Na_2SiO_3含量对等离子体电解氧化Al_2O_3-ZrO_2复合陶瓷层形成机制的影响

Effects of Sodium Silicate on Formation Mechanism of Al_2O_3-ZrO_2 Ceramic Coatings Formed by Plasma Electrolytic Oxidation

铸造Al-Si合金表面ZrO2陶瓷层可有效提高基体的隔热及抗高温氧化性能,采用等离子体电解氧化方法在Al-Si合金表面制备了氧化锆涂层.涂层的组成、结构通过SEM、XRD进行研究.结果表明:K2ZrF6体系成膜速度较快,30min膜厚可达92μm,膜层表面和截面没有明显的等离子体放电形成的微孔,大量聚集的Zr(OH)4在等离子体放电产生的热化学作用下分解为ZrO2,表面出现大量2μm～5μm的陶瓷颗粒.K2ZrF6复合Na2SiO3体系成膜速度较慢,30min膜厚仅为27μm,表面和截面存在较多喷射状孔洞,随着溶液浓度的增大,成膜速度均呈先增后减的趋势.K2ZrF6复合Na2SiO3体系中,陶瓷层主要由α-Al2O3、γ-Al2O3、Al2(OH)3F3和m-ZrO2组成,α-Al2O3为陶瓷层的主晶相.K2ZrF6体系中陶瓷层的主要成分为t-ZrO2、m-ZrO2、α-Al2O3和γ-Al2O3,t-ZrO2为涂层的主晶相.涂层中m-ZrO2较少,而t-ZrO2含量高,表明生成的α-Al2O3起到稳定高温相t-ZrO2的作用.

Zirconia coating was produced on A1-Si alloys by plasma electrolytic oxidation （PEO）. The composition and structure of the coating were investigated by SEM and XRD. The results show that the growth rate of the coating is faster in K2ZrF6 solution and the thickness of coating ups to 92 μm at 30min. The surface and cross section of coating have small micropores formed by plasma discharge. A large accumulation of Zr（OH）4 dehydrates and forms ZrO2 under the thermochemical action generated by plasma discharge process. Finally, many micro-particles of 2 μm～5μm appear on the coating surface. The growth rate of the coating is slower in K2ZrF6-Na2SiO3 solution and the thickness of coating is only 27 μm in 30 min. The surface and cross section have more spray holes. With the increase of concentration of the solution, the growth rate of the coating increases firstly and then decreases. In K2ZrF6-Na2SiO3 solution, the coating consists of a-Al2O3, γ-A1203, A12 （OH）3F3 and m-ZrO2, and a- A12O3 is the main phase of the ceramic coating. In K2 ZrF6 solution, the coating is composed of t-ZrO2 ,m -ZrO2 ,a-A12O3 and γ-Al2O3, and t-ZrO2 is the main phase. The content of m-ZrO2 is less, while the content of t-ZrO2 is high. ＇ It indicates that the high-temperature phase of t-ZrO~ has been stabilized by generated a-Al2O3.