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High performance cooling devices made by PM
of conditions and fatigue testing was in a Wohler machine. Peened and unpeened specimens were compared. Fractures were examined to study crack initiation and propagation. S/N curves were compared to assess effects of shot peening on fatigue endurance. It was shown that the endurance limit can be increased by 57% through shot peening. SURFACE HARDENING OF TUNGSTEN BASED HEAVY ALLOYS SEroglu et al. (Tubitak-MRC, Turkey.) A method for surface hardening of W heavy alloys was described. This involves carburizing of W to WC at 1200°C in CH,-Ar. The process was discussed in terms of thermodynamics. Effects of CH, content and gas flow rate on carburizing were investigated. Vickers microhardness was reported to be 3000 at a 100 g load. The microstructures were analysed. MORPHOLOGY OF INDUSTRIAL DIAMOND POWDERS F.Marian et aZ. (DACIA Synthetic Diamond Factory, Romania.) It was noted that particles of synthetic diamond may be cubic or octahedral in shape depending on crystal conditions. growth and process Properties are reported to be related to the particle morphology.
Mechanical properties EFFECTS OF NOTCHES ON FRACTURE OF SINTERED STEELS AMolinari et al. (University of Trento, Italy. ) The influence of pores, as stress intensifiers in PM materials, on fracture was discussed with regard to difficulties in quantifying the effects. Experimental and numerical approaches to the problem were proposed. Bend and tensile tests were carried out on notched specimens of two steels at two levels of porosity. The results were analysed by a finite element procedure to assess the stress/strain distribution and stress triaxiality. A triaxiality parameter was plotted against plastic strain to define a fracture criterion. It was shown that behaviour of the steel can be explained with reference to notch effect of pores. EFFECTS OF PROCESS PARAMETERS ON INDUCTION HARDENING OF PM STEEL PARTS M.Drozda, M.Rosso. (Polytechnico di Torino, Italy.) Induction hardening of PM alloy steels was discussed with regard to porosity and inhomogeneities in sin-
40 MPR November 1998
tered materials. A study of induction hardening of a MO alloy steel, with the object of determination of effects of process variables, was described. Hardness, microscopy and X-ray diffraction were used. Presence of retained austenite was investigated. WEAR BEHAVIOUR OF NITROCABBURIZED SINTERED STEELS M.Rosso, G.Scavino. (Polytechnic0 di Torino, Italy.) Effects of gaseous nitrocarhurizing, plasma nitriding and sulpho-nitrocarburizing of alloy and plain C sintered steels were investigated using microscopy, microhardness and X-ray diffraction. Wear. under 50 kg loads, was measured to evaluate friction, weight loss, dimensional loss and surface changes. A compact surface is shown to increase wear resistance. STRUCTURE AND PROPERTIES OF POWDERS CONSOLIDATED BY LASER ENGINEERED NET SHAPING J.E.Smugeresky et al. (Sandia National Laboratories, USA.) Net shaping of powders by laser was discussed. The process uses computer controlled laser heating to produce a part directly from powder without the use of a mould. Surface modification is possible and higher strengths are attained than with conventional PM processing. The process was described and relationships between structure and properties were discussed with respect to process conditions.
Applications HIGH PERFORMANCE COOLING DEVICES MADE BY PM SKohler. (Planscc GmbH, Reutte, Austria.) The need for high efficiency cooling devices, in microelectronic applications, where there has been miniaturization and increase in power was discussed. The required properties for heat sink materials were said to be low thermal expansion, with the need to match expansion of the semiconductor device, and high thermal conductivity. These can be met by alloys such as W-Cu and Mo-Cu. Special requirements can be met by varying the alloy composition. Standard PM process such as inliltration of a W skeleton with Cu can be used to make heat sinks. MO-Cu can be rolled into sheet and stamped into parts.
Advanced materials EVALUATION OF CORROSION RESISTANCE OF STAINLESS STEEL
A.J.Martin et al. (University of Barcelona, Barcelona, Spain.) Methods of assessing corrosion resistance of stainless steel were reviewed. Salt-fog tests were considered to be imprecise and lengthy, although widely used. Potentiometric tests provide a rapid and precise guide to corrosion resistance. A study of corrosion resistance of 3431, and 410L stainless steels, sintered under various conditions, was described. Cyclic potentiodynamic and polarization resistance tests were used and their reliability evaluated. IRON MATRIX COMPOSITES REINFORCED WITH NIOBIUM CARBIDE J.M.Ruiz-Roman et al. (Polytechnic University of Madrid, Spain.) Investigations into the production of Fe-NbC composites for structural applications were described. Materials were prepared from elemental powders by mixing or by mechanical alloying of Fe and NbC mixtures. The prepared powders were pressed and sintered and characterized for mechanical properties. The properties were reported to be adequate to allow use of the materials in applications where high alloy Cu-Ni steels are currently used. ALUMINIUM BASE METAL MATRIX COMPOSITES REINFORCED WITH CARBIDES J.M.Ruiz-Roman et al. (Polytechnic University of Madrid, Spain.) It was reported that a range of Al4.5wt%Cu-0.7%Si-0.5%Mg matrix composites, reinforced with NbC, VC, TaC, TIC and MO&, had been prepared. The matrix was prepared by mechanical alloying and the composites were milled in a planetary mill. The powders were pressed at 300 MPa and were extruded at 500°C with a graphite lubricant. Structure and mechanical properties were evaluated. EVALUATION OF HEAVY ALLOYS BY CHARPY TESTS J.J.Bucki et al. (Technical University of Warsaw. Poland.) Processing of W heavy alloys, by liquid phase sintering, structure, properties and applications were discussed. It was reported that hydroextrusion had been used to process W-7%Ni-3%Fe by 10 to 30% reduction. Un-notched Charpy tests were carried out on an instrumented testing machine and fractures were examined by scanning electron microscopy Load/deflection and energy/deflection curves were used to demonstrate deformation under heavy impact loading.
