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

Powder metallurgy techniques were used to manufacture metal matrix composit es. M3/2 high-speed steel was used as the matrix, and NbC and TaC, in diffe rent 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 va cuum sintering (at 1190 degrees C and 1230 degrees C) for 30 min. Their cha racterisation included a broad microstructural study by optical and scannin g electron microscopy (SEM). The wear behaviour of all the sintered materia ls was studied. Wear tests were carried out on polished samples through a p in-on-disc test, using alumina as countermaterial. Wear tracks were analyse d 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 deta ched and spread across the wear track. NbC composites show a wear track cle an of carbide particles. (C) 2000 Elsevier Science S.A. All rights reserved .