Effect of compositional tailoring on the glass-forming ability and mechanical properties of TiZr-based bulk metallic glass matrix composites

A large amount of free volume (FV) or the precipitation of ductile dendrites from the glass matrix generally leads to the enhanced plasticity of bulk metallic glasses (BMGs). In this study, the structural relaxation enthalpy ΔHrel (the measure of FV amount) is found to increase after adding Nb or Fe to the glass matrix. As a result, a series of centimeter-scale plastic BMGs is fabricated. Among these TiZr-based BMGs, the sample (Ti32.8Zr30.2Cu9Ni5.3Be22.7)0.9Nb10 (at%) possesses the largest plastic strain (εp) of 8.3% and ultimate strength (σmax) of 2080 MPa. By further precisely tailoring the composition, a TiZr-based BMG matrix composite (BMGMC) (Ti38.8Zr28.8Cu6.2Be16.2Nb10, at%) possessing both the precipitation of β-Ti and β-Zr dendrites simultaneously has been fabricated. The TiZr-based BMGMC has both the distinguished plastic strain (εp) of 12% and ultimate strength (σmax) of 2150 MPa. The values of yielding strength (σy) significantly decreased with the increase of suction casting diameter, whereas the work-hardening phenomenon is more obvious. Therefore, a critical size and volume fractions corresponding to the best mechanical properties of TiZr-based BMGMC should exist. The ductile dendrites are crucial to impeding shear band propagation and generating multiple shear bands in the glass matrix. Results indicate that a large amount of lattice distortions, pile-ups of dislocations and shear steps can be attributed to distinguished plasticity, and these constitute the deformation mechanism of TiZr-based BMGMC.