Research On High Performance Welding Fillers For Gtaw Titanium-Steel Clad Plates

Titanium-steel clad plate are combined with high corrosion resistance of titanium and excellent mechanical properties of steel,which has been urgent needed in the oceaneering,chemical,power and other industries.Owing to a great difference of physical and chemical performance between titanium and steel,a large number of brittle intermetallic compounds are produced during GTAW titanium-steel clad plates which weakening the mechanical properties of the joint,even lead to cracking.Thus it is difficult to weld bonding layer of titanium-steel clad plates directly.Ti-Fe-Ni-Cu-V,Ti-Fe-Ni-Cu-Cr and Ti-Fe-Ni-Cu-Co high-performance alloyed welding metals for GTAW bonding layer of titanium-steel clad plates are designed and prepared according to high entropy alloying of transition weldmetal and first principle of thermodynamics.The microstructure of fusion welding butt joint are analyzed.Then the hardness distribution of the joint and the electrochemical corrosion resistance of clad weld surface are tested.The results indicate that:According to the first principle calculation,the elastic coefficient of three transition zone weld alloy are calculated.The calculation results show that Ti18.18Fe18.18Ni18.18Cu18.18V27.27,Ti18.18Fe18.18Ni18.18Cu18.18Cr27.27 and Ti20Fe20Ni20Cu20Co20 are considered possessing excellent plasticity.Ti12Fe15Ni23Cu25V25,Ti12Fe18Ni24Cu24Cr25 and Ti10Fe12Ni25Cu25Co28 are inferred and considered as high-performance welding materials,which are suitable for the direct GTAW bonding layer of titanium-steel clad plates.Under the direct TIG welding conditions of welding current I=127A,welding speed V=90mm/min and argon gas flow rate Q=17L/min,the joint that using three kinds of transition layer alloy welding materials have a good formation,being full and uniformly continuous without weld defects such as collapses and porosities.When using Ti12Fe15Ni23Cu25V25 welding material,the microstructure of transition zone weld is made up by equiaxed crystals and a little dendrites,which is formed by Ti-Fe-Ni-Cu-V high entropy alloy with FCC+BCC simple solid solution structure.Cu-rich FCC phase are formed in the dendritic gap for the positive mixed enthalpy of Cu and other elements,so the transition zone weld shape is improved.The combination of weld and base metal interfaces are well for little cracks.Each weld are also fusion better.The hardness of cladding weld is rised to 475～520HV,because(Ti)solid solution and a small amount of TiCu3,TiV and other compounds generating in the cladding weld.Transition weld zone has a hardness of 270～320HV,which is between the base weld and transition zone weld.Transition zone weld of joint are composed by(Ti,Fe,Ni,Cu,Cr)solid solution phase with FCC and BCC structures when using the Ti12Fe15Ni24Cu24Cr25 welding material GTAW bonding layer of titanium-steel clad plates.The hardness of transition zone weld is 320～370HV,which is between the base metal and cladding weld.Furthermore,when using Ti10Fe12Ni25Cu25Co28 welding material,the joint transition zone weld is formed by single FCC solid solution structure.The hardness of transition zone weld is 260-280HV,which is between the base metal and cladding weld.When the main element V of high-performance welding materials is replaced by Cr and Co elements,the joint are taken on flawless and interfaces are combine perfectable.The micro-hardness of each joint is roughly same:from the base weld metal to the transition zone weld,hardness are gradually increased until the cladding weld part reaches the highest level.The electrochemical corrosion test results of each cladding weld of titanium-steel clad plate shows that:in 3.5%NaCl solution,the polarization curve of cladding weld by TIG fusion clad plates bonding layer with Ti10Fe12Ni25Cu25Co28 welding material is closest to cladding TA2,and which shows optimum resistance to electrochemical corrosion.Followed by cladding weld with Ti12Fe15Ni23Cu25V25 and Ti12Fe15Ni24Cu24Cr25 welding materials.