Effect of hydrogen on super-elastic behavior of NiTi shape memory alloy wires: Experimental observation and diffusional-mechanically coupled constitutive model

Han M Jiang; Chao Yu; Qianhua Kan; Bo Xu; Chuanping Ma; Guozheng Kang

doi:10.1016/j.jmbbm.2022.105276

Effect of hydrogen on super-elastic behavior of NiTi shape memory alloy wires: Experimental observation and diffusional-mechanically coupled constitutive model

J Mech Behav Biomed Mater. 2022 Aug:132:105276. doi: 10.1016/j.jmbbm.2022.105276. Epub 2022 May 20.

Authors

Han M Jiang¹, Chao Yu², Qianhua Kan¹, Bo Xu³, Chuanping Ma⁴, Guozheng Kang¹

Affiliations

¹ Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province, School of Mechanics and Aerospace Engineering, Southwest Jiaotong University, Chengdu, Sichuan, 610031, China.
² Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province, School of Mechanics and Aerospace Engineering, Southwest Jiaotong University, Chengdu, Sichuan, 610031, China. Electronic address: chaoyu@home.swjtu.edu.cn.
³ Failure Mechanics and Engineering Disaster Prevention, Key Laboratory of Sichuan Province, Sichuan University, Chengdu, Sichuan, 610065, China.
⁴ School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, 610031, China.

PMID: 35642861
DOI: 10.1016/j.jmbbm.2022.105276

Abstract

NiTi shape memory alloys (SMAs) are inevitably in contact with hydrogen in specific service environments, which can degrade their mechanical behaviors. In this work, the effect of hydrogen on the super-elasticity of NiTi SMA orthodontic wires is investigated experimentally and theoretically. Firstly, cathodic hydrogen charging was performed for the wires at a current density of 10A/m² with various charging times (2.5min, 5min, 7.5min and 10min) and charging lengths (20 mm, 40 mm, 60 mm and 80 mm) in 0.5 mol/L H2SO4+2 g/L CH4N2S electrolyte solution at room temperature. Then, ex-situ tension-unloading tests were carried out shortly after the hydrogen charging. The stress-strain responses showed a two-step martensite transformation (MT), i.e., the start stress of MT for the region with hydrogen charging is much larger than that without hydrogen charging. Based on the experimental observations, a diffusional-mechanically coupled constitutive model is constructed. Elastic strain, transformation strain, transformation-induced plasticity (TRIP) and hydrogen swelling deformation are considered. The effect of hydrogen on the thermo-mechanical behavior of NiTi SMA is taken into account by introducing the hydrogen concentration (HC)-dependent critical temperatures of MT and slip resistance of TRIP. The thermodynamic driving forces of MT and TRIP are derived from the constructed Helmholtz free energy and dissipation inequality. The balance equation of hydrogen diffusion is obtained by the chemical potential and Fick's diffusion law. To obtain the overall response of the wire with a heterogeneous HC field, a scale transition rule is proposed. The capability of the proposed model to describe the super-elasticity of NiTi SMA with various hydrogen charging times and charging lengths is validated by comparing the predicted results with the experimental ones.

Keywords: Constitutive model; Diffusional-mechanical coupling; Hydrogen diffusion; Martensite transformation; NiTi shape memory alloy.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Dental Alloys
Elasticity
Hydrogen*
Materials Testing
Orthodontic Wires
Shape Memory Alloys*
Temperature
Titanium

Substances

Dental Alloys
Shape Memory Alloys
Hydrogen
Titanium