Relaxation and Devitrification of Mg₆₆Zn₃₀Ca₄ Metallic Glass

Mg₆₆Zn₃₀Ca₄ metallic glass is a promising biodegradable material due to its high strength, corrosion resistance, and excellent glass-forming ability. In this study, we investigated its thermal stability, structural relaxation, and crystallization behavior using high-energy synchrotron-based X-ray diffraction and DSC analysis. The glass exhibits a wide supercooled liquid region of 58 K, allowing for thermoplastic forming. Structural relaxation experiments revealed nearly a complete relaxation in the first cycle below the first crystallization peak. Upon heating, the alloy undergoes a complex, multi-step devitrification involving successive formation of crystalline phases: Mg₅₁Zn₂₀ (orthorhombic), Mg (hexagonal), and a Ca-Mg-Zn intermetallic compound Ca₈Mg_26.1Zn_57.9, denoted as IM3. Phase identification was carried out by Rietveld refinement, and the evolution of lattice parameters demonstrated anisotropic thermal expansion, particularly in the Mg₅₁Zn₂₀ phase. Notably, the presence of the IM1 Ca₃Mg_xZn_15-x, with the 4.6 ≤ x ≤ 12 phase reported in earlier studies, was not confirmed. This work deepens the understanding of phase stability and crystallization mechanisms in Mg-based metallic glasses and supports their future application in biodegradable implants.