# Wear Properties of Sc-Bearing Zr-Based Composite BMG with Nano-CuZr\({}_{2}\) under Lubrication
## 3 Results and Discussion
### Worn Surface Characteristic  
Figure 5 exhibits the images of wear tracks under different conditions after sliding wear tests on the surface of the 440C steel disk. The debris of (Zr55 Cu30 Ni10 Al5)99.98 Sc0.02 composite BMG scaled off from the pin with adhesive composite BMG, and patches adhered to the disk surface. The patches were plowed across the disk surface, formed cavities, and dragged traces along the wear track. More transferred materials were observed for the (Zr55 Cu30 Ni10 Al5)99.98 Sc0.02 composite BMG than for the (Cu55 Zr40 Al5)98 Er2 composite BMG [19; 21], and the disk surface was ploughed severely. The SEM (scanning electron microscopy) images of the composite BMG are shown in Figure 6. The composite BMG has experienced severe plastic deformation evidenced by the morphology of the track in Figure 6. The worn surface of the (Zr55 Cu30 Ni10 Al5)99.98 Sc0.02 composite BMG exhibited distinct grooves and craters. In addition, a higher number of cracks appeared on the (Zr55 Cu30 Ni10 Al5)99.98 Sc0.02 composite BMG surface.  
Figure 5: Disk (440C steel) surface images of a wear track under a 20 N load at sliding velocities of (**a**) 0.043 m/s, (**b**) 0.064 m/s, (**c**) 0.085 m/s, (**d**) 0.107 m/s, and (**e**) 0.128 m/s.  
Because of the severe plastic deformation during the sliding test, the worn surface of the (Zr\({}_{55}\)Cu\({}_{30}\)Ni\({}_{10}\)Al\({}_{5}\))\({}_{99.98}\)Sc\({}_{0.02}\) composite BMG exhibited fine abrasion marks, tearing, and grooving [1]. Besides the plastic deformation, evidently distinct grooves and debris occurred on both sides of the grooves. Previous studies have reported these wear features [19,21]. The chemical analyses of the selected worn surfaces are depicted in Figure 7 for the (Zr\({}_{55}\)Cu\({}_{30}\)Ni\({}_{10}\)Al\({}_{5}\))\({}_{99.98}\)Sc\({}_{0.02}\) composite BMG. Most debris adhered to the (Zr\({}_{55}\)Cu\({}_{30}\)Ni\({}_{10}\)Al\({}_{5}\))\({}_{99.98}\)Sc\({}_{0.02}\) composite BMG surface, and least to the disk surface of 440C stainless steel. Debris I on the worn surface from the energy-dispersive X-ray spectroscopy (EDX) exhibited the same constituent elements as those exhibited by the (Zr\({}_{55}\)Cu\({}_{30}\)Ni\({}_{10}\)Al\({}_{5}\))\({}_{99.98}\)Sc\({}_{0.02}\) composite BMG (Figure 7). Debris II exhibited a strong iron peak in the EDX analysis that originated from the 440C steel disk (Figure 7).  
Figure 6: Scanning electron microscopy (SEM) images of a worn surface tested under a 20 N load at sliding velocities of (**a**) 0.043 m/s, (**b**) 0.064 m/s, (**c**) 0.085 m/s, (**d**) 0.107 m/s, and (**e**) 0.128 m/s for the Sc-bearing Zr-based composite BMG.  
Figure 7: Scanning electron microscopy (SEM) image of a worn surface under a 20 N load, and the compositions of Debris I and II at a sliding velocity of 0.064 m/s.  
The composition of EDX analysis in Figure 7 for debris I on the worn surface is as follows: Zr 54.98, Cu 29.96, Al 9.99, Ni 4.97, C 0.06, and O 0.04 in at%. That for debris II is Zr 53.83, Cu 28.15, Fe 7.81, Al 6.67, Ni 3.45, C 0.05, and O 0.04 in at%. Although a contamination of iron peak originating from the 440C steel disk, the compositional difference between these two sources of debris is not very significant at around 1 at%.