Design Of Steel-titanium Heterogeneous Material Transition Layer And Microstructure/Performance Control Under LAM

The steel-titanium composite warhead shell produced by traditional processing technology has disadvantages such as difficulty in forming,high residual stress,and poor bonding strength.The core reason is that the thermal and physical properties of the steel-titanium interface are very different,and the metallurgical reaction forms a coarse,hard and brittle Laves phase.The laser melting deposition technology can adjust the dilution rate to achieve the interface composition gradient design.Based on this,the transition layer composition gradient relieves the residual stress and inhibits the formation of hard and brittle phases.Solving the above problems is the key to realizing the integral molding of the steel-titanium composite warhead shell.This paper uses laser meltingdeposition technology to prepare 316 stainless steel-high-entropy alloy-TC4 titanium alloy heterogeneous components,and conducts research on the gradient of heterogeneous interface composition,microstructure,and mechanical properties.It is proved that the FeCrCuV high-entropy alloy transition layer can alleviate the two core problems of steel-titanium heterogeneous connection.The good bonding strength obtained by heterogeneous materials under this scheme provides a reference for the field of steel-titanium heterogeneous connection.Aiming at the fact that traditional single-principal alloys cannot stably exist and produce intermetallic compound precipitation when preparing 316 stainless steel-TC4 interface by laser melting deposition,the use of Fe and Ti can form a simple disordered solid solution design idea with CrCuV alloy,and the design and preparation are excellent Mechanical properties FeCrCuV dual-phase(FCC+BCC)high-entropy alloy transition layer,and the composition of the high-entropy alloy of the printed FeCrCuxV system under different Cu contents was optimized,and the FeCrCuV equimolar ratio high-entropy alloy with the best comprehensive performance was determined as Transition layer composition.Laser melting and deposition of TC4 titanium alloy on the FeCrCuV transition layer was carried out,and the influence of the tissue compatibility and mechanical compatibility of the diffusion layer formed by the diffusion of TC4 alloy on the FeCrCuV transition layer was studied.Focus on the analysis of the influence of laser process parameters on the evolution of FeCrCuTixV diffusion layer formed during the dilution process,and verify that the FeCrCuTixV high-entropy alloy system forms a solid solution in a certain range of Ti element diffusion concentration.By analyzing the cooling conditions of the as-cast and printed FeCrCuTiV high-entropy alloys,the microstructure evolution laws under different cooling conditions are studied,and the corrosion mechanism of different microstructure states in the heterogeneous interface is explored.The FeCrCuTiV high-entropy alloy in the fast cooling state shows fine grains It also has smaller Cu-rich phase segregation and better corrosion resistance.Aiming at the problem of using 316 stainless steel as the substrate to directly deposit FeCrCuV high-entropy alloy by laser melting,good forming quality cannot be obtained in the entire parameter range.Analysis of the formation mechanism of pore defects shows that the difference in vapor pressure difference of each principal element is the direct cause of this phenomenon.Direct laser printing is used to solve this problem again with low energy density parameter fusion method,and the best forming parameters of FeCrCuV high-entropy alloy are obtained based on the single factor experiment of power and scanning speed.Using the process of direct laser printing of TC4,single-factor experiments of power and scanning speed were carried out on the printed FeCrCuV high-entropy alloy transition layer,and the best forming parameters of TC4 were obtained.The connection strength of the prepared 316-FeCrCuV-TC4 heterogeneous component reaches 253MPa.The interface characterization results of 316-FeCrCuV-TC4 heterogeneous components show that:(1)The recrystallization process existing between heterogeneous interfaces is an important way to reduce the interfacial stress caused by the mismatch of linear expansion coefficient;(2)FeCrCuV-TC4 interface The 6μm wide solid solution region delays the precipitation of Laves phase in the two dimensions of space and elements.The results of the study on the effect of FeCrCuV transition layer element diffusion on the mechanical properties and phase structure of TC4 show that the phase stabilization of Fe,Cr,Cu,V elements and the thermal cycle of laser melting and deposition lead to the formation of coarse phase grains,which are the pull of the bottom of the molten pool.The main reason for the sharp deterioration of the tensile properties(maximum tensile strength of 344 Mpa)was verified by the Jmatpro simulation results of the mechanical properties and phase composition of TC4 under the diffusion of elements in the transition layer at different concentrations.