Development of prediction method of grain boundary and intragrain microstructures at an atomistic scale by utilizing GC Monte-Carlo methods.

MonteCarlo模拟已被应用于检查在晶界和附近的沉淀结构的微观结构的发展，了解无沉淀区的形成机制和空位和溶质原子耗尽PFZ形成动力学的影响。为了实现晶界和晶内同时析出，我们采用蒙特-卡罗模拟，将晶界设置为一个质量库。这使得我们可以将整个体系看作刚性晶格体系，晶界附近的空位耗尽只是延迟了整个沉淀过程，没有观察到明显的PFZ形成。相比之下，同时晶界和晶粒内沉淀导致形成定义明确的无沉淀区，其界面由沉淀物的突然消失限定，而没有沉淀物的数量密度或尺寸的任何平滑变化。另一方面，这个同步过程对PFZ宽度和粒子间距离提出了相当严格的限制，它们应该在同一个数量级。这不一定与报告的实验观察一致。我们发现，在沉淀前的长距离溶质贫化可能导致PFZ结构，其PFZ宽度远大于沉淀物的颗粒间距离，这在许多情况下与实际PFZ结构相一致。该代码仍然没有足够的效率来模拟足够大的模型系统，以检查PFZ形成的包括长程耗尽区的大小。这一点需要进一步发展。

Monte Carlo simulations have been applied to examine microstructural developments of precipitation structure at and near the grain boundary, to understand the formation mechanism of precipitation-free zone and influences of vacancy and solute atom depletions on the kinetics of PFZ formation. To realize simultaneous grain boundary and intragrain precipitations, we adopted Monte-Carlo simulation with the grain boundary set as a mass reservoir. This enabled us treating the whole system on a rigid lattice system.Vacancy depletion near the grain boundary simply delayed the whole precipitation kinteics, and no clear formation of PFZ was observed. In contrast, simultaneous grain boundary and intra grain precipitation lead to a formation of well-defined precipitation free zones, whose interface is defined by an abrupt extinction of precipitates, without any smooth change in the number density or size of precipitates. On the other hand, this simultaneous process poses a rather strict limitation between the PFZ width and interparticle distance, which should lie in the same order of magnitude. This does not necessarily agree with reported experimental observations. We found that a long-range solute depletion prior to precipitaion may lead to a PFZ microstructure whose PFZ width is far more larger than the interparticle distances of the precipitates, which agreed with actual PFZ microstructures in many cases.For the mutinary calculation required to examine the effects of vacancy-solute and solute-solute interaction, the code is still not efficient enough to simulate a model system large enough to examine the size including long-range depletion area for PFZ formation. This point needs further development.