Effect of fast frequency double pulse current on microstructural characteristics and mechanical properties of wire arc additively manufactured Ti-6Al-4V alloy

This study introduces an innovative technique known as fast-frequency double pulse wire arc metal additive manufacturing (FFDP-WAAM). This method employs periodic fluctuations in arc plasma and force to enhance the stirring effect within the molten pool, resulting in the fragmentation of beta grains and the formation of finer prior- beta grains. The microstructure primarily comprises alpha', attributed to the high cooling rates and minimal heat accucmulation. Compared to the conventional gas tungsten arc welding-based WAAM (CGT-WAAM) process, FFDP-WAAM significantly reduces a-variant selection, thereby achieving a more uniform a phase orientation distribution. Additionally, ultrasonic vibration in the FFDP-WAAM process facilitates recrystallization and mitigates residual strain. The tensile strength and elongation of the FFDP-WAAM specimens reached 939.2 MPa and 9.0 %, respectively, whereas the CGT-WAAM specimens showed a lower tensile strength of 830 MPa and elongation of 9.2 %. The enhanced strength, fatigue life and microhardness of Ti-6Al-4V produced by FFDP-WAAM is ascribed to the refined grain-size distribution. Furthermore, the low Schmid factor (SF) distribution and the stable triangular structure of Category I a-clusters are anticipated to contribute to the increased strength of the FFDP-WAAM-fabricated wall.