Study On The Additive Manufacture Technology Of Titanium Alloy Synchronous Feed Powder

Laser additive manufacturing technology is a method of manufacturing solid parts by means of gradual accumulation of materials in CAD data.It is a "bottom-up" manufacturing method that compared to traditional material removal-cutting technology.As a typical metal additive manufacturing technology,taking advantages of high efficiency and high performance,laser additive manufacturing technology has become an important mean of titanium alloy complex parts direct forming and a high-profile method in laser processing technology currently,that widely used in the fields of aircraft manufacturing and heavy machinery and so on.This paper operate 4kW fiber coupled semiconductor laser on laser additive manufacturing experiment of TC4 titanium.This thesis mainly studied the effect of laser power,scanning speed and powder feed rate on surface morphology,melting height and melting width of the deposition layer.Base on the optimum process parameters acquired in single channel,conducted the multichannel experiment by change overlap rate and obtained deposition layer with favorable forming surface and satisfied the process requirements.By using the optimum process parameters obtained to product the tensile specimens and the specimens were normalized at different temperatures,and be conducted the tensile test for specimen under the optimum parameters by the universal tensile testing machine.By using metallographic microscope,scanning electron microscopy(SEM)and Xray diffraction(XRD),analyzed the organization structure and phase composition of deposition layer,main conclusions are as follows.The results show that the optimum parameter of single channel deposition is laser power2200 W,scanning speed 800mm/min,pulverized disc speed 0.9r/min,overlap rate is 50% by multichannel test.The samples were normalized treatment,the results show that the microstructures of960℃ and below the normalizing temperature are lamellar structure,and with the increase of normalizing temperature,the microstructures were obviously coarsened and the order of α phase decreased;when the normalizing temperature is 990℃,the microstructure is widmanstatten microstructure.As the normalizing temperature increases,the tensile strength and yield strength in both XY direction and Z direction decrease,and the tensile strength in XY direction is significantly higher than that in Z direction,but the plasticity in Z direction is obviously better than that in XY direction.The results show that the fracture micromorphology in both XY direct and Z direct areductile fracture with full of dimple.The optimum mechanical properties are obtained under the above optimum process parameters and normalizing treatment conditions(Heating temperature is810℃,heat preservation time is 2h,AC),the tensile strength is 921 MPa,yield strength is917.3MPa,elongation is 12.8% and section contraction rate is 27.5% in XY direction,the tensile strength is 906.1MPa,yield strength is 900.2MPa,elongation is 15.8% and section contraction rate is 49.3% in Z direction.A large TC4 titanium alloy structure with a size of 570mm×470mm×210mm was directly formed by the above optimum process parameters.After normalizing treatment,the microstructure is lamellar microstructure,tensile strength is 904.17 MPa,yield strength is900.13 MPa,elongation is 12.5% and section contraction rate is 42.5%.Compared with the national standard values of forgings,the comprehensive performance of TC4 titanium alloy by laser additive manufacturing after normalizing treatment is better than that of forgings,and satisfied the actual needs of the customers.