高濃度軽元素含有チタン積層造形材の力学機能化

抄録

Laser powder bed fusion (LPBF) process, which is one of the additive manufacturing technologies, is useful for fine and unique microstructures formation of metal materials due to ultra-rapid solidification and cooling behavior. Titanium (Ti) alloys show a high specific strength by adding rare metals such as vanadium, zirconium, molybdenum and niobium. In this study, from a viewpoint of sustainable development goals (SDGs), we clarify a role of the ubiquitous light elements, in particular nitrogen (N) solute atoms on the fine microstructures formation and improved mechanical properties of LPBF Ti materials, and finally establish a new alloying design of Ti materials with no rare metals. Core-Shell structured Ti-N composite powders coated with Ti₂N/TiN thin layers were developed as starting materials. LPBF Ti with a very few N contents (0.01 wt.%) shows continuous epitaxial growth of α-Ti grains with a strong crystallographic texture, which causes an anisotropic tensile properties. On the other hand, Ti-0.31 wt.% N alloy formed different microstructures and textures from LPBF pure Ti by introduction of refined martensite grains with random crystallographic orientations. As a result, its anisotropic tensile properties were remarkably reduced, resulting an improved tensile strength (1065.7 MPa) and high ductility (24.5%).