High strain rate behavior of GTM-900 titanium alloy

Abstract

GTM-900 is an α+β alloy of titanium used in low-pressure (LP) compressor blades of gas turbine (GT) engines. The maximum allowable operating temperature of this alloy is 500°C. Silicon is added to enhance the creep resistance at elevated temperatures. The aim of this work is to establish the microstructural stability of this alloy and determine the high strain rate Johnson-Cook (J-C) material parameters such as A, B, and n. The material parameters are subsequently used by designers to simulate the "blade-off"and "casing containment"capability of the LP compressor blade. Split Hopkinson tensile bar was used to conduct high strain rate tests at about 2,000 s-1, and at three different temperatures, viz., 25°C, 300°C, and 500°C, to simulate critical conditions. Data obtained from these testing were used to construct a J-C model. Flow stress increased with an increase in strain rate and decreased with an increase in temperature because of thermal softening. Characterization, using optical and electron microscopes, indicated that the microstructure was stable even after the deformation at 500°C. The presence of needle-like silicide phase was observed under transmission electron microscopy and the composition was verified with X-ray diffraction results. A high strain hardening rate was observed even at elevated temperatures in this alloy (n ≈ 0.54 at 2,000 s-1 and 500°C) compared to Ti-6Al-4V titanium alloy (n ≈ 0.28). Considering good strength and microstructural stability up to 500°C, the present material offers to be an attractive alternate to other contemporary titanium alloys currently used in GT engine applications. Copyright © 2021 by ASTM International.