Effect of Nb on thermal stability of Ni-Co-W-B metallic glasses: A kinetic study

Abstract

In this study, the effect of Nb addition on the continuous heating diagram of the Ni-Co-W-B metallic glass alloy system was investigated, and the improvement in glass-forming ability and thermal stability was demonstrated. Based on differential scanning calorimetry (DSC) analyses performed under non-isothermal conditions, a theoretical continuous heating diagram was constructed using the well-known Kissinger kinetic equation. Furthermore, the boundary line of the transition from the amorphous to the crystalline phase was validated through isothermal heat treatments. The findings indicate that modifying the refractory element content by incorporating 6 at. % Nb into the alloy composition improves thermal stability at higher temperatures. The XRD results also demonstrate that the addition of Nb enhances the alloy's glass-forming ability threefold and increases the critical casting thickness from 0.5 mm to 1.5 mm. The local activation energy values calculated for different crystallization fractions indicate that the activation energies required for any given crystallization fraction in the Ni_32.75Co_22.55W_23.7B₁₅Nb₆ alloy are higher than those in Ni_35.116Co_24.184W_23.7B₁₇ the alloy. Furthermore, the primary crystallization phase boundary line in the continuous heating transformation diagram shifts to both higher temperatures and longer times. These results highlight the role of Nb addition in retarding the crystallization in the Ni-Co-W-B alloy system.