Study On Heat Treatment Process Of TC4 Titanium Alloy By Laser Deposition Manufacturing

Laser Deposition Manufacturing(LDM)has the advantages of low manufacturing cost and high production efficiency.It is widely employed in the field of areonautic and astronautic,medical device and automobile.LDM uses highly energy density laser to scan the parts surface and form molten pool then the metal powder is sent into the molten pool by coaxial powder feeding nozzle.The molten pool rapidly solidify step by step,and directly form the three-dimensional parts.The characteristics of rapid solidification of laser deposition manufacturing technology is bound to have large internal stress in the laser deposition manufacturing parts,and the internal microstructure is uneven,and the mechanical properties are unstable.Heat treatment is an important way to adjust microstructure and improve mechanical properties.A more perfect laser deposition process for TC4 titanium alloy heat treatment process is explored,which makes laser deposition technology more potential.The tensile properties of LDMed TC4 titanium alloy had been tested and analyzed by OM,SEM and XRD and the phase transition and phase transition mechanism of microstructure during heat treatment was studied.The deposited samples was founded that the microstructure was typical columnar microstructure.The anistrophy of mechanical properties might have related to the direction between the grain boundary and the tensile force and the obstruction of grain boundary to the microstructure.The deposited samples were carried out after different heat treatments,and it was found that after annealing,the strength did not change significantly,but the plasticity increased slightly.After solution and aging treatment the strength is increased,but the plasticity decreases obviously.Finally,eight different temperatures were selected to annealing at temperatures ranging from 750? to 990? degrees,the results show that the columnar grain begins to equiaxed when the annealing temperature over 900?;the columnar grain is transformed into the equiaxed grain when the annealing temperature over beta transition temperature.The microstructure is uniform after annealing treatment at 810? to 840? and the comprehensive mechanical properties were better.The alpha phase was coarser when the annealing temperature over 900? degrees.The mechanical properties still showed anisotropic after annealing treatment.