Ni-Ti形状记忆合金的热拉拔工艺

doi:10.13251/j.issn.0254-6051.2025.07.044

摘要/Abstract

摘要： 以50.8Ni-Ti合金8 mm圆棒为对象,在450、550、650、750 ℃进行减径量30%的热拉拔试验,分析其显微组织变化和相变规律,并通过热压缩试验分析了合金在750 ℃热拉拔至减径量大于25%时频繁断裂的原因。结果表明:随着热拉拔温度的升高,Ni-Ti合金晶粒细化作用减弱,晶粒再结晶明显且晶粒尺寸显著增大。750 ℃热拉拔时,随着减径量增加,Ni-Ti合金相变由B19′→B2型相变转变为B19′→R→B2型两步相变,在减径量为25%时组织中存在菱方型结构R相,而减径量大于25%时合金拉拔断裂频繁的原因是合金的屈服强度随温度升高而下降明显,因热拉拔时直径减小的同时拉拔应力远超过合金流变应力,达到材料塑性变形极限而断裂。50.8Ni-Ti合金8 mm圆棒热拉拔合适的温度为650~700 ℃,减径量大于25%时应降低热拉拔温度或采用冷拉方式继续生产。

关键词: Ni-Ti形状记忆合金, 热拉拔, 再结晶, 相变

Abstract: Taken 50.8Ni-Ti alloy 8 mm round bar as the object, the hot drawing test at 450, 550, 650 and 750 ℃ with reduction of 30% was carried out to analysis the microstructure change and phase transformation law, and the reason of frequent fracture of the alloy hot drawing to the reduction of more than 25% at 750 ℃ was analyzed by hot compression test. The results show that with the increase of hot drawing temperature, the grain refinement effect of the Ni-Ti alloy is weakened, the grain recrystallization is obvious and the grain size increases significantly. When hot drawing at 750 ℃, with the increase of reduction, the phase transformation of the Ni-Ti alloy changes from B19′→B2 type to B19′→R→B2 two-step type, and rhombohedral R phase is observed when the reduction is 25%. The reason for the frequent fracture of the alloy hot drawing to the reduction of more than 25% is that the yield strength of the alloy decreases significantly with the increase of temperature, due to the diameter decreases during hot drawing, the drawing stress far exceeds the flow stress of the alloy, resulting in the fracture happens when it reaching the plastic deformation limit. The suitable optimum hot drawing temperature of the 50.8Ni-Ti alloy 8 mm round bar is 650-700 ℃. When the reduction is more than 25%, it is necessary to reduce the hot drawing temperature or use cold drawing to continue the production.

Key words: Ni-Ti shape memory alloy, hot drawing, recrystallization, phase transformation

中图分类号:

TG356.3⁺3

章涛, 孔永华. Ni-Ti形状记忆合金的热拉拔工艺[J]. 金属热处理, 2025, 50(7): 297-303.

Zhang Tao, Kong Yonghua. Hot drawing process of Ni-Ti shape memory alloy[J]. Heat Treatment of Metals, 2025, 50(7): 297-303.

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