Macroscopic analysis of time dependent plasticity in Ti alloys

TL;DR

This study investigates the mechanisms of time-dependent plasticity in titanium alloys at low temperatures through stress relaxation tests, revealing how alloy composition and temperature influence fatigue behavior and material properties.

Contribution

It provides new insights into how alloying elements and microstructure affect the time-dependent plasticity and fatigue of titanium alloys at various temperatures.

Findings

Activation volume and energy increase with temperature in all alloys.

Oxygen alloying enhances dwell fatigue effects.

Mo addition suppresses dwell fatigue.

Abstract

Component failure due to cold dwell fatigue of titanium and its alloys is a long-standing problem which has significant safety and economic implications to the aviation industry. This can be addressed by understanding the governing mechanisms of time dependent plasticity behaviour of Ti at low temperatures. Here, stress relaxation tests were performed at four different temperatures on three major alloy systems: commercially pure titanium (two alloys with different oxygen content), Ti-6Al-4V (two microstructures with differing beta phase fractions) and Ti-6Al-2Sn-4Zr-xMo (two alloys with different Mo content x= 2 or 6, and portion of beta phase). Key parameters controlling the time dependent plasticity were determined as a function of temperature. Both activation volume and energy were found to increase with temperature in all six alloys. It was found that the dwell fatigue effect is more significant by oxygen alloying but is suppressed by the addition of Mo. The presence of the beta phase did not strongly affect the dwell fatigue, however, it was suppressed at high temperature due to the low strain rate and strain rate sensitivity.