Experimental Research And Numerical Analysis Of Repairing Nickel-base Superalloy With The Hybrid Laser Additive And Subtractive Technology

Laser repairing has many advantages,such as high efficiency,less deformation,high interface bonding strength and low residual stress.Laser repairing has become a research hotspot because of its obvious advantages compared with conventional repair technologies.The damaged parts should be polished and cleaned before laser repairing,and the redundant materials of restoration area should be removed to improve the repairing accuracy and the surface finish after repairing.Currently,the pre-and post-processing of laser repairing is done with mechanical tools.However,this has some drawbacks such as tool wearing and narrow-area that is hard to machining,which affect the quality of workpiece.Therefore,the technology of hybrid laser additive and subtractive is proposed in this research.Inconel 718 nickel-based superalloy was selected as experimental materials.Three kinds of fiber lasers were employed in the repairing process of Nickel-base Superalloy by the laser crack cleaning,laser material addition repairing,laser precision material reduction and laser polishing,respectively.In order to explore the repairing technology of hybrid full laser additive and subtractive,the repairing process was divided into the following four steps:(1)A pulsed laser was used to clean and etch the crack through material subtractive,and the U-shaped grooves with smaller oxide layer were obtained.(2)A high-power continuous wave(CW)laser and preset-powder cladding process were used to repairing crack.Continuous,uniform and defect-free repairing zones were obtained and the defect in the repaired zone was metallurgically bonded with the matrix.(3)The same pulsed fiber laser as in step 1 was applied to remove the excessive materials in the repairing zone to obtain a surface with less heat affected zone and higher efficiency of material removal.(4)The CW fiber laser with 5kHz modulated frequency was applied to the polishing surface,and the surface with roughness of Ra 1.44 ?m was obtained.Based on the optimization results of laser repairing process,the mechanical properties such as microstructure,phase,microhardness,tensile strength and friction and wear of the full laser repairing parts and matrix were analyzed.The study found that an excellent metallurgical bonding between the repaired area and the matrix was obtained.The microstructures of the repaired area were uniform and fine.The comprehensive mechanical properties of the repaired area could reach over 85% of the matrix,shown a significant improvement over traditional process.In order to observe the mechanism of laser repairing more clearly,a three-dimensional finite element model of laser repairing was established.The ANSYS finite element software was used to simulate the temperature field of laser repairing process.The effect of laser power and repairing speed on laser repair temperature field was analyzed.The numerical results and experimental results were compared and proved that the laser repairing model was reliable.