双相高熵合金在长时间高温退火后的屈服强度不敏感性
Yield strength insensitivity in a dual-phase high entropy alloy after prolonged high temperature annealing
AI总结：
本文研究了FeMnCoCr双相高熵合金在1200°C长时间退火后的微观结构与力学性能，发现尽管晶粒尺寸增大近四倍，屈服强度仍保持不变，其机制是板条间距减小分割奥氏体晶粒，抵消了晶粒长大弱化效应。
摘要：
近期对FeMnCoCr基高熵合金的研究展示了不常见的变形行为，如相变诱导塑性，这在很大程度上被认为仅限于特定系列的钢。结合高温下高对称相熵稳定的潜力，该体系代表了一类在极端环境中具有结构应用前景的材料。然而，相变诱导塑性机制对微观结构参数显著敏感，且文献中提供了高熵合金在热处理下发生有害分解的例子，这引发了对其力学性能韧性的担忧。在此，我们评估了一种FeMnCoCr高熵合金在高温下长时间热处理后的微观结构和力学性能演变。研究发现，在1200°C下热处理长达48小时后，微观结构仍保留其特有的奥氏体/马氏体特征，母相面心立方晶粒被密排六方板条分割。力学测试结果揭示了该合金对晶粒长大诱导弱化效应的异常不敏感性。即，尽管晶粒尺寸增加了近四倍，FeMnCoCr样品的屈服强度在所有热处理条件下均保持恒定。对热处理后微观结构的仔细检查表明，在较长持续时间下，板条间距显著减小，从而分割了母相奥氏体晶粒。这种晶体分割通过引入额外的位错塞积障碍，抵消了传统晶粒长大诱导的弱化。这些结果为这种相变诱导塑性高熵合金在长时间高温热处理下的力学韧性提供了新的见解。
英文摘要：
Recent studies of FeMnCoCr-based high entropy alloys have demonstrated uncommon deformation behaviors such as transformation-induced plasticity, which were largely believed to be restricted to select families of steels. Coupled with the potential for entropy stabilization of high symmetry phases at high temperatures, this system represents a promising class of materials for structural applications in extreme environments. Yet, transformation-induced plasticity mechanisms are notably sensitive to microstructure parameters and the literature offers examples of deleterious decomposition of high entropy alloys under heat treatment, which raises concerns of resiliency in mechanical performance. Here, we evaluate the evolution of microstructure and mechanical properties of a FeMnCoCr high entropy alloy after prolonged heat treatment at high temperature. Microstructures are found to retain their characteristic austenite/martensite features, with parent face-centered cubic grains partitioned by hexagonal close-packed laths after heat treatment at 1200 C for up to 48 hours. Results of mechanical testing reveal an unusual insensitivity of this alloy to grain growth-induced weakening effects. Namely, the yield strengths of FeMnCoCr samples are observed to remain constant across all heat treatment conditions, despite a near four-fold increase in the grain size. Close examination of post-heat treatment microstructures reveals a dramatic decrease in the inter-lath spacing at longer durations, which segments parent austenite grains. This crystal partitioning counteracts conventional grain growth-induced weakening by introducing additional barriers for dislocation pile-up. These results offer new insights into the mechanical resiliency of this transformation-induced plasticity high entropy alloy under prolonged high temperature heat treatment.
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