Crystallization-induced dramatic enhancement of wear resistance in a Zr-based bulk metallic glass

Whether bulk metallic glass (BMG) of unique disordered atomic structure exhibits better wear resistance than its crystalline counterpart or not, poses an essential yet unsolved question. To this motive, the wear resistances of as-cast Zr 60.14 Cu 22.31 Al 9.7 Fe 4.85 Ag 3 BMG (in amorphous state), Zr 60.14 Cu 22.31 Al 9.7 Fe 4.85 Ag 3 master alloy (in crystalline state), and crystallized Zr 60.14 Cu 22.31 Al 9.7 Fe 4.85 Ag 3 BMG (in crystalline state), are examined using Si 3 N 4 as the counter-friction material. Similar wear procedures are observed for the three different Zr 60.14 Cu 22.31 Al 9.7 Fe 4.85 Ag 3 samples, which exhibit a running-in stage and gradually transit into dynamic stable wear stage. Intriguingly, both Zr 60.14 Cu 22.31 Al 9.7 Fe 4.85 Ag 3 master alloy and crystallized Zr 60.14 Cu 22.31 Al 9.7 Fe 4.85 Ag 3 BMG show a wear resistance five times better than the as-cast Zr 60.14 Cu 22.31 Al 9.7 Fe 4.85 Ag 3 BMG in both air and phosphate buffer saline (PBS) solution. The main wear mechanisms of all the three Zr 60.14 Cu 22.31 Al 9.7 Fe 4.85 Ag 3 samples in the dynamic stable stage are identified as ploughing, squeezing, and oxidative wear. The inferior wear resistance of as-cast Zr 60.14 Cu 22.31 Al 9.7 Fe 4.85 Ag 3 BMG which shows similar nanoindentation hardness to its crystalline counterparts, is attributed to severe cracking and peeling-off of the tribo-oxide layer from the wear track. This work provides new insights into understandings on the wear resistance of BMGs and their crystalline counterparts.