t s of metal as a result of using t h e q u e n c h bath. DYNAMIC CONSOLIDATION O F POROUS COPPER IRON AND T U N G S T E N C.N. Elias. ( I n s t i t u t e of Military Engineering, Rio de Janeiro, Brasil.) Microstructure and properties of explosively c o m p a c t e d cu, W,. Fe a n d W-Fe alloy p o w d e r s w e r e d e s c r i b e d . It w a s reported t h a t interparticle bonding, a high degree of densification a n d high h a r d n e s s e s were attained.