Under nitrogen diffusion treatments, N-expanded austenite (γN) can form at the surface of self-passivating Fe-Cr, Ni-Cr, and Co-Cr alloys at low temperatures, which provides beneficial hardening and enhancements in wear resistance without reducing corrosion resistance. Given the wide research interests in multicomponent equimolar alloys, an equimolar quaternary FeCoNiCr high entropy alloy (HEA) was investigated after active-screen plasma nitriding at 430–480 °C in this study. Firstly, the formation of γN-FeCoNiCr case at 430 °C was demonstrated with the bright case appearance after metallographic etching, the lattice expansion under XRD, the FCC electron diffraction patterns and the shear bands under TEM. Secondly, the thick treatment cases at ∼9–16 μm first indicated that N interstitial diffusion was not sluggish in the FeCoNiCr surface. Thirdly, analogous to stainless steels, the onset of dark regions in the etched γN-FeCoNiCr case was owing to the formation of a cellular mixture of CrN + γ-(Fe, Co, Ni) nano-lamellae at elevated treatment temperatures. The residual bright regions in γN-FeCoNiCr at 480 °C showed ∼1–3 nm CrN nanoprecipitates with no substantial Cr segregation. Additionally, a significant nanocrystalline layer was seen at the topmost surface at 480 °C, which is most likely associated with the high substrate Cr content.

中文翻译：

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等摩尔季 FeCoNiCr 高熵合金在主动筛选等离子体渗氮后氮吸收及微观结构的研究


在氮扩散处理下，自钝化 Fe-Cr、Ni-Cr 和 Co-Cr 合金表面可在低温下形成 N-膨胀奥氏体 （γN），这提供了有益的硬化和增强耐磨性，而不会降低耐腐蚀性。鉴于对多组分等摩尔合金的广泛研究兴趣，本研究在 430–480 °C 下进行主动筛选等离子体渗氮后研究了等摩尔季 FeCoNiCr 高熵合金 （HEA）。首先，在430 °C时通过金相刻蚀后的光壳外观、XRD下的晶格膨胀、TEM下的FCC电子衍射图和剪切带证明了γN-FeCoNiCr表面的形成。其次，∼9–16 μm 的厚处理案例首先表明 N 间隙扩散在 FeCoNiCr 表面并不迟缓。第三，与不锈钢类似，刻蚀 γN-FeCoNiCr 案例中暗区的出现是由于在较高的处理温度下形成 CrN + γ-（Fe， Co， Ni） 纳米薄片的细胞混合物。在 480 °C 时，γN-FeCoNiCr 中残留的亮区显示 ∼1-3 nm CrN 纳米沉淀物，没有明显的 Cr 偏析。此外，在 480 °C 时，在最顶部表面可以看到明显的纳米晶层，这很可能与高衬底 Cr 含量有关。