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Sintering of two phase lamellar microstructure
PM
m i c r o s c o p y were used to follow t h e sintering process. The wires were found to weld and micropores were eliminated. The activation energy for welding is reported to be lower than that for grain boundary diffusion of Fe in stainless steel. Initial welding rates were found to be independent of wire size. SINTERING OF TWO PHASE LAMELLAR MICROSTRUCTURE T.H. Courtney, (University of Virginia, USA), Scripta Metall. MaWr. Vol 25, No 7, 1991, 1741-1746. Studies of sintering in systems in which lamellar microstructure are formed are discussed with reference to the presence of inert phases. These are said to reduce the neck growth Xand densification rates. The study is reported to provide a means of assessing the effect of an inert phase on sintering of lamellar structures by the use of sintering diagrams.
LITERATURE
REVIEW
sity, Philadelphia, Pennsylvania, USA), Int. J. Powder Metallurgy, Vol 28, No 2, 1992, 121-132. It is shown the control of PM processing is an art as well as a science because process knowledge is written in linguistic form using 'fuzzy' statements of experience and incomplete models and hypotheses. Process control therefore requires d e v i a t i o n from c o n v e n t i o n a l c o n t r o l methodologies, the application of fuzzy controls, expert systems and knowledge based controls. The paper presents an analysis of strategies in the control of atomization, sintering HIP and spray forming.
PRODUCTS: AluminJurn STRUCTURE AND PROPERTIES OF RAPIDLY SOLIDIFIED HIGH STRENGTH ALUMINIUM M. De Sanctis, (University of Pisa, Italy),
FUNDAMENTALS ANALYSIS OF THERMAL STRESSES IN A METAL/CERAMIC JOINT WITH A THERMAL EXPANSION MISMATCH O. Kimura and T. Kawashima, (Shonan Inst of Technology, Kanagawa, Japan), J. J a p a n
Soc. Powder a n d Powder Metallurgy, Vol 39, No 1, 1992, 28-32. (In Japanese). The thermal stresses arising from a thermal expansion mismatch between a metal substrate and a ceramic coating are analysed for a cylindrical compressive joint in which the ceramic expands less shan the metal. A tensile stress is shown to exist in the surface of the ceramic. The tensile joint when the ceramic expands more than the metal is also considered. Finite element methods are used in the analysis. PERSPECTIVES ON PROCESS CONTROL IN POWDER METALLURGY D. Apelian, (Worcester Polytechnic Inst, Worcester, Massachusetts, USA), Int. J. Powder Metallurgy, Vol 28, No 2, 1992, 117-118. Some aspects of process control are reviewed with respect to productivity and product quality. Three components are identified, a definitive understanding of the process and its models, sensors which e n a b l e t h e d e t e r m i n a t i o n of p r o c e s s parameters and process control using online feedback which enables 'out of control' conditions to be corrected and productivity and product quality to be consistent. PROCESS CONTROL STRATEGIES IN POWDER METALLURGY P. Mathur and A. Lawtey, (Drexel Univer-
38 MPR September 1992
Materials Science and Engineering A, Vol AI41, No 1, 1991, 103-121. A comparison between PM and bulk spray deposited (SD) A1-Zn-Mg-Cu alloy is reported. Both forms have high strength because of a high concentration of solute atoms in solution close to equilibrium solubilities. The microstructure, mechanical and corrosion properties in heat treated conditions were compared. The SD m a t e r i a l s had an acceptable strength/ductility combination and the largest increase in fatigue properties. Extruded materials showed a reduction in fracture toughness which was associated with dimpled fractures. It is suggested that t h e m a t e r i a l s are capable of f u r t h e r improvements in properties. DEVELOPMENT OF WEAR RESISTANT ALUMINIUM ALLOYS CONTAINING SILICON CARBIDE PARTICLES Y. Ohkubo et al, (Sumitomo Light Metals, Hyogo, Japan), Sumitomo Light Metals Tech. Rep., Vol 32, No 2, 1991, 8-13. (In Japanese). It is reported that the addition of 0.5 wt% SiC particles to PM A1 alloys results in an increase in wear resistance without increase in wear of the counter part. Additions of up to 5% SiC had little further effect on wear but reduced the fatigue strength. New wear resistant Al alloys with SiC particles 2 to 5 9m in size are reported. E F F E C T OF DEGASSING CONDITIONS ON MECHANICAL PROPERTIES OF ALUMINIUM-SILICON-IRON ALLOY F. Sato and M. Abo, (Sumitomo Light Metals, Hyogo, Japan), Sum/tomo L/ght Metals Tech. Rep. Vol 32, No 2, 1991, 14-
21. (In Japanese). The effects of water, adsorbed on the surface of A1-Si-Fe powders, in increasing porosity and reducing strength of the consolidated alloy are discussed. Degassing processes are described and the effects of degassing conditions on structure and properties are described. The results are discussed and it is considered that w i t h o u t d e g a s s i n g o x i d e on p o w d e r surfaces reduces bonding during pressing, i n c r e a s e s H c o n t e n t and lowers t he mechanical properties.
