Long-range-diffusion-assisted but interface-controlled crystallization of a Mg-Ni-Mm glass below its glass-transition temperature

A metallic glass of nominal composition Mg(75)Ni(20)Mm(5) (Mm: mischmetal) when heated shows primary crystallization to Mg2Ni. Transmission electron microscopy studies, including annealing experiments in situ, supported by differential scanning calorimetry and X-ray diffraction, reveal the remarkable complexity of this crystallization. The crystals are lens-shaped and at constant temperature show linear (constant-rate) growth, despite marked partitioning of nickel from the glass to the crystal. The growth, constrained by atomic rearrangement at the glass-crystal interface, gives a crystalline phase that is partially disordered and has almost half of its magnesium sites vacant. The combination of solute partitioning and isothermal linear growth challenges usual assumptions about the characteristics of primary and polymorphic crystallization. This hybrid behavior is interpreted in terms of the widely differing diffusivities of the atomic species in this system. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

The heating of a metallic glass with nominal composition Mg(75)Ni(20)Mm(5) revealed primary crystallization to Mg2Ni. The study of this crystallization process showed complexity in crystal shape, linear growth, and internal disorder within the crystal.