The effect of additional high dose carbon implantation on the tribological properties of titanium implanted steel
The tribological properties and the structural changes of hardened steel implanted with titanium followed by carbon were investigated as a function of additional carbon dose. The dose of Ti was 5×10 17 Ti cm -2 and the additional C doses were 0, 4×10 17, 8×10 17 and 1.2×10 18 C cm -2. After Ti implantation, the steel surface transformed to a FeTiC ternary amorphous phase. Additional implantation of carbon to a dose of 4×10 17 C cm -2 produced fine TiC precipitates dispersed in the ternary amorphous matrix. When the additional C dose exceeded 8×10 17 C cm -2, very fine graphite precipitates appeared in the ternary amorphous phase. The steel surface with very fine graphite precipitates exhibited superior tribological properties. The benefits provided by additional high dose carbon implantation are considered as follows: strengthening of the amorphous phase, thickening of the modified layer, dispersion strengthening of the implanted layer by very fine graphite precipitates and lubrication effect by graphite particles. Comparing the friction properties of Ti+C implanted steel with that of C implanted steel, the role of Ti implantation is to reduce the friction of the surface during sliding and the role of C implantation is to increase the lifetime of the surface against wear.