Copper ROLE OF GAS ATMOSPHERES IN THE EVOLUTION OF MICROSTRUCTURE DURING THE SINTERING OF COPPER POWDER S.S. Chang, Doctoral Dissertation, University of Florida~ US,~ The thesis describes the effects of sintering atmosphere on the sintering and microstructural evolution of Cu. Surface tension of solid Cu was measured for atmospheres of pure H and mixtures of H with o t h er gases. It is reported t h a t addition of CO reduces surface tension and sintering force. Changes in the path of structural evolution are attributed to this. Competition between surface rounding and densification mechanisms is altered by atmospheric composition. CO or Ar are reported to favour surface rounding and H promotes densification. The curvature distribution of solid surfaces was studied. H was found to give a smaller range of curvatures than when CO or Ar are added. Study of the three-dimensional character of pore surfaces suggests that the network of porosiW is analogous to the triple and quadruple point network in polycrystal with branches tending to meet at angles of 109 ° and t h a t p o r e n e t w o r k e v o l u t i o n is analogues to the grain edge network during grain growth. MICROSTRUCTURE CHANGES IN COPPER-LEAD ALLOY POWDERS BY MECHANICAL ALLOYING T. Ohashi and Y. Tanaka, (Nagwo Inst of Technology, Japan), Mater/als Transactions Japan lnst, of Metals, Vol 32, No 7, 1991, 587-592. The effectiveness of MA in redistributing Pb in gas a t o m i z e d Cu powder and structural deformation was described and discussed. The powders were progressively deformed and pulverization was complete in about 10 minutes. The powder was found to contain crystallites, 50 nm in size, and amorphous material. It is suggested that the crystallites are formed from t he amorphous material which is unstable at the grinding temperatures. The stored
m i c r o s c o p y were used to follow t h e sintering process. The wires were found to weld and micropores were eliminated. The activation energy for welding is reported to be lower than that for grain boundary diffusion of Fe in stainless steel. Initial welding rates were found to be independent of wire size. SINTERING OF TWO PHASE LAMELLAR MICROSTRUCTURE T.H. Courtney, (University of Virginia, USA), Scripta Metall. MaWr. Vol 25, No 7, 1991, 1741-1746. Studies of sintering in systems in which lamellar microstructure are formed are discussed with reference to the presence of inert phases. These are said to reduce the neck growth Xand densification rates. The study is reported to provide a means of assessing the effect of an inert phase on sintering of lamellar structures by the use of sintering diagrams.
LITERATURE
REVIEW
sity, Philadelphia, Pennsylvania, USA), Int. J. Powder Metallurgy, Vol 28, No 2, 1992, 121-132. It is shown the control of PM processing is an art as well as a science because process knowledge is written in linguistic form using 'fuzzy' statements of experience and incomplete models and hypotheses. Process control therefore requires d e v i a t i o n from c o n v e n t i o n a l c o n t r o l methodologies, the application of fuzzy controls, expert systems and knowledge based controls. The paper presents an analysis of strategies in the control of atomization, sintering HIP and spray forming.
