Figure 1b shows the XRD pattern of the HEA coating. Compared to the XRD pattern of the HEA powder, there was one minor diffraction peak determined as the Laves phase on the pattern at about 36°, which is consistent with the phase constituent of as-cast CoCrFeNiNbx HEAs reported by Jiang et al., and the peak intensity of the Laves phase was significantly lower than that of the FCC phase, indicating the FCC phase is the main phase of the alloy.
Figure 2a exhibits the low magnification morphology of longitudinal section, illustrating that the thickness of the coating on the Q235 steel substrate was approximately 500um and that the surface of the coating was uneven. Figure 2b is an enlarged view of the longitudinal section of the bonding surface between the HEA coating and the substrate. It can be seen that there is a clear interface between the coating and the substrate; however, the combination between the two parts was tight and only a small amount of pores was observed. The longitudinal section of the coating shows a distinct elongated dendritic and interdendritic structure parallel to the surface of the substrate, which exhibits the traces of expansion and subsequent solidification of the melt HEAs droplets on the substrate during plasma spraying.
Figure 1. X-ray diffractometer (XRD) patterns of (CoCrFeNi)95Nb5 high-entropy alloy (HEA) powderb(a) and coating (b)
Figure 2. SEM images of (CoCrFeNi)95Nb5 HEA coating: (a) longitudinal section, (b) high magnification morphology of longitudinal section, (c) coating surface, (d) high magnification morphology of the coating surface. DR: dendrites with white contrast; ID: interdendrites with gray contrast.
Figure 2c presents the microstructure of cross section of the (CoCrFeNi)95Nb5 HEA coating. It was found that the dendrites with white contrast (marked as DR) and interdendrites with gray contrast (marked as ID) show an approximately equiaxed morphology, and black areas are pores. The chemical composition of the dendritic phase and the interdendritic phase was analyzed by EDS. It has been demonstrated that Cr and Nb elements are enriched in the interdendritic phase, while Co, Fe and Ni are mainly concentrated in the dendritic region. Similar composition segregation phenomena have also appeared in the study of Liu et al.. It is noteworthy that a lot of rounded precipitates (marked as P) are found in the gray phases, as shown in the inset of Figure 2d and the corresponding elemental composition was analyzed by EDS. From Table 1, the precipitated phase is rich in Co, Fe, and Nb.
In order to analyze the elemental partitioning behavior across the coating-substrate interface, the EDS line scan performs on the white line on Figure 3a, and the distributions of different alloying elements are shown in Figure 3b-f.Elemental composition does not sharply change at the interface; however, thete is a distinct diffusion transition zone with a width of about 2 um between coating and substrate, indicating that the HEA coating and Q235 steel substrate are combined by metallurgical bonding, and the heat-affected zone is narrow during plasma spraying process.
Figure 3. (a) SEM image of the HEA coating longitudinal section, (b–f) distributions of alloying elements by EDS line scanning.
本文由桑尧热喷涂网收集整理。本站文章未经允许不得转载；如欲转载请注明出处，北京桑尧科技开发有限公司网址：http://www.sunspraying.com/
|
