Effect of Ta content on microstructure, martensitic transformation, and shape memory effect of (Ni52.2Ti47.8)100-xTax alloys

• Published in: Journal of alloys and compounds 2024-10, Vol.1003, Article 175621
• Main Authors: Liu, J.C., Mei, H., Chen, F., Li, L., Tong, Y.X.
• Format: Article
• Language: English
• Subjects: Martensitic transformation; Microstructure; NiTiTa; Shape memory alloy; Shape memory effect
• ISSN: 0925-8388
• DOI: 10.1016/j.jallcom.2024.175621

This work focuses on the effects of Ta addition on the microstructure, martensitic transformation, mechanical properties and shape memory effect (SME) of (Ni52.2Ti47.8)100-xTax alloys with a fixed Ni/Ti ratio of 1.09. The solubility limit of Ta in (Ni52.2Ti47.8)100-xTax alloys is determined to be within 3–4 at%. Excessive Ta leads to the formation of secondary phases, the majority of which are (Ta,Ti)2Ni phases. The addition of Ta can effectively refine the grains of NiTiTa alloys. Transformation temperatures are elevated remarkably until Ta content reaches 4 at% and then increase slightly at higher Ta contents, which is due to the change of valence electron concentration. The thermal hysteresis is widened by adding Ta and applying a constraint stress. The addition of Ta remarkably improves the ductility while decreases the hardness. By modifying the content of Ta, a considerable SME is achieved with the maximum recovery strain up to 7.0 %. •Ta addition can effectively refine the grains of NiTi alloys.•The Ta-rich (Ta, Ti)2Ni phase is formed due to the addition of Ta.•An appropriate alloying of Ta considerably improves the ductility NiTi alloys.•A considerable shape memory effect with 7.0 % recovery strain is achieved.•Transformation temperatures are elevated remarkably by adding no more than 4 at% Ta.