Microstructure And Properties Of Ti-Fe-Ni-Cu-V(Cr) High Entropy Alloys

The high entropy effect promotes the formation of a simple solid solution structure in a multi-principal alloy and inhibits the production of brittle intermetallic compounds,It has the wide application potential in the field of refractory difficult-to-weld metals and heterogeneous hard-to-weld metals.This study based on the high-entropy criterion has designed a high-toughness alloy system suitable for welding titanium and steel according to the first-principles calculation method.Producted the Φ3mm high performance alloy wire by vacuum arc melting and copper die casting,researched the effect of Ti content on the microstructure and mechanical properties of the alloy.Optimizing wire composition and using it improve the TIG butt welding of titanium plate surfacing and TA2/0Cr18Ni9 thin plate,The microstructure of the welded zone was analyzed,and the hardness distribution of the joint was tested.The results showing that:The two high toughness of two alloy systems are Ti-Fe-Ni-Cu-V and Ti-Fe-Ni-Cu-Cr respectively the first principle calculation,and the corresponding high-toughness alloy components are Ti₁₀Fe₂₉Ni₃₂Cu₂₂V₇ and Ti₁₀Fe₃₀Ni₃₂Cu₂₂Cr₆.The microstructure of Fe₃₂Ni₃₆Cu₂₄V₈ alloy consists of dendrites and a small amount of equiaxed crystals,which is a single-phase FCC solid solution structure,and it’s hardness is 161HV,yield strength is 269MPa.The microstructure of Tix[Fe₃₂Ni₃₆Cu₂₄V₈]100-x alloys are dendritic.When the x is 3%and 5%,alloys are FCC phase.When the x is 8%,a small amount of V-rich phase precipitated between FCC dendrites.x is 10%and 12%,the phase of the alloys don’t change.x is 14%,the V-rich phase disappears and the alloy consists of the FCC phase and the（Ti,V）phase.With the increase of Ti content,the hardness and strength of the alloys showed an increasing trend,the hardness of the alloys increased from 161HV to 424HV,and the yield strength increased from 269MPa to 674MPa,and plasticity decrease.The microstructure of Fe₃₃Ni₃₆Cu₂₄Cr₇ alloy is dendritic,which is a single-phase FCC solid solution with a hardness of 153HV and a yield strength of 233MPa.With the increase of Ti content,the microstructure of Tix[Fe₃₃Ni₃₆Cu₂₄Cr₇]100-x alloys are still dendritic.When x=3,5,the alloys are the FCC solid solution phase;when x=8,10,12,14,the alloys consists of the FCC phase and the（Ti,Fe）phase.With the increase of Ti content,the hardness and yield strength of the alloys show a monotonous increase,the hardness of the alloys increased from 153HV to 571HV,and the yield strength increased from 233MPa to 1045MPa,and the plasticity decreased.The analysis data of the microstructures and properties of Ti-Fe-Ni-Cu-V and Ti-Fe-Ni-Cu-Cr alloys are in agreement with the calculation results of the alloy design.Under the condition of welding current I=65A,welding speed V=90mm/min,argon flow rate Q=12L/min,Ti₈Fe₃₀Ni₃₃Cu₂₂V7,Ti₁₀Fe₂₉Ni₃₂Cu₂₂V₇,Ti₈Fe₃₀Ni₃₃Cu₂₂Cr₇ and Ti₁₀Fe₃₀Ni₃₂Cu₂₂Cr₆ two kinds of four components of the welding wire were used fou TA2 sheet welded.The micro structure of the joint between the high-entropy alloy and the TA2 sheet of the cladding layer is coarse columnar crystals and dendrites,and the micro structure of the cladding layer is composed of staggered dendrites.The hardness of the cladding layer obtained from the Ti₈Fe₃₀Ni₃₃Cu₂₂V₇ welding wire is 533HV.The hardness of the cladding layer obtained from the Ti₈Fe₃₀Ni₃₃Cu₂₂Cr₇ welding wire is 595HV.Under the condition of welding current I=60A,welding speed V=90mm/min,argon flow rate Q=12L/min,the optimized welding wires are used for TIG butt welding of TA2/0Cr18Ni9 sheet,the obtained joints have complete shape without no obvious weld defects.From the bonding zone to the center of the weld,the grains change from coarse columnar crystals to dendrites and equiaxed crystals.The microstructure of weld center is an FCC solid solution consisting of dendrites and a small amount of equiaxed crystals,and no brittle intermetallic compounds are produced.The hardness of the weld of TA2/0Cr18Ni9 joints obtained by Ti₈Fe₃₀Ni₃₃Cu₂₂V₇、Ti₈Fe₃₀Ni₃₃Cu₂₂Cr₇ welding wire are low.