Chapter 8 - Additive manufacturing of titanium alloys: microstructure and texture evolution, defect formation and mechanical response

Abstract

Additive manufacturing (AM) has shown great potential in recent times to fabricate near net-shape 3D products from various materials systems including titanium (Ti) and Ti alloys. Here we present a comprehensive discussion on AM of Ti alloys outlining the microstructure and texture evolution plus defect formation and their subsequent effect over mechanical properties. We take a specific example of Laser-Engineered Net Shaping (LENS™) processed Ti-6Al-4V alloy and discuss how microstructure, texture, defects, and mechanical properties are connected in this system. In AM (LENS™) processing, graded microstructure forms in as-deposited bulk specimen for two-phase (α+β) alloys, for example, Ti-6Al-4V in terms of prior β grain morphology, different phase formation (α' -martensite, lamellar α, plus grain boundary α phases, etc.) plus their distribution depending on the deposition parameters. In addition, the microstructure exhibits spheroidization of α phase in as-deposited condition. The AM processing parameters also leads to strong macro- and microtexture evolution, macrozone elimination, and texture transition at the interface of various heat-affected zones. AM leads to various defect formations like porosity and residual stress within the bulk specimen. As a concomitant effect, mechanical properties along different orientations vary in coordination with the microstructure and texture evolution plus defect distribution with respect to the build direction.