document: Fig. 11 shows the wear-mode map of RH ceramics, in which the early-stage friction coefficients and the surface roughness of the pure surface were chosen. The value of the fracture toughness of RH ceramics was calculated based on the reference data in other literature [22]. The Sc of RH ceramics was smaller than Sc,critical under all tested conditions during the initial stage of friction. Thus, the initial wear mode of RH ceramics was powder formation or plowing. In addition, powder formation and plowing can be distinguished using a dimensionless parameter (Sc⁎) and a critical parameter (Sc,critical⁎).(3)Sc⁎=HvRmaxKIc(4)Sc,critical⁎=51+10μwhere Hv is the Vickers hardness of RH ceramics [Pa]. The initial wear mode of RH ceramics was determined as powder formation under all tested conditions, as demonstrated in Fig. 12(a). Furthermore, the wear-mode map at 2×104 cycles was constructed, as shown in Fig. 12(b). In the map, all plots moved near the transition curve to plowing. In particular, the plots for RH ceramics sliding against stainless steel or Al2O3 balls were nearer than SiC or Si3N4 balls. Therefore, RH ceramics sliding against SiC and Si3N4 balls showed relatively higher wear than the other counterpart materials. Nevertheless, these results from the wear-mode maps indicated that the wear mode of RH ceramics was powder formation accompanied with microcracks under all tested conditions in this study, resulting in low wear (<5×10−9mm2/N). Indeed, the observation of the worn surfaces revealed that the catastrophic wear of RH ceramics accompanied by large brittle fracture was prevented overall, as shown in Fig. 13.
extractive_keyphrases: al2o3 balls critical parameter dimensionless parameter plowing powder formation sc⁎ sic and si3n4 balls sic or si3n4 balls stainless steel vickers hardness
abstractive_keyphrases: sc,critical⁎ sc⁎=hvrmaxkic(4)sc,critical⁎=51+10μ wear-mode map wear-mode maps