采用大气等离子喷涂法在Q235钢上喷涂了常规微米、纳米Al_2O_3-13%TiO_2复合涂层,对2种涂层进行了高温热氧化实验.利用XRD对比分析了2种涂层及其相应粉末的相组成,利用SEM观察了涂层的表面、截面形貌,并运用EDS对2种涂层的组分分布情况进行分析,比较2种涂层的不同结构及热氧化性能,初步探讨了涂层热氧化失效的原因.结果表明:2种粉末在喷涂之后,涂层中的α-Al_2O_3均有所减少,生成了γ-Al_2O_3,金红石TiO_2相转变成了板钛矿型TiO_2相,增加了涂层的内应力,加剧了裂纹的扩展;常规微米涂层中的孔洞细小但密集,纳米涂层中的孔洞较大但不密集,且大部分的气孔都存在于部分熔化区的内部;涂层在喷涂过程中所生成的气孔以及热氧化过程中由于热应力而产生的裂纹是造成涂层失效的直接原因.
The conventional and nano-structured Al_2O_3-13%TiO_2 composite coatings were prepared on the substrate Q235 steel by atmosphere plasma spraying. The thermal oxidization experiment was investigated, the phase composition before and after spraying was analyzed by XRD and the distribution of components was studied by EDS. All above were done in order to find out the differences of microstructure and thermal oxidization properties and the failure mechanism of those two kinds of as-sprayed coatings. The results show that α-Al_2O_3 in the two kinds of coatings decreases while the γ-Al_2O_3 increases after spraying. Rutile-TiO_2 transforms to brookite-TiO_2 and the innerstress of coating was increased so as to aggravate the expansion of cracking. The pores are small but dense in the conventional coating while bigger but loose in the nano-structured coating. The pores in the nano-structured coating exist almost inside the partially melted region. The pores generated during spraying and the cracks generated during the course of thermal oxidization because of thermal stress are the direct reasons why coatings fail.
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