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Relating micro-segregation to site specific high temperature deformation in single crystal nickel-base superalloy castings

机译：单晶镍基高温合金铸件中微观偏析与特定部位高温变形的关系

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摘要

Thermo-mechanical deformation of the solid on cooling following solidification has been studied quantitatively in a Ni-base single crystal superalloy, CMSX-4 used in turbine blade applications. In the as-cast state, the alloy has location specific properties due to micro-segregation of alloying elements during solidification; this effect become increasingly important with smaller specimen cross-section in thermo-mechanical tests. Accordingly, normalised resistance/resistivity tests have been used to classify samples with varying micro-segregation, given the different γ and γ phase resistivities. Increased normalised resistance corresponds to increased local solvus temperature, which determines the plastic strain and stress evolution during cooling. Upon cooling from above the γ solvus temperature, dislocation creep occurs within the γ phase accompanied by a small increase in stress. A critical precipitation γ' volume fraction is reached as the material cools, leading to precipitation hardening as measured by a dramatic resistance change and thereby stress increase at lower temperatures. Short-term creep tests capturing the history-dependent deformation, as demonstrated by controlled cooling experiments, gives steady-state creep, enabling parameter measurement for a Norton-type constitutive equation in a given temperature range. Implications of these results to modelling of plastic strain and stress during cooling from close to solvus temperature during casting has been discussed.
机译：在用于涡轮叶片应用的镍基单晶高温合金CMSX-4中，已经定量研究了凝固后冷却后固体的热机械变形。在铸态下，由于凝固过程中合金元素的微偏析，合金具有特定位置的性能；在热机械测试中，随着样品横截面的减小，这种影响变得越来越重要。因此，考虑到不同的γ和γ相电阻率，已使用归一化电阻/电阻率测试对具有不同微观偏析的样品进行分类。归一化电阻的增加对应于局部固溶体温度的升高，这决定了冷却期间的塑性应变和应力演变。从γ固溶线温度以上冷却后，在γ相内会发生位错蠕变，并伴随着应力的小幅增加。随着材料的冷却，达到临界的沉淀γ'体积分数，导致沉淀硬化（通过剧烈的电阻变化测量），从而在较低温度下应力增加。如受控冷却实验所证明的那样，短期蠕变测试捕获了与历史有关的变形，从而给出了稳态蠕变，从而可以在给定温度范围内对诺顿型本构方程进行参数测量。讨论了这些结果对浇铸过程中从接近固溶温度的冷却过程中塑性应变和应力建模的影响。

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