Effect of Compound-Layer Elimination and Introducing Compressive Residual Stress by FPB Treatment on Fatigue Properties of Plasma-Carburized Ti-6Al-4V Alloy
Tatsuro MORITA, Takayuki OHTOMO, Chuji KAGAYA, Shinichi TANAKA and Noriyoshi TSUJI
Abstract:The effect of a duplex surface modification on the fatigue properties of Ti-6Al-4V alloy was examined. This method was composed of plasma carburizing and fine particle bombarding (FPB) treatment. Plasma carburizing at the first stage was conducted to form a hardened layer due to the diffusion of carbon. FPB treatment at the next stage was aimed for eliminating the brittle compound layer which was formed at the outermost surface and introducing compressive residual stress. In the case of the material plasma-carburized for 14.4 ks at 1123 K, cracks were initiated from the compound layer at relatively low stress amplitude level, so that the fatigue strength was greatly reduced. When the plasma-carburized material was further FPB-treated using SiC particles and high hardness steel particles, the compound layer was completely eliminated and compressive residual stress was introduced. As a result, the initiation sites of fatigue cracks were moved to the inside of the material just under the hardened layer and the fatigue strength was recovered to about the fatigue strength level of the untreated alloy. The above results showed that the duplex surface modification method examined in this study was effective to form the hardened layer which can improve the wear resistance without the great reduction in the fatigue strength of Ti-6Al-4V alloy. Key Words:Titanium Alloy, Ti-6Al-4V, Plasma Carburizing, Fine Particle Bombarding, Fatigue Properties, Compound Layer, Compressive Residual Stress