Influence of boron-doping on the effectiveness of grain boundary hardening in Ni3Al

The influence of boron-doping on the effectiveness of grain boundary hardening in Ni₃Al has been investigated by measuring microhardness profiles across grain boundaries of binary and boron-doped Ni₃Al bicrystals. It was found that although boron gives rise to significant solution strengthening in Ni₃Al, the effectiveness of grain boundary hardening in Ni₃Al 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.