The Corrosion Behavior And Hydrogen Embrittlement Resistance Of AlCoCrFeNi2 Multi-principal Element Alloy

In this work,the mechanical properties and corrosion resistance of AlCoCrFeNi2 multi-principal element alloy in different microstructure were investigated by micro structure observation,slow strain rate tensile tests,electrochemical tests,real-time detection of element dissolution,phase analysis and other methods.The optimal scheme of cold rolling and heat treatment for the alloy with both strength-ductility and corrosion resistance was determined.And the composition and structure models of the passive film were established.In addition,the hydrogen embrittlement resistance of AlCoCrFeNi2 alloy with the optimal scheme was studied with multi-scale characterization techniques.The hydrogen distribution and diffusion process in the two-phase alloy were detected.Moreover,the effect of hydrogen on the two phases during the deformation was investigated.And the hydrogen induced cracking mechanism was revealed.The results were as follows:When the heat treatment temperature were 650,750,850 and 950 ℃,the AlCoCrFeNi2 alloy still retained the heterlamellar structure with alternating arrangement of FCC phase and B2 phase.The lamellar region and the island-like region were composed of grains with uniform orientation distribution,and the grain sizes of the two phases were less than 1 μm.When the heat treatment temperature was 1200℃,the AlCoCrFeNi2 alloy was composed of recrystallized grains larger than 1 μm.The finer grains,uniform orientation and reduced lamellar length could simultaneously improve the strength and ductility of the alloy.Among them,the AlCoCrFeNi2 alloy under 950℃heat treatment achieved the best match with strength and ductility,the yield strength,ultimate tensile strength and elongation were about 876 MPa,1.2 GPa,20.7%,respectively.The cold rolling and heat treatment could refined the grain size,equalized the grain orientation and reduced the composition difference between the two phases,which increased the passive film thickness of the alloy and the proportion of Cr2O3 in the passive film,and meanwhile reduced the micro-galvanic corrosion between the two phases.Compared with the cast alloy,the corrosion potential of the AlCoCrFeNi2 alloy with optimal microstructure in the surfuric acid solution was more positive.the passive current density decreased to about 3.5 μA/cm2,and the passive region increased by 120 mV.The passive films formed in natural condition and applied potential condition had the same composition,both of which were dominated by oxides and hydroxides of Al,Cr and Fe,and the proportion of the above elements decreased in turn.However,the applied potential increased the oxides proportion of the passive film compared with that of the passive film formed in natural condition,especially the Fe and Cr oxides/hydroxides.Both of the passive films had double layer,and the passive film could be divided into inner layer and outer layer according to the composition distribution of Cr element and Fe element.In addition,the passive film formed by applied potential reduced the dissolution rates of the five elements in the acid solution were by two orders of magnitude compared with that formed in natural condition.The microstructure regulation also improved the hydrogen embrittlement resistance of the AlCoCrFeNi2 alloy.Compared with the cast alloy,the fine and uniform microstructure reduced the hydrogen enrichment and stress concentration of the AlCoCrFeNi2 alloy,and the shorter lamellae were conducive to the inhibition of hydrogen-induced crack propagation,which simultaneously improved the hydrogen resistance of AlCoCrFeNi2 alloy.In addition,hydrogen tended to enrich in grain boundaries and phase boundaries based on the SKPFM observation,which was consistent with the hydrogen-induced cracking paths.Based on the observation of dislocation morphology,it was found that the effect of hydrogen on the phases of the AlCoCrFeNi2 alloy during deformation was mainly borne by FCC phase.Hydrogen increased the dislocation density of FCC phase during the deformation process,resulting in dislocation plugging,and the visible Burgers vector of the dislocations was basically 1/2<-1 1 0>,while hydrogen had no obvious effect on the dislocation density of B2 phase.In summary,it could be found that the microstructure regulation improved the mechanical properties,corrosion resistance and hydrogen embrittlement resistance of AlCoCrFeNi2 alloy,which was conducive to the application of the multi-principal element alloy.