Research On Thermal Deformation,Microstructure And Mechanical Properties Of By Directed Energy Deposition Based On Thermal Characteristics

Directed energy deposition(DED),as one of the additive manufacturing(AM)processes,is attracting extensive attention worldwide.However,the quality issue products cannot meet the requirement of different industry sectors.The temperature field has a critical influence on the microstructure,thermal deformation and residual stress.In the study,in-situ temperature monitoring and numerical modelling were applied to study the temperature distribution during the DED process.Typical thermal characteristics were extracted from the thermal signatures.The mechanism of thermal deformation and residual stress was studied.The relationship between characteristics and thermal deformation,microstructure and mechanical properties was developed.The main research contents are listed as follow:The in-situ monitoring system and thermal characteristics extraction algorithm.Considering the severe processing environment,the proper sensors were chosen and the monitoring system was built.After that,thermal characteristics extraction algorithms were developed in Matlab.The thermal numerical model was developed using ‘birth and death' method.The effect of parameters on thermal characteristics was studied.The effect of thermal characteristics on thermal deformation and thermal-mechanical numerical model for simulating the residual stress.The influence of spatial temperature gradient and heating area on the thermal deformation was explored.The volume of material experienced plastic strain plays an important role in the angular distortion.The thermal-mechanical coupled numerical model was developed to analyze the stress evolution and predict residual stress.The thermal characteristics-microstructure-mechanical properties relationship.The effect of parameters on the temperature gradient in the solidification interface and the solidification rate was explored.Thermal characteristics were used as the thermal metrics of the primary dendrite arm spacing(PDA)and CET.The tensile properties and microhardness were analyzed.The prediction relationship among thermal characteristics-microstructure-mechanical properties was finally developed based on the Hall-Petch relationship.