晶界偏析以及界面相和纳米晶材料力学性能的调控

A Review on Grain Boundary Segregation,Interfacial Phase and Mechanical Property Adjusting-controlling for Nanocrystalline Materials

介绍晶界偏析理论并总结了三种经典平衡偏析理论模型,简述晶界偏析工程理论和晶界偏析对材料力学性能的影响、讨论晶界偏析与界面相的关系并详细阐述了“界面相”。根据原子尺度界面结构特征将界面相分为六类,介绍了由晶界热力学决定的界面相转变。界面相转变后在晶界处形成新结构,而新界面结构根据其不同性质既可能提高材料性能,也可能产生不利的影响。晶界处的Ⅵ型界面相(如非晶晶间膜)抑制裂纹形核和降低晶界损伤,而削弱晶界处原子键强度的Ⅱ型界面相和Ⅲ型界面相(如Ni合金晶界处成分为Bi的双原子层界面相)产生晶界脆化。同时,纳米晶金属材料的强度高但是热稳定性和塑性较差,一直是研究的热点。界面相使晶界能显著降低和钉扎晶界而优于晶界偏析,因此界面相能显著提高纳米晶金属材料的热稳定性。而非晶晶间膜(Ⅵ型界面相)作为位错的形核点和吸收体,可提高纳米材料的延展性。同时,非晶晶间膜能提高晶界抗剪切能力,抑制纳米晶金属材料的晶粒滑动和旋转,从而进一步提高纳米晶金属材料的强塑性。最后,总结了晶界偏析和界面相对材料性能的调控并展望了以后的发展。

The theory of grain boundary segregation was introduced,and three classical models of equilibrium segregation were summarized,while the theory related with grain boundary segregation engineering and the influence of grain boundary segregation on mechanical properties of materials were also briefly introduced.The relationship between grain boundary segregation and interface phase was discussed.The interfacial phases can be divided into six types according to the structural characteristics of interfaces in atomic scale,and the interfacial phase transitions determined by grain boundary thermodynamics were introduced.The interfacial phase transformation leads to the formation of new structures at grain boundaries,which may either improve the properties of materials or have adverse effects on them.The type VI interfacial phase at grain boundary(such as amorphous intergranular film)inhibits the nucleation of crack and reduces the damage of grain boundary,however,the type II and type III interfacial phases that weaken the atomic bond strength at the grain boundary(such as the bi-atomic interfacial phase at the grain boundary of Ni alloy with Bi component)produce grain boundary embrittlement.At the same time,nanocrystalline metal materials have high strength but poor thermal stability and plasticity,which has always been the focus of research.The interfacial phase can significantly reduce grain boundary energy and pin grain boundaries rather than segregates at grain boundaries.Therefore,the interfacial phase can significantly improve the thermal stability of nanocrystalline metallic materials.As the sites for nucleation and absorption of dislocations,the amorphous intercrystalline film(VI interface phase)can improve the ductility of nanomaterials.Whilst,amorphous intercrystalline films can improve the shear resistance of grain boundaries and inhibit grain sliding and rotation of nanocrystalline metallic materials,thus further improving the plasticity of nanocrystalline metallic materials.Finally,the effects of grain boundary segregation and interface on material properties were also summarized and the future development was prospected.