Elevated temperature tensile behaviour of a Cu–4.5Ti alloy

Abstract

The high temperature tensile properties of a Cu–4.5Ti alloy have been investigated in the temperature range from room temperature (RT) to 550 °C in solution treated (ST) and peak-aged (PA) conditions. Yield strength (YS) and tensile strength (TS) in solution treated condition were found to be independent of test temperature up to 350 °C followed by a marginal increase at 450 °C and decreased, thereafter up to 550 °C. In situ age hardening during testing at 450 °C resulting in the precipitation of ordered, metastable and coherent Cu 4Ti, β′ phase is attributed to the increase in strength. Coarsening of β′ precipitate particles at 450 °C and precipitation of equilibrium phase β at 550 °C decrease the strengths. In the peak-aged condition, the YS and TS were found to be constant up to 350 °C, beyond which they decreased with increasing test temperature. The decrease in strengths beyond 350 °C in the peak-aged alloy is attributed to the coarsening of β′ precipitate particles, as well as precipitation of equilibrium phase β at 550 °C. High temperature tensile properties of Cu–4.5Ti are superior to those of Cu–Be alloy (C17200). Transmission electron microscope (TEM) analysis of the alloy confirms the presence of metastable and coherent Cu 4Ti, β′ precipitate when tested at 450 °C and both Cu 4Ti, β′ and equilibrium precipitate Cu 3Ti, β at the test temperature of 550 °C in solution treated as well as peak-aged conditions. Ductile mode of fracture was observed in both solution treated and peak-aged conditions of the alloy tested at RT as well as at elevated temperatures, i.e. 350, 450 and 550 °C.