Multi-principal element alloys (MPEAs) have drawn great interest due to their superior mechanical properties compared to the conventional alloys. However, it is unclear in these two aspects: i) how to predict the brittle-to-ductile transition temperature (BDTT) and fracture toughness of MPEAs using theory and model; ii) how to quantify the influences of the complicated alloy composition variation and microstructural parameter on the BDTT and fracture toughness of MPEAs. These issues are critical to both the underlying mechanisms and practical engineering applications. Here, we develop a dislocation theory-based model accounting for the modified lattice friction stress model, the composition-dependent strength model, and the critical energy model to determine the BDTT and corresponding fracture toughness in body-centered cubic MPEAs. The calculated yield stress and BDTT of the as-cast MPEA agree well with the experiments. Subsequently, the BDTT and fracture toughness of TiVNbTa-based MPEAs are obtained as a function of the element concentration fluctuation. The effects of microstructure parameters, such as component randomness and short-range ordering described by the standard deviation of the interplaner potential perturbation and short-range correlation length, on the BDTT and fracture toughness are further elucidated. Importantly, a microstructure-based BDT criterion is proposed to evaluate whether MPEA is ductile or brittle at a given temperature. These results are conducive to the development and application of MPEAs in extreme environments.

中文翻译：

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基于位错理论的多主元合金脆性转变模型


与传统合金相比，多主元素合金（MPEA）由于其优异的机械性能而引起了人们的极大兴趣。然而，在这两方面尚不清楚：i）如何利用理论和模型预测MPEA的脆塑转变温度（BDTT）和断裂韧性； ii) 如何量化复杂的合金成分变化和微观结构参数对 MPEA 的 BDTT 和断裂韧性的影响。这些问题对于底层机制和实际工程应用都至关重要。在这里，我们开发了一种基于位错理论的模型，考虑了修正的晶格摩擦应力模型、成分相关强度模型和临界能量模型，以确定体心立方 MPEA 的 BDTT 和相应的断裂韧性。计算得出的铸态 MPEA 的屈服应力和 BDTT 与实验结果吻合良好。随后，获得了 TiVNbTa 基 MPEA 的 BDTT 和断裂韧性作为元素浓度波动的函数。进一步阐明了微观结构参数（例如由面间势扰动的标准差和短程相关长度描述的成分随机性和短程有序性）对 BDTT 和断裂韧性的影响。重要的是，提出了一种基于微观结构的 BDT 标准来评估 MPEA 在给定温度下是韧性还是脆性。这些结果有利于极端环境下MPEA的开发和应用。