Design Of Low Vacuum Laser Cladding Deposition System And The Effectof Forced Water Cooling On Microstructures Of TC4 Alloy

Titanium and its alloysare widely used in aviation,aerospace,shipbuilding and other fields with high specific strength,excellent corrosion resistance and good heat resistance.However,the process of laser cladding deposition needs to be under the hypoxic atmosphere with the protection of inert gas,because titanium alloys react violently with oxygen inhigh temperature.In this paper,a set of vacuum system applied to laser cladding depositionbased on TC4 alloy was designed,the method of combining simulation and experiment was used to study the effect of substrate water cooling onmicrostructure of TC4 alloy fabricated by this system.First,in order to provide a platform for laser cladding depositionbased onTC4 alloy powder,a low vacuum forming environment was designed and the system was completed,and a LCD forming software was developed tocontrol 3D platform automatically.Then,processingexperiments about the single channel was conducted by orthogonal method.Process parameters are as followed: laser power is 600 W,scanning speed is 5mm/s,feedingrate is 4.3 g/min.Overlapping experimentswere conducted by the single factor experimental method.Process parameters are as followed: the optimal overlap rate is 30%.Using the optimal parameters for forming the solid parts and the internal oxygen content and the mechanical propertieswere tested.The results are as followed: internal oxygen content of parts formed in the vacuum than under protection of inert gas is decreased by 48%.With the increase of internal oxygen content,the tensile strength and yield strength increase,while the elongation decreases by 59.3%.The tensile strength of forming parts fabricated in different atmosphere has little difference,but is higher than that(910 MPa)of the matrix by about 35%.The yield strength of two parts is about 38% higher than that(850 MPa)of the matrix.Experimental results show that the vacuum system is effective to control theinternal oxygen content of the forming parts.Finally,the temperature field aboutforming process of the laser cladding deposition experimentin differentsubstrateconvective heat transfer coefficients based on TC4 alloy powderwas simulated by ANSYS.The results show that the temperature gradient of the molten pooldecreases from the bottom to the top.High convective heat transfer coefficient stetted on the substrate increasestemperature gradient,especially at the bottom of the molten pool.The direction of temperature gradient has a changing trend parallel to the direction of the deposition.Internal cooling rate of forming parts also increases.Moreover,the forming experimentwas operatedin the vacuum systemaccording to the optimized process parameters,and the effect of substrate water cooling on microstructure was studied.The results show that the macrostructure of forming parts is the huge columnar grains that grow epitaxial along the deposited direction.The? columnar grain gains the greater competitive advantage andsustainable growth.The microstructure is changed from Widmanstatten to the basket weave due to the influence of laser cladding in interlayer and intertrack.Hence,the experimental results and the resultsof simulation are close to lay a good foundation for the study of the "control" of microstructures.