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Effect of internal stress on yield criteria of porous metals
of intergrowth between hot compacted powders and hence the quality of the compacts has been investigated. Plasticity and fracture toughness were increased in the case of a sponge iron powder. This was a t t r i b u t e d to increased m i g r a t i o n of intergrowth boundaries during heating. PRODUCTION OF BIMETALLIC MATERIALS BY EXTRUSION S.G. Agbalyan et al, Poroshkovaya Metab lurgiya, No 1, 1991, 53-58, (In Russian). The use of extrusion of powdered metals to f a b r i c a t e b i m e t a l l i c m a t e r i a l s is described. The process combines pressing and sintering. The properties of materials with differential properties is discussed with regard to thermal expansion and elasticity.
EFFECT OF PROCESS VARIABLES ON M COMPACTING OF METAL C H M G. HShne, G. Schubert, (Bergakademie, Freiberg, Germany), Neue H~te, Vol 36, No 2, 1991, 41-46, (In German). Consolidation of metal chips has been investigated with regard to the mechanism of densification during compacting and the effects of p r o c e s s p a r a m e t e r s were determined. Compacting pressure was found to be the main controlling influence on compact density.
STABILITY OF LIQUID FILMS DURING LIQUID PHAKE 8 1 N T E S I ~ OF CEMENTED CARBIDlS$
A.F. IAsovsky, Porositkovaya Metallurgiya, No 1, 1991, 11-17, (In Russian). Surface thermodynamics of solid/liquid interfaces in cemented carbides of W and Cr with Co, Cu and Ni matrices and Ni-Pb alloys during liquid phase sintering have been determined. It was shown that there is a critical liquid film thickness which influences the stability of the film. Below the critical thickness the films form and grow by liquid metal migration. The films are stable above the critical thickness. STRUCTURE AND MECHANICAL PROPERTIES OF IRON SINTERED BY ELECTRIC-CONTACT HEATING
Russian). The effects of process variables on electrical contact sintering and mechanical properties of compacts, formed from Fe powder, have been determined. It was shown that the specific porous structure, which is of effect in determination of the m e c h a n i c a l properties, is caused by accelerated h e a t i n g to the s i n t e r i n g t e m p e r a t u r e . The o p t i m u m s i n t e r i n g t e m p e r a t u r e , for b e s t m e c h a n i c a l properties, was found to be 1300°C. No benefit was gained from extended heating at the sintering temperature.
FUNDAMENTALS
G. HShne, G. Schubert, (Bergakademie, Freiberg, Germany), Naue H~te, Vol 36, No 3, 1991, 81-85, (In German). The strength of compacts made from metal chips rather t h a n conventional powders has been investigated. Interlocking of the chips, which depends on chip shape and surface quality, as a factor controlling strength of the compacts, is discussed. It is suggested that with metal chips with a high degree of shape similarity the strength of the metal determines the strength of the compacts.
DYNAMIC TESTING OF MATERIALS INCLUDING COMPOSITES IN M ~ . N N I N G ELECTRON MICROSCOPE
M. Cabrera, F. Heredero, Deform. Metal., Vol 15, No 155, 1989, 70-75, (In Spanish). The results of a comparative study of the effects of 1% of different compaction lubricants are presented. Compaction load/specimen compression curves are given. Two criteria were used to compare the results: comparison of specimens of the same density or weight. It was found that ethylene diamine deoctadecanoate was superior to zinc stearate.
USE OF CHANGE8 IN DYNAMIC YOUNG'S MODULUS AS A CRITERION OF OXIDATION V.I. Lavrentiev, Poroshkovaya Metallurgiya, No 11, 1990, 91-95, (In Russian). A procedure for the measurement of Young's modulus, under dynamic conditions, of an oxidizing material is described. The method has been used to study the oxidation of B fibres in the range 350 to 650°C. A change in the oxidation mechanism at the oxide melting point of 450°C was noted. The kinetic parameters of oxide film growth were determined.
L.O. A n d r u s h c h i k et al, Poroshkovaya Metallurgiya, No 1, 1991, 17-22, (In
STRENGTH OF COMPACTS PREPARED FROM METAL CHIPS
COMPARISON OF COMPACTION LUBRICANTS
method and in the range 400 to 2200°K by the m e t h o d of m i x t u r e s . I s o t h e r m a l C o m p r e s s i b i l i t y is estimated from the results.
