Grain boundary impurity and porosity effects on the yield strength of nanocrystalline materials

Abstract

The effect of impurities on the equilibrium and nonequilibrium boundaries is analyzed for nanocrystalline materials. Due to the purity of equilibrium grain boundaries, the strength levels off to a limiting value in the range of nano grain sizes. This limiting value increases with the total impurity content. Due to nonequilibrium grain boundaries and their effect on impurity segregation, the strength may decrease with decreasing grain size in the nanosize regime. These considerations can explain all the observed effects of grain size on strength without invoking other mechanisms for the nanosize grains. By controlling the impurity content and porosity of the grain boundaries, it is possible to synthesize ultrastrong and ductile materials. © 2007 American Institute of Physics.