Effect of heat treatment on the microstructure and hardness of the SLMed TC4 alloy specimens

Titanium alloys have outstanding properties such as corrosion resistance, high strength-to-weight ratio even at high temperatures, which makes them a suitable candidate for high demanding applications such as in aerospace industry. Among the Ti-alloy families, Ti6Al-4V(TC4) has been widely used in additive manufacturing as well as traditional processing such as casting and forging. Additive manufacturing can be used to fabricate titanium alloys with complex geometrical features and reduce material waste, production time and costs. There are many researches about the effect of heat treatment on as-cast or as-forged microstructures.1,2 As additive manufacturing appears, the microstructure features and the effect heat treatment on the additive manufactured specimens come to be the research focus. Jiao et al.,3 found that α laths have a plate morphology, and they precipitated out from β phase following a tetrahedral relationship, a special morphology with mixture of plate-like and rod-like α phase in the fabricated Ti-10V-2Fe-3Al alloy specimen by laser melting deposition additive manufacturing. Aziz4 &Murr5 Thijs6 & Kobyrn7 & Zhu8 & Song9 investigated the microstructure of TC4 titanium alloy in selective laser manufacturing. SLMed samples own good mechanical properties except of ductility. Thus, researchers investigated the way how to improve the ductility by heat treatment. Erhard10 studied the effect of heat treatment on the microstructure and mechanical properties of samples made by SLM. Sabban11 proposed repeated thermal cycling close to but below the β transus temperature to form globular α phase, eliminating the need for plastic deformation prior to heat treatment, which led to the bimodal microstructure consisting of globular α in additively manufactured TC4 alloy. In order to provide the understanding how to improve the mechanical properties, the TC4 titanium alloy samples were made by SLM method and they were heat treated, the effect of heat treatment on microstructure was symmetrically investigated.