Graphene enables equiatomic FeNiCrCoCu high-entropy alloy with improved TWIP and TRIP effects under shock compression

Graphene(Gr)reinforced high-entropy alloy(HEA)matrix composites are expected as potential candidates for next-generation structural applications in light of outstanding mechanical properties.A deep comprehension of the underlying deformation mechanisms under extreme shock loading is of paramount importance,however,remains lacking due to experimentally technical limitations in existence.In the present study,by means of nonequilibrium molecular dynamics simulations,dynamic deformation behaviors and corresponding mechanisms in equiatomic FeNiCrCoCu HEA/Gr composite systems were investigated in terms of various shock velocities.The resistance to dislocation propagation imparted by Gr was corroborated to encourage the elevated local stress level by increasing the likelihood of dislocation interplays,which facilitated the onset of twins and hexagonal close-packed(HCP)martensite laths.Meanwhile,the advent of Gr was demonstrated to endow the HEA with an additional twinning pathway that induced a structural conversion from HCP to parent face-centered cubic(FCC)inside HCP martensite laths,different from the classical one that necessitated undergoing the intermediate procedure of extrinsic stacking fault(ESF)evolution.More than that,by virtue of an increase in flow stress,the transformation-induced plasticity(TRIP)effect was validated to be additionally evoked as the predominant strain accommodation mechanism at higher strains on the one hand,but which only assisted plasticity in pure systems,and on the other hand,can also act as an auxiliary regulation mode together with the twinning-induced plasticity(TWIP)effect under intermediate strains,but with enhanced contributions relative to pure systems.One may expect that TRIP and TWIP effects promoted by introducing Gr would considerably inspire a synergistic effect between strength and ductility,contributing to the exceptional shock-resistant performance of FeNiCrCoCu HEAs under extreme regimes.

Amorphization transformation in high-entropy alloy FeNiCrCoCu under shock compression

High-entropy alloys(HEAs)possess immense potential for structural applications due to their excellent mechanical properties.Deeply understanding underlying deformation mechanisms under extreme regimes is crucial but still limited,due to the restrictions of existing experimental techniques.In the present study,dynamic deformation behaviors in equiatomic FeNiCrCoCu HEAs were investigated in terms of various shock velocities through nonequilibrium molecular dynamics simulations.The amorphous atoms by amorphization transformation were corroborated to be conducive to dislocation nucleation and propagation.Also,the dominant plasticity pattern was confirmed to be taken over by amorphization under higher velocities,while dislocation slips merely prevailed for lower shock ones.More importantly,for a shock velocity of 1.4 km/s,multi-level deformation modes appearing in deformation,first amorphization and then a combination of amorphization and dislocation slip,was demonstrated to substantially contribute to the shock wave attenuation.These interesting findings provide important implications for the dynamic deformation behaviors and corresponding mechanisms of the FeNiCrCoCu HEA system.

Graphene Oxide-Induced Substantial Strengthening of High-Entropy Alloy Revealed by Micropillar Compression and Molecular Dynamics Simulation

Plastic deformation mechanisms at micro/nanoscale of graphene oxide-reinforced high-entropy alloy composites(HEA/GO)remain unclear.In this study,small-scale mechanical behaviors were evaluated for HEA/GO composites with 0.0 wt.%,0.3 wt.%,0.6 wt.%,and 1.0wt.%GO,consisting of compression testing on micropillar and molecular dynamics(MD)simulations on nanopillars.The experimental results uncovered that the composites exhibited a higher yield strength and flow stress compared with pure HEA micropillar,resulting from the GO reinforcement and grain refinement strengthening.This was also confirmed by the MD simulations of pure HEA and HEA/GO composite nanopillars.The immobile<100>interstitial dislocations also participated in the plastic deformation of composites,in contrast to pure HEA counterpart where only mobile 1/2<111>perfect dislocations dominated deformation,leading to a higher yield strength for composite.Meanwhile,the MD simulations also revealed that the flow stress of composite nanopillar was significantly improved due to GO sheet effectively impeded dislocation movement.Furthermore,the mechanical properties of HEA/1.0 wt.%GO composite showed a slight reduction compared with HEA/0.6 wt.%GO composite.This correlated with the compositional segregation of Cr carbide and aggregation of GO sheets,indicative of lower work hardening rate in stress-strain curves of micropilar compression.