Microstructure and mechanical properties of a copper containing three phase titanium alloy

In this study we attempt to improve the strength of titanium alloys by utilizing the precipitation hardening technique, a route that is relatively unexplored in titanium alloy development. It was found that copper satisfies the conditions necessary for precipitation hardening in titanium alloys and hence the following alloy, Ti–6Al–1.5V–2.5Cu (TAVC), was chosen for our studies. It was decided to ascertain the performance of this alloy in comparison to a standard titanium alloy, Ti–6Al–4V (TAV). Both the alloys were melted using a double Vacuum Arc Melting technique followed by forging and rolling in α–β regime. Subsequently, the alloys were β heat treated at 1010 °C and water quenched. Following this the alloys were aged at 500 °C. The aging characteristics were studied systematically through hardness and tensile testing techniques. While TAVC exhibited typical aging characteristics (hardening followed by softening), TAV displayed monotonic increase in strength following heat treatment. The yield strength of TAVC following peak aging is 1059 MPa which is 70 MPa higher than TAV heat treated under similar conditions. The higher, albeit limited strengthening, of TAVC vis-a-vis TAV was attributed to the formation of metastable precipitates of Ti–Cu which were revealed by TEM studies. The Mott–Nabarro model was able to rationalize the strengthening provided by the precipitates.