This paper investigates the effect of nitriding potential under well-defined gas nitriding conditions on the formation and growth of a compound layer called “white layer” on a FeAl40 (with the composition of 40 at. pct Al) iron aluminide alloy. The nitriding potential was systematically varied in the range of 0.1 to 1.75 bar−1/2 at 590 °C for 5 hour nitriding time with an ammonia-hydrogen-nitrogen atmosphere. Characterization of the microstructure and phases formed within the white layer was performed using optical and scanning electron microscopy, X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and glow discharge optical emission spectroscopy (GDOES). Experimental results indicated that the nitriding potential strongly influences morphology and crystal structure of the white layer. The nitride compound layer consists of the phases γ′-Fe4N, ε-Fe2-3N, and AlN. A mechanism is proposed for the formation and growth of the white layer, depending on the effect of the nitriding potential.

中文翻译：

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氮化电位KN对铝化铁合金“白层”形成和生长的影响

本文研究了在明确定义的气体渗氮条件下渗氮电位对 FeAl40（成分为 40 at. pct Al）铁铝合金上称为“白层”的化合物层的形成和生长的影响。渗氮电位在 0.1 到 1.75 bar-1/2 的范围内系统地变化，在 590 °C 下，在氨-氢-氮气氛下渗氮时间为 5 小时。使用光学和扫描电子显微镜、X 射线衍射 (XRD)、电子背散射衍射 (EBSD) 和辉光放电发射光谱 (GDOES) 对白色层内形成的微观结构和相进行表征。实验结果表明，渗氮电位对白层的形貌和晶体结构有很大影响。氮化物层由相 γ'-Fe4N、ε-Fe2-3N 和 AlN 组成。根据渗氮电位的影响，提出了一种形成和生长白层的机制。