Microstructural evolution and mechanical properties of Ti-6Al-4V wall deposited by pulsed plasma arc additive manufacturing. (15th July 2016) - Lin, J.J.
Abstract: Pulsed plasma arc additive manufacturing (PPAM) is a novel additive manufacturing (AM) technology due to its big potential in efficiency, convenience and cost-savings comparing with other AM process. In this research, several Ti-6Al-4V thin walls were deposited by an optimized weld wire-feed PPAM process, in which the heat input was gradually decreased layer by layer. The deposited thin wall consisted of various morphologies with different microstructure, such as epitaxial growth of prior β-grains, martensite and horizontal layer bands of Widmanstätten, which depend on the heat input, multiple thermal cycles and gradual cooling rate in the deposition process. Reducing heat input of each bead and using pulsed current in the PPAM process, the microstructure of thin wall was refined. Meanwhile, the thin wall was strengthening and toughening. The average yield strength (YS) and ultimate tensile strength (UTS) reach 909 MPa and 988 MPa, respectively, and elongation reaches about 7.5%. The thin wall exhibited excellent performance in the aeronautical applications owing to the high values of mechanical properties in the room temperature. Graphical abstract: Deposited Ti-6Al-4V wall by pulsed plasma arc additive manufacturing (PPAM) consisted various morphologies with different microstructure. The evolution of horizontal layer bands and varying prior β grains are related to pulsed frequency and gradually decrease heat input of layer by layer. The phase transformation of β-α follows the Burgers orientation relationship, and three orientations out of the twelve possibilities occupy dominating orientations, which finally form triangular stars or rhombic patterns. Highlights: The pulsed plasma arc additive manufacturing(PPAM)process deposited Ti-6Al-4V thin-wall by an optimized weld wire-feed PPAM process, in which the heat input was gradually decreased layer by layer. The results show the mechanical properties of the deposited wall at room temperature exceed the standard of casting wall, and the strength is even higher than that of forged wall. It is Indicate that both of the morphology of horizontal Layer Bands(LBs) and prior β grains are affected by the gradually reduced heat input of the pulsed plasma arc. The transformation of β-α occurs follows the Burgers orientation relationship, and three orientations out of twelve possibilities occupy dominate orientation formed triangular stars or into rhombic patterns