Crack Susceptibility And High Temperature Oxidation Resistance Of Ni-base Superalloy Fabricated By Laser Additive Manufacturing Technology

Nickle-base superalloy is a kind of key material for fabrication of advanced aero-engine and gas turbine blade.However,In traditional directional solidification method,there are some problems,such as deteriorated microstructures,high cost and low yield.It cost the increased produce cost of superalloy,difficult in microstructure controlled,low pass percent of parts and so on.The search for new production methods is imminent.In this study,the latest Laser additive manufacturing technology applied to nickel-based single crystal superalloy,this technology can achieve the rapid manufacture of compact metal parts,parts manufactured are better than the traditional processing methods.In this study,SRR99 alloy was machined and fabricated by Laser additive manufacturing technology.the effects of laser power,feed rate and defocusing amount on the laser remelting of Ni-base single crystal superalloy were studied.The depth and width of laser remelting pool were decreased with the increase of scanning speed.As the laser power increases,both the depth and width of the remelting pool increase.The effect of defocusing amount on laser remelting pool depends on the laser power:when the laser power is large,the bath depth increases with the increase of the defocusing amount;when the laser power is small,the depth of the pool decreases with the increase of the defocusing amount.In the process of laser additive manufacturing technology,when the current layer is deposited,the former layer is subjected to reheat cycle,?+?' Low-melting point eutectic at the grain boundary liquefaction to form liquid film,in the deposition process with the gradual increase of the residual tensile stress was pulled under the action of the formation of cracks.The influence of alloying elements on the crack initiation is also discussed.The addition of Mo and Re can suppress the formation of cracks.The addition of W can promote the formation of cracks,while the addition of different content of Co has little effect on the formation of cracks in the alloy.Superalloys often work under the high temperature environment.Therefore,the high temperature oxidation resistance of the superalloy is an important index for consideration of superalloy.The results show that the high temperature oxidation resistance of DZ408 alloy is better than that of DD98M alloy.The high temperature oxidation resistance of DZ408 has reach to the highest value.It can produce a continuous,dense oxide film at high temperature.Basically meet the nickel-based superalloy as a turbine engine blade antioxidant performance requirements.The oxidation process of DD98M and DZ408 alloy belongs to selective oxidation,the oxide film is mainly composed of Cr2O3 and Al2O3,and there is a small amount of NiCr2O4 and TaO2.The addition of an excessive amount of Ta leads to the delamination of the oxide film,which affects the oxidation of the alloy,resulting in the deterioration of the adhesion between the oxide film and the substrate.The oxide film is prone to defects voids and easy peeling from the substrate.While the proper addition of Hf can enhance the adhesion between the oxide film and the matrix.