Ti-Ni超弹合金B2相与R相的氢脆敏感性比较研究

Comparative study on hydrogen embrittlement susceptibility of B2 phase and R phase in Ti-Ni superelastic alloys

Ti-Ni超弹性丝材应用于牙齿正畸弓丝时常面临着氢脆的问题,通过热处理调控获得了室温组织分别为B2与R相的样品,并比较了两种样品的氢脆行为。结果表明,在相同的充氢工艺下,室温组织为R相的样品具有更高的伸长率与抗拉强度。此外,随充氢时间的延长,应力诱发B2→B19’相变的临界应力值显著提高,表明氢会显著阻碍B2→B19’马氏体相变,而氢对应力诱发R→B19’相变的临界应力水平影响不大。断口分析表明,随着充氢时间的延长,室温组织为B2与R相的两种样品的断面收缩率都明显下降,断裂方式由延性断裂转变为脆性断裂,室温组织为R相的样品延脆转变受充氢影响更小。以上研究表明,通过引入R相能够降低Ti-Ni超弹性丝材的氢脆敏感性。

Ti-Ni superelastic wires are often faced with the problem of hydrogen embrittlement when applied to dental orthodontic arch wires. Samples with B2 and R phases at room temperature were obtained by heat treatment, and the hydrogen embrittlement behaviors of the two samples were compared. The results showed that under the same hydrogen charging process, the samples with R phase at room temperature had higher elongation and tensile strength. In addition, the critical stress value of the stress-induced B2→B19′ phase transition increased significantly with the hydrogen charging time, indicating that hydrogen significantly hinder the B2→B19′ martensitic phase transition, while hydrogen had little effect on the critical stress level of the stress-induced R→B19′ phase transition. Fracture analysis showed that with the extension of hydrogen charging time, the area shrinkage rate of the two samples with B2 and R phases at room temperature decreased significantly, and the fracture mode changed from ductile fracture to brittle fracture. The ductile fracture to brittle fracture transition of samples with R-phase microstructure at room temperature was less affected by hydrogen charging. The above studies showed that the hydrogen embrittlement susceptibility of Ti-Ni superelastic wires could be reduced by introducing R phase.