Additive Processing of Ti-17 by Wire Arc Directed Energy Deposition: An Investigation of the Microstructure and Mechanical Properties

This study investigates the processing of Ti-17 by wire arc directed energy deposition. The investigation focused primarily on the microstructure and mechanical properties in both the as-built and heat-treated states. Significant microstructural banding is observed in the as-built state as a consequence of the process intrinsic heat treatment. A strong correlation is identified between the position within each band and the α lamellae width and subsequently the hardness (a spread of up to 133 HV1 was observed). The mechanisms involved in developing the microstructural bands are discussed, and a proposed pathway for their formation is presented. In tensile tests, the processed Ti-17 outperformed the conventional alloy in terms of strength (exceeding 1100 MPa), but lacked ductility in both the as-built and heat-treated state. The main reason for the low ductility is identified as a continuous film of α phase (GBα) at the grain boundary of prior β grains. Conventional heat treatment resulted in the growth of existing GBα, thereby proving ineffective. The observed anisotropy in the tensile properties between the build-up and deposition directions is found to be closely related to the loading direction of GBα at prior β grain boundaries.