Cu-Hf-Ti-Ag-Ta bulk metallic glass composites and their properties

Multi-component (Cu_0.50Hf_0.35Ti_0.10Ag _0.05)_{100 - x}Ta_x (x = 0, 1, 3, 5, 8, 12) bulk metallic glass (BMG) composites containing in situ formed dendrites were prepared successfully. With increasing Ta content, both compressive fracture strength (σ_f) and elastic-plastic strain (ε_f) increase from 2180 MPa and 2.1% for x = 0, to 2770 MPa and 19.2% for x = 8, respectively, but yield strength and elastic modulus decrease. The precipitation of a high volume fraction of the dendrites (V_dendrite) causes the compositional variation of the dendrites and its counterpart glass matrix. Composition analysis shows that both Hf and Ti elements exhibit an opposite behavior of dissolving into the dendrites during the cooling. About 7-11 at.% component elements (Ti, Cu and Ag) were detected in Ta-rich dendrites, but no Hf element was found. With increasing V_dendrite, the content of component elements dissolving into Ta-rich dendrites decreases from 11.35 at.% for V_dendrite = 4.3% and 7.97 at.% for V_dendrite = 26.5%. Indentation testing was also performed to evaluate the properties of the composites. With increasing V_dendrite, the hardness of the dendrites decreases from 6.0 GPa for x = 3 to 5.21 GPa for x = 12, and its elastic modulus increases from 151.2 GPa for x = 3 to 156.9 GPa for x = 12. The hardness and elastic modulus of the glassy matrix also decrease, respectively, from 9.66 and 148.7 GPa for x = 0 to 9.36 and 137.4 GPa for x = 12 with increasing precipitation of the dendrites. The variation of the properties is due to the compositional change originating from the opposite behavior of Hf and Ti elements to dissolve into the dendrites.