Abstract

The influence of heating and cooling routes prior to aging of the Ti–22Nb–6Zr shape memory alloy (at %) on the intensity of formation of the isothermal ω_iso phase in the temperature range from 250 to 350°C for 1 and 3 h is studied by X-ray diffraction. It is shown that, for intense formation of the ω_iso phase, the most efficient scheme for entering the aging interval includes rapid water cooling water to room temperature from an annealing temperature of 600°C and subsequent rapid heating to an aging temperature of 300°C. All other routes used for entering in the aging interval, including slow cooling and/or heating, do not lead to the formation of an X-ray identifiable amount of the ω_iso phase, whereas, the β → ω_iso transformation in the temperature range from 250 to 350°C has a pronounced C-shaped kinetics with a maximum at 300°C. Aging in the entire range of 250–350°C leads to the dispersion hardening and an increase in the hardness of the alloy compared to the initial state. Moreover, the hardness gradually increases with an increase in the aging temperature from 250 to 300°C and remains constant in the temperature range of 300–350°C. The β-phase lattice parameter of Ti–22Nb–6Zr alloy remains unchanged over the entire aging temperature range of 250–350°C, which indicates the absence of noticeable diffusional redistribution of elements in the solid solution during the formation of the ω_iso phase. The w_iso phase formed during the aging of the Ti–22Nb–6Zr alloy over the entire temperature range of 250–350°C has the ratio c_ω/a_ω = 0.613 ± 0.002, which is similar to the ratio c_ω/a_ω for the shear-type athermal ω_ath phase, which in turn further emphasizes the identity of these two phase varieties.

中文翻译：

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加热和冷却对 Ti-22Nb-6Zr 合金等温 β → ω 转变的影响

摘要

Ti-22Nb-6Zr 形状记忆合金老化前加热和冷却路径（at %）对等温 ω 等相在 250 至 350°C 温度范围内 1 和 3 小时形成强度_的影响通过 X 射线衍射研究。结果表明，对于ω等相的强烈形成，_进入时效区间的最有效方案包括从600°C退火温度快速冷却水至室温，然后快速加热至300°时效温度C。用于进入老化区间的所有其他途径，包括缓慢冷却和/或加热，不会导致形成 X 射线可识别量的 ω _iso相，而 β → ω _iso在 250 至 350°C 的温度范围内，转变具有明显的 C 形动力学，最大值在 300°C。与初始状态相比，在 250–350°C 的整个范围内时效会导致弥散硬化和合金硬度的增加。此外，随着时效温度从 250 到 300°C 的增加，硬度逐渐增加，并在 300-350°C 的温度范围内保持不变。_{Ti-22Nb-6Zr 合金的 β 相晶格参数在 250-350°C 的整个时效温度范围内保持不变，这表明在 ω等}相形成过程中固溶体中元素没有明显的扩散再分布. 国际_{标准化组织}Ti-22Nb-6Zr 合金在 250-350°C 的整个温度范围内时效期间形成的相具有c _ω / a _{ω = 0.613 ± 0.002 的比率，这与}c _ω / a _ω的比率相似剪切型非热 ω _ath相，这反过来又进一步强调了这两个相变体的特性。