Improvement of Wear and Fatigue Properties of Alloy 718 by Radical Nitriding

Abstract

In order to improve the wear and fatigue properties, radical nitriding was applied to Ni-base superalloy, Alloy 718, which is difficult to nitride at low temperature because of its stable passive film. Nitriding conditions selected were at 500°C∼570°C and for 10h∼20h in consideration of practical application. Compound layers formed by these nitriding conditions were 4μm∼10μm in thickness. By nitriding at higher temperature and for longer time, base alloy was softened, though the thickness of compound layer was increased. Wear properties were improved by the nitriding at both of room temperature and 500°C, especially at room temperature. The improvement of wear properties was caused by surface hardening. Moreover, fatigue strength at room temperature increased. The increase in fatigue strength was mainly caused by suppression of fatigue crack initiation due to compound layer.