Effect of thermal exposure on microstructure and tensile properties of laser deposited Ti60A alloy

A near α high-temperature titanium alloy Ti60A (Ti5.54Al3.38Sn3.34Zr0.37Mo0.46Si) was fabricated by laser melting deposition (LMD) manufacturing process. Room-temperature tensile properties before and after 600 °C/100 h thermal exposure were evaluated. Microstructural changes and tensile fracture characteristics were examined by OM, SEM and TEM equipped with EDX. Results indicate that α lamellae coarsening and the precipitation of incoherent silicides and coherent Ti3Al in the alloys after thermal exposure cause the degradation of tensile properties. The silicides are confirmed to be hexagonal quasi-S2 type (TiZr0.3)6Si3, with a=0.71 nm and c=0.37 nm by electron diffraction analysis. Compared to wrought Ti60A alloy with coarse Widmanstatten microstructure, laser deposited Ti60A alloy with fine basket-weave microstructure exhibits slightly higher strength and ductility after thermal exposure. The effect of thermal exposure on tensile properties related to the precipitation of Ti3Al and silicides is discussed.