Sliding Wear Behavior and Phase Transformation of Single Crystal Silicon

The friction and wear behavior of single crystal silicon as a function of velocity at room temperature and low contact stress was studied. Thus the sliding tests of Si-Si_3N_4 pair were conducted on a UMT-2MT test rig, in ambient air and under unlubricated condition. The morphologies and chemical features of the worn silicon surfaces under various sliding conditions were analyzed by means of scanning electron microscopy and Raman spectroscopy. It was found that the friction coefficient and the wear rate of the single crystal silicon decreased with increasing sliding velocity. Friction-induced phase transformation of silicon was involved during the sliding process, which allowed the generation of Si-III, Si-XII, and amorphous silicon on the worn silicon surface. Such a kind of friction-induced phase transformation of silicon was closely dependent on the sliding conditions and had great effect on the wear mechanisms of the silicon. Namely, the worn surface of the single crystal silicon under a smaller sliding velocity and duration was characterized by micro-fracture and had a moderate plasticity, while the micro-fracture and plasticity on the worn surface tended to be decreased at a prolonged sliding duration. The plasticity of the worn silicon surface was attributed to the friction-induced phase transformation of silicon. Although Si-III phase was detected by Raman spectroscopy on the worn silicon surface at a larger sliding velocity, it needed further work to clarify the factors affecting the wear mechanism of single crystal silicon in this case.