Theoretical Study On Stacking Faults Of Close-Packed Hexagonal ZrHfTi-based Multi-Component Alloy

Multi-component alloy is a new concept of material design,which greatly expands the design range of alloy composition and properties.With the development of new materials,multi-component alloys with disordered structures have been proved to possess many excellent properties,and can breakthough the limitations of traditional materials with one or two metal elements as the main elements,so are very important to optimize and develop the potential properties of new materials.In recent years,researchers have focused on the design and development of new multi-component alloys and multi-component ceramics with special properties.The accurate prediction of the properties of multi-component alloys has become a hot research area in chemistry and material science.The stacking fault（SF）is the basis of understanding the mechanical behavior of materials and is closely related to the structural phase transition of materials,which is also the key factor to fully understand the properties of multi-component alloys.In this paper,the stacking faults in the base plane of hexagonal close-packed medium entropy alloy ZrHfTi and high entropy alloy Hf_0.25Ti_0.25Zr_0.25Sc_0.25-xAl_x（x<0.15）are studied by combining the Density functional theory（DFT）and the special quasi-random structure（SQS）.The obtained SFEs were used as a basic parameter of the deformation behavior and mechanical properties of the alloys,especially the ductility.Furthermore,the mechanical properties and possible slip behavior of multi-component alloys were studied in terms of stacking fault energy（SFE）.The detailed research contents are as follows:Based on the DFT method and SQS structural model,the stacking fault of hexagonal close-packed medium entropy alloy ZrHfTi was studied,and the mechanism affecting the SFEs and the related properties of ZrHfTi were analyzed.The present results show that unlike the case of Cr Co Ni-based alloys,the derived SFEs for intrinsic and twin-like stacking faults of alloy ZrHfTi are relatively high.From the evolution features of stacking fault energies from unitary to binary and ternary materials,the SFEs of alloys are intermediate between component materials due to merely mixing effect.Because the SFEs of the constituent elements are relatively large,the SFEs of multi-component alloys are not necessarily small.The SFE of ZrHfTi is obviously affected by alloying of constituent elements with strong structural propensity.Based on the generalized stacking fault energy,mechanical properties and deformation characteristics are further studied.The results demonstrate that ZrHfTi has good ductility and high yield strength,and deformation twin in ZrHfTi is also very possible based on the twinning criteria.The stacking fault energies of basal plane for novel hexagonal close-packed high entropy alloys Hf_0.25Ti_0.25Zr_0.25Sc_0.25-xAl_x（x<0.15）are further studied by DFT using SQS to model the chemical disorder,and the effect of aluminum is emphasized.With increase of Al content,the lattice constant a decreases,while c/a increases.Especially,the addition of Al is favorable to reduce the unstable and stable stacking fault energies of the studied alloys.The lower SFE further improves the ductility,creep resistance and yield strength of materials.Moreover,with replacement of Sc by Al,lowerγ_ISF/γ_USFratio of stable intrinsic SFE to unstable intrinsic SFE and higherγ_USF/γ_UTF ratio of unstable intrinsic SFE to unstable twin-like SFE suggest that although both the dislocation decomposition and twinning are favored,the dislocation decomposition is still predominant due to stronger decrease ofγ_ISF/γ_USF.Furthermore,the much larger unstable twin-like SFE also indicates that the main deformation mechanism in high entropy alloys Hf_0.25Ti_0.25Zr_0.25Sc_0.25-xAl_x（x<0.15）may be dislocation slip.The further calculated electronic structure shows that replacement of Sc by Al enhances the interatomic interaction of Hf_0.25Ti_0.25Zr_0.25Sc_0.25-xAl_x（x<0.15）,and reduces the energy difference during the sliding process,thus lower the SFEs.The present investigation has important reference significance for understanding and developing the high performance of new hexagonal close-packed multi-component alloys,and is helpful for designing and developing more valuable high performance multi-component alloys.