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Solid phase diffusion of tungsten in alloys during liquid phase sintering
CONSOLIDATION MODEL FOR POWDER MAGNETIC MATERIALS LA. Berkov et al (Technical University, Chelyabinsk, Russia). A model of die compaction, based on solution of partial differential equations for elastoplastic isotropic materials with irrerversible shear deformation, was described. The calculations were confirmed for ferrites, Sm-Co and Nd-Fe-B ring specimens. FINITE ELEMENT SIMULATION OF HOT ISOSTATIC PRESSING LA Berkov et al (Technical University, Chelyabinsk, Russia). A model of HIP, based on solution of partial differential equations for viscoplastic isotropic porous materials, was described. The consitutive equations were written for cylndrical coordinates. Calculations for the problem of hardening in high speed steels in a mild steel shell were done using Lagrange’s difference method. COLD COMPACTION OF IRON POWDERS BY EXPERIMENTS AND SIMULATIONS G. Coccoz et al (Ecole des Mines de Paris, Sophia Antipolis, France). Triaxial tests were carried out on an Fe based powder which allowed the formulation of experimental load surfaces. A Cam-Clay constitutive model was developed and implemented in the finite element computer program. Simulation of cold compaction was reported to agree well with the experimental observations. MICROMECHANICAL MODEL OF MULTIAXIAL POWDER DENSIFICATION C.D. Turner (Ttibiak Mamara Research Centre, Kocaeli, Turkey). A micromechanical model for the initial stage of multiaxial densification of metal powders, using virtual work theory and pressure/density relations, was developed. It was assumed that the microscopic strain rate between particle centres was the same as the macroscopic strain rate. It was predicted that the pressure to attain a given density by uniaxial pressing is about double that for hydrostatic pressing.
DENSIFICATION OF POWDER COMPOSITES - EFFECT OF INCLUSION MORPHOLOGY
DRIVINGFORCEFORACTD’ATED SINTERING OF TUNGSTEN DOPED WITH NICKEL
F. Delie et al (Laboratory for Sols, Solids and Structures CRNS, Grenoble, France). Theoretical and experimental studies of consolidation were described use being made of HIP of metal powders with ceramic inclusions and also die compaction. A model of densitication was constructed and compared with the experimental results. A new approach for dealing with inclusion shape, based on calculation of deformation, was described.
W. Miss01 (Inst. of Non-Ferrous Metals, Gliwice, Poland). The mechanism of activated sintering of W by addition of Ni was discussed and an investigation described. An equation for the additional driving force for activated sintering was deduced from thermodynamics. It was considered that the presence of Ni leads to enhanced selfdiffusion in W.
Modelling of sintering LIQUID PENETRATION AND PARTICLE GROWTH DURING LIQUID PHASE SINTERING OF TUNGSTEN ALLOYS L. Ekbom, A. Eliasson (Royal Inst. of Technology, Stockholm, Sweden). The initial mechanisms of liquid phase sintering of W-Ni-Fe heavy alloys was discussed. The process was said to involve dissolution of W in the matrix and disintegration of W particles by grain boundary penetration in the W. The time scale was reported to be short, 10 to 20 seconds. Effects of solution and penetration of particles was calculated. NEW CONCEPTS IN THE THEORY OF SINTERING A.P. Savitskii (Inst. for Strength Physics and Materials Science, Tomsk, Russia). Mechanisms of liquid phase sintering of systems with interacting constituents were discussed with regard to the formation of solid solutions and intermetallic compounds. It was considered that dissolution of solid into the liquid phase is by diffusion of liquid into the solid until the limit of solid solubility, or the composition of an intermetallic, is reached. It was suggested that the commonly used two-particle model is inaccurate because it does not take pores between particles into account. A multiparticle model was proposed. Analytical equations were derived to express quantitativly porosity and volume changes as a result of alloy phase formation during liquid phase sintering.
NUMERICAL SIMULATION OF HOT ISOSTATIC PRESSING OF METAL POWDER
A MODEL TO ANALYSE MICROSTRUCTURE IN PARTICLE REARRANGEMENT DURING LIQUID PHASE SINTERING
AM. Habraken et al (University of Liege, Liege, Belgium). Constitutive models for HIP at high temperatures were presented. The thermal behaviour of the metal powder was described and incorporated in the model. Results for a HIP problem were shown to demonstrate the influence of the constitutive equations.
J.M. Chaix (Inst. National Polytechnique de Grenoble, St. Martin d’Heres, France). It was noted that an explanation of poor densification in liquid phase sintering in systems with negligible solubility had been proposed. Microstructure formation was discussed on the basis of a twodimensional simulation. The importance of local inhomogeneities was emphasized.
