In this work, molecular dynamics simulations to explore the crack propagation and fracture behavior of Cu/Nb metallic nanolayered composites (MNCs) were performed. The results of this study are consistent with the previous experimental results, which illustrated that cracks in Cu and Nb layers may exhibit different propagation paths and distances under the isostrain loading condition. The analysis reveals that the interface can increase the fracture resistance of the Nb layer in Cu/Nb MNCs by providing the dislocation sources to generate the plastic strain at the front of the crack. Increasing the layer thickness can enhance the fracture resistance of both Cu and Nb layers, as the critical stress for activating the dislocation motion decreases with the increment of the layer thickness. In addition, grain boundaries (GBs) in polycrystalline Cu/Nb samples would decrease the fracture resistance of Nb layer by promoting the crack propagate along the GBs, i.e., intergranular fracture, while the effect of interface and layer thickness on the fracture resistance of MNCs will not be altered by introducing the GBs in MNCs.

A comparison of microstructure, mechanical properties and fracture behavior of Mg–9Gd–3Y–xZn–0.5Zr (x = 0, 0.2, 0.5, 1.0, and 1.5) (wt%) alloys under different thermal treatment conditions was investigated in this study. The results showed that the as-cast alloys were comprised of Mg matrix, eutectic compounds and cuboid-shaped phases. The eutectics were Mg24(Gd, Y)5 in the alloys of Zn content ≤0.2 wt%, while (Mg, Zn)3RE in the other three alloys. Fine lamellar long period stacking ordered structure formed inside of matrix of the as-cast Zn-containing alloys and its quantity increases with raising Zn content. Mg12(Gd, Y)Zn was observed at grain boundary of Mg matrix after solution treatment in the alloys of Zn content ≥0.5 wt%. Peak-aged Mg–9Gd–3Y–0.5Zn–0.5Zr alloy exhibited a desirable combination of strength and elongation with 244 MPa in yield strength, 371 MPa in ultimate tensile strength and 3.8% in EL. Meanwhile, the fracture behavior of the studied alloys was also investigated.

The fracture behavior of precracked nanocrystals with grain size gradients is simulated using the molecular dynamics method. A large grain size gradient is found to elevate resistance to crack propagation and transform the fracture mode from intergranular to intragranular when the crack is obstructed by a coarse grain. But the intragranular crack is nipped in its bud due to the difficulty of intragranular fracture. However, intergranular fractures can be always kept in nanocrystals with a small grain size gradient. Both the Schmid factors for the slip systems of grains near the crack tip and the critical stress intensity factors are calculated, and energy partitioning is conducted to analyze the mechanisms behind this phenomenon. The research exhibits the key role of grain size gradient in improving the antifracture ability of nanocrystals.

The effect of high-energy electropulsing treatment (EPT) on the microstructure evolution, mechanical properties, and fracture behavior of as-treated Ti–6Al–4V alloy strips was investigated. EPT was found to accelerate phase transition and microstructure evolution of quasi-single-phase titanium alloy strips at a relatively low temperature, and obtain characteristic duplex microstructure and Widmanstatten microstructure. The EPT-induced microstructural changes increased elongation-to-failure remarkably with a slight decrease in tensile strength. Fracture surface observation and three-dimensional analysis showed that transition from small-shallow dimple colony to big-deep colony fracture took place with an increase in frequency of EPT. The rapid phase change of the Ti–6Al–4V alloy strip under EPT was attributed to the enhancement of nucleation rate and atomic diffusion resulting from the coupling of the thermal and athermal effects. It is supposed that EPT can provide a highly efficient method for the intermediate-softening annealing of titanium alloy sheet/strips.