Refractory metal alloys, such as Mo–Si–B systems, can extend high-temperature capability more than commercial Ni-based superalloys, but Mo–Si–B alloys require surface coatings to improve their poor oxidation resistance. In this study, aluminide coating layers were created on Mo–3Si–1B (wt%) alloys by pack cementation with NH4Cl, Al and Al2O3 powder. The aluminide coating layers consisted of MoAl4, Mo3Al8, and precipitates. The growth kinetics of the coating layers were estimated by identifying diffusion behaviors. The aluminide coating layer growth constant (k0) was estimated as ~ 741.3 μm/h0.5, and the activation energy (Q) for the growth of the diffusion coating layer was evaluated as ~ 44.2 kJ/mol for the examined coating temperatures of 800, 900 and 1000 °C. The thicknesses of the coating layers calculated by an estimated kinetic equation were compared with the experimental results. The coating layer successfully protected the Mo–Si–B substrate during isothermal oxidation at 1400 °C under an air atmosphere. The growth kinetics of the coated layer and oxidation behaviors were discussed in terms of microstructural analyses.

中文翻译：

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多相 Mo-Si-B 合金上铝化物包覆涂层的生长动力学和等温氧化行为

难熔金属合金，如 Mo-Si-B 系统，可以比商业镍基高温合金更能扩展高温能力，但 Mo-Si-B 合金需要表面涂层以改善其较差的抗氧化性。在本研究中，通过用 NH4Cl、Al 和 Al2O3 粉末填充胶结在 Mo-3Si-1B（wt%）合金上形成铝化物涂层。铝化物涂层由 MoAl4、Mo3Al8 和沉​​淀物组成。通过识别扩散行为来估计涂层的生长动力学。铝化物涂层生长常数 (k0) 估计为 ~ 741.3 μm/h0.5，扩散涂层生长的活化能 (Q) 评估为 ~ 44.2 kJ/mol，所检测的涂层温度为 800 , 900 和 1000 °C。通过估计的动力学方程计算的涂层厚度与实验结果进行比较。在空气气氛下 1400°C 等温氧化过程中，涂层成功地保护了 Mo-Si-B 基体。根据微观结构分析讨论了涂层的生长动力学和氧化行为。