Synthesis, thermal stability and properties of [(Fe_1-xCo _x)₇₂Mo₄B₂₄]₉₄Dy ₆ bulk metallic glasses

A series of [(Fe_1-xCo_x)₇₂Mo ₄B₂₄]₉₄Dy₆ (x = 0.1, 0.2, 0.3, 0.4 and 0.5 at.%) bulk metallic glasses (BMGs) in rod geometries with critical diameter up to 3 mm were fabricated by copper mold casting method. This alloy system exhibited good thermal stability with high glass transition temperature (T_g) 860 K and crystallization temperature (T_x) 945 K. The addition of Co was found to be effective in adjusting the alloy composition deeper to eutectic, leading to lower liquidus temperature (T_l). The [(Fe_0.8Co_0.2)₇₂Mo₄B ₂₄]₉₄Dy₆ alloy showed the largest supercooled liquid region (ΔT_x = T_x - T_g = 92 K), reduced glass transition temperature (T_rg = T_g/T _l = 0.622) and gamma parameter (γ = T_x/(T _g + T_l) = 0.424) among the present system. Maximum compressive fracture strength of 3540 MPa and micro-Vickers hardness of 1185 kg/mm² was achieved, resulting from the strong bonding structure among the alloy constituents. The alloy system possessed soft magnetic properties with high saturation magnetization of 56.61-61.78 A m²/kg and coercivity in the range of 222-264.2 A/m, which might be suitable for application in power electronics devices.