It was noted that reduced use of lubricants and use of lightweight materials, such as Mg alloys, were current engineering issues. Use of coatings to reduce wear and friction was discussed. Such coatings could be hardmetal or ceramic primary layers with a polymer/solid lubricant or MoS, as a working surface. Such coatings were reported to have good tribological properties.
New sintered composite materials with improved wear resistance et al. (Ames SA, Barcelona, Spain.)
Investigations of metal matrix composite materials, with solid lubricants incorporated, made by PM techniques, were described. These were reported to have high wear resistance in applications with low or no lubrication. Results of tribological tests were presented with case studies of applications. It was shown that it may be possible to substitute these materials for ball bearings.
Tribological properties of titanium nitride films with implanted halogen ions A.Mitsuo,
) The effects of F and Cl, ion-implanted into XN films on high speed steel substrates, on tribological properties against steel counter-bodies, was investigated by pin-on-disc tests. There was no adhesion of material from the counterbody to the implanted films. Cl reduced the coefficient of friction and the amount of wear debris. F did not influence the coefficient of friction. The differences were attributed to differences in interaction of halogens with the counter-materials.
Effects of density, warm compaction, ejection cracks and shot-peening on fatigue of steels A.Bergmmk.
High cycle tests were carried out to determine the effects of %Cu (0 or 2%), %C(O.2 or 0.8) and density (7.lor 7.4 g.cmF3) of selected steels. In some double pressed/sintered samples there were ejection cracks and resulting low endurance. Changes were made to tooling and warm compaction was used. Shot peening was shown to aid in healing ejection cracks in sintered specimens but did not increase endurance.
Comparison of rotating bend and tensile fatigue tests MSato
et al. (Kobe
Steel Co, Ltd, Japan.)
Methods for fatigue testing were reviewed. Rotating bend, tensile and tensile/compression tests were compared using carburized low alloy steel as the test material. Results for each type of test were correlated with the steel and compared.
Fracture toughness of sintered pm-alloyed steel compacts using small punch tests
outside layers and the core, which imposes a compressive stress in the outer layers increasing strength and toughness. Self propagating high temperature synthesis and pseudo-HIP were used to fabricate Ti-B-Ni and X-BN-Ni systems which were evaluated.
Development of recycling for tungsten carbide-cobalt hardmetals K.Kanu&,
Recycling of W and Co in hardmetals was discussed with regard to cost of W and Co. A new method, involving treatment of the hardmetal with molten Sn, was described. Sn forms a brittle intermetallic compound with Co. The material is subsequently treated chemically and mechanically to yield 6O%WC with a particle size of 1 to 5 pm.
Recycling of scrap hardmetal M.Tasic et al. (Scientific Research Centre, Yugoslavia.)
Investigations aimed at recycling scrap WCCo powders were described. The powders were heated at 700 to 900 “C. WO was recovered by chemical means and reduced to W in H at 900 “C in presence of Pd as catalyst. The W powders were characterized for composition and morphology.
Performance of sintered bearings at high and low speeds
(Hitachi Powders Metals Co Ltd,
) The performance of oil-impregnated sintered bearings, operating under boundary film lubrication, was investigated at low and high speeds. Good performance requires the material to have high wear resistance and high oil film strength. A range of materials was studied. The best performance was given by a sintered Cu-C steel with a hydrocarbon wax lubricant.
Strength and toughness Quantitative analysis of fatigue properties of PM material
Mechanical properties of sintered manganesechromium-vanadiummolybdenum steels A.S&ketal.
et al. (Tohoku University,
Strength and fracture toughness of 4 Ni-Mo steels were investigated with reference to density, composition and structure using a small punch test. Samples were spark plasma sintered. Strength and Jj, fracture toughness were determined from the load/displacement curve and showed clear dependencies on density and composition. Effects of microstructure were discussed.
The low cost and high affinity for 0 of alloy elements Mn and Cr, used in steels, were noted. Mechanical properties of steels with 1 to 3%Mn and up to 0.25%C were evaluated. Samples were die pressed at 600 MPa, and sintered at 1120 “C for 1 hour in cracked NH,. The relationship between %Mn and properties was evaluated. Tensile strength up to 925 MPa was attained.
Symmetrical compositionally graded materials ofScience and
Y.Serio et al. (Toyota Motor Carp, Japan.)
The need for further investigation of fatigue in high strength steels was discussed. An analy sis of the effects of defects in PM materials on fatigue nronerties was uresented.
Structural symmetrical compositionally graded materials were discussed with regard to means of production. These were made with differing thermal expansions between two
S.Rossi et al. (University
Corrosion and protection of steel PM parts was discussed with reference to the methods used. Electrodeposition of Zn was shown to be effective but costly and a study of hot dip galvanizing was described. Hot dip galvanized parts were characterized for structure and corrosion resistance as functions of composition, density and part shape.
Dimensional control of copper-carbon steel parts H.Ishikaw
et al. (Kawasaki Steel Carp, Japan.)
Dimensional accuracy and retention of part shape of PM Cu-C steels were discussed with regard to difficulties in attaining these aims. A study to clarify the factors influencing dimensions and minimizing variations between parts, by application of segregation-free technology and quality management of powders, was described.
Environmentally friendly steel sintering technology
Hotdip galvanizing of PM parts for corrosion protection
Measures for environmentally friendly sintering were described. Heat for dewaxing was generated by after-burning protective atmospheres and evolved waxes. Use was made of recuperative gas burners to reduce energy consumption. There was a significant reduction in energy usage.