Production of Zr added NiTi shape memory alloys by hot isostatic pressing and investigation of their properties
Project no. 20798 · Status: Kapanmış (Yayın bekleniyor) · 2019
Summary
<p>Besides their mechanical properties, NiTi-based shape memory alloys have attracted the attention of the industry due to their biocompatibility, shape recovery, and superelasticity. There is a need to increase the transformation temperatures of these alloys, especially in the aerospace industry where high temperatures dominate, as their applications are limited to temperatures below 100°C. NiTiZr alloys have a significant advantage over other (Au, Pt, Pd, Hf doped NiTi) high-temperature shape memory alloys in that they are cheaper and lighter. These alloys have excellent properties but also the disadvantage of difficult machinability.</p><p> Focusing on material characterization, this study aims to investigate the effects of Zr added at different ratios on the alloy system. In addition, it aimed to investigate the contribution of the mechanical alloying process applied to elemental powders before hot isostatic pressing. In the present study, using the hot isostatic pressing method, which is successful in obtaining geometries with clear shapes, binary NiTi (Ni60Ti40 %wt) and ternary NiTiZr (Ni60Ti30Zr10 %wt), (Ni60Ti25Zr15 %wt) alloys were produced. To form alloys with different chemical compositions, elemental powders were used. Mechanical alloying was applied to the powder mixtures of some sample groups to investigate its effect. The alloys produced were subjected to DSC analysis to determine the transformation temperatures, SEM-optical microscope examinations for microstructure characterization, and XRD analysis to determine the phase structures. Vickers Hardness measurements and density measurements by Archimedes Principle were also performed. It was observed that the transformation temperatures increased with increasing Zr content. The hardness values increased considerably with the increase in the mechanical alloying process time due to the formation of TiO, TiO2 (anatase), and Ti3O5 in the alloy composition.</p><p> It is thought that the information obtained in the thesis study can guide future studies with different NiTiZr alloys and help to determine the potential of these alloys in application areas requiring high temperatures.</p>