gradient nano grained structure materials

 

 

DING Song, ZHOU Jian qiu

 

(College of Mechanical and Power Engineering, Nanjing Technology University, Nanjing 211800, China)

 

 

Abstract: Aiming at the problem that nanocrystalline materials possess high strength but low ductility, the nanocrystalline materials which own good ductility were summarized, and the microstructure and deformation mechanism of the gradient nanograined (GNG) materials with both high strength and high ductility were studied. A new theoretical model based on the grain size and GB misorientation was proposed to describe the specific deformation mechanisms of the GNG structure with grain size varying from 20nm~300nm. The dislocations piling up in the grain boundary under the GB sliding process were studied and the energy characteristics of the GB sliding and GB migration was described. According to the energy method, the energy difference for GB sliding and GB migration on the grain size and the GB misorientation angle was calculated and analyzed. The analysis demonstrates that there are two main deformation mechanisms competing in the GNG structure so that the GNG materials not only own high strength but also own good ductility. The GB migration is the dominant deformation mechanism for grains smaller than 170nm, and the GB sliding becomes dominant above this size.

 

Key words: gradient nano grained (GNG) structure; energy characteristic; GB misorientation angle; deformation mechanism