| Titanium alloys have performance advantages such as high specific strength,and is widely used in engine blades,wheels,aircraft landing gear,fuselage structure and so on.However,for the more and more complex working conditions of aircraft,the performance of single alloy parts can not meet the requirements gradually,and the dual alloy parts can better meet the performance requirements of different parts of the same component.At the same time,additive manufacturing technology has obvious advantages in rapid prototyping of dual alloys and gradient materials.However,the electron beam additive manufacturing technology has been seldom studied in the metal forming process and the influence law on the microstructure and performance.This subject mainly studies the forming process ? microstructure and properties of TC4/TC11 dual titanium alloy manufactured by electron beam additive manufacturing.The results show that electron beam flow,forming speed,wire feeding speed and lap ratio are the main factors affecting forming quality.The best process parameters of multi-layer metal formed by electron beam additive are electron beam current of 15 m A,forming speed of 300 mm / min,wire feeding speed of 20 mm / s and overlap ratio of35%.The optimum process parameters are used to test the additive forming of TC4 /TC11 dual titanium alloy.At the same time,the results show that the surface morphology of the samples is good without obvious defects,and the grain size of the single alloy gradually changes from fine columnar crystal to coarse columnar crystal from the bottom to the top of the deposit layer.The inside of the dual alloy is composed of thick ? columnar crystals,and the grain boundary is a continuous grain boundary ? phase,and the edge of the grain boundary is parallelly arranged with a lamellar ?? bundle structure.And the inside of the grain is the basket-weave structure composed of the strip ? phase.The boundary of transition layer is clear.The microhardness increases significantly from the TC4 side to the TC11 side,and the average hardness of the alloy on the same side is not much different.The change of crystal orientation has little effect on the tensile strength of the formed sample,the strength is better than that of the forged TC4 alloy,the plasticity is slightly lower than that of the forged alloy,and the fracture mode is typical dimple fracture.After annealing treatment,the microstructure of the dual alloy is coarsened to a certain extent,the basket-weave structure is not obvious,some areas of the structure dissolves to form massive or granular ? phase,the microstructure of the alloy on both sides of the transition layer tends to be the same,and the boundary is even less obvious than that of the deposited samples.After annealing,the hardness has little change compared with the deposited state.Compared with the deposited samples,the tensile strength is lower,the plasticity is significantly improved,and the fracture mode is dimple fracture.After solution aging treatment,the basket-weave structure of the sample changed into fine acicular ?? phase,the grain boundary was broken,the lamellar ?? cluster at the edge of the grain boundary disappeared,the structure of TC4 side was more sparse than that of TC11 side,and the boundary of transition layer was clear.After the change of crystal orientation,the lamellar ?? cluster at the grain boundary and the basket-weave structure inside the grain change to acicular martensite ??.The microstructure on both sides of the transition zone is crisscross arrangement of acicular martensite ??,the size of acicular martensite ?? on TC4 side is longer,and the size of martensite ?? on TC11 side is quite different.The hardness and tensile strength of the alloy are higher than that of the deposited state,but the plasticity of the sample is decreased significantly. |
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