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Development of porosity during recrystallization of granules
POWDER PRODUCTION
PRESSING A N D SINTERING
PREPARATION A N D P R O P E R T I E S OF ULTRAFINE NON-STOICHIOMETRIC T U N G S T E N CARBIDE POWDER BY A RADIO-FREQUENCY PLASMA TECHNIQUE
INTERPARTICLE B O N D I N G A N D PROPERTY EVOLUTION DURING HOT D E F O R M A T I O N OF POWDER MATERIAL
et al, Poroshkovaya Metallurgiya, No 2, 1991, 32-38, (In
B.Y. D o r o f e e v T. Kameyama et al, J. Japan Soc, Powder and Powder Metallurgy, Vol 38, No 2, 1991, 109-113, (In Japanese). The p r o d u c t i o n of u l t r a f i n e WCI_x p o w d e r by a RF p l a s m a t e c h n i q u e is described. The specific surface of the powder was measured at 34 m2/g and a mean particle size of 10 nm was calculated. The powder was stable up to 1000°C and above this decomposed into W2C.
Russian). The use of a reducing atmosphere in sintering, hot compaction and extrusion of powder metals to give improvements in properties is considered. It is suggested that the improvements are due to increased interparticle bond strengths.
STUDY OF PHYSICAL P R O C E S S E S DURING HOT COMPACTION O F METAL POWDERS IN CERAMIC D I E S KINETICS OF CARBOTHERMIC SYNTHESIS OF SILICON CARBIDE FROM SILICA
T. Shimoo, K. Okamura, J. Japan Soc, Powder and Powder Metallurgy, Vol 38, No 2, 1991, 121-126, (In Japanese). The synthesis of SiC from SiO 2 by carbothermic reduction has been studied. Reactions of SiO2 with graphite powder w e r e m e a s u r e d by t h e r m o g r a v i m e t r i c analysis (TGA) in the range 1675 to 1775°C in Ar. Products of the reactions were examined by chemical analysis and microscopy and SiC and SiO were found on the surface of the graphite particles. The initial reaction rate was determined by gaseous conditions and later rates by diffusion of C through the SiC surface layers.
P R O D U C T I O N OF E L O N G A T E D IRON POWDER BY A R E D U C T I O N P R O C E S S
S. Yue et al, (Chengdu Univ of Science and Technology, China), PM Technology, Vol 9, No 1, 1991, 21-22, (In Chinese). The production of elongated Fe powder particles of length 100 nm and length to d i a m e t e r r a t i o of 5:1 is d e s c r i b e d . Elongated ferric hydroxide particles were precipitated from aqueous solution, filtered off and reduced to Fe in H at high temperature. The powder was protected from s u b s e q u e n t o x i d a t i o n by storage under ethanol in Ar.
K r i s t i n e t al, P o r o s h k o v a y a Metallurgiya, No 2, 1991, 97-101, (In
V.K.
Russian). The development of a procedure for the study of physical p r o c e s s e s o c c u r r i n g during hot compacting is described. The technique is said to allow determination of d a t a relating to variations in process p a r a m e t e r s . A m e t h o d for control of temperature, by m e a s u r e m e n t of overheating in ceramic dies, for use in hot-compacting is proposed. COMPUTER SIMULATION OF EVOLUTION OF MICROSTRUCTURE IN POLYDISPERSED MATERIALS D U R I N G SINTERING
R.M. Kadushnikov et al, Poroshkovaya Metallurgiya, No.2, 1991, 18-24, (In Russian). A computer based model of structure formation during sintering is described. Geometrical description of particle shapes at all stages is introduced. A method for simulation of sintering of spherical powders is suggested. The process is modelled in two dimensions using disks.
