晶粒尺寸对纳晶双峰材料断裂韧性的影响

Effect of Grain Size on the Fracture Toughness of Bimodal Nanocrystalline Materials

摘要:

为了描述由纳晶基体和粗晶颗粒组成的纳晶双峰材料的断裂韧性，通过建立一个粘聚力模型来研究纳晶双峰材料的临界应力强度因子KIC（表征材料断裂韧性）。考虑到纳晶双峰材料的一个典型情况：裂纹位于2个纳晶颗粒的交界面处，裂纹尖端与粗晶粒的晶界相交，假设粘聚区的尺寸等于纳晶颗粒的尺寸d。裂纹的钝化和扩展过程受位错和粘聚力的共同影响，刃型位错是从粘聚力裂纹的尖端发射，该过程对裂纹产生屏蔽效应。模型计算结果显示：当粗晶颗粒尺寸D确定时，KIC随着纳晶材料晶粒尺寸d的增大而增大；当纳晶材料晶粒尺寸d确定时，KIC随着粗晶材料晶粒尺寸D的增大而增大；相对于纳晶颗粒的尺寸，断裂韧性对粗晶晶粒的尺寸更加敏感。

Abstract:

To describe the fracture toughness of bimodal nanocrystalline (BNC) materials which are composed of nanocrystalline (NC) matrix and coarse grains, we have developed a theoretical model to study the critical stress intensity factor (which characterizes toughness) of BNC materials. A typical case has been considered where crack lies at the interface of two neighboring NC grains and the crack tip intersect at the grain boundary of the coarse grain, while the cohesive zone size is assumed to be equal to the grain size d of the NC matrix. Blunting and propagating processes of the crack is controlled by a combined effect of dislocation and cohesive zone. Edge dislocations emit from the cohesive crack tip and make a shielding effect on the crack. It is found that the critical stress intensity factor increases with the increasing of grain size d of the NC matrix as well as the coarse grain size D. Moreover, the fracture toughness is relatively more sensitive to the coarse grain size than that of NC matrix.