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G. Vekinis et al, (Univ of Cambridge, Cambridge, UK), Metals and Materials, Vol 7, No 5, 1991, 279-284. Techniques for the testing of materials, p a r t i c u l a r l y cermets, composites and c e r a m i c s , in the s c a n n i n g e l e c t r o n microscope are described. In particular sub-critical cracking is considered since this is said to have considerable influence on the mechanical properties. The objective is to determine the micromechanisms of cracking a n d fracture a n d to apply knowledge of these to fracture a n d damage models.
THERMODYNAMIC PROPERTIES OF LaB4 A.S. Bolgar et al, Poroshkovaya Metallurgiya, No 11, 1990, 72-75, (In Russian). Thermodynamic properties, heat capacity, e n t h a l p y a n d t e m p e r a t u r e coefficients of LaB4 have been measured in the range 60 to 300°K by an adiabatic
DETERMINATION OF POROSITY FUNCTIONS OF POWDER BODIES UNDER SIMPLE LOADING V.M. Leshchinsky et al, Poroshkovaya Metallurgiya, No 12, 1990, 15-17, (In Russian). Porosity functions of compacted porous media were determined and related to stress analysis of the compacting process. The results are said to show that the porosity functions of the spherical portion of the stress tensor do not depend on the composition of the porous material. The porosity functions were found to depend on the deviation part of the stress tensor which d e p e n d s on c o m p o s i t i o n a n d mechanical properties of the material.
PREDICTION OF POROSITY IN POWDER COATINGS Kharlamov, Poroshkova~a MetaUurgiya, No 12, 1990, 36-41, (In Russian).
Y~
A model for gas thermal coating of spherical and cylindrical particles has been constructed with respect to porosity. The model predicted a porosiw of 9.3% for cylinders and 25.9% for spheres. A shape related factor, used to link porosity with strength, was suggested.
EFFECT OF INTERNAL STRE88 ON YIELD CRITERIA OF POROUS METALS V.Z. Midukov, Poroshkovaya Metallurgiya, No 1, 1991, 1-7, (In Russian). The p a p e r d e m o n s t r a t e s t h a t the densification of porous metals, leading to material ductility, is governed by an equation of elliptical form. There is a shift towards a compressive s t r e ~ state which is a t t r i b u t e d to self b a l a n c i n g stresses developed in pressing and redistribution of stresses at defects in the structure.
MPR July/August 1991 53
EFFECT OF PROCESS VARIABLES ON M COMPACTING OF METAL C H M G. HShne, G. Schubert, (Bergakademie, Freiberg, Germany), Neue H~te, Vol 36, No 2, 1991, 41-46, (In German). Consolidation of metal chips has been investigated with regard to the mechanism of densification during compacting and the effects of p r o c e s s p a r a m e t e r s were determined. Compacting pressure was found to be the main controlling influence on compact density.
STABILITY OF LIQUID FILMS DURING LIQUID PHAKE 8 1 N T E S I ~ OF CEMENTED CARBIDlS$
A.F. IAsovsky, Porositkovaya Metallurgiya, No 1, 1991, 11-17, (In Russian). Surface thermodynamics of solid/liquid interfaces in cemented carbides of W and Cr with Co, Cu and Ni matrices and Ni-Pb alloys during liquid phase sintering have been determined. It was shown that there is a critical liquid film thickness which influences the stability of the film. Below the critical thickness the films form and grow by liquid metal migration. The films are stable above the critical thickness. STRUCTURE AND MECHANICAL PROPERTIES OF IRON SINTERED BY ELECTRIC-CONTACT HEATING
Russian). The effects of process variables on electrical contact sintering and mechanical properties of compacts, formed from Fe powder, have been determined. It was shown that the specific porous structure, which is of effect in determination of the m e c h a n i c a l properties, is caused by accelerated h e a t i n g to the s i n t e r i n g t e m p e r a t u r e . The o p t i m u m s i n t e r i n g t e m p e r a t u r e , for b e s t m e c h a n i c a l properties, was found to be 1300°C. No benefit was gained from extended heating at the sintering temperature.
