Studies were carried out by scanning electron microscopy, images of powder particles were obtained at a magnification of 100-1,000 times. The results are presented in fig. 1 (a-d).
According to the study results, it was found that the powder is a hollow sphere with a typical particle size of 70-100 microns. Due to the high brittleness and small wall thickness of the particles, some of them are destroyed, as evidenced by numerous fragments.
An X-ray microanalysis of the powder sample was carried out to determine the chemical composition. In order to improve the accuracy of the method, the analysis was carried out at three points of various powder particles of one sample, the analysis scheme is shown in Figure 2, the analysis results are given in Tables 1 and 2.
Table 1 – Results of X-ray microanalysis
Table 2 – Estimated average composition of the powder by the content of oxides %
The content of hafnium in powders of this type is the norm due to the peculiarities of the technological process for production of metallic zirconium.
The powder coating was applied to the prepared samples made of ZhS6U alloy with a metal sublayer made of an alloy of the Ni-Cr-Al-Y system. The coating was applied by atmospheric plasma spraying using an F4 plasma torch and plasma-forming gases of argon and nitrogen. During application, a slight scattering of particles from the burner axis (< 5°) was observed, which indicates a high degree of sphericity of the powder. The utilization rate of the material during application was 28.95%. The structure of the resulting coating is shown in fig. 3.
Based on the results of the coating structure analysis, it was found that the coating corresponds to the typical standards of ceramic layers of heat-shielding coatings obtained from partially stabilized zirconium dioxide powder in terms of porosity, thickness distribution, and surface roughness.
The X-ray microanalysis of the coating sample was carried out to determine the chemical composition. In order to improve the accuracy of the method, the analysis was carried out at three points, the analysis scheme is shown in Figure 4, the analysis results are given in Tables 3 and 4.
Table 3 – Results of X-ray microanalysis
Table 4 – Estimated average composition of the powder by the content of oxides %
According to the analysis results, an increase in the content of hafnium in the coating was found in comparison with the initial powder material. This phenomenon is due to the peculiarity of the processes of melting and evaporation of ceramic oxygen-containing materials and is not a deviation.
Based on the combination of characteristics, the powder under study is a high-quality advanced product suitable for applying the thermal barrier ceramic layers of heat-shielding coatings. Also, while examining the sample of foreign powder of the Metco 204NS brand (Oerlikon AG), if this powder is sifted through a sieve with a mesh size of 70 microns, it is not possible to distinguish it from the powder under study, because they are probably produced using the same technology.