STRUCTURE AND TOUGHNESS MODULATION OF A Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ METALLIC GLASS BY SURFACE MECHANICAL ATTRITION TREATMENT

As a new type of structural material, the toughness of metallic glasses (MGs) needs to be further improved. The methods of improving the toughness of MGs include introducing dendrite phase, tuning their compositions to change the Poisson's ratios in order to affect the formation and spread of shear bands and cracks, etc. In this paper, we use the method of surface mechanical treatment to alter the microstructure and toughness of MGs. A Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ (at. %) MG (Vit105) plate was prepared by arc melting in vacuum and centrifugal casting system for thin plates in the metastable state. Surface mechanical attrition treatment (SMAT) is introduced to form nanoscale local crystal-like ordered structure in Vit105. Through differential scanning calorimetry and nano-indentation experiments, we find that the relaxation enthalpy near the surface of the SMAT-treated Vit105 plate is reduced, and its microstructure is more homogenous and stable The analysis by Vickers hardness tester shows that the hardness of the regions near the surface is increased and the hardness values distribute more narrowly after the SMAT treatment. Three-point bending fracture experiment reveals that notch toughness of the plate is also improved by SMAT. By SMAT treatment, the notch toughness increases from 70.7 ± 4.7 MPa·m^1/2 to 112.8 ± 3.7 MPa·m^1/2. Meanwhile, the density of shear bands becomes larger near the fracture surface as compared to the untreated sample. The enhancement of the toughness of Vit105 plate treated by SMAT originates from the promotion of the formation of shear bands. Our studies show that surface mechanical treatment leads to the formation of local crystal-like ordered structure in MGs with the enhancement of structural homogeneity. The hardness and toughness of MGs are improved, being associated with the formation of profusive shear bands. As a novel approach of improving the properties of materials, surface mechanical treatment has a broad application prospect in future.