Evaluation of Sliding Wear Resistant Property of C.P. Titanium and SP-700 Titanium Alloy Surface-hardened by Ar–5%CO Gas

Abstract

Sliding wear resistant properties of C.P. titanium and SP-700 alloy surface-hardened by Ar–5%CO gas were evaluated using a counterpart material of a bearing steel, JIS SUJ-2 steel and Nishihara type of sliding wear testing machine. In the latter, two disk specimens were rotated at different rotating speeds under a given compressive applied load, yielding a sliding ratio of 20%. Wear tests were repeated intermittently for several times, and a respective test time period in each series of wear tests was primarily varied. The mass loss in both disks was measured after each test. Wear resistance of annealed C.P. titanium without surface hardening was inferior to that of annealed SUJ-2 steel, but surface hardened C.P. titanium resulted in superior wear resistance over quench-tempered SUJ-2 steel with a hardness of 720 in Hv. Observation results of worn surfaces in both disks indicate that preferential wear occurred in the convex region of a furrow-like pattern formed by a lathe machining, resulting in a reduction of surface roughness values with wear progress. When a respective test time period was extended to 21.6 ks, adhesive wear took place between worn surfaces in both specimens, and the mass loss ratio in titanium disk increased at a much higher rate compared with that of a respective test time period of less than 14.4 ks. The steel debris torn off from worn surface of SUJ-2 steel disk was observed to adhere to the worn surface in surface hardened C.P. titanium disk. Wear resistant property of surface hardened SP-700 alloy was also superior to quench-tempered SUJ-2 steel.