EFFECT OF STRUCTURAL-CHANGE OF ALPHA-SIC FILM SYNTHESIZED BY DYNAMIC ION MIXING ON SURFACE HARDNESS AND FRICTION COEFFICIENT

Mild steel specimens were treated by dynamic ion mixing in which Si-deposition and 40 keV C-ion implantation were carried out simultaneously. A mixed layer of Si phase and alpha-SiC phase is synthesized when the Si-deposition rate is 0.10 nm/s and the C-ion current density is 20 mu A/cm(2). The Si phase transforms to alpha-SiC phase, which grows to form a monolithic alpha-SiC layer as the C-ion current density increases up to 30 mu A/cm(2). With a further increase in the C-ion current density or a decrease in the Si-deposition rate, the implanted C species accumulate to form a graphite phase, resulting in the growth of a graphite layer. The friction coefficient during a reciprocal motion wear test decreases and the surface hardness increases as the C-ion current density increases from 20 mu A/cm(2) to 30 mu A/cm(2), i.e. as the alpha-SiC phase grows to form the monolithic alpha-SiC layer. The friction coefficient increases and the surface hardness decreases with a further increase in the C-ion current density or a decrease in the Si-deposition rate, i.e. as the graphite layer grows.