An experimental methodology to quantify the resistance of grain boundaries to fatigue crack growth in an AA2024 T351 Al-Cu Alloy

The growth behaviors of the short fatigue cracks initiated from the micro-notches, 30×15 μm², fabricated using FIB in some coarse grains, were investigated across grain boundaries in an AA2024-T351 Al-Cu-Mg alloy in four-point bend fatigue at 20 Hz, R=0.1, and room temperature in air. The resistance to short crack growth at the grain boundary that the crack crossed was quantified from the measured decrease in growth rate at the boundary. It was found that the decrease in crack growth rate followed a linear relationship with the twist component (α) of crack deflection at the boundary, as revealed in EBSD and FIB experiments. The resistance of grain boundaries to short crack growth was revealed to a Weilbul-type function of α, which quantitatively verified Zhai's minimum α criteria for short fatigue crack growth across grain boundaries in planar slip alloys.