Hydrogen effect on the austenite–martensite transformation of the cycled Ni-Ti alloy

Gamaoun, Fehmi; Skhiri, Imen; Bouraoui, Tarak; Zineb, Tarak Ben

doi:10.1177/1045389x13502868

Cited by 22 publications

(19 citation statements)

References 27 publications

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“…Moreover, it was shown that for an amount greater than 50-200 ppm, fracture occurred in a brittle manner at an earlier stage of plastic deformation [3]. In addition, in our previous work [4], we noticed that the occurrence of embrittlement was detectable, in particular, during the martensite transformation. This embrittlement was related to the distribution of hydrogen that diffused from the sub-surface into the bulk volume during aging.…”

Section: Introductionmentioning

confidence: 67%

Rate Dependency During Relaxation of Superelastic Orthodontic NiTi Alloys After Hydrogen Charging

Letaief

Hassine

Gamaoun

2016

Shap. Mem. Superelasticity

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The relaxation behavior under tensile loading of a superelastic NiTi alloy was investigated after hydrogen charging with respect to aging from one to 77 days in air at room temperature. The specimens were immersed for 3 h in a 0.9 % NaCl aqueous solution and then relaxed with an imposed strain of 4.8 %-which results in half of the martensite transformation-for different strain rates of 10-4 , 10-3 , and 5 9 10-3 s-1. For the non-charged specimens, the relaxed stress at the beginning exhibited a temporary dependence on the strain rates and then reached the same equilibrium stress after 2.5 h. After hydrogen charging, this equilibrium stress did not vary for the ascharged specimen. Nevertheless, the greater the aging period is the greater the equilibrium stress is. This behavior can be attributed to the diffusion of hydrogen into the entire specimen, which hinders the relaxation mechanism of the martensite bands.

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Section: Introductionmentioning

confidence: 67%

Rate Dependency During Relaxation of Superelastic Orthodontic NiTi Alloys After Hydrogen Charging

Letaief

Hassine

Gamaoun

2016

Shap. Mem. Superelasticity

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“…This behavior is attributed to the interaction between the higher diffused quantity of hydrogen in the volume of the NiTi SMA and the thermo-mechanical aspect of the nucleation and growth of martensitic bands. For lower diffused hydrogen contents in the archwire, after loading and unloading with an imposed strain rate of 10 −4 s −1 , an embrittlement is detected during the martensite trasformation [22,31]. Furthermore, this embrittlement is detected for the imposed deformation at the beginning and the middle of the plateau of the austenite-martensite transformation and not at the end of the plateau of the austenite transformation.…”

Section: Introductionmentioning

confidence: 91%

“…It has been reported in many investigations that immediately after hydrogen charging with a high current density or for a long time of immersion, the absorbed hydrogen is more located in the subsurface of the archwire rather than the center [26]. This latter behavior is characterized by an increase in the hardness of the cross section and a typical fragile surface fracture in the affected zone [22,32]. In several alloys like Ti-based [33] and austenitic steel [34,35], the dissolved hydrogen expands the crystal lattice of the parent phase, causing a distortion that gives rise to a series of changes in physical properties.…”

Section: Introductionmentioning

confidence: 98%

“…This hydrogen is mainly produced by the fluoride acid, which is contained in toothpastes and prophylactic agents [19][20][21]. After a few hours of a cathodic hydrogen charging, the superelastic NiTi SMA is fractured in the plateau of the austenite-martensite transformation [22,23]. The embrittlement of the archwire, after immersion in NaCl 0.9%, is found to be strongly related to the stress-induced martensite transformation when the amount of absorbed hydrogen is higher than 200 ppm [24,25].…”

Section: Introductionmentioning

confidence: 99%

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Hydrogen Effect on the Cyclic Behavior of a Superelastic NiTi Archwire

Sarraj

Kessentini

Hassine

et al. 2019

Metals

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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.

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“…However, we notice that the hardening-like slope of the phase-transformation pseudo-plateau grows slightly and a minor reduction of the plateau is detected. According to our previous results [5][6][7], this could be attributed to the hindrance of the austenite transformation by the absorbed hydrogen. In addition, this result indicates that after 3 h of immersion, the amount of diffused hydrogen is not enough to cause an increase in the critical stress for introducing martensite or to generate an embrittlement during the austenite transformation.…”

Section: Methodsmentioning

confidence: 99%

Effect of Hydrogen on the Stress Relaxation of Aged NiTi Shape Memory Alloys

2016

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The susceptibility of the NiTi shape memory alloy to relaxation after the hydrogen charging in an aqueous solution has been investigated with respect to ageing during one to six days in air at room temperature. The orthodontic wires have been prepared by immersing in a 0.9% NaCl solution for 3 h, under applied current density of 10 A/m 2 and then relaxed with an imposed deformation in a fully austenite state of structure and in a state with 1/3 and 2/3 of the martensite volume fraction. Through the stress relaxation, the hydrogen-charged specimen has shown a significant decrease of the stress, compared to the non-immersed alloy, when the imposed deformation was located in the plateau of the austenite-martensite transformation. It was also found that a longer ageing period is important and the properties of the wires with longer stress relaxation are similar to the those of non-charged wires. Nevertheless, no difference has been detected between the as-received and the as-charged specimens when the imposed deformation was located in the elastic deformation region of the fully austenitic structure. This behavior is attributed to the effect of the gradient of absorbed hydrogen, existing between the surface and the center axis of the studied wires, which facilitates the mobility of the martensite bands during the stress relaxation.

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Hydrogen effect on the austenite–martensite transformation of the cycled Ni-Ti alloy

Cited by 22 publications

References 27 publications

Rate Dependency During Relaxation of Superelastic Orthodontic NiTi Alloys After Hydrogen Charging

Rate Dependency During Relaxation of Superelastic Orthodontic NiTi Alloys After Hydrogen Charging

Hydrogen Effect on the Cyclic Behavior of a Superelastic NiTi Archwire

Effect of Hydrogen on the Stress Relaxation of Aged NiTi Shape Memory Alloys

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