Fretting at high temperatures

The fretting damage to an austenitic stainless steel, type 321, in CO₂ is much reduced at temperatures above 400°C by the formation of a glaze type oxide. Increasing the normal pressure from 2 to 6.9 MN m⁻² at 650°C greatly increased the extent and quality of the glaze. The nickel-based alloy, Inconel 718, developed glaze oxide when fretted at 540°C in air, as indicated by a low coefficient of friction and wear rate. At 280°C, the glaze was only found at greater amplitudes of slip. Although the titanium alloy Ti-6Al-4V in air at 200 to 400°C developed a surface oxide which had some of the superficial features of a glaze, it nevertheless did not reduce the coefficient of friction to values characteristic of glaze. The common feature of high-temperature alloys which develop protective glaze oxides is that they are capable under conditions of sliding and fretting of forming a spinel type oxide which, however, must be adequately supported by a creep-resistant substrate at the operating temperature