Unusual plastic deformability in a Zr-based bulk metallic glass after structural relaxation

The structural stability is an essential problem for engineering application of bulk metallic glasses (BMGs). Constant-heating dilatometric measurements were conducted for 2 mm Zr63.78Cu14.72Ni10Al10Nb1.5 BMG rods and two visible structural relaxation processes below Tg were found, which correspond to the obvious annihilation of free volume (FV) and the continuous decrease in coefficient of linear thermal expansion (α). After annealing the BMGs near the temperature of the main structural relaxation processes and Tg for 3600 s, the BMG rods have much FV relaxed, but still remain the amorphous structure. The microhardness of the annealed samples increases with increasing the annealing temperature, but the plastic strains remain unchanged considering the uncertainty of uniaxial compression after annealing the BMGs at the temperature below Tg. The excellent plasticity of the BMGs experienced the structural relaxation is absolutely different from those previous results of embrittlement after structural relaxation below Tg. The mechanisms of this unusual plastic deformability for the BMGs experienced the structural relaxation below Tg is discussed in the light of apparent activation volume.