Room temperature and high temperature (HT=500℃) wear resistance of the plasma sprayed AlCoCrFeNi HEA coating was investigated against an Al2O3 ball as a counter body at a 10 N load over a sliding distance of 1000 m. The profile of the wear track was evaluated by 3D optical profilometry and is shown in Fig. 1(a) and Fig.1(b). Fig. 10(c) represents the 2D depth and width profile of two tracks measured at the point shown by white arrow in Fig. 1(a) and (b). The 2D depth and width profiles evidenced that the wear track was deeper and wider at RT and, about 4 times deeper than that at HT. The diminution in depth and width of the wear track at HT indicates the high thermal stability, hot strength, and minimal plastic flow of the TS HEA coating. Joseph et al. reported the high temperature wear performance of AlCoCrFeNi HEAs, with considerable decrease in width and depth ofwear tracks with increasing temperature (RT, 300 ℃, 600℃ and 900 ℃); signifying good hot strength of AlCoCrFeNi HEAs.
Fig. 1. Wear surface profilometry of (a) room temperature (RT) wear track, (b) high temperature wear track (500℃), and (c) 2D wear depth profiles corresponds to bottom point of wear tracks as shown by white arrow and, (d) volume wear rate for APS AlCoCrFeNi coatings.
The wear volume loss was calculated using laser confocal microscopy, which was further used to quantify the volume wear rate as per the Archard wear equation. As illustrated in Fig. 10(d), the RT wear rate (3.91×10_4 mm3/N-m) of plasma sprayed AlCoCrFeNi coating was approximately two times higher than the HT wear rate (2.08×10_4 mm3/N-m). The friction coefficient values recorded were in the range of 0.86e0.92 and 0.39e0.46 for testing conducted at RT and HT, respectively. Hence, the outcome of wear testing postulated that plasma sprayed AlCoCrFeNi HEA coating exhibited superior wear resistance at HT (500℃) as compared to RT.
The high values of friction coefficient (0.86e0.92) at RT indicated dominance of 2-body abrasion (sliding) between the HEA coating and counter body and, also represent the severity of wear. However, during HT testing, the coating samplewas initially heated to 500 ℃, and when temperature was stabilized, wear testing was carried out. An oxide layer could develop on the coating surface due to the increased test temperature. The oxide layer would act as a lubricant layer and prevent direct contact between two mating surfaces; thus, lowering the friction between two surfaces. The friction coefficient values obtained at HT (0.39e0.46) were almost half of the RT values and, also suggested operation of 3-body abrasion; i.e., rolling, between the two surfaces.
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