论文标题
关于固态扩散转化中均质成核的临界大小的可变性
On the Variability of Critical Size for Homogeneous Nucleation in a Solid-State Diffusional Transformation
论文作者
论文摘要
在涉及成核和生长的固态扩散相变，均匀过程的临界核的大小（r* homo = r*）被认为是转化的时间不变常数。与该过程相关的应变具有正能量贡献，并导致R*的值增加，相对于液体的成核。随着这种转化的进展，存储在基质中的应变能增加并在以后的阶段形成核会遇到紧张的基质。使用散装金属玻璃作为模型系统的Devitrification，我们证明R*不是均质成核的基本时间不变常数，并且根据应变能损伤可以增加或减少。我们表明，关于r*恒定的假设仅在转换的早期阶段才是正确的，并确定转换的进展会导致r*的变化，这是微结构细节，几何变量和物理参数的函数。借助高分辨率晶格条纹成像和R*的计算，我们进一步认为，“液体样”均质成核可以发生，并且结论适用于一组广泛的固态扩散转换。上述效应“打开”纯粹由系统内部变量引起的较低屏障变换途径。
In a solid-state diffusional phase transformation involving nucleation and growth, the size of the critical nucleus for a homogeneous process (r*homo=r* ) has been assumed to be a time invariant constant of the transformation. The strain associated with the process has a positive energy contribution and leads to an increase in the value of r*, with respect to that for nucleation from a liquid. With the progress of such a transformation, the strain energy stored in the matrix increases and nuclei forming at a later stage encounter a strained matrix. Using devitrification of a bulk metallic glass as a model system, we demonstrate that r* is not a cardinal time invariant constant for homogeneous nucleation and can increase or decrease depending on the strain energy penalty. We show that the assumption regarding the constancy of r* is true only in the early stages of the transformation and establish that the progress of the transformation leads to an altered magnitude of r*, which is a function of the microstructural details, geometrical variables and physical parameters. With the aid of high-resolution lattice fringe imaging and computations of r*, we further argue that, 'liquid-like' homogeneous nucleation can occur and that the conclusions are applicable to a broad set of solid-state diffusional transformations. The above effect 'opens up' a lower barrier transformation pathway arising purely from the internal variables of the system.
