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arXiv 1808.06286cond-mat.softcond-mat.mtrl-sci
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低温热循环对非晶合金时效、再生和力学性能的影响

The effect of cryogenic thermal cycling on aging, rejuvenation, and mechanical properties of metallic glasses

Nikolai V. Priezjev

摘要:

采用分子动力学模拟研究了模型玻璃在热循环作用下的结构弛豫、势能态和力学性能。我们研究了一种非添加剂的二元混合物,它是从液相退火到低于玻璃化转变的低温不同的冷却速率。通过在恒定压力下反复加热和冷却系统来施加热处理,从而在热膨胀时暂时引起内应力。我们发现,退火不良的玻璃被重新定位到逐步降低水平的势能在连续的周期,而退火良好的玻璃可以在足够大的幅度的热循环再生。此外,对于所有冷却速率,在一定温度幅值下检测到100次循环后的最低水平的势能。到不同能态的结构转变伴随着原子的集体非仿射位移,这些原子被组织成团簇,其典型尺寸随着冷却速率或温度振幅的增加而变大。我们发现,弹性模量和峰值的应力过冲表现出明显的最大值的循环振幅,这对应于最小的势能。模拟结果表明,屈服峰作为循环振幅的函数,快速退火的玻璃表示在较低的冷却速率制备的玻璃中的最大应力的下限。

英文摘要:

The structural relaxation, potential energy states, and mechanical properties of a model glass subjected to thermal cycling are investigated using molecular dynamics simulations. We study a non-additive binary mixture which is annealed with different cooling rates from the liquid phase to a low temperature well below the glass transition. The thermal treatment is applied by repeatedly heating and cooling the system at constant pressure, thus temporarily inducing internal stresses upon thermal expansion. We find that poorly annealed glasses are relocated to progressively lower levels of potential energy over consecutive cycles, whereas well annealed glasses can be rejuvenated at sufficiently large amplitudes of thermal cycling. Moreover, the lowest levels of potential energy after one hundred cycles are detected at a certain temperature amplitude for all cooling rates. The structural transition to different energy states is accompanied by collective nonaffine displacements of atoms that are organized into clusters, whose typical size becomes larger with increasing cooling rate or temperature amplitude. We show that the elastic modulus and the peak value of the stress overshoot exhibit distinct maxima at the cycling amplitude, which corresponds to the minimum of the potential energy. The simulation results indicate that the yielding peak as a function of the cycling amplitude for quickly annealed glasses represents a lower bound for the maximum stress in glasses prepared with lower cooling rates.

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