Oxidation and Stress Enhanced Oxidation of Ti-6-2-4-2

摘要

Oxidation kinetics of Ti-6-2-4-2 has been investigated in the temperature range of 450°C-750°C with the aid of weight gain experiments for a duration of 100 h. As oxidation is more severe under stress, oxidation during 4-point bending experiments has also been investigated in the maximum service temperature range of 450°C to 550°C for 100 h. At these temperatures for the chosen duration practically no oxide scale is formed, so that the only influence of oxidation considered is diffusion of oxygen into the alloy. The difference between oxidation under stress and without stress is investigated with the aid of hardness measurements in the oxygen diffusion zone (by nanoindentation; results not yet available) and mechanical testing. Three-point bending experiments at room temperature revealed premature cracking of the surface due to embrittlement as a result of oxygen uptake. The influence of stress during oxidation on this embrittlement was found to be relatively small in comparison with unstressed specimens (a decrease of failure strain of～ 3.5 % for the treatment at 550°C was found). The main reason for this limited influence is expected to be the stress relaxation which takes place during the 4-point bending oxidation experiment. The drop in maximum stress e.g. at 550°C of 644 MPa (0.2% yield stress at 550°C) to 67 MPa after 100 h reduces the additional stress induced uptake of oxygen.