TRIBOLOGY AND MECHANICAL-PROPERTIES OF EXCIMER LASER MIXED TI-SI-C SURFACE ALLOYS

We have examined the wear and friction and surface hardness of the mixed phase Ti-Si-C alloy formed by excimer laser surface processing of Ti layers on SiC substrates. The friction between a ruby pin and the mixed surface shows a complex behavior depending on relative humidity, a behavior clearly moderated by the chemistry of the interface between the sliding pin and the surface. The friction is sometimes much lower and sometimes comparable to that between the ruby pin and the unalloyed substrate. Wear in the unalloyed case is characterized by fatigue fracture and flaking of the SiC surface which leads to abrasive wear of the ruby pin. In the alloyed case, a transfer film forms and even in the worst case, a smooth wear track results in the alloy and the pin is undamaged. The surface hardness is intermediate between that of the SiC and the unalloyed Ti surface layer. The wear results are understood in terms of changes in the grain boundary structure of the surface induced by the laser alloying process.