Formation of Cr-modified silicide coatings on a Ti–Nb–Si based ultrahigh-temperature alloy by pack cementation process
Formation of Cr-modified silicide coatings on a Ti–Nb–Si based ultrahigh-temperature alloy by pack cementation process
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DOI：
10.1016/j.apsusc.2010.05.091
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发表时间：
2010-10
影响因子：
6.7
通讯作者：
Yan-qiang Qiao;Xiping Guo
中科院分区：
文献类型：
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作者：
Yan-qiang Qiao;Xiping Guo
采用 Si-Cr 共沉积法在 Ti-Nb-Si 基超高温合金上分别在 1250°C、1350°C 和 1400°C 下沉积 5-20h 制备 Cr 改性硅化物涂层。研究发现，随着共沉积温度和保温时间的增加，涂层结构和相组成均发生显着变化。在 1250°C 5-20h 下制备的所有涂层的外层均由 (Ti,X)5Si3（X 代表 Nb、Cr 和 Hf 元素）组成。在1250℃处理5和10h制备的两种涂层中，发现(Ti,X)5Si4是中间层中唯一的相成分，但在1250℃处理15和20h制备的涂层中，中间层主要由(Ti,X)5Si3相组成，该相是由(Ti,X)5Si4相分解产生的。 1350℃、5h制备的涂层中，其最外层发现单相(Ti,X)5Si3，与1250℃制备的涂层外层相同；但在1350℃、10~20h制备的涂层中，除(Ti,X)5Si3相外，最外层还发现了(Nb1.95Cr1.05)Cr2Si3三元相。在1400℃、5~20h制备的涂层中，(Nb1.95Cr1.05)Cr2Si3三元相是其最外层的单相成分。随着共沉积时间的延长，1350和1400℃制备的涂层中间层发生了(Ti,X)5Si4→(Ti,X)5Si3+Si的相变，与1250℃共沉积15和20h制备的涂层的情况类似，但随着共沉积温度的升高，这种相变加速了。所有涂层中的过渡层主要由(Ti,X)5Si3相组成。在研究的Si-Cr共沉积过程中，共沉积温度对Cr原子扩散能力的影响大于Si原子的扩散能力。在所有三种共沉积温度下，涂层的生长均遵循反对数定律。 1350℃氧化10h制备的Si-Cr共沉积涂层由于在1250℃氧化10h后形成SiO2和Nb、Cr掺杂的TiO2氧化皮，表现出良好的抗氧化性。
Cr-modified silicide coatings were prepared on a Ti–Nb–Si based ultrahigh temperature alloy by Si–Cr co-deposition at 1250°C, 1350°C and 1400°C for 5–20h respectively. It was found that both coating structure and phase constituents changed significantly with increase in the co-deposition temperature and holding time. The outer layers in all coatings prepared at 1250°C for 5–20h consisted of (Ti,X)5Si3(X represents Nb, Cr and Hf elements). (Ti,X)5Si4was found as the only phase constituent in the intermediate layers in both coatings prepared at 1250°C for 5 and 10h, but the intermediate layers in the coatings prepared at 1250°C for 15 and 20h were mainly composed of (Ti,X)5Si3phase that was derived from the decomposition of (Ti,X)5Si4phase. In the coating prepared at 1350°C for 5h, single (Ti,X)5Si3phase was found in its outmost layer, the same as that in the outer layers in the coatings prepared at 1250°C; but in the coatings prepared at 1350°C for 10–20h, (Nb1.95Cr1.05)Cr2Si3ternary phase was found in the outmost layers besides (Ti,X)5Si3phase. In the coatings prepared at 1400°C for 5–20h, (Nb1.95Cr1.05)Cr2Si3ternary phase was the single phase constituent in their outmost layers. The phase transformation (Ti,X)5Si4→(Ti,X)5Si3+Si occurred in the intermediate layers of the coatings prepared at 1350 and 1400°C with prolonging co-deposition time, similar to the situation in the coatings prepared at 1250°C for 15 and 20h, but this transformation has been speeded up by increase in the co-deposition temperature. The transitional layers were mainly composed of (Ti,X)5Si3phase in all coatings. The influence of co-deposition temperature on the diffusion ability of Cr atoms was greater than that of Si atoms in the Si–Cr co-deposition processes investigated. The growth of coatings obeyed inverse logarithmic laws at all three co-deposition temperatures. The Si–Cr co-deposition coating prepared at 1350°C for 10h showed a good oxidation resistance due to the formation of SiO2and Nb, Cr-doped TiO2scale after oxidation at 1250°C for 10h.