Brian Welk, Nevin Taylor, Samuel Kuhr, G.B Viswanathan, Hamish L. Fraser

Center for the Accelerated Maturation of Materials, Department of Materials Science and Engineering, The Ohio State University, Columbus, OH, USA

There are a number of defects associated with the additive manufacturing (AM) of titanium alloys. These include the formation of coarse columnar microstructures, generally parallel to the growth/deposition direction in builds produced by blown powder, the presence of porosity, and residual stresses. This talk focuses on the first of these, coarse microstructures. Emphasis has been on the use of alloying to effect an equiaxed microstructure through modification of the solidification mechanism, by inducing a columnar to equiaxed transition (CET). The experiments have employed a combinatorial approach developed in our laboratory, where a LENS™ (blown powder) AM device with two powder hoppers has been used to produce variations in the minor alloying elements of interest, such that modifications to microstructure can be directly related to changes in composition. The microstructures produced as a result of the additive manufacturing process have been characterized. In the main, the use of selective alloying has been successful in terms of effecting a CET, such that refined equaixed grains are produced. A variety of microstructures may be produced during subsequent heat-treatment, and the underlying mechanism of formation of these has been studied. The mechanical properties of new Ti alloys, with alloying additions that result in CETs, have been assessed and their values have been compared with those predicted by a machine learning approach. These comparisons will be discussed.