Advances in investment casting of Ti-6Al-4V alloy: a review

This paper presents a comprehensive review of the state of the art and challenges involved in investment casting of Ti-6Al-4V(Ti-6-4) alloy to improve the quality, costs and manufacturing of Ti parts. More than one hundred selected reports and articles on melting, casting and secondary processes such as hot isostatic pressing (HIPing) and heat treatment of the Ti-6-4 alloy system were reviewed to prepare this paper. The microstructure, composition and mechanical properties of Ti-6-4 alloy are discussed in detail. One of the main objectives of this paper was to identify means of improving the quality of castings, e. g. improving the mechanical properties through microstructure development and control to eliminate the casting factor, in particular for castings for use in aerospace applications. This work supports the M777 lightweight howitzer (LWH) programme, where investment casting was selected over machining and welding titanium plate to reduce part count and associated manufacturing expense for several LWH components. Another goal of this work was better to understand the investment casting process of Ti-6-4 alloy to eliminate/minimise defects in LWH components and provide useful insights to meet aggressive schedule requirements by minimising experimental production trials.