The influence of boron-doping on the effectiveness of grain boundary hardening in Ni 3Al

Abstract

The influence of boron-doping on the effectiveness of grain boundary hardening in Ni 3Al has been investigated by measuring microhardness profiles across grain boundaries of binary and boron-doped Ni 3Al bicrystals. It was found that although boron gives rise to significant solution strengthening in Ni 3Al, the effectiveness of grain boundary hardening in Ni 3Al is lessened by the addition of boron. Furthermore, the contribution of grain boundary hardening to the overall strength decreases as the segregation extent of boron at the grain boundary increases. A theoretical model of grain boundary hardening considering the various effects of boron-doping has been developed. Application of the model can deconvolute the individual effects of boron-doping on solution hardening, distribution of microcavities along grain boundaries and the interaction of dislocations on different slip systems. Analyzing the experimental results with the model suggests that boron-doping can (i) improve the transfer efficiency of shear stress across a grain boundary by reducing the amount of microcavities along the grain boundary; (ii) suppress the hardening effect from the interaction of dislocations moving on different slip systems and (iii) cause a significant solution hardening effect.