Richeton Thiebaud, Wagner Francis, Chen Cai, Toth Laszlo S
Université de Lorraine, CNRS, Arts et Métiers ParisTech, LEM3, F-57000 Metz, France.
Laboratory of Excellence on Design of Alloy Metals for Low-Mass Structures (DAMAS), Université de Lorraine, 57073 Metz, France.
Materials (Basel). 2018 Jun 26;11(7):1088. doi: 10.3390/ma11071088.
This work analyzes the role of both the grain size distribution and the crystallographic texture on the tensile behavior of commercially pure titanium. Specimens with different microstructures, especially with several mean grain sizes, were specifically prepared for that purpose. It is observed that the yield stress depends on the grain size following a Hall⁻Petch relationship, that the stress⁻strain curves have a tendency to form a plateau that becomes more and more pronounced with decreasing mean grain size and that the hardening capacity increases with the grain size. All these observations are well reproduced by an elasto-visco-plastic self-consistent model that incorporates grain size effects within a crystal plasticity framework where dislocations’ densities are the state variables. First, the critical resolved shear stresses are made dependent on the individual grain size through the addition of a Hall⁻Petch type term. Then, the main originality of the model comes from the fact that the multiplication of mobile dislocation densities is also made grain size dependent. The underlying assumption is that grain boundaries act mainly as barriers or sinks for dislocations. Hence, the smaller the grain size, the smaller the expansion of dislocation loops and thus the smaller the increase rate of mobile dislocation density is. As a consequence of this hypothesis, both mobile and forest dislocation densities increase with the grain size and provide an explanation for the grain size dependence of the transient low work hardening rate and hardening capacity.
这项工作分析了晶粒尺寸分布和晶体织构对工业纯钛拉伸行为的作用。为此专门制备了具有不同微观结构、特别是具有几种平均晶粒尺寸的试样。观察到屈服应力取决于晶粒尺寸，遵循霍尔-佩奇关系；应力-应变曲线倾向于形成一个平台，且随着平均晶粒尺寸的减小，该平台变得越来越明显；硬化能力随晶粒尺寸的增加而提高。所有这些观察结果都能通过一个弹粘塑性自洽模型很好地再现，该模型在晶体塑性框架内纳入了晶粒尺寸效应，其中位错密度是状态变量。首先，通过添加一个霍尔-佩奇型项，使临界解析剪应力取决于各个晶粒尺寸。然后，该模型的主要创新之处在于，可动位错密度的增殖也取决于晶粒尺寸。其基本假设是，晶界主要作为位错的障碍或汇。因此，晶粒尺寸越小，位错环的扩展就越小，可动位错密度的增加速率也就越小。基于这一假设，可动位错密度和林位错密度都随晶粒尺寸的增加而增加，这就解释了瞬态低加工硬化率和硬化能力对晶粒尺寸的依赖性。
