Investigation On Thermomechanical Behavior,Microstructure And Stress Of Laser Melting Depositing Nickel-Based Superalloys

The complex thermomechanical behavior of laser melting deposition(LMD)has an important influence on the microstructure and stress evolution.Finite element numerical simulation of thermodanamic behavior during LMD of Inconel 625 was performed using the ANSYS software.Based on the combination of simulation and experimental results,relation of thermal behavior and microstructure and the effect of stress behavior on the forming quality was investiged.Relation of thermal behavior and microstructure evolution in molten pools of LMD-processed Inconel 625 was investigated.The results showed that temperature gradient of at the top,bottom and edge of the molten pool was 7.3×10~5?/m?2.5×10~6?/m and 4.6×10~6?/m,respectively.The maxium cooling rate at the top,bottom and edge of the molten pool was 7.6×10~5?/s?3.7×10~5?/s and 1.8×10~5?/s,respectively.The value of the G/R was increased from 7.3×10~5? s/m~2 at the top of the molten pool to 1.22×10~7? s/m~2 at the bottom.Columnar grains were generated at the bottom of the molten pool,while equiaxed grains were formed at the top.Besides,due to the lower cooling rate at the edge region than that of the bottom region,columnar grains generated at the edge region were coarser compared with that at the bottom of the molten pool.Thermal behavior along the laser scanning direction of a deposited track and its influence on microstructure evolution during LMD of Inconel 625 were investigated.The results showed that the heat accumulation at the initial and terminal location was more severe.Consequently,the maximum coling rate of at the initial,central and terminal location of the deposition track was 7.6×10~5?/s?3.7×10~5?/s and 1.8×10~5?/s,respectively.Furthermore,the liquid lifetime at the initial central and terminal location of the deposition track was predicted equal to 4.4 ms,3 ms and 4.8 ms,respectively.The exoerimental results showed that columnar grains with average primary dendrite arm spacing of 3.42?m and 3.77?m was observed at the cross-section of the initial and terminal location,respectively.In comparison,finer columnar grains with average primary dendrite arm spacing of 2.55?m were found at the central location due to the highest cooling rate and the shortest liquid lifetime.Besides,columnar grains with average primary dendrite arm spacing of 3.21?m,2.68?m,and 3.59?m was found at the longitudinal-section of the initial,centeral and terminal locaton,respectively.Stress behavior and strain behavior during LMD of Inconel 625 was investiged during the process of LMD,the laser irradiation zone was in compressive stress state.The tensile stress was obtained in the fabricated component.The tensile stress and the plastic srain long the laser scanning direction(Y-axis direction)were the lagerst.When the component was completely cooled,the residual stress along the Y-axis direction was still the largest(1130 MPa).The experimental resuls showed that long crack(perpendicular to the laser scanning direction)was formed in the longitudinal-section.The simulation could accurately predict the magnitude and the distribution of residual stress.