The formation and evolution of Ni2Cr precipitates in Ni–Cr model alloys as a function of stoichiometry characterized by synchrotron x-ray diffraction
The formation and evolution of Ni2Cr precipitates in Ni–Cr model alloys as a function of stoichiometry characterized by synchrotron x-ray diffraction
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DOI：
10.1016/j.msea.2022.143930
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发表时间：
2022-09
期刊：
影响因子：
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通讯作者：
N. Aerne;D. Sprouster;J. Tucker
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文献类型：
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作者：
N. Aerne;D. Sprouster;J. Tucker
含有大量铬的镍基合金在高温下长期使用期间可能会析出新相。在 Ni-Cr 模型合金中，Ni2Cr 的形成已被发现会影响材料性能，包括在低于 590 °C 临界温度的等温时效后的强度和延展性。在这项工作中，我们量化了四种 Ni-Cr 二元模型合金（Ni/Cr = 1.8、2.0、2.2、2.4）在 373 至 475 °C 温度下等温时效长达 10,000 小时后长程有序的形成和演化。通过硬度测试和基于同步加速器的 X 射线衍射对合金进行表征，以量化 Ni2Cr 相分数和沉淀物尺寸对机械性能的影响。经过 500 小时的等温时效后，在 475 °C 的温度下，所有四种合金中均检测到 Ni2Cr 的形成。在化学计量合金样品（Ni/Cr = 2.0）中，分别在 418 和 373 °C 时效 500 和 3000 小时后发现 Ni2Cr 的形成。我们发现基体晶格收缩和 Ni2Cr 相分数在早期时效后均达到饱和。这与硬度和 Ni2Cr 沉淀物尺寸形成鲜明对比，两者都随着时效时间的增加而持续增加。我们的结果强调，硬度的变化与 Ni2Cr 沉淀物尺寸而不是相分数线性相关。通过了解 Ni2Cr 的形成如何影响强度和延展性，这种重要的结构-性能关系可能有助于直接确定 Ni-Cr 基部件的寿命。我们发现，具有弱耦合位错的临界解析剪切应力的沉淀硬化模型与通过实验测量量化的材料性能变化表现出良好的一致性。
Ni-based alloys containing significant amounts of Cr, may precipitate new phases during long-term service at elevated temperatures. In Ni–Cr model alloys, the formation of Ni2Cr has been found to impact the material properties, including the strength and ductility after isothermal aging below the critical temperature of 590 °C. In this work, we quantify the formation and evolution of long-range ordering in four Ni–Cr binary model alloys (Ni/Cr = 1.8, 2.0, 2.2, 2.4) after isothermal aging up to 10,000 h at temperatures between 373 and 475 °C. The alloys were characterized by hardness testing and synchrotron-based x-ray diffraction to quantify the impact of Ni2Cr phase fraction and precipitate size on mechanical properties. After 500 h of isothermal aging, the formation of Ni2Cr was detected in all four alloys at 475 °C. In the stochiometric alloy samples (Ni/Cr = 2.0),the formation of Ni2Cr was found after 500 and 3000 h aging at 418 and 373 °C, respectively. We found that the matrix lattice contraction and Ni2Cr phase fraction both saturate after early aging times. This is in stark contrast to the hardness and Ni2Cr precipitate size that both continue to increase with increasing aging time. Our results highlight that changes in hardness correlate linearly with Ni2Cr precipitate size rather than phase fraction. This important structure-property relationship can potentially help define Ni–Cr-based component lifetimes directly through an understanding of how Ni2Cr formation impacts strength and ductility. We find that a precipitation hardening model for critical resolved shear stress with weakly coupled dislocations shows good agreement with the material property changes quantified from experimental measurements.