Microstructure And Properties Control Of Laser Melting Deposited Steel/Titanium Heterogeneous Interface

It is possible to manufacture equipment with high quality and high precision using stainless steel/titanium alloy dissimilar material integration forming,which has a wide range of application possibilities in the energy and chemical industries,maritime equipment,and other disciplines.When the conventional welding procedure is used for a steel/titanium direct connection,hard and brittle intermetallic compounds,such as coarse FeTi and Fe2Ti,are easily generated at the heterogeneous interface,leading to low bond strength,poor mechanical characteristics,and easy breaking at its interface.As a result,steel/titanium dissimilar materials are restricted in their engineering applications.To address this problem,this paper proposes a transition layer that can achieve multicomponent solid solution with Fe and Ti between steel and titanium,and uses laser melting deposition technology to prepare the transition layer and realize the regulation of the microstructure and properties of the transition layer at the steel/titanium heterogeneous interface.This prevents the precipitation of intermetallic compounds such as FeTi and Fe2Ti at the steel/titanium interface and relieves the residual stress at the interface,thus solving the problems of cracking and low bond strength at the interface of steel/titanium dissimilar materials.First of all,this paper designed the transition layer of two systems of CrCuxNi and CrCuxV(x=0.2,0.6,1 and 1.4)medium entropy alloy(MEAs),using the Ω-δ criterion and the valence electron concentration(VEC)criterion to predict MEAs itself and whether it can form a solid solution structure with Fe and Ti elements,studied the influence of Cu content on its structure and properties,determined and selected the alloy composition with the best comprehensive performance to connect steel/titanium.It was found that with the increase of Cu element content,the Cu-rich phase of the entropic alloy in the CrCuxNi system increased,while its tensile strength increased from 350 MPa(CrCu0.2Ni)to 675 MPa(CrCuNi),and the elongation increased from 1%to 19.7%,and the fracture behavior changed from brittle fracture to ductile fracture.While the CrCuxV system mesoentropic alloy changed from a single-phase(BCC)structure to a two-phase(BCC+FCC)structure with the increase of Cu content,its tensile strength increased from 240 MPa(CrCu0.2V)to 580 MPa(CrCuV),and the elongation increased from 0.7%to 2.8%accordingly.The above studies were combined to select the alloy composition with the best overall performance of CrCuNi(FCC structure)and CrCuV(BCC+FCC structure)in the same molar ratio as the transition layer for the steel/titanium connection.Following that,it was investigated how the steel/CrCuNi/titanium and steel/CrCuV/titanium dissimilar materials’ melt pool morphology and deposited layer quality were affected by the laser melting deposition procedure.Based on orthogonal experiments,the effects of laser process parameters on the melting height,melting depth,melting width,and dilution rate of the samples during deposition were examined.Finally,CrCuNi and CrCuV MEAs were produced on TC4 substrates using a laser melting deposition process,and the interfacial microstructure and mechanical properties of the dissimilar materials prepared from the transition layers of the two MEAs were thoroughly examined.In the TC4/CrCuNi/316L dissimilar material,the CrCuNi/316L interface is composed of Cr-rich phase,Cu-rich phase,and Fe-containing solid solution,and its shear strength can reach 320 MPa.The TC4/CrCuNi interface is composed of Ti-Ni intermetallic compound,Ti solid solution,and matrix phase.The shear fracture reveals that the dissimilar material fractures on the TC4/CrCuNi side,and the Ti-Ni intermetallic compound continues to have an impact on the material’s overall mechanical properties.In the TC4/CrCuV/316L dissimilar material,the TC4/CrCuV interface is composed of β-Ti,a Cu-rich phase,and a Ti-containing solid solution,while the CrCuV/316L interface is composed of CrV phase,a Cu-rich phase,and a solid solution that contains Fe.Since no intermetallic compound is formed on either side,the intermetallic mechanical properties are significantly improved.