Effects of size and geometry on the thermomechanical properties of additively manufactured NiTi shape memory alloy

Abstract

Effect of size and shape of the additively manufactured Nickel-Titanium (NiTi) alloys on their thermomechanical properties is experimentally studied. Although additive manufacturing is shown as a solution to the difficulties of machining of NiTi shape memory alloys (SMAs), our understanding of the effect of various processing (e.g., laser power, scanning pattern, etc.) and part characteristics (e.g., part geometry) on the resulting properties is not complete. During the SLM fabrication process, various factors influence the properties of the final product. In this study, we investigated the effect of size and shape of the SLM samples on the thermomechanical behavior of the parts. Tensile specimens with different thicknesses and shapes were fabricated for this investigation. The accuracy of fabrication is discussed for all of the specimens. Differential scanning calorimetry (DSC) measurements were conducted to compare the transformation temperatures of specimens with different size and shape. Moreover, tensile tests including loading, unloading, and heating were done for all of the specimens and the mechanical responses were compared with each other. Digital image correlation (DIC) was used for strain measurements as a more accurate strain measurement tool. The transformation temperatures of the fabricated parts were similar for parts with different shapes and sizes. From the mechanical tests, higher strength was observed for the thinner parts in both rectangular and oval specimens. Also, from the mechanical behavior of different shapes, it was observed that the rectangular showed higher critical stress than their equivalent oval specimens.