Study On Microstructure And Performance Of Titanium Alloy With Strengthening And Toughening Array Structure Fabricated With Electron Free Form Fabrication

Aiming at the strengthening and toughening of titanium alloy,based on the strengthening and toughening mechanism of array structure,this paper explored the strengthening and toughening mechanism of TC4-TA1 array structure under electron freeform fabrication process.The relationship between microstructure and properties of TC4 under different processes was studied on this basis.Based on the optimized process parameters,the microstructure characteristics of TC4-TA1 array structure interface and the effect of array structure on the coordination of strength and toughness were studied.Through the subsequent heat treatment of fabrication,theβ→αsolid phase transformation was controlled,the microstructure characteristics of TC4 were regulated,the structure and properties of TC4-TA1 array structure were improved,and the strengthening and toughening of titanium alloy was further realized.By comparing the microstructure of TC4 under different electron freeform fabrication processes,the microstructures of different TC4 samples all presented the obvious anisotropy.The microstructures of single-layer TC4 samples were composed of equiaxed crystal in the bottom area and the columnar crystal in the upper area.The microstructures of multilayer TC4samples consisted of equiaxed crystal in the bottom area,columnar crystal in the middle area,and equiaxed crystal in the top area.The difference of microhardness of multilayer TC4 samples along the building direction was the largest.By changing the cooling time between each layer,TC4 block with the multi-layer and multi-channel exhibits a unique crystal grain layered structure along the height direction.It is further found that the heat accumulation during the electron freeform fabrication process changes the temperature gradient,causing that the grains coarsen and the microhardness slightly decreases.The TC4-TA1 component with the array structure was fabricated basing on the optimized formation parameters of TC4.The organizational characteristics of TC4 still exist,and the area of the columnar crystal region was the largest.However,the microstructure of TA1 area was an equiaxed crystal structure,and there is no zoning feature similar to TC4.The fabricated process parameters have a significant effect on the interface structure between TC4 and TA1 areas,and the element composition in the interface was affected by each other areas.The mechanical properties of the TC4-TA1 component with the array structure were anisotropic.The static compressive strength and plasticity along the horizontal direction are slightly lower than that of TC4 samples,but the mechanical properties along the building direction was greatly improved,which was higher than that of the TC4 samples.The microstructure of solid phase transformation of titanium alloy was controlled by the heat treatment of TC4 and TC4-TA1 array structural samples.The effect of heat treatment temperature on the microstructure is more obvious.Coarseβgrains was obtained by both solid solution and aging heat treatments above T_βtemperature.The microhardness of the TC4 block in the top area is higher than that of the deposited TC4,but the microhardness of the TC4 block in the middle area becomes lower.The microstructure of TC4 sample transforms into a dual-state structure with the heat treatment near the T_βtemperature.The tensile strength and compressive strength of TC4 sample in the height direction were lower than that in the deposited state,but the elongation became higher.The basket structure was obtained by heat treatment under T_βtemperature,and the compressive strength and plastic deformation in the height direction were slightly improved.The transition zone in the TC4-TA1 sample with array structure increases after the heat treatment.The microstructure of TC4 changed,but the microstructure of TA1 had no obvious change.After the solution and aging heat treatment below the T_βtemperature,the static and dynamic compressive strengths of the TC4-TA1 sample at the interface are higher than that of samples with the solution and aging heat treatment above the T_βtemperature in the horizontal and height directions.