Ultrasonic assisted sieving

degassed at different temperatures to evaluate annealing effects, cold pressed and vacuum sintered at 650°C to a density of 98.7%. Properties were Brine11 hardness, 88, tensile strength, 283 MPa, and 4.5% elongation. These figures were about 7% less than the double-pressdouble-sinter materials. PROCESSING AND STRUCTURAL EVOLUTION OF MEXI-IANICALLY ALLOYED IRON-COPPER S.A.El-Badry et al (Al-Azhar University, Cairo, Egypt.) Studies of mechanical alloying of Fe(20 to 8O)%Cu, 200 mesh in size, were described. Milling was at ambient temperature, in sealed stainless steel containers, with hardened steel balls, at a ball to powder weight ratio of 8:l. Powder was characterized for structure and morphology. A single face centred cubic phase was found at 40 to 80% Cu and a single body centred cubic phase at 20 to 3O%Cu. DISPERSION STRENGTHENED COPPER BY MEXXANICAL ALLOYING WITH CERAMIC POWDERS VVergara et al. (University of Conception, Conception, Chile.) Four Cu base composites were prepared by mechanical alloying. The powders were consolidated and characterized for strength up to 4OO”C,electrical conductivity and structure. The composites contained carbides of Cr, Si or Zr, or Zr boride. The ceramic powders were below 325 mesh. Milling parameters were described. The alloys, in as-rolled condition, had tensile strengths of 700 to 900 MPa, with 75 to 85% conductivity on the International Annealed Cu Scale. Composite materials had higher strength and conductivity than many conventional Cu alloys.

TLibology and friction PSEUDO-PITMNG IN PM MATERIALS B.A.Kubicki, M.J.Kubicki. (University of Melbourne, Melbourne, Australia.) Investigations of pseudo-pitting of PM parts subjected to wear were described. Stress distribution is altered by the presence of pores in the contact area and the effect of lubricant pillows. These produce high stress levels and local damage in the contact area. The stress distribution was studied by photo-elasticity techniques and was modelled by finite element analysis. Some limitations in application of PM materials and practical methods for improvement in part reliability were indicated.

40 MPR September 1999

TRIROLOGICAL CHARAC’IXRISTICS OF SINTEXED IRON COMPOSITES C.Peytour-Chansac. (Renault, BoulogneBillancourt, France.) It was noted that the tribological character of Fe based materials can be modified by addition of second phases. The effects of simultaneous addition of Cu,P and hard ceramic particles were investigated. The characteristics of the additives were considered in optimizing material composition. Evolution of phases during sintering was determined. The materials were wear tested on pin-on-disc machines at ambient temperature up to 100°C in oil against hardened steel. The results were compared against Cu as a reference material. It was reported that the alloys studied had advantages in terms of wear properties and stability of the coefficient of friction. METAL MATRIX COMPOSITE MATERIAL FOR COMMERCIAL VEHICLE BRAKE LININGS N.de Leon et al. (Roplunds Fabriker AS, Odense, Denmark.) Development of a brake lining material, based on graphite, Fe powder, Fe fibre, bronze powder and A&O,, was reported. The constituents were mixed, pressed and sintered under conditions to ensure that high levels of graphite were incorporated in the matrix. Processing was described. The material was shown to have high wear resistance, high friction and low noise. Test results for these were presented. EFFECT OF ADDITIONS OF CARBON FIBRE INTO A PM FRICTION MATERIAL

Fatigue testing was monitored to give descriptions of fatigue strain, temperature and electrical resistivity. Cyclic hardening or softening occurred, depending on structure, pore shape and stress ratio, and influenced crack initiation and propagation. Structural investigation showed surface slip features and micro-cracks for each material and stress ratio studied. Equations linking mean stress and fatigue limit were discussed. APPLICATION OF LONGITUDINAL VIBRATIONS TO SINTERED PARTS GArghir et al. (Technical University of Cluj-Napoca, Cluj-Napoca, Romania.) A device for longitudinal vibration of sintered metals was testing described. The vibrations are induced by impact. The device was validated using dense steel and was used to determine Young’s modulus. A relationship between Young’s modulus and density was established. Test pieces were made from Fe powder and sintered in H. DIMENSIONAL CONTROL IN PRODUCTION OF THIN WALLED PM ROTORS KKarthikeyan, S.Srinivasan. (Sundram Fasteners Ltd, Hosur, India.) It was noted that PM is an established process for production of pump rotors and that variations in wall thickness may lead to production problems. Effects of alloying method, to reduce segregation, improvements in die filling and sizing rotors after sintering on dimensional tolerances were discussed. ULTRASONICASSISTED SlEVING

C.Mircea, C.Novac. (SC Metav SA Aviation Metallurgy, Bucharest, Romania.) The effect of replacing some of the matrix metal, Cu, in a PM friction material by chopped coated carbon fibre was investigated. The properties of the two materials, with and without C flbre, were described and compared.

Testing, measurement and control INFLUENCE OF &IRANSTRESS ON FATIGUE OF SINTERED STEEL A.Piotrowski, G.Biallas. (University of Essen, Essen, Germany.) Fatigue of Fe-1.2%Cu, sintered at 1120 and 1280°C and Fe-1.2%Cu0.6%C, sintered at 112O”C, all at a density of 7.0 g.cmA3, was investigated.

R.Zust. (Telsonic AG, Bronschhofen, Switzerland.) Conventional sieving is based on vibration of the sieve. Superimposition of ultrasonic energy transmits oscillations to the sieve in the pm range. This results in increased throughput, continuous cleaning of the sieve, efficient sieving at small apertures, more uniform sizing and break up of agglomerates. It was suggested’that the method could be applied to many different sieving machines. USE OF POWDER METALLURGY TO PREPARE ANALYTICAL STANDARDS C.Edtmaier et al. (University of Technology, Vienna, Austria.) It was noted that standard materials for trace element analysis must have a uniform distribution of the trace