Rejuvenation of metallic glasses by disordering and relaxation controlling

玻璃合金的松弛通常被认为是源于本征随机结构的重要现象之一。由于金属玻璃的结构、相变、力学和磁学性质与其有很强的相关性，因此在工业应用中必须仔细控制玻璃的弛豫态。弛豫态依赖于略高于玻璃化转变温度的冷却速率Tg。我们通过实验和分子动力学(MD)模拟研究了几种玻璃合金在Tg以上的低温退火和不同的冷却条件对低弛豫态的恢复。在较高的降温速率下进行低温退火，弛豫热增大，机械软化明显。分子动力学模拟清楚地表明，当冷却速度高于初始冷却速度(即玻璃制备初期的冷却速度)时，玻璃合金可以通过在Tg上进行热处理而恢复年轻。这种复壮在高于Tg的150K以上的温度范围内是饱和的。计算结果与铜型铸造实验结果基本一致。本论文对恢复和控制弛豫态的研究为金属玻璃的应用提供了有用的信息。

Relaxation of glassy alloys is generally regarded as one of the important phenomena originating from the intrinsic random structure. Due to a strong correlation with structure, transformation, mechanical and magnetic properties of metallic glasses, we have to control the relaxation state carefully for industrial use. Relaxation state depends on a cooling rate just above glass transition temperature, Tg. We have investigated the recovery of the less relaxation state by low temperature annealing just above Tg and various cooling conditions in several glassy alloys by experimental and molecular dynamics (MD) simulation studies. The enthalpy of relaxation increases by such low temperature annealing at higher cooling rates with a significant mechanical softening. The MD simulation clearly indicates that the glassy alloys can be rejuvenated in the case of higher cooling rates than the initial one (i.e., cooling rate in the initial preparation of glass) by annealing over Tg. Such rejuvenation is saturated in the temperature range over 150 K above Tg. The result is consistent with the experimental one using Cu mold casting. The present study on recovering and controlling relaxation state provides useful information on the application of metallic glasses.