This study presents a unique Mg-based alloy composition in the Mg–Zn–Yb system which exhibits bulk metallic glass, metastable icosahedral quasicrystals (iQCs), and crystalline approximant phases in the as-cast condition. Microscopy revealed a smooth gradual transition from glass to QC. We also report the complete melting of a metastable eutectic phase mixture (including a QC phase), generated via suppression of the metastable-to-stable phase transition at high heating rates using fast differential scanning calorimetry (FDSC). The melting temperature and enthalpy of fusion of this phase mixture could be measured directly, which unambiguously proves its metastability in any temperature range. The kinetic pathway from liquid state to stable solid state (an approximant phase) minimizes the free-energy barrier for nucleation through an intermediate state (metastable QC phase) because of its low solid–liquid interfacial energy. At high undercooling of the liquid, where diffusion is limited, another approximant phase with near-liquid composition forms just above the glass-transition temperature. These experimental results shed light on the competition between metastable and stable crystals, and on glass formation via system frustration associated with the presence of several free-energy minima.

这项研究提出了一种在Mg-Zn-Yb系统中独特的基于Mg的合金成分，该合金在铸态下具有块状金属玻璃，亚稳态二十面体准晶体（iQCs）和晶体近似相。显微镜显示从玻璃到QC的平滑过渡。我们还报告了通过使用快速差示扫描量热法（FDSC）在高加热速率下抑制亚稳态到稳态的相变而产生的亚稳态共晶混合物（包括QC相）的完全熔融。可以直接测量该相混合物的熔融温度和熔融焓，这清楚地证明了其在任何温度范围内的亚稳定性。从液态到稳定固态（近似相）的动力学路径由于其较低的固-液界面能而使通过中间态（可置换QC相）成核的自由能垒最小化。在高度过冷的液体中（扩散受到限制），刚好在玻璃化转变温度之上形成了另一种具有接近液体成分的近似相。这些实验结果阐明了亚稳晶体与稳定晶体之间的竞争，以及由于存在若干自由能极小值而引起的系统挫败而形成的玻璃。