Enhanced strength and ductility in thin Ti-6Al-4V alloy components by alternating the thermal cycle strategy during plasma arc additive manufacturing

There is microstructural heterogeneity in titanium alloy deposited by high-energy-density beam additive manufacturing (AM) technologies in an as-built condition that leads to anisotropy of mechanical properties, especially poor ductility. To resolve this problem, use of an alternating thermal cycle strategy during plasma arc AM has been studied. The results show that the equivalent thermal balance is maintained in the process, preventing the coarsening microstructure from growing along a single direction. As a result of the change of the maximum temperature gradient, the close-packed plane growth of the alpha phase deviated from the preferred orientation direction; i.e., the alpha phase deviated from the growth of {0002} and {10 (1) over bar0} planes in the vertical direction but {10 (2) over bar0} and (10 (1) over bar0} planes in the horizontal direction. The grain size and the width of lamellar alpha are refined, specially the layer band region. The horizontal as-built mechanical properties are higher than those of the forging standards, with elongation of 11.6 +/- 0.2%, and 28 +/- 1.8% reduction of area. Meanwhile, the average vertical tensile properties were also commensurate with the forging strength, thus anisotropy and heterogeneity of the microstructure and mechanical properties are effectively weakened without post heat treatment.