The Effect Of Heat Treatment On Microstructure And Tensile Properties Of TC4 By Laser Additive Manufacturing

At present,the service conditions of parts are becoming more and more stringent in the aerospace field.In addition to safety and service life,structural integration and weight reduction have also become factors to consider.Sometimes,Structural components cannot directly be produced by traditional welding,riveting,forging,etc.Laser additive manufacturing technology makes up for the shortcomings of traditional processes,As a high-strength lightweight alloy,titanium alloy combined with laser additive manufacturing technology provides new opportunities for the production of parts in the aerospace field.Therefore,it is of great value to study on the structural parts of titanium alloy by laser additive manufacturing.In this paper,the author used laser additive manufacturing equipment to prepare TC4 parts,and used eight different heat treatment processes to study the influence of heat treatment process on the micro structure and properties by means of OM,SEM,TEM,EBSD and tensile.The conclusions are as follows:The as-deposited specimen is composed of coarse primary β-columnar grains grown by epitaxy through multiple deposition layers,which have obvious anisotropy.The tensile strength of the specimens in horizontal direction is 29.04%higher than that in vertical direction,and the elongation after fracture is 64.71%lower than that in vertical direction.Among the specimens after annealing treatments of HT1-HT6,the microstructure changes obviously,from the original basket-wave microstructure to widmanstatten microstructure.The average thickness of a lamella gradually increased with the increase of annealing temperature,from 0.752μm of HT1 to 3.802 μm of HT6.In the heat treatment of HT4-HT6,with the increase of annealing temperature,the volume fraction of Widmanstatten gradually increased from 80.556%to 88.095%,and the size of a colony gradually increased from 58.911 μm to 66.086 μm.The solution aging heat treatment of HT7 results in the appearance of crab-like a phase and the average thickness of a lamella 0.878 μm;and the average thickness of lamellae obtained by double annealing of HT8 is 1.790 μm;The double annealing of HT8,the number of massive a phase increased,and the average thickness of a lamella was 1.790μm;Under the condition that α/β interface phase can be formed,the higher the temperature is,the straighter and smoother the α/β interface phase is,and the enriched elements V and Fe in β phase,and the enriched elements A1 and Ti in α phase and α/βinterface phase.In the specimens of as-deposited and HT1-HT6,the strength decreased with the increase of the average thickness of the a lamella.Among all the transverse tensile specimens at room temperature,the tensile strength of the as-deposited specimen is the highest,reaching 1127.4 MPa,fine acicular α’martensite is easy to cause dislocation packing,which can improve the strength;and the elongation after fracture of HT8 is the best,which is 13.8%,this is due to the equiaxed α increases the slip deformation ability,which in turn increases the plasticity.The as-deposited,HT1,HT5-HT7 tensile specimens are ductile and brittle mixed fractures,and the HT2-HT4 and HT8 tensile specimens are plastic fractures.In the horizontal tensile specimens at 400℃,the strength value of 795.53 MPa is the maximum tensile strength,and the elongation after fracture of HT8 is the best,which is 12.75%.tof the horizontal specimens,the as-deposited and HT5-HT7 tensile specimens are ductile and brittle mixed fractures,and the HT1-HT4 and HT8 tensile specimens are plastic fractures.