PRODUCTS: AluminJurn STRUCTURE AND PROPERTIES OF RAPIDLY SOLIDIFIED HIGH STRENGTH ALUMINIUM M. De Sanctis, (University of Pisa, Italy),
FUNDAMENTALS ANALYSIS OF THERMAL STRESSES IN A METAL/CERAMIC JOINT WITH A THERMAL EXPANSION MISMATCH O. Kimura and T. Kawashima, (Shonan Inst of Technology, Kanagawa, Japan), J. J a p a n
Soc. Powder a n d Powder Metallurgy, Vol 39, No 1, 1992, 28-32. (In Japanese). The thermal stresses arising from a thermal expansion mismatch between a metal substrate and a ceramic coating are analysed for a cylindrical compressive joint in which the ceramic expands less shan the metal. A tensile stress is shown to exist in the surface of the ceramic. The tensile joint when the ceramic expands more than the metal is also considered. Finite element methods are used in the analysis. PERSPECTIVES ON PROCESS CONTROL IN POWDER METALLURGY D. Apelian, (Worcester Polytechnic Inst, Worcester, Massachusetts, USA), Int. J. Powder Metallurgy, Vol 28, No 2, 1992, 117-118. Some aspects of process control are reviewed with respect to productivity and product quality. Three components are identified, a definitive understanding of the process and its models, sensors which e n a b l e t h e d e t e r m i n a t i o n of p r o c e s s parameters and process control using online feedback which enables 'out of control' conditions to be corrected and productivity and product quality to be consistent. PROCESS CONTROL STRATEGIES IN POWDER METALLURGY P. Mathur and A. Lawtey, (Drexel Univer-
38 MPR September 1992
Materials Science and Engineering A, Vol AI41, No 1, 1991, 103-121. A comparison between PM and bulk spray deposited (SD) A1-Zn-Mg-Cu alloy is reported. Both forms have high strength because of a high concentration of solute atoms in solution close to equilibrium solubilities. The microstructure, mechanical and corrosion properties in heat treated conditions were compared. The SD m a t e r i a l s had an acceptable strength/ductility combination and the largest increase in fatigue properties. Extruded materials showed a reduction in fracture toughness which was associated with dimpled fractures. It is suggested that t h e m a t e r i a l s are capable of f u r t h e r improvements in properties. DEVELOPMENT OF WEAR RESISTANT ALUMINIUM ALLOYS CONTAINING SILICON CARBIDE PARTICLES Y. Ohkubo et al, (Sumitomo Light Metals, Hyogo, Japan), Sumitomo Light Metals Tech. Rep., Vol 32, No 2, 1991, 8-13. (In Japanese). It is reported that the addition of 0.5 wt% SiC particles to PM A1 alloys results in an increase in wear resistance without increase in wear of the counter part. Additions of up to 5% SiC had little further effect on wear but reduced the fatigue strength. New wear resistant Al alloys with SiC particles 2 to 5 9m in size are reported. E F F E C T OF DEGASSING CONDITIONS ON MECHANICAL PROPERTIES OF ALUMINIUM-SILICON-IRON ALLOY F. Sato and M. Abo, (Sumitomo Light Metals, Hyogo, Japan), Sum/tomo L/ght Metals Tech. Rep. Vol 32, No 2, 1991, 14-
21. (In Japanese). The effects of water, adsorbed on the surface of A1-Si-Fe powders, in increasing porosity and reducing strength of the consolidated alloy are discussed. Degassing processes are described and the effects of degassing conditions on structure and properties are described. The results are discussed and it is considered that w i t h o u t d e g a s s i n g o x i d e on p o w d e r surfaces reduces bonding during pressing, i n c r e a s e s H c o n t e n t and lowers t he mechanical properties.
Copper ROLE OF GAS ATMOSPHERES IN THE EVOLUTION OF MICROSTRUCTURE DURING THE SINTERING OF COPPER POWDER S.S. Chang, Doctoral Dissertation, University of Florida~ US,~ The thesis describes the effects of sintering atmosphere on the sintering and microstructural evolution of Cu. Surface tension of solid Cu was measured for atmospheres of pure H and mixtures of H with o t h er gases. It is reported t h a t addition of CO reduces surface tension and sintering force. Changes in the path of structural evolution are attributed to this. Competition between surface rounding and densification mechanisms is altered by atmospheric composition. CO or Ar are reported to favour surface rounding and H promotes densification. The curvature distribution of solid surfaces was studied. H was found to give a smaller range of curvatures than when CO or Ar are added. Study of the three-dimensional character of pore surfaces suggests that the network of porosiW is analogous to the triple and quadruple point network in polycrystal with branches tending to meet at angles of 109 ° and t h a t p o r e n e t w o r k e v o l u t i o n is analogues to the grain edge network during grain growth. MICROSTRUCTURE CHANGES IN COPPER-LEAD ALLOY POWDERS BY MECHANICAL ALLOYING T. Ohashi and Y. Tanaka, (Nagwo Inst of Technology, Japan), Mater/als Transactions Japan lnst, of Metals, Vol 32, No 7, 1991, 587-592. The effectiveness of MA in redistributing Pb in gas a t o m i z e d Cu powder and structural deformation was described and discussed. The powders were progressively deformed and pulverization was complete in about 10 minutes. The powder was found to contain crystallites, 50 nm in size, and amorphous material. It is suggested that the crystallites are formed from t he amorphous material which is unstable at the grinding temperatures. The stored