TC4合金表面扩散渗硅涂层的高温氧化行为和失效机制

High Temperature Oxidation Behavior and Failure Mechanism of Silicide Diffusion Coating Deposited on TC4 Alloy

为提高钛合金的高温抗氧化性能,采用固体粉末扩散渗方法在其表面制备了扩散渗硅涂层,研究了涂层的组织结构、高温氧化行为和失效机制。结果表明,所制备涂层具有致密的多层梯度组织结构,主要由TiSi_(2)外层,TiSi中间层和Ti_(5)Si_(4)+Ti_(5)Si_(3)内层组成。高温氧化实验结果表明,涂层在850℃空气中氧化时表面形成了由SiO_(2)和TiO_(2)混合组成的保护膜,高温抗氧化性能优良;氧化过程中,涂层与基体合金中Si和Ti的互扩散引起氧化膜内TiO_(2)含量增加及Si源不足,导致氧化膜保护性变差;氧化产物与涂层之间较高的P-B比、氧化膜与涂层组织间热膨胀系数不匹配导致了氧化膜开裂和剥落。

Silicon diffusion coating was prepared on TC4 alloy by pack cementation technique to improve its high temperature oxidation resistance. The microstructure, high temperature oxidation behavior and failure mechanism of the coating were studied. The results show that the coating has a dense multilayer structure, mainly consisting of a TiSi_(2) outer layer, a TiSi middle layer, and a Ti_(5)Si_(4)+Ti_(5)Si_(3) inner layer. The high temperature oxidation experiment results show that a protective scale composed of SiO_(2) and TiO2 forms on the surface of the coating during oxidization at 850 °C in air, leading to relatively good anti-high temperature oxidation property of the coating. The inter-diffusion of Ti and Si between the coating and the substrate causes the increase of TiO_(2) content in the scale and the lack of Si source, resulting in the degeneration of the protective scale. The high P-B ratio between the oxides and the coating, and the mismatch of the thermal expansion coefficients among the oxides and the coating are the main factors responsible for the cracking and spallation of the scale.