MATHEMATICAL M O D E L L I N G OF NONISOTHERMAL S I N T E R I N G
V.A. Invensen and V.Z. Belenky, Poroshkovaya Metallu~iya, No 2, 1991, 24-31, (In Russian). The time dependence of pore volume reduction during non-isothermal sintering was i n v e s t i g a t e d e x p e r i m e n t a l l y a n d
compared with a mathematical model. The model was found to be sufficiently accurate to allow estimation of sintering time and the relationships with heating rate, time a n d d e v i a t i o n s in c o n d i t i o n s w e r e considered. Pore volume reduction was found to be determined mainly by powder properties which could be incorporated in the mathematical equations.
S T U D I E S OF INITIAL STAGES OF SINTERING
V.M Svistunov and V.A. Strelsov, Poroshkovaya Metallurgiya, No 2, 1991, 38-44, (In Russian). A model, which sets out to explain anomalously high mass transfer during sintering, is proposed. The main elements are the cohesive forces which develop at the instant of neck formation between particles. The equations were formulated and the process analysed with regard to the concept of mobile boundaries. It is shown that the times for the initial stage of sintering are less than those deduced from diffusion laws. The roles of surface and volume diffusion are considered.
FUNDAMENTALS WETTING OF CERAMIC MATERIALS BY MOLTEN METALS
H. Hausner, (Technological Univ of Berlin, Germany), Powder Metall, Int., Vol 23, No 3, 1991, 192-195, (In German). The importance of wetting at interfaces b e t w e e n s o l i d a n d l i q u i d p h a s e s is discussed with respect to joining and other processes. Interface energies between phases, related to the wetting of ceramics, such as SiC and molten metals such as Ni and other cermet materials are considered. Factors affecting wetting are taken into account. D E V E L O P M E N T OF POROSITY DURING RECRYSTALLIZATION OF GRANULES
V.V. Sobolev, Poroshkovaya Metallurgiya, No 2, 1991, 1-3, (In Russian.) The f o r m a t i o n of p o r o s i t y d u r i n g recrystallization of granules was analysed mathematically. It was shown that the zone of porosity is located in the surface layers of the particles and that conditions favouring pore formation increase with increase in particle surface curvature during transition from plane to spherical surfaces.
MPR September 1991 65
PRESSING A N D SINTERING
PREPARATION A N D P R O P E R T I E S OF ULTRAFINE NON-STOICHIOMETRIC T U N G S T E N CARBIDE POWDER BY A RADIO-FREQUENCY PLASMA TECHNIQUE
INTERPARTICLE B O N D I N G A N D PROPERTY EVOLUTION DURING HOT D E F O R M A T I O N OF POWDER MATERIAL
et al, Poroshkovaya Metallurgiya, No 2, 1991, 32-38, (In
B.Y. D o r o f e e v T. Kameyama et al, J. Japan Soc, Powder and Powder Metallurgy, Vol 38, No 2, 1991, 109-113, (In Japanese). The p r o d u c t i o n of u l t r a f i n e WCI_x p o w d e r by a RF p l a s m a t e c h n i q u e is described. The specific surface of the powder was measured at 34 m2/g and a mean particle size of 10 nm was calculated. The powder was stable up to 1000°C and above this decomposed into W2C.
Russian). The use of a reducing atmosphere in sintering, hot compaction and extrusion of powder metals to give improvements in properties is considered. It is suggested that the improvements are due to increased interparticle bond strengths.
STUDY OF PHYSICAL P R O C E S S E S DURING HOT COMPACTION O F METAL POWDERS IN CERAMIC D I E S KINETICS OF CARBOTHERMIC SYNTHESIS OF SILICON CARBIDE FROM SILICA
T. Shimoo, K. Okamura, J. Japan Soc, Powder and Powder Metallurgy, Vol 38, No 2, 1991, 121-126, (In Japanese). The synthesis of SiC from SiO 2 by carbothermic reduction has been studied. Reactions of SiO2 with graphite powder w e r e m e a s u r e d by t h e r m o g r a v i m e t r i c analysis (TGA) in the range 1675 to 1775°C in Ar. Products of the reactions were examined by chemical analysis and microscopy and SiC and SiO were found on the surface of the graphite particles. The initial reaction rate was determined by gaseous conditions and later rates by diffusion of C through the SiC surface layers.
