Effect Of The Electropulsing On The Microstructure And Mechanical Properties Of 3D Printing Titanium Alloys

Optimizing the structure and mechanical properties of the additive manufacturing(3D printing)two-phase titanium alloy(?+?)is an important issue in both scientific and engineering fields.When the pulse current passes through the metal material,recrystallization,phase transformation,amorphous crystallization and other phenomena will be caused by the Joule heat and electronic wind force in the material,to achieve grain refinement,electroplasticity,damage repair and performance improvement.In this paper,combining with the electropulsing treatment(EPT)and additive manufacturing materials,the two-phase titanium alloy of selective laser melted Ti-6Al-4V(SLM-TC4)and laser melting deposition Ti-6.5Al-3.5Mo-1.5Zr-0.3Si(LMD-TC11)is selected for EPT,to explore optimal the structure and mechanical properties of additive manufacturing titanium alloy.X-ray diffraction(XRD),optical microscopy(OM),scanning electron microscopy(SEM),electron backscattered diffraction(EBSD)and transmission electron microscopy(TEM)analysis were used to characterize the evolutions of ? and ? grains and dislocation structures.Vickers microhardness and tensile testing are carried out to compare the material strength and mechanical properties,the main research results are as follows:The TC4 alloy was prepared by selective laser melting technique,and the formation mechanism of ? grains and ? lath martensite in front of XOZ,YOZ and XOY were observed and studied.Using electrical pulse processing technology to optimize the structure of TC4 alloy,it is found that with the increase of pulse voltage parameters,the front ? columnar crystals sequentially undergo the process of boundary straight columnar crystals,boundary curved columnar crystals,fine equiaxed crystals,and coarse equiaxed crystals,and the ?-lath martensite undergoes a process of growth,coarsening and recrystallization,refinement and the mechanical properties of the alloy undergo a process of softening and then hardening.The softening and hardening of the alloy are mainly caused by the growth and coarsening of ?-lath martensite,the decrease of dislocation density and the refinement of recrystallization of ?-lath martensite.The TC11 alloy was prepared by laser melting deposition technology,and the formation mechanism of the molten pool,front ? grains and internal ?-lath martensite in the XOZ,YOZ,and XOY planes was observed and studied.Using electrical pulse processing technology to optimize the structure of TC11 alloy,it is found that with the increase of pulse voltage parameters,the macrostructure sequentially undergoes the process of broadband disappearance,columnar crystal becoming equiaxed crystal and equiaxed crystal growing successively,and the ?-lath martensite underwent a process of Crab-like martensite disappearance and ?-lath martensite refinement.In the mechanical properties of the alloy,the hardness and tensile strength go through the process of softening and hardening,the L direction(parallel to the deposition direction)yield and tensile strength are always less than the T direction(perpendicular to the deposition direction),while the plasticity is the opposite;anisotropy(L,T difference)does not change much;the change of alloy structure is caused by recrystallization at the ? transformation point,and the difference in mechanical properties is caused by the texture of the alloy.