FUNDAMENTALS
G. HShne, G. Schubert, (Bergakademie, Freiberg, Germany), Naue H~te, Vol 36, No 3, 1991, 81-85, (In German). The strength of compacts made from metal chips rather t h a n conventional powders has been investigated. Interlocking of the chips, which depends on chip shape and surface quality, as a factor controlling strength of the compacts, is discussed. It is suggested that with metal chips with a high degree of shape similarity the strength of the metal determines the strength of the compacts.
DYNAMIC TESTING OF MATERIALS INCLUDING COMPOSITES IN M ~ . N N I N G ELECTRON MICROSCOPE
M. Cabrera, F. Heredero, Deform. Metal., Vol 15, No 155, 1989, 70-75, (In Spanish). The results of a comparative study of the effects of 1% of different compaction lubricants are presented. Compaction load/specimen compression curves are given. Two criteria were used to compare the results: comparison of specimens of the same density or weight. It was found that ethylene diamine deoctadecanoate was superior to zinc stearate.
USE OF CHANGE8 IN DYNAMIC YOUNG'S MODULUS AS A CRITERION OF OXIDATION V.I. Lavrentiev, Poroshkovaya Metallurgiya, No 11, 1990, 91-95, (In Russian). A procedure for the measurement of Young's modulus, under dynamic conditions, of an oxidizing material is described. The method has been used to study the oxidation of B fibres in the range 350 to 650°C. A change in the oxidation mechanism at the oxide melting point of 450°C was noted. The kinetic parameters of oxide film growth were determined.
L.O. A n d r u s h c h i k et al, Poroshkovaya Metallurgiya, No 1, 1991, 17-22, (In
STRENGTH OF COMPACTS PREPARED FROM METAL CHIPS
COMPARISON OF COMPACTION LUBRICANTS
method and in the range 400 to 2200°K by the m e t h o d of m i x t u r e s . I s o t h e r m a l C o m p r e s s i b i l i t y is estimated from the results.
I
I
I
I
II
I
G. Vekinis et al, (Univ of Cambridge, Cambridge, UK), Metals and Materials, Vol 7, No 5, 1991, 279-284. Techniques for the testing of materials, p a r t i c u l a r l y cermets, composites and c e r a m i c s , in the s c a n n i n g e l e c t r o n microscope are described. In particular sub-critical cracking is considered since this is said to have considerable influence on the mechanical properties. The objective is to determine the micromechanisms of cracking a n d fracture a n d to apply knowledge of these to fracture a n d damage models.
THERMODYNAMIC PROPERTIES OF LaB4 A.S. Bolgar et al, Poroshkovaya Metallurgiya, No 11, 1990, 72-75, (In Russian). Thermodynamic properties, heat capacity, e n t h a l p y a n d t e m p e r a t u r e coefficients of LaB4 have been measured in the range 60 to 300°K by an adiabatic
DETERMINATION OF POROSITY FUNCTIONS OF POWDER BODIES UNDER SIMPLE LOADING V.M. Leshchinsky et al, Poroshkovaya Metallurgiya, No 12, 1990, 15-17, (In Russian). Porosity functions of compacted porous media were determined and related to stress analysis of the compacting process. The results are said to show that the porosity functions of the spherical portion of the stress tensor do not depend on the composition of the porous material. The porosity functions were found to depend on the deviation part of the stress tensor which d e p e n d s on c o m p o s i t i o n a n d mechanical properties of the material.
PREDICTION OF POROSITY IN POWDER COATINGS Kharlamov, Poroshkova~a MetaUurgiya, No 12, 1990, 36-41, (In Russian).
Y~
A model for gas thermal coating of spherical and cylindrical particles has been constructed with respect to porosity. The model predicted a porosiw of 9.3% for cylinders and 25.9% for spheres. A shape related factor, used to link porosity with strength, was suggested.
EFFECT OF INTERNAL STRE88 ON YIELD CRITERIA OF POROUS METALS V.Z. Midukov, Poroshkovaya Metallurgiya, No 1, 1991, 1-7, (In Russian). The p a p e r d e m o n s t r a t e s t h a t the densification of porous metals, leading to material ductility, is governed by an equation of elliptical form. There is a shift towards a compressive s t r e ~ state which is a t t r i b u t e d to self b a l a n c i n g stresses developed in pressing and redistribution of stresses at defects in the structure.
MPR July/August 1991 53