48
MPR May 1995
LIQUID PHASE SINTERED STAINLESS STEEL COMPOSITES WITH CHROMIUM BORIDE ADDED L.R. Jensen (Technical University of Denmark, Lyngby, Denmark). An investigation of liquid phase sintering of 316L stainless steel with lOvol% ceramic particles and up to 2%CrB was described. It was reported that CrB enhances densification and improves mechanical properties. Densities above 95% were attained. Structure/property relationships were established. CHARACTERISTICS OF COMPOSITE FORMATION BY LIQIUD PHASE SINTERMG I.A. Lavrinenko, Y.V. Naidich (Inst. for Problems of Materials Science, Kiev, Ukraine). An investigation of liquid phase sintering in systems with different characteristics of interaction between constituents was described. Wettability was considered to be the most important factor. The study was concerned with hard materials and the principles underlying the formation of composites were established. SOLID PHASE DIFFUSION OF TUNGSTEN IN ALLOYS DURING LIQUID PHASE SINTERING C. Chausse, F. Nardou (University of Limoges, Limoges, France). Densification of W alloys before the onset of liquid phase sintering was discussed with regard to diffusion mechanisms. Limits of W content and temperatures of diffusion were determined. It was reported that a NiCoFeW phase is formed in W alloys with a NiCoFe matrix. Sintering experiments at 500 to 1400°C were described. LIQUID PHASE SINTERING OF TITANIUM BORIDE-TITANIUM/IRON COMPOSITES H. Pastor et al (European Centre for Research in Powder Metallurgy, Grenoble, France). A study of liquid phase sintering in TiBzPhase TiFez alloys was described.
DENSIFICATION OF POWDER COMPOSITES - EFFECT OF INCLUSION MORPHOLOGY
DRIVINGFORCEFORACTD’ATED SINTERING OF TUNGSTEN DOPED WITH NICKEL
F. Delie et al (Laboratory for Sols, Solids and Structures CRNS, Grenoble, France). Theoretical and experimental studies of consolidation were described use being made of HIP of metal powders with ceramic inclusions and also die compaction. A model of densitication was constructed and compared with the experimental results. A new approach for dealing with inclusion shape, based on calculation of deformation, was described.
W. Miss01 (Inst. of Non-Ferrous Metals, Gliwice, Poland). The mechanism of activated sintering of W by addition of Ni was discussed and an investigation described. An equation for the additional driving force for activated sintering was deduced from thermodynamics. It was considered that the presence of Ni leads to enhanced selfdiffusion in W.
Modelling of sintering LIQUID PENETRATION AND PARTICLE GROWTH DURING LIQUID PHASE SINTERING OF TUNGSTEN ALLOYS L. Ekbom, A. Eliasson (Royal Inst. of Technology, Stockholm, Sweden). The initial mechanisms of liquid phase sintering of W-Ni-Fe heavy alloys was discussed. The process was said to involve dissolution of W in the matrix and disintegration of W particles by grain boundary penetration in the W. The time scale was reported to be short, 10 to 20 seconds. Effects of solution and penetration of particles was calculated. NEW CONCEPTS IN THE THEORY OF SINTERING A.P. Savitskii (Inst. for Strength Physics and Materials Science, Tomsk, Russia). Mechanisms of liquid phase sintering of systems with interacting constituents were discussed with regard to the formation of solid solutions and intermetallic compounds. It was considered that dissolution of solid into the liquid phase is by diffusion of liquid into the solid until the limit of solid solubility, or the composition of an intermetallic, is reached. It was suggested that the commonly used two-particle model is inaccurate because it does not take pores between particles into account. A multiparticle model was proposed. Analytical equations were derived to express quantitativly porosity and volume changes as a result of alloy phase formation during liquid phase sintering.
NUMERICAL SIMULATION OF HOT ISOSTATIC PRESSING OF METAL POWDER
A MODEL TO ANALYSE MICROSTRUCTURE IN PARTICLE REARRANGEMENT DURING LIQUID PHASE SINTERING
AM. Habraken et al (University of Liege, Liege, Belgium). Constitutive models for HIP at high temperatures were presented. The thermal behaviour of the metal powder was described and incorporated in the model. Results for a HIP problem were shown to demonstrate the influence of the constitutive equations.
J.M. Chaix (Inst. National Polytechnique de Grenoble, St. Martin d’Heres, France). It was noted that an explanation of poor densification in liquid phase sintering in systems with negligible solubility had been proposed. Microstructure formation was discussed on the basis of a twodimensional simulation. The importance of local inhomogeneities was emphasized.
48
MPR May 1995
LIQUID PHASE SINTERED STAINLESS STEEL COMPOSITES WITH CHROMIUM BORIDE ADDED L.R. Jensen (Technical University of Denmark, Lyngby, Denmark). An investigation of liquid phase sintering of 316L stainless steel with lOvol% ceramic particles and up to 2%CrB was described. It was reported that CrB enhances densification and improves mechanical properties. Densities above 95% were attained. Structure/property relationships were established. CHARACTERISTICS OF COMPOSITE FORMATION BY LIQIUD PHASE SINTERMG I.A. Lavrinenko, Y.V. Naidich (Inst. for Problems of Materials Science, Kiev, Ukraine). An investigation of liquid phase sintering in systems with different characteristics of interaction between constituents was described. Wettability was considered to be the most important factor. The study was concerned with hard materials and the principles underlying the formation of composites were established. SOLID PHASE DIFFUSION OF TUNGSTEN IN ALLOYS DURING LIQUID PHASE SINTERING C. Chausse, F. Nardou (University of Limoges, Limoges, France). Densification of W alloys before the onset of liquid phase sintering was discussed with regard to diffusion mechanisms. Limits of W content and temperatures of diffusion were determined. It was reported that a NiCoFeW phase is formed in W alloys with a NiCoFe matrix. Sintering experiments at 500 to 1400°C were described. LIQUID PHASE SINTERING OF TITANIUM BORIDE-TITANIUM/IRON COMPOSITES H. Pastor et al (European Centre for Research in Powder Metallurgy, Grenoble, France). A study of liquid phase sintering in TiBzPhase TiFez alloys was described.