恒应力约束时效 Ni-48.85Ti-0.3Cr 形状记忆合金的马氏体相变与功能特性的影响

Influence of constrained aging treatment on martensitic transformation and functional properties of Ni-48.85Ti-0.3Cr shape memory alloy

摘要

利用 DSC、TEM 和 DMA 等设备系统探究约束时效工艺对 Ni-48.85Ti-0.3Cr 系形状记忆合金微观组织、马氏体相变及功能性能的影响。实验表明，约束时效后合金基体内会弥散析出定向分布的 Ni₄Ti₃ 相。400 ℃/100 MPa 条件下，延长约束时效时长可以显著增加 Ni₄Ti₃ 相的长度；在 1 h/100 MPa 工艺条件下，升温会同步增大析出相的长宽尺寸，使其由细小颗粒状转变为较大透镜状，长宽比也会随之增大。400 ℃/100 MPa 时，约束时效时间从 0.5 h 延长至 2 h，R 相变与 B19′相变温度均升高，这归因于 Ni₄Ti₃ 相析出降低了基体 Ni 元素含量。在 1 h/100 MPa 条件下，400 ℃时效会导致析出相尺寸增大、基体强化作用减弱，从而使相变温度升高；当温度达到 500 ℃时，相变将从两步变为三步，析出相近端发生 A→R→M₁ 相变，远端发生 A→M₂ 相变。等温熵变测试表明，400 ℃/1 h 时，等温熵变随着约束应力升高而减小；400 ℃/100 MPa 时，等温熵变随着时效时间的延长先增后减；1 h/100 MPa 时，等温熵变随着时效温度的升高呈先升后降的变化趋势。

Abstract

This study systematically investigates the effects of the constrained aging process on the microstructure，martensitic transformation，and functional properties of Ni-48.85Ti-0.3Cr shape memory alloys using DSC，TEM and DMA. The experimental findings reveal that following constrained aging，directionally distributed Ni₄Ti₃ phase is discretely precipitated within the alloy matrix. Under the condition of 400 ℃/100 MPa，extending the constrained aging time leads to a significant increase in the length of Ni₄Ti₃ phase. When subjected to the process of 1 h/100 MPa，raising the temperature not only increases the length and width of the precipitated phases simultaneously but also transforms their morphology from fine granular to larger lenticular，resulting in a corresponding improvement in the aspect ratio. At 400 ℃/100 MPa，when the constrained aging time is prolonged from 0.5 h to 2 h，both the R transformation and B19′ martensitic transformation temperatures rise. This can be attributed to the precipitation of Ni₄Ti₃ phase，which reduces the Ni element content in the matrix. Under the condition of 1 h/100 MPa，aging at 400 ℃ enlarges the size of the precipitated phases and weakens their strengthening effect on the matrix，thereby facilitating the increase in the transformation temperature. At 500 ℃，the transformation process shifts from a two-step to a three-step，with A→R→M₁ transformation occurring in the regions near the precipitated phases and A→M₂ transformation in the regions far from them. Isothermal entropy change tests indicate that at 400 ℃/1 h，the isothermal entropy change decreases as the constrained stress increases. At 400 ℃/100 MPa，the isothermal entropy change initially increases and then decreases with the extension of the aging time. Similarly，at 1 h/100 MPa，the isothermal entropy change also exhibits a trend of first increasing and then decreasing as the aging temperature rises.

关键词

NiTiCr / 形状记忆合金 / 马氏体相变 / 微观组织

Key words

NiTiCr / shape memory alloy / martensitic transformation / microstructure

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基金资助

国家自然科学基金资助项目(52371181)

黑龙江省重点研发计划(2025ZX01A08)