Experimental study of the mechanisms of nanoparticle influencing the fatigue crack growth in an in-situ TiB2/Al-Zn-Mg-Cu composite

To investigate the mechanisms of nanoparticles influencing the fatigue crack growth (FCG) of metal matrix composites, an in-situ TiB2/7050Al composite was systematically investigated. The nanoscale TiB2 showed a morphology of particle bands coexisting with grain boundaries (GBs) along extrusion direction. The TiB2/7050Al composite presented a finer grain size compared to the 7050Al alloy. The TiB2/7050Al composite exhibited a lower, the similar and a higher FCG rate over the 7050Al alloy at the low, intermediate and high stress intensity factor (Delta K) range, accordingly. The microstructure and Delta K correlated FCG mechanisms of TiB2/7050Al composite were discussed in detail. Inside grains, caused by the finer grain size and the increasing Delta K, the TiB2/7050Al composite exhibited the similar FCG rate compared to 7050Al alloy at low Delta K range, while showed a higher FCG rate at intermediate and high Delta K range. At GBs, along with the increasing Delta K, the TiB2 bands induced fatigue crack deflection, fatigue crack trapping and microvoid coalescence led to the lower FCG rate of TiB2/7050Al composite at low and intermediate Delta K range and the higher FCG rate at high Delta K range, accordingly.