Improvement of fatigue resistance and ductility of TiAl6V4 processed by selective laser melting

Generative processes or additive layer manufacturing like selective laser melting (SLM) enable the fabrication of highly precise and complex component geometries that are otherwise difficult, costly, or even impossible to realize using conventional techniques. Titanium alloys and in particular TiAl6V4 are suited well for processing by SLM. However, a careful optimization procedure of the process parameters is necessary to obtain a high quality material: firstly, the optimization of the initial process parameters for the minimization of inherent defects, and secondly, the optimization of the further thermomechanical treatment to minimize internal stresses and adjust the microstructure. These two stages of optimization are represented here. For the initial program more than 40 small TiAl6V4 cuboids were produced with the variable scan parameters and two- and three dimensionally analyzed. The reducing of the porosity by 6–10 times is shown. The optimized process parameters were used for further manufacturing of the test specimen, some of them were then thermomechanically treated: annealed or hot-isostatically pressed. The hardness, tensile properties and high cycle fatigue resistance of all samples were tested and the similar tests were also conducted for the reference material: wrought TiAl6V4 alloy. The microstructure, porosity and the received mechanical properties were analyzed and compared, and the influence of thermomechanical treatment was evaluated. As a result of this double optimization, a significant improvement of ductility (ɛ = 19.4%) and fatigue resistance compatible to the wrought TiAl6V4 for the SLM produced material was achieved. Furthermore, since some surfaces in complex components such as the channels in the turbine blade cannot be machined or polished, both treated (‘machined’) and untreated (‘as built’) surface conditions were considered and discussed.