Wang Shuo, Yang Xiao, Chen Jieming, Pan Hengpei, Zhang Xiaolong, Zhang Congyi, Li Chunhui, Liu Pan, Zhang Xinyao, Gao Lingqing, Wang Zhenzhong
Luoyang Ship Material Research Institute, Luoyang 471023, China.
Key Laboratory of Bionic Engineering, Ministry of Education, Jilin University, Changchun 130022, China.
Micromachines (Basel). 2023 Aug 31;14(9):1711. doi: 10.3390/mi14091711.
For NiTi alloys prepared by the Laser Powder Bed Fusion (LPBF), changes in the building directions will directly change the preferred orientation and thus directly affect the smart properties, such as superelasticity, as well as change the distribution state of defects and impurity elements to affect the phase transformation behaviour, which in turn affects the smart properties at different temperatures. In this study, the relationship between impurity elements, the building directions, and functional properties; the effects of building directions on the crystallographic anisotropy; phase composition; superelastic properties; microhardness; geometrically necessary dislocation (GND) density; and impurity element content of NiTi SMAs fabricated by LPBF were systematically studied. Three building directions measured from the substrate, namely, 0°, 45° and 90°, were selected, and three sets of cylindrical samples were fabricated with the same process parameters. Along the building direction, a strong <100>//vertical direction (VD) texture was formed for all the samples. Because of the difference in transformation temperature, when tested at 15 °C, the sample with the 45° orientation possessed the highest strain recovery of 3.2%. When tested at the austenite phase transformation finish temperature (Af)+10 °C, the 90° sample had the highest strain recovery of 5.83% and a strain recovery rate of 83.3%. The sample with the 90° orientation presented the highest microhardness, which was attributed to its high dislocation density. Meanwhile, different building directions had an effect on the contents of O, C, and N impurity elements, which affected the transformation temperature by changing the Ni/Ti ratio. This study innovatively studied the impurity element content and GND densities of compressive samples with three building directions, providing theoretical guidance for LPBFed NiTi SMA structural parts.
对于通过激光粉末床熔融（LPBF）制备的镍钛合金，构建方向的变化将直接改变择优取向，从而直接影响诸如超弹性等智能性能，同时也会改变缺陷和杂质元素的分布状态，进而影响相变行为，这反过来又会影响不同温度下的智能性能。在本研究中，系统地研究了杂质元素、构建方向与功能性能之间的关系；构建方向对晶体学各向异性、相组成、超弹性性能、显微硬度、几何必要位错（GND）密度以及通过LPBF制造的镍钛形状记忆合金（SMA）的杂质元素含量的影响。从基板测量的三个构建方向，即0°、45°和90°被选定，并使用相同的工艺参数制造了三组圆柱形样品。沿构建方向，所有样品均形成了强烈的<100>//垂直方向（VD）织构。由于转变温度的差异，在15℃测试时，45°取向的样品具有最高的3.2%的应变回复率。在奥氏体相变终了温度（Af）+10℃测试时，90°样品具有最高的5.83%的应变回复率和83.3%的应变回复率。90°取向的样品具有最高的显微硬度，这归因于其高位错密度。同时，不同的构建方向对O、C和N杂质元素的含量有影响，通过改变Ni/Ti比来影响转变温度。本研究创新性地研究了具有三个构建方向的压缩样品的杂质元素含量和GND密度，为LPBF制备的镍钛SMA结构部件提供了理论指导。