P R O D U C T I O N OF E L O N G A T E D IRON POWDER BY A R E D U C T I O N P R O C E S S
S. Yue et al, (Chengdu Univ of Science and Technology, China), PM Technology, Vol 9, No 1, 1991, 21-22, (In Chinese). The production of elongated Fe powder particles of length 100 nm and length to d i a m e t e r r a t i o of 5:1 is d e s c r i b e d . Elongated ferric hydroxide particles were precipitated from aqueous solution, filtered off and reduced to Fe in H at high temperature. The powder was protected from s u b s e q u e n t o x i d a t i o n by storage under ethanol in Ar.
K r i s t i n e t al, P o r o s h k o v a y a Metallurgiya, No 2, 1991, 97-101, (In
V.K.
Russian). The development of a procedure for the study of physical p r o c e s s e s o c c u r r i n g during hot compacting is described. The technique is said to allow determination of d a t a relating to variations in process p a r a m e t e r s . A m e t h o d for control of temperature, by m e a s u r e m e n t of overheating in ceramic dies, for use in hot-compacting is proposed. COMPUTER SIMULATION OF EVOLUTION OF MICROSTRUCTURE IN POLYDISPERSED MATERIALS D U R I N G SINTERING
R.M. Kadushnikov et al, Poroshkovaya Metallurgiya, No.2, 1991, 18-24, (In Russian). A computer based model of structure formation during sintering is described. Geometrical description of particle shapes at all stages is introduced. A method for simulation of sintering of spherical powders is suggested. The process is modelled in two dimensions using disks.
MATHEMATICAL M O D E L L I N G OF NONISOTHERMAL S I N T E R I N G
V.A. Invensen and V.Z. Belenky, Poroshkovaya Metallu~iya, No 2, 1991, 24-31, (In Russian). The time dependence of pore volume reduction during non-isothermal sintering was i n v e s t i g a t e d e x p e r i m e n t a l l y a n d
compared with a mathematical model. The model was found to be sufficiently accurate to allow estimation of sintering time and the relationships with heating rate, time a n d d e v i a t i o n s in c o n d i t i o n s w e r e considered. Pore volume reduction was found to be determined mainly by powder properties which could be incorporated in the mathematical equations.
S T U D I E S OF INITIAL STAGES OF SINTERING
V.M Svistunov and V.A. Strelsov, Poroshkovaya Metallurgiya, No 2, 1991, 38-44, (In Russian). A model, which sets out to explain anomalously high mass transfer during sintering, is proposed. The main elements are the cohesive forces which develop at the instant of neck formation between particles. The equations were formulated and the process analysed with regard to the concept of mobile boundaries. It is shown that the times for the initial stage of sintering are less than those deduced from diffusion laws. The roles of surface and volume diffusion are considered.
FUNDAMENTALS WETTING OF CERAMIC MATERIALS BY MOLTEN METALS
H. Hausner, (Technological Univ of Berlin, Germany), Powder Metall, Int., Vol 23, No 3, 1991, 192-195, (In German). The importance of wetting at interfaces b e t w e e n s o l i d a n d l i q u i d p h a s e s is discussed with respect to joining and other processes. Interface energies between phases, related to the wetting of ceramics, such as SiC and molten metals such as Ni and other cermet materials are considered. Factors affecting wetting are taken into account. D E V E L O P M E N T OF POROSITY DURING RECRYSTALLIZATION OF GRANULES
V.V. Sobolev, Poroshkovaya Metallurgiya, No 2, 1991, 1-3, (In Russian.) The f o r m a t i o n of p o r o s i t y d u r i n g recrystallization of granules was analysed mathematically. It was shown that the zone of porosity is located in the surface layers of the particles and that conditions favouring pore formation increase with increase in particle surface curvature during transition from plane to spherical surfaces.
MPR September 1991 65