Electromagnetic Induction Assisted Laser Additive Manufacturing Titanium Matrix Composite Process Experiment And Mechanical Properties Analysis

With the rapid development of aviation industry,the key components of aero-engine will face more severe service environment,and new materials,new processes and new structures will contribute more than 50%to the improvement of aero-engine performance.Titanium Matrix Composites(TMC),as a material with great development potential,has attracted more and more attention.Among them,Ti Cp-reinforced TMC is expected to replace nickel-based superalloys in key parts of aeroengines such as engine fans,high-pressure compressor blades and casings.Although the addition of Ti C_p effectively improves the hardness of titanium alloy,the developed brittle dendrites in the microstructure reduce the tensile strength of titanium-based composite.Therefore,in order to improve the tensile properties of Ti C_p reinforced TC4composites,electromagnetic induction assisted laser additive manufacturing(EMI-LAM)was proposed.Process experiments and finite element analysis were carried out to reveal the underlying mechanism of electromagnetic induction assisted laser additive manufacturing,and the internal relationship between the hybrid process,microstructure and mechanical properties was clarified.The specific research contents and conclusions are as follow:(1)The EMI-LAM experimental system was designed and built mainly including induction heating equipment selection,induction coil design and mechanical coupling fixture design;the heating characteristics of the electromagnetic induction system were measured.The results show that the preheating temperature rise rate of the electromagnetic induction system has a first-order attenuation exponential function with time,and tends to be stable after 10 s.When the heating time of the electromagnetic induction system reaches 60 s,the input current of the system should be less than 21 A.(2)Process experiments were carried out to reveal the evolution behavior of microstructure such as primary Ti C and bonding interface,and the variation law of tensile strength was clarified.10 wt.%Ti C_p reinforced TC4 composites were prepared by LAM and EMI-LAM,respectively,and the macro morphology,microstructure and mechanical properties under the two process conditions were analyzed.The results show that the thin-walled parts prepared by LAM and EMI-LAM have good macroscopic morphology,but the thickness of the latter is larger.Primary Ti C and eutectic Ti C are found in the microstructure,and primary Ti C andα-Ti have semi-coherent interface.However,the primary Ti C in the LAM sample is developed dendrite,and the number is large.In the EMI-LAM sample,a large number of granular Ti C with particle size of about 1.5μm and uniform distribution appear,while the size of dendritic Ti C decreases,and the number decreases by about 26.2%.Due to the loading strengthening of granular Ti C particles,the tensile strength of the composite increased from 893±4.1 MPa to960±11.5 MPa,which increases by 8%.(3)The EMI-LAM numerical model was established to reveal the influence mechanism of Joule heat and Lorentz force on the molten pool in EMI-LAM process.Compared with LAM,due to the effect of Joule heat of gradient distribution,the maximum temperature changes little,but the heat-affected zone expands significantly during EMI-LAM process.Due to the preheating and slow cooling effect of EMI,the maximum cooling rate and maximum temperature gradient of the surface center point of the molten pool decrease by 4.3%and 1.0%respectively when the molten pool is not solidified.At the same time,the temperature gradient at the solid-liquid interface decreases and the growth rate increases,thereby increasing the constitutional supercooling and promoting the nucleation of granular Ti C.In addition,the current passing through the solid-liquid interface improves the interface stability and weakens the tendency of grain growth to the dendrite.The compressive force and shear force produced by nonuniform alternating electromagnetic force and solute-driven remelting in the molten pool increase the dendrite fragmentation rate of Ti C and refine the coarse DPT.After the molten pool has been solidified,it is attributed to the preheating and slow cooling effect of the inductor that the average temperature at the center point of the surface increases by 16.4%,while the maximum cooling rate and the maximum temperature gradient decrease by 4.2%and 0.5%,respectively.