Mechanical properties EFFECTS OF NOTCHES ON FRACTURE OF SINTERED STEELS AMolinari et al. (University of Trento, Italy. ) The influence of pores, as stress intensifiers in PM materials, on fracture was discussed with regard to difficulties in quantifying the effects. Experimental and numerical approaches to the problem were proposed. Bend and tensile tests were carried out on notched specimens of two steels at two levels of porosity. The results were analysed by a finite element procedure to assess the stress/strain distribution and stress triaxiality. A triaxiality parameter was plotted against plastic strain to define a fracture criterion. It was shown that behaviour of the steel can be explained with reference to notch effect of pores. EFFECTS OF PROCESS PARAMETERS ON INDUCTION HARDENING OF PM STEEL PARTS M.Drozda, M.Rosso. (Polytechnico di Torino, Italy.) Induction hardening of PM alloy steels was discussed with regard to porosity and inhomogeneities in sin-
40 MPR November 1998
tered materials. A study of induction hardening of a MO alloy steel, with the object of determination of effects of process variables, was described. Hardness, microscopy and X-ray diffraction were used. Presence of retained austenite was investigated. WEAR BEHAVIOUR OF NITROCABBURIZED SINTERED STEELS M.Rosso, G.Scavino. (Polytechnic0 di Torino, Italy.) Effects of gaseous nitrocarhurizing, plasma nitriding and sulpho-nitrocarburizing of alloy and plain C sintered steels were investigated using microscopy, microhardness and X-ray diffraction. Wear. under 50 kg loads, was measured to evaluate friction, weight loss, dimensional loss and surface changes. A compact surface is shown to increase wear resistance. STRUCTURE AND PROPERTIES OF POWDERS CONSOLIDATED BY LASER ENGINEERED NET SHAPING J.E.Smugeresky et al. (Sandia National Laboratories, USA.) Net shaping of powders by laser was discussed. The process uses computer controlled laser heating to produce a part directly from powder without the use of a mould. Surface modification is possible and higher strengths are attained than with conventional PM processing. The process was described and relationships between structure and properties were discussed with respect to process conditions.
Applications HIGH PERFORMANCE COOLING DEVICES MADE BY PM SKohler. (Planscc GmbH, Reutte, Austria.) The need for high efficiency cooling devices, in microelectronic applications, where there has been miniaturization and increase in power was discussed. The required properties for heat sink materials were said to be low thermal expansion, with the need to match expansion of the semiconductor device, and high thermal conductivity. These can be met by alloys such as W-Cu and Mo-Cu. Special requirements can be met by varying the alloy composition. Standard PM process such as inliltration of a W skeleton with Cu can be used to make heat sinks. MO-Cu can be rolled into sheet and stamped into parts.
Advanced materials EVALUATION OF CORROSION RESISTANCE OF STAINLESS STEEL
A.J.Martin et al. (University of Barcelona, Barcelona, Spain.) Methods of assessing corrosion resistance of stainless steel were reviewed. Salt-fog tests were considered to be imprecise and lengthy, although widely used. Potentiometric tests provide a rapid and precise guide to corrosion resistance. A study of corrosion resistance of 3431, and 410L stainless steels, sintered under various conditions, was described. Cyclic potentiodynamic and polarization resistance tests were used and their reliability evaluated. IRON MATRIX COMPOSITES REINFORCED WITH NIOBIUM CARBIDE J.M.Ruiz-Roman et al. (Polytechnic University of Madrid, Spain.) Investigations into the production of Fe-NbC composites for structural applications were described. Materials were prepared from elemental powders by mixing or by mechanical alloying of Fe and NbC mixtures. The prepared powders were pressed and sintered and characterized for mechanical properties. The properties were reported to be adequate to allow use of the materials in applications where high alloy Cu-Ni steels are currently used. ALUMINIUM BASE METAL MATRIX COMPOSITES REINFORCED WITH CARBIDES J.M.Ruiz-Roman et al. (Polytechnic University of Madrid, Spain.) It was reported that a range of Al4.5wt%Cu-0.7%Si-0.5%Mg matrix composites, reinforced with NbC, VC, TaC, TIC and MO&, had been prepared. The matrix was prepared by mechanical alloying and the composites were milled in a planetary mill. The powders were pressed at 300 MPa and were extruded at 500°C with a graphite lubricant. Structure and mechanical properties were evaluated. EVALUATION OF HEAVY ALLOYS BY CHARPY TESTS J.J.Bucki et al. (Technical University of Warsaw. Poland.) Processing of W heavy alloys, by liquid phase sintering, structure, properties and applications were discussed. It was reported that hydroextrusion had been used to process W-7%Ni-3%Fe by 10 to 30% reduction. Un-notched Charpy tests were carried out on an instrumented testing machine and fractures were examined by scanning electron microscopy Load/deflection and energy/deflection curves were used to demonstrate deformation under heavy impact loading.