Department of Mechanical Engineering, Birla Institute of Technology & Science (BITS), Pilani, Hyderabad Campus, Jawahar Nagar, Kapra Mandal, Medchal District, Telangana - 500 078, India.
Department of Mechanical Engineering, Birla Institute of Technology & Science (BITS), Pilani, Hyderabad Campus, Jawahar Nagar, Kapra Mandal, Medchal District, Telangana - 500 078, India.
Mater Sci Eng C Mater Biol Appl. 2019 Sep;102:730-742. doi: 10.1016/j.msec.2019.04.070. Epub 2019 Apr 24.
Among shape memory alloys, nitinol alloy is biocompatible in nature and thus widely used in bone tissue engineering, stents, dental and orthopedic implants. To improve mechanical properties and extend its application window, in this paper, the NiTi (nitinol) sheets are processed by constrained groove pressing (CGP) process, which is one of the effective severe plastic deformation (SPD) techniques for refining microstructure and enhancing mechanical properties in sheet metals. The microstructure and X-ray diffraction studies of CGPed sheets show uniform grain refinement and increase in martensitic variant. Based on tensile and micro-hardness tests on water quenched (WQ) and CGPed nitinol alloy, the results show about up to 2.5 times increment in ultimate tensile strength and yield strength, significant enhancement in micro-hardness and change in strain hardening behavior. For characterizing the strain hardening behavior, Holloman and Voce models have been determined to have strong correlation with the experimental data for WQ and CGPed nitinol alloy respectively. Thus, nitinol alloy after CGP exhibits grain refinement and microstructural evolution, showing an increase in stress induced martensite phase which indicates superior mechanical properties such as high strength, uniform deformation regime and microhardness. These enhancements will help in reduction of other supporting materials generally used for improving structural integrity and load bearing capacity in biomedical applications of nitinol alloy.
在形状记忆合金中，镍钛诺合金本质上具有生物相容性，因此被广泛应用于骨组织工程、支架、牙科和矫形植入物。为了提高机械性能并扩展其应用范围，本文采用约束槽压（CGP）工艺对镍钛（nitinol）片进行了处理，CGP 是一种有效的细化微观结构和提高板材力学性能的剧烈塑性变形（SPD）技术之一。CGP 处理后的板材的微观结构和 X 射线衍射研究表明，晶粒均匀细化，马氏体变体增加。基于对水淬（WQ）和 CGP 处理的镍钛合金的拉伸和显微硬度测试，结果表明，极限拉伸强度和屈服强度提高了约 2.5 倍，显微硬度显著提高，应变硬化行为发生变化。为了表征应变硬化行为，Holloman 和 Voce 模型分别与 WQ 和 CGP 处理的镍钛合金的实验数据具有很强的相关性。因此，CGP 后的镍钛合金表现出晶粒细化和微观结构演变，马氏体相的应力诱导增加，表明其具有优异的机械性能，如高强度、均匀变形阶段和显微硬度。这些改进将有助于减少通常用于提高生物医学应用中镍钛合金结构完整性和承载能力的其他支撑材料。
