Thermally sprayed coatings from the single oxides and binary compositions of the Al2O3-Cr2O3-TiO2 system show multifunctional properties. Ternary compositions are promising for further improvement in their performance. The stability of the composition during coating formation is an important issue for blended feedstock powders in order to obtain the desired properties. This work focuses on the compositional changes of a ternary blend of Al2O3, Cr2O3 and TiOx powders of equal content by mass in a conventional atmospheric plasma spraying (APS) process using an Ar/H2 plasma gas mixture. By increasing the argon flow rate at constant hydrogen flow rate, the total plasma gas flow rate and the Ar/H2 ratio were varied. For the highest argon flow rate, this resulted in an average particle velocity of 140% and an average particle temperature of 90% of the initial values, respectively. Coating composition and microstructure were studied by optical microscopy, SEM, including EDS analyses, and XRD. In addition, the coating hardness and electrical impedance were also measured. Differences in the “difficulty of melting factor” (DMF) and the thermal diffusivity of the three oxides appear to be responsible for the dramatic change of the coating composition with an increasing argon flow rate. For the highest argon flow rate applied, besides TiO2, the coating contains only 8 wt.% Al2O3, while the Cr2O3 content remained almost constant. At the same time, the change of the Ar/H2 ratio resulted in the formation of stoichiometric TiO2 in the coating by oxidation of TiOx in the feedstock powder. Moreover, a small content of titanium was found in the Cr2O3 splats, showing that there are only limited interactions between the large oxide powder particles. Thus, the study has shown that stability of the chemical composition during spraying of ternary powder blends is strongly influenced by the process conditions.

中文翻译：

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Al2O3-Cr2O3-TiO2 三元粉末混合物的 APS 工艺条件引起的涂层成分变化

由 Al2O3-Cr2O3-TiO2 系统的单一氧化物和二元组成的热喷涂涂层显示出多功能特性。三元组合物有望进一步提高其性能。涂层形成过程中组合物的稳定性是混合原料粉末以获得所需性能的一个重要问题。这项工作的重点是在使用 Ar/H2 等离子气体混合物的常规大气等离子喷涂 (APS) 工艺中，按质量计等量的 Al2O3、Cr2O3 和 TiOx 粉末的三元混合物的成分变化。通过在恒定的氢气流速下增加氩气流速，等离子体气体的总流速和 Ar/H2 比率会发生变化。对于最高的氩气流速，这分别导致平均粒子速度为初始值的 140% 和平均粒子温度为初始值的 90%。通过光学显微镜、SEM（包括 EDS 分析）和 XRD 研究了涂层成分和微观结构。此外，还测量了涂层硬度和电阻抗。“熔化系数”(DMF) 的差异和三种氧化物的热扩散率的差异似乎是涂层成分随着氩气流速增加而发生剧烈变化的原因。对于应用的最高氩气流速，除 TiO2 外，涂层仅包含 8 wt.% 的 Al2O3，而 Cr2O3 的含量几乎保持不变。同时，Ar/H2 比的变化导致通过原料粉末中的 TiOx 氧化在涂层中形成化学计量的 TiO2。而且，在 Cr2O3 片中发现少量钛，表明大氧化物粉末颗粒之间只有有限的相互作用。因此，研究表明，在喷涂三元粉末混合物期间，化学成分的稳定性受到工艺条件的强烈影响。