氧乙炔燃流氧化处理制备氧化物包覆ZrB_2/SiC核壳结构粉末特征与机理的研究

Research on Characteristics and Mechanism of Oxide-coated ZrB_2/SiC Core-Shell Powder by Oxyacetylene

ZrB_2/SiC复合粉体熔点高,在等离子喷涂过程中难以获得良好的熔融状态,变形颗粒间存在大量缺陷,导致涂层抗氧化性能急剧下降。为此,本文设计了氧化物包覆ZrB_2/SiC复合粉末,并探索采用氧乙炔火焰热处理方法进行核壳结构粉末的制备。采用扫描电镜对不同试验阶段粉体表面及截面进行观察,发现氧化热处理后的粉体可以得到明显核壳结构的团聚粉,粉体的致密性也得到了明显的提高。采用EDS对三种粉体的成分分布进行了观察,探究了原位氧化法制备得到的核壳结构的粉体中Zr、Si、O主要元素的分布情况,结合XRD进行的物相分析,进一步证实了扫描电镜观察的结果,并对结果形成原因进行了分析。

With the development of aerospace technology, the flight speed of hypersonic aircraft has been continuously improved. Due to the aerodynamic heating, the temperature in the nose cone of the aircraft can reach above 1800 ℃. C/C has the advantages of high temperature stability, low thermal expansion coefficient and stable high temperature mechanical properties, and is one of the main materials for preparing hot end parts of aircraft. However, C/C materials have serious defects in oxidative ablation in high-temperature aerobic environment, and an effective method for improving their anti-oxidation ablation performance is urgently needed. Among the many methods, ultra-high temperature ceramic anti-oxidation ablation coatings have received wide attention and are expected to solve this bottleneck problem. After a lot of exploration and comparison, among many ultra-high temperature ceramic materials, ZrB 2 /SiC has the advantages of high melting point, good thermal stability, proper viscosity and vapor pressure at high temperature. At different temperatures, the formation of oxide actsas a sealing pore in the anti-ablative process and blocks the diffusion of oxygen, which has become the focus of research. The ZrB 2 /SiC composite powder has a high melting point, and it is difficult to obtain a good molten state during plasma spraying, and a large number of defects exist between the deformed particles, resulting in a sharp drop in the oxidation resistance of the coating. To this end, the oxide coated ZrB 2 /SiC composite powder was designed in this paper, and the preparation of core-shell structure powder by oxyacetylene flame heat treatment was explored. In this experiment, the raw material powder was spay-dried and granulated to obtain agglomerated powder of ZrB 2 :SiC=6:4. The ZrB 2 /SiC agglomerated powder prepared by spray drying process has good sphericity and uniform composition distribution, but due to raw materials. The particle shape matching is poor, and the deionized water vaporizes the structure in a short time, which causes a large number of defects on the surface and inside of the powder, which not only reduces the strength of the powder itself, but also becomes an oxygen diffusion channel, which cannot meet the requirements of powder oxidation heat treatment. Then, the agglomerated powder is sintered by atmospheric plasma spheroidization, and two kinds of powders are obtained after atmospheric plasma sintering: one is a dense powder, because the passivation of the granularity of the granular structure and the sealing of the rapidly fused structure during the high temperature process The density is obviously improved;the other is non-dense powder, because the content of fused structure is small, the effective sealing is not achieved, but the denseness is improved compared with ZrB 2 /SiC agglomerated powder, and the oxidation heat treatment is achieved. The powder was oxidized by oxyacetylene gun, and the composite powder with ZrB 2 /SiC as the core and ZrO 2 as the shell was finally prepared. The powder with obvious core-shell structure was prepared by oxyacetylene combustion oxidation heat treatment. The core layer structure of the powder is ZrB 2 and SiC, and the shell structure is an oxide in which a small amount of SiO 2 exists mainly as ZrO 2. The oxidation product of the shell layer can improve the powder structure and increase the density of the powder. Scanning electron microscopy was used to observe the surface and cross section of the powder in different test stages. It was found that the powder after oxidative heat treatment can obtain agglomerated powder with obvious core-shell structure, and the compactness of the powder is also obviously improved. The composition distribution of the three powders was observed by EDS. The distribution of the main elements of Zr, Si and O in the core-shell structure prepared by in-situ oxidation method was investigated. The results of scanning electron microscopy were further confirmed. The reasons for the formation of the results were analyzed.