超音速火焰喷涂制备Cr涂层及其高温氧化性能

Preparation of Cr Coating by HVOF and Its Oxidation Performance

目的探索一种高效制备核电用包壳材料锆合金表面涂层的方法,以应对反应堆失水事故,提高核电安全性。方法采用超音速火焰喷涂技术在Zr-4合金表面制备Cr涂层,高温氧化试验在1200℃空气中进行,氧化时间30 min。通过X射线衍射仪(XRD)、扫描电镜(SEM)研究Cr涂层氧化前后的结构和显微组织。采用划痕法测试涂层与基体结合力。采用金相显微镜(OM)观察划痕形貌。结果采用HVOF技术可以在锆合金基体上制备的涂层主要为体心立方结构的金属Cr同时含有约21.9%密排六方结构(HCP)的Cr_(2)O_(3)。抛光可以减少Cr_(2)O_(3)至约10.1%。涂层由层状结构、未熔颗粒和少量孔隙组成。Cr_(2)O_(3)主要分布在层状结构中,未熔颗粒形成的不规则块状结构基本不含氧,主要为金属Cr。涂层与基体的结合力为77~94 N。喷涂工艺参数为煤油流量23 L/h、氧气流量880 L/h、喷涂距离330 mm的涂层样品结合力最高,为94 N。在1200℃空气中氧化30 min后,涂层靠近基体界面处形成11~14μm厚的连续致密层,而靠近界面处的基体衬度变暗,能谱信息显示含有Cr,因此判断该区域为Zr-Cr过渡层,厚度约为5μm,说明存在基体与涂层的互扩散层,且Zr向涂层的扩散速率明显大于Cr向基体的扩散速度。有Cr涂层的Zr基体没有发生氧化,涂层内部也基本没有氧化,而没有涂层覆盖的基体氧化层厚度在120μm以上。结论采用HVOF可以在锆合金表面制备出结构致密、与基体结合紧密且抗高温氧化性能优良的金属Cr涂层。

The purpose of this study is to explore an efficient method of preparing zirconium alloy surface coating for nuclear power cladding material,in order to improve the high temperature oxidation performance of zirconium claddings resisting sever accidents.Due to the advantages of dense coating,high bonding strength and low oxidation,High-velocity oxy-fuel(HVOF)thermal spraying was used to prepare Cr coating on Zr-4 alloy.Microstructure was observed by X-ray diffractometer(XRD)and scanning electron microscopy(SEM)coupled with energy dispersion spectroscope.The adhesion between Cr coating and substrate was measured by scratch tests,The macro-scratch morphology was observed by optical microscopy(OM).Results show that Cr coating prepared by HVOF is composed of Cr with body centered cubic(bcc)structure and approximately 21.9% Cr_(2)O_(3) with hexagonal close-packed(HCP)structure.Polishing can reduce the Cr_(2)O_(3) content to about 10.1%.The morphology of Cr coating consists of un-melted white particle and lamellar structure in majority and pores in minority.Cr_(2)O_(3) is mainly distributed in the layered structure,and the irregular massive structure formed by un-melted particles containing little oxygen is mainly Cr metal.Adhesion between Cr coating and substrate if of 77 N in minimum and 94 N in maximum.The maximum adhesion is 94 N under the spraying process with parameters of kerosene flow rate of 23 L/h,oxygen flow rate of 880 L/h,and coating spraying distance of 330 mm.The oxidation test in air at 1200℃ for 30 min shows that a mutual diffusion layer about 14μm to 16μm is formed.The mutual diffusion layer consists of a compact Cr-Zr layer approximately 11μm to 14μm containing Zr in coatings next to the interface of matrix and approximately 5μm dark Zr-Cr layer the matrix next to the interface of the coating.This indicates a faster diffusion of Zr from the matrix to the Cr coating than that of Cr from the coating to the matrix.Cr coatings prepared by HVOF oxidized little after the exposure of air at 1200℃for 30 min.Zr matrix covered by Cr coatings covered by Cr coating is not oxidized while oxide films of Zr matrix uncovered with Cr coating is above 120μm in thickness,which illustrates that Cr coating prepared by HVOF has an excellent protective property to Zr matrix.