Hydrogen Effect on the Cyclic Behavior of a Superelastic NiTi Archwire

Metals

Ali Algahtani¹  Fehmi Gamaoun¹  Amir Kessentini¹  Tarek Hassine²  Rihem Sarraj² 

[1] Department of Mechanical Engineering, College of Engineering, King Khalid University, Abha 61421, Saudi Arabia;Laboratory of Mechanics of Sousse, National Engineering School of Sousse, University of Sousse, Sousse 4054, Tunisia;

关键词: hydrogen;    NiTi alloys;    superelastic;    martensite;    cyclic effect;   

DOI  :  10.3390/met9030316

来源: DOAJ

【 摘 要 】

In this work, we are interested in examining the strain rate effect on the mechanical behavior of Ni–Ti superelastic wires after hydrogen charging and ageing for 24 h. Specimens underwent 50 cycles of loading-unloading, reaching an imposed deformation of 7.6%. During loading, strain rates from 10−4 s−1 to 10−2 s−1 were achieved. With a strain rate of 10−2 s−1, the specimens were charged by hydrogen for 6 h and aged for one day showed a superelastic behavior marked by an increase in the residual deformation as a function of the number of cycles. In contrast, after a few number of cycles with a strain rate of 10−4 s−1, the Ni-Ti alloy archwire specimens fractured in a brittle manner during the martensite transformation stage. The thermal desorption analysis showed that, for immersed specimens, the desorption peak of hydrogen appeared at 320 °C. However, after annealing the charged specimens by hydrogen at 400 °C for 1 h, an embrittlement took place at the last cycles for the lower strain rates of 10−4 s−1. The present study suggests that the embrittlement can be due to the development of an internal stress in the subsurface of the parent phase during hydrogen charging and due to the creation of cracks and local zones of plasticity after desorption.

【 授权许可】

Unknown