MoSi2和(Mo,W)Si2涂层的宽温域氧化过程

采用包渗法在Mo及Mo?W基体上分别制备MoSi2及(Mo,W)Si2涂层，研究了W掺杂对MoSi2涂层抗氧化性能的影响规律和作用机理。结果表明，W元素固溶到MoSi2涂层中，形成(Mo,W)Si2固溶体，涂层微观结构更加致密化。在1600℃高温下静态氧化，(Mo,W)Si2涂层抗氧化失效时间长达70 h，1200℃下氧化1000 h仍具有良好的防护性能，抗氧化性能大幅提升。加入W元素阻碍了Si元素与基体间的扩散反应，降低了涂层中Si元素的消耗速率，显著增强了(Mo,W)Si2涂层抗高温氧化性能。在500℃低温下静态氧化50 h，与MoSi2涂层相比，(Mo,W)Si2涂层氧化产生明显的“Pest”现象，涂层严重粉化失效。加入W元素降低了涂层中Si元素的扩散速率，导致低温下涂层表面无法形成致密氧化层，加剧涂层的快速氧化。

Oxidation processes of MoSi2 and (Mo,W)Si2 coatings in wide temperature range

MoSi2 and (Mo,W)Si2 coatings were prepared on Mo and Mo?W substrates respectively by means of pack cementation, and the effects and mechanisms of W element doping on the oxidation resistances of MoSi2 coating were investigated systematically. XRD, SEM and EDS were used to determine the phase structure, morphology and composition of the coatings. The results showed that W element was dissolved in MoSi2 coating in the form of (Mo,W)Si2 solid solution, and the microstructure of (Mo,W)Si2 coating was denser compared with that of MoSi2 coating as a result of W element doping. After static oxidation at 1600℃, the antioxidant life of (Mo,W)Si2 coating reached 70 h, while MoSi2 coating was failed after 25 h oxidation due to severe weight loss. Moreover, (Mo,W)Si2 coating exhibited excellent high-temperature protection performance after oxidation at 1200℃ for 1000 h. At the initial stage of the oxidation, the oxidation rate of (Mo,W)Si2 coating was higher than that of MoSi2 coating owing to W element doping, which led to lower formation velocity of dense oxide layer on the surface of (Mo,W)Si2 coating. After the dense SiO2 covering the surface completely, the oxidation rate of (Mo,W)Si2 coating decreased dramatically. The diffusion reaction between the Si element and the substrate was hindered by the addition of W element, the consumption rate of Si element in the coating was reduced remarkably, and the high-temperature oxidation resistance of (Mo,W)Si2 coating was enhanced significantly. After static oxidation at 500℃, comparing with MoSi2 coating, (Mo,W)Si2 coating exhibited a typical “Pest” phenomenon after oxidation for 50 h, and the coating failed in the form of disintegration. The addition of W element reduced the diffusion rate of Si element in the coating, therefore, a dense oxide layer could not be formed on the coating surface at low-temperature, which caused the rapid oxidation of the coating.