Toward Structural Fatigue Analysis of Horizontally-Fabricated NiTi via Selective Laser Melting

Abstract

NiTi (Nitinol) is a shape memory alloy with distinctive properties, such as shape memory, superelasticity, biocompatibility, and low density. All these unique properties make NiTi a great candidate in different applications. However, the conventional fabrication of NiTi encounters many challenges that significantly limits the practical applications of the alloy. As a solution, the Selective Laser Melting (SLM) which is an Additive Manufacturing (AM) technique has been recently used for the fabrication of NiTi parts. Although complex geometries can be fabricated directly from CAD files via SLM, different process parameters significantly affect the parts’ quality and must be optimized for each application. In most of the potential applications, NiTi components undergo cyclic loads and therefore its structural fatigue must be fully studied and considered in the design process. However, due to the nature of the SLM process, the fatigue behaviour of SLM fabricated NiTi is different from the conventional ones. In this work, as an initial step, the fatigue behaviour of the SLM fabricated NiTi in the horizontal direction is studied and the reasons for failure have been discussed. To this end, strain-controlled fatigue tests were performed on NiTi dog-bone samples, and fractography was used to analyze the different defects which could cause the failure or scatter in the results.

Additive Manufacturing of NiTi Shape Memory Alloy for Biomedical Applications: Review of the LPBF Process Ecosystem

“…The presence of such defects in NiTi tensile samples results in premature failure, lower fatigue life, and higher irrecoverable strain. 106,107 The type, size, and location of defects play a key role in the performance of LPBF-processed NiTi alloys. We have shown that, in parts with a vertical build direction, failure occurs sooner in comparison with samples fabricated horizontally.…”