Toward low and high cycle fatigue behavior of SLM-fabricated NiTi: Considering the effect of build orientation and employing a self-heating approach

Build orientation is one of the important parameters in the selective laser melting (SLM) process that could alter the mechanical and fatigue properties of the fabricated parts. In the first section of this paper, the monotonic tensile and low-cycle fatigue behavior of the SLM NiTi dog-bone samples fabricated in three different orientations are investigated. Based on the results, the highest fatigue life was for the samples fabricated in 45 degrees with respect to the build plate, and the lowest fatigue life was for the samples fabricated on their edge. Furthermore, horizontally fabricated samples showed the highest scatter in fatigue life. It was revealed using SEM analysis that based on the build orientation, different types of defects, such as lack of fusion, entrapped gas porosities, and surface flaws could be generated inside the parts that could lead to a premature failure. In the second section of the paper, for the first time, the self-heating approach is utilized to investigate the high-cycle fatigue behavior of SLM NiTi samples fabricated in the horizontal direction. By considering the same origin for the fatigue damage and the one that generates the heat dissipation, self-heating approach can be used to predict the fatigue properties of the material. Using the self-heating approach, the fatigue limit for the virgin as well as pre-strained samples were evaluated. Similar to the conventional metals, the pre-strained sample showed a higher mean fatigue limit in comparison with the virgin samples.