HPPS制备SiC陶瓷涂层组织特征及抗烧蚀性能

Microstructure and Ablation Resistance of SiC Ceramic Coating Deposited by HPPS

为了提高C/C基体材料在高温有氧环境中的抗烧蚀性能,尝试采用高能等离子喷涂工艺(high power plasmaspraying, HPPS)在C/C基体表面制备SiC涂层。在对SiC涂层制备工艺探索优化过程中共设计了3组HPPS喷涂参数,利用氧乙炔火焰对得到的涂层试验进行抗烧蚀性能考核,考核温度为1500℃,时间为150和300 s。通过XRD、SEM和EDS等方法对烧蚀前后涂层样品的成分及组织进行了表征。结果表明:3组参数所制得SiC涂层的孔隙率分别是21.3%、17.4%和15.3%。孔隙率逐渐减小原因是在主气流量相对较高和辅气流量较低的条件下,SiC粉末与等离子射流场特征匹配较好,SiC粉末颗粒加热较为充分,达到更好的熔融状态,而且获得较大的动能,因此所得涂层沉积率逐渐升高而孔隙率逐步降低;在涂层制备过程中SiC颗粒均发生了一定程度的氧化,导致涂层中含有一定量的非晶态SiO_2;经过300 s高温烧蚀考核后,SiC涂层为C/C基体提供了有效的防护。由于烧蚀过程中存在温度梯度,导致涂层表面在烧蚀后呈现3种不同的烧蚀形貌,分别是中心致密区、过渡区和边缘疏松区。在烧蚀过程中,涂层中心区域表面形成的SiO_2玻璃层,有利于阻挡O_2的渗入,起到了抗氧化的作用。

A SiC coating was deposited by high power plasma'spraying (HPPS)on carbon/carbon(C/C)composites.Three sets of parameters were selected to optimize the properties of the coating.The anti-ablation property of the SiC coating was investigated by oxyacetylene torch flame at 1500 ℃.The phase composition,microstructure and component of coatings were analyzed by different methods including X-ray diffraction (XRD),scanning electron microscopy (SEM)and energy dispersive spectroscopy (EDS),respectively. The results show that the porosity of three sets of coatings is 21.3%,17.4%and 15.3%.The plasma jet field has a more suitable temperature field and velocity field under the condition that the main gas flow is relatively high and the auxiliary gas flow is low.SiC powders are heated more fully to achieve better melting state and obtain larger kinetic energy.Therefore,the deposition rate of the coating increases gradually and the porosity decreases gradually.SiC powders are oxidized to form amorphous SiO2.After having been ablated for 300 s,the SiC coating provides effective protection for the matrix.Because of the temperature gradient caused by the oxyacetylene on the surface of the sample,the coating forms three kinds of ablation morphology after ablation,including a central dense area,a transition area and a edge loose area.During the ablation,a dense SiO2 glass layer is generated on the surface of central area coating,which is beneficial to blocking the infiltration of oxygen.