Influence of thermoplastic deformation on mechanical properties of Zr-based bulk metallic glasses at room temperature

The influence of thermoplastic deformation on the mechanical properties of Zr55Al10Cu30Ni5 and Zr60Al10Cu25Ni5 bulk metallic glasses (BMGs) at room temperature (RT) was studied. These BMGs lose their strength and become brittle at RT when heated under conditions that exceed their time–temperature–transformation (TTT) curves. For a general-purpose furnace, such conditions can be industrially represented by the upper limit temperature. In fact, these BMGs can be plastically deformed at a temperature considerably lower than the upper limit temperature. However, the strength at RT after thermoplastic deformation can be decreased with deformation under a hot condition, even if the temperature is lower than the upper limit temperature. It is assumed that the decrease in the strength and embrittlement is caused by the crystallization induced by thermoplastic deformation. The increase in the thermoplastic strain tends to decrease the fracture stress at RT. However, a high strain rate and low temperature are effective to avoid the decrease in the fracture stress at RT associated with an increase in the thermoplastic strain.