Grain boundaries (GBs) are often known as intergranular cracking sources in alloys at high temperatures, resulting in limited high-temperature strength and ductility. Here, we propose a GB-dual-carbide (denoted as GB-DC) strengthening strategy and have developed a high-performance (NiCoFeCr)99Nb0.5C0.5 high-entropy alloy (HEA) with exceptional strength-ductility synergy at 1073 K. Chain-like coherent M23C6 carbides have been successfully introduced at GBs and remain a cube parallel crystallographic orientation with the face-centered cubic (FCC) matrix during deformation. Nano-scale NbC particles are distributed alternatively between M23C6 carbides and inhibit their coarsening. Both strength and ductility of the GB-DC HEA increase dramatically at strain rates ranging from 10−4 to 10−2 s−1 at 1073 K, compared with those of the single-phase NiCoFeCr HEA. Specifically, yield strength of 142 MPa, ultimate tensile strength of 283 MPa, and elongation of 34 % were obtained, which are twice that of the reference NiCoFeCr HEA (82 MPa, 172 MPa, and 18 %, respectively). EBSD investigations demonstrated that chain-like carbides enhance the GB cohesion at high temperature, and TEM analysis revealed that dislocations can go through the coherent phase boundaries (CPBs) and activate dipoles inner M23C6 carbides, which weakened the stress concentration in GBs. This substantially reduces the critical stress for dislocation generation and transmission to a stress level lower than that required for intergranular fracture. Theoretical estimation suggests that carbides result in a much higher activation energy (∼510 kJ/mol) for GB sliding and a rather low interface energy (∼101 mJ/m2) compared with the GB energy (1000 mJ/m2), which rationalizes the enhanced GB cohesion by carbides.

中文翻译：

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通过在晶界处通过链状双碳化物同时显著提高高熵合金的高温强度和延展性


晶界 （GB） 通常被称为高温合金中的晶间开裂源，导致高温强度和延展性有限。在这里，我们提出了一种 GB 双碳化物（表示为 GB-DC）强化策略，并开发了一种高性能 （NiCoFeCr）99Nb0.5C0.5 高熵合金 （HEA），在 1073 K 下具有非凡的强度-延展性协同作用。链状相干 M23C6 碳化物已成功引入 GBs，并在变形过程中保持立方体平行晶体取向，具有面心立方 （FCC） 基体。纳米级 NbC 颗粒交替分布在 M23C6 碳化物之间并抑制其粗化。与单相 NiCoFeCr HEA 相比，GB-DC HEA 的强度和延展性在 1073 K 时在 10-4 到 10-2 s-1 的应变速率范围内急剧增加。具体来说，获得了 142 MPa 的屈服强度、283 MPa 的极限拉伸强度和 34% 的伸长率，是参考 NiCoFeCr HEA 的两倍（分别为 82 MPa、172 MPa 和 18 %）。EBSD 研究表明，链状碳化物增强了高温下的 GB 内聚力，TEM 分析表明，位错可以穿过相干边界 （CPB） 并激活 M23C6 碳化物内部的偶极子，从而削弱了 GB 中的应力集中。这大大降低了位错产生和传递的临界应力，使其低于晶间断裂所需的应力水平。理论估计表明，碳化物导致 GB 滑动的活化能 （∼510 kJ/mol） 高得多，与 GB 能量 （1000 mJ/m2） 相比，界面能 （∼101 mJ/m2） 相当低，这使碳化物增强的 GB 内聚力合理化。