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 (ΔK) range, accordingly. The microstructure and ΔK correlated FCG mechanisms of TiB₂/7050Al composite were discussed in detail. Inside grains, caused by the finer grain size and the increasing ΔK, the TiB₂/7050Al composite exhibited the similar FCG rate compared to 7050Al alloy at low ΔK range, while showed a higher FCG rate at intermediate and high ΔK range. At GBs, along with the increasing ΔK, 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 ΔK range and the higher FCG rate at high ΔK range, accordingly.