Optimal microstructures on fatigue properties of friction stir processed NiAl bronze alloy and its resistant fatigue crack growth mechanism

摘要

Friction stir processing (FSP) is a feasible way to improve mechanical properties of nickel-aluminum bronze (NAB) alloy. However, not all the microstructures obtained by FSP have high fatigue properties. in this paper, various microstructures of FSPed NAB alloy were prepared by different FSP tools, and optimal microstructures on fatigue properties was obtained. The resistant fatigue crack growth mechanism of the microstructures was also systematically studied. The results show that optimal microstructure contains fine equiazed alpha grain, lots of micron and nano kappa phase and few residual beta phase (beta' phase). The strengthening mechanisms mainly contain grain refinement, second phase strengthening, work-hardening and nanotwin strengthening, and the fine equiaxed alpha grains and large quantity of micron and nano kappa phase make a main contribution to the better fatigue properties. Finally, Zener-Holloman parameter for forming the optimized microstructures was estimated by theoretical calculation.