Exceptional fatigue resistant NiTi wire mediated by R-phase. (April 2023)

• Record Type: Journal Article
• Authors: Zhao, Yang; Yu, Zunyue; Ren, Xuepeng; Wang, Qianyu; Zhang, Beibei; Chen, Jianhao; Xu, Wei; Ren, Shubin; Qu, Xuanhui
• Is Part Of: International journal of fatigue. Volume 169(2023)
• Publication Date: 2023-04
• Subjects: NiTi alloy -- Microstructure -- R-phase -- Fatigue performance -- Fracture mechanism; Materials -- Fatigue -- Periodicals; Materials -- Fatigue; Periodicals; 620.1122
• DOI: 10.1016/j.ijfatigue.2022.107494
• Languages: English
• ISSNs: 0142-1123

Abstract

Highlights: Ni50.2 Ti49.8 wire with R-phase as the matrix was produced in the as-drawn state. Cyclic phase transformation in Ni50.9 Ti49.1 initiates microcracks in phase boundaries. The absence of R-phase to B19′ transformation in Ni50.2 Ti49.8 helps avoid microcracks. The fatigue life of Ni50.2 Ti49.8 is approximately 12 times that of Ni50.9 Ti49.1. Abstract: Ni50.2 Ti49.8 and Ni50.9 Ti49.1 wires in cold-drawn state were compared regarding tensile fatigue life and fatigue fracture mechanism. Through process control, Ni50.2 Ti49.8 with R-phase matrix at room temperature was achieved in as-drawn state without post heat treatment. The R-phase imparts exceptional fatigue performance to Ni50.2 Ti49.8 wire with fatigue life approximately twelve times of that for Ni50.9 Ti49.1 which comprises B2 phase and a small amount of B19′ under the same test conditions. The cyclic phase transformation under loading initiates microcracks in phase boundaries, leading to premature fracture of Ni50.9 Ti49.1 . In contrast, the R-phase presents exceptional stability against fatigue failure upon cyclic loading.