Scholarlink

<p>Very-high-cycle fatigue (VHCF) data for superelastic NiTi beyond 10<sup>7</sup> cycles remain limited, particularly for wrought, precipitate-tuned conditions tested under ultrasonic loading. Here, the VHCF response of a Ni-rich wrought NiTi (Ni50.8Ti49.2) was quantified by coupling calorimetry and monotonic mechanics with 20&#xa0;kHz axial ultrasonic fatigue in fully reversed loading (R =  − 1) using pulse-pause control and forced-air cooling to mitigate self-heating. The alloy was solutionized at 1000&#xa0;°C for 2&#xa0;h and aged at 600&#xa0;°C for 1&#xa0;h to promote Ni4Ti3 precipitation. DSC showed suppressed transformation temperatures relative to the non-heat-treated state, with a two-step B2 → R → B19′ sequence on cooling and a sharp reverse transformation on heating (A<sub>f</sub> = 9–10&#xa0;°C). Room-temperature tensile tests confirmed a fully austenitic starting state (E = 61.9 GPa) and a stress-induced martensitic transformation (SIMT) onset near 223&#xa0;MPa with a 250–300&#xa0;MPa transformation plateau. S–N data spanning 10<sup>5</sup> to 10<sup>9</sup> cycles were fitted by a Basquin relation (σ<sub>f</sub>’ = 653.7&#xa0;MPa, b =  − 0.089), indicating a gradual fatigue-strength reduction with increasing life and increased scatter in the VHCF regime without a clear endurance limit. Fractography and EDS revealed a stress-dependent transition in crack initiation: higher-amplitude failures were dominated by surface slip/damage, whereas VHCF failures initiated subsurface at Ti − rich non-metallic inclusions (TiC and Ti2NiOx). These results provide a benchmark VHCF dataset for wrought NiTi under R =  − 1 ultrasonic loading and clarify how precipitation-tuned transformation behavior and inclusion populations govern VHCF crack initiation.</p>

错误：搜索内容不能为空，请输入英文关键词
错误：关键词超出字数限制，请精简
高级检索

Very High Cycle Fatigue of Wrought NiTi Shape Memory Alloys

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年2月26日

查看全文
  • Pete Angelo Rocco,
  • Alireza Behvar,
  • Harsh Kamlash Bajaj,
  • Meysam Haghshenas,
  • Mohammad Elahinia

摘要

Very-high-cycle fatigue (VHCF) data for superelastic NiTi beyond 107 cycles remain limited, particularly for wrought, precipitate-tuned conditions tested under ultrasonic loading. Here, the VHCF response of a Ni-rich wrought NiTi (Ni50.8Ti49.2) was quantified by coupling calorimetry and monotonic mechanics with 20 kHz axial ultrasonic fatigue in fully reversed loading (R =  − 1) using pulse-pause control and forced-air cooling to mitigate self-heating. The alloy was solutionized at 1000 °C for 2 h and aged at 600 °C for 1 h to promote Ni4Ti3 precipitation. DSC showed suppressed transformation temperatures relative to the non-heat-treated state, with a two-step B2 → R → B19′ sequence on cooling and a sharp reverse transformation on heating (Af = 9–10 °C). Room-temperature tensile tests confirmed a fully austenitic starting state (E = 61.9 GPa) and a stress-induced martensitic transformation (SIMT) onset near 223 MPa with a 250–300 MPa transformation plateau. S–N data spanning 105 to 109 cycles were fitted by a Basquin relation (σf’ = 653.7 MPa, b =  − 0.089), indicating a gradual fatigue-strength reduction with increasing life and increased scatter in the VHCF regime without a clear endurance limit. Fractography and EDS revealed a stress-dependent transition in crack initiation: higher-amplitude failures were dominated by surface slip/damage, whereas VHCF failures initiated subsurface at Ti − rich non-metallic inclusions (TiC and Ti2NiOx). These results provide a benchmark VHCF dataset for wrought NiTi under R =  − 1 ultrasonic loading and clarify how precipitation-tuned transformation behavior and inclusion populations govern VHCF crack initiation.