Wear mechanisms in high speed steel reinforced with (NbC)p and (TaC)p MMCs

Powder metallurgy techniques were used to manufacture metal matrix composites. M3/2 high-speed steel was used as the matrix, and NbC and TaC, in different percentages, as reinforcements. Graphite was added to the M3/2 powders, to compensate carbon losses during sintering, and copper-phosphorous (Cu-P) to promote liquid phase sintering. The conventional powder metallurgy (P/M) route consists of dry mixing, uniaxially compacting (at 700 MPa) and vacuum sintering (at 1190 degrees C and 1230 degrees C) for 30 min. Their characterisation included a broad microstructural study by optical and scanning electron microscopy (SEM). The wear behaviour of all the sintered materials was studied. Wear tests were carried out on polished samples through a pin-on-disc test, using alumina as countermaterial. Wear tracks were analysed by SEM to clarify wear mechanisms. Wear is abrasive in all the materials and both NbC and TaC withstand wear. Only some TaC particles have been detached and spread across the wear track. NbC composites show a wear track clean of carbide particles. (C) 2000 Elsevier Science S.A. All rights reserved.