The Variation of the Yield Stress of Ti Alloys with Strain Rate at High Temperatures

Abstract

This study extended investigation on the elevated-temperature yield-strength dependence of beta-phase titanium alloys on strain rate and temperature. Yield stresses were found to increase substantially with increasing strain rate at elevated temperatures due to the high strain-rate sensitivity of titanium at high temperatures. Above 1000 °C, the strain-rate sensitivities were found to increase substantially with increasing temperature and/or decreasing strain rate. The six alloys examined were TIMETAL 21S, Ti-15-3, Ti-6-4, Ti-13-11-3, Beta C, and Beta III. There was particular interest in determining the strain-rate sensitivity of these alloys through strain-rate change tests above 1000 °C. The yield stresses of all the titanium alloys at temperatures above 1093 °C were less than 1% of their ambient temperature values. Strain hardening was negligible in the alloys tested at these high temperatures. Extended tensile ductilities of 100 to 200% were observed due to the pronounced strain-rate sensitivity. The rate controlling mechanism for plasticity, based on activation energy and the strain-rate sensitivity measurements, is discussed.