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/100h 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 (TiZr_0.3)₆Si₃, with a=0.71nm and c=0.37nm 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.