Characterization of shear banding in La-based bulk metallic glasses through indentation

La64Al14(Cu,Ni)(22), La(63.1)All(5.2)(Cu,Ni)(21.7), La57.6Al17.5(Cu,Ni)(24.9), and La55Al25Cu10Ni5Co5 bulk metallic glasses (BMGs) with low glass transition temperature (T-g) were prepared by copper-mould casting method. The homologous temperature (the ratio of room temperature to T-g) of the four BMGs ranges from 0.64 to 0.73. Plastic deformation behavior of the BMGs at various loading rates was studied by nanoindentation. The results showed that the loading rate dependency of serrated flow, which is related to the nucleation and propagation of shear bands, depends strongly on the homologous temperature. The alloys with relatively high homologous temperature exhibit an increase in flow serration with increasing loading rate. whereas. the alloys with low homologous temperature exhibit prominent serrations at low rates. No distinct shear band is observed around the indents for all alloys after nanoindentation at all the studied loading rates. Alternately, shear band pattern are characterized through macro-indentation. which shows that shear band spacing decreases with the increase of the homologous temperature.