Creep Feed Profile Grinding Of Turbine Blade Root Of Single Crystal Nickle-based Superalloy With Microcrystalline Alumina Wheels

The single crystal nickel-based superalloys are the key materials to fabricate the turbine blades of the advanced aero-engine with high thrust-weight ratio.The excellent mechanical properties of single crystal nickel-based superalloy at elevated temperatures are resulting from the single grain that grows to the whole turbine blade and eliminates the grain boundary defects of polycrystalline material.The blade root is a critical part for one turbine blade.The machining quality of the blade root influences the service performance of turbine blade directly,while the machining efficiency of the blade root affects the manufacture cycle of an aero-engine significantly.At present,creep feed grinding with high porosity alumina wheels has been the common method for precision machining of the turbine blade root of single crystal nickel-based superalloy.However,there exists huge challenges,such as the low grinding efficiency due to the insufficient knowledge on the grindability of single crystal nickel-based superalloys and due to the rapid tool wear and low machining quality consistency when using the common alumina wheels,the great difficulty in controlling the grinding burn due to the unknown of the temperature field during profile grinding,and the limitation in obtaining the high quality products of single crystal nickel-based superalloy due to the poor understanding of nano microstructure of surface layer after grinding.Therefore,the current study was to investigate the creep feed profile grinding of turbine blade root of single crystal nickel-based superalloy using newly developed microcrystalline alumina wheels in terms of the grinding efficiency,grinding burn and the nano microstructure of surface layer.Combined the results of experimental trails,simulation analysis and application verification,the bottleneck problems mentioned above can have a breakthrough for the grinding of single crystal turbine blade root.The main contents and conclusions are summarized as follows:(1)The creep feed grinding of three nickel-based superalloys,i.e.,wrought superalloy GH4169,directionally solidified cast superalloy DZ408,and single crystal superalloy DD6,was conducted by using two alumina wheels(i.e.,microcrystalline alumina(MA)wheel and brown alumina(BA)wheel).The grinding force,grinding temperature,ground surface topography,and wheel wear behavior were studied comparatively.The grindability of single crystal nickel-based superalloy was analyzed and the better performance of MA wheel during grinding was obtained compared to the BA wheel.Meantime,the strong wheel clogging and severe wheel wear were found to be the main difficulty in the grinding of single crystal nickel-based superalloy.(2)The finite element method to predict the three dimensional(3D)temperature field of turbine blade root of single crystal nickel-based superalloy during grinding was established considering the coupling effect of grinding heat,force and the blade root workpiece profile.The 3D temperature distribution during grinding of the blade root workpiece was clarified.The effects of the blade root workpiece profile on the changes of temperature peak values were revealed.On the basis of the simulation results and experimental vilification,it was found that grinding burn occurred more easily in the blade root peak regions than in the blade root valley regions.(3)The nano microstructure of surface layer during grinding the blade root of single crystal nickel-based superalloy was characterized.The evolution of gradient nano microstructure along the depth of the surface layer was revealed.The transition process and its mechanism of single crystal to submicron and nano microstructures was analyzed.By using the nanoindentation technique,the corresponding mechanical properties were detected.It was found that the dislocation behavior of single crystal nickel-based superalloy induced by grinding had the predominated influence on the formation of gradient nano microstructure and the change of mechanical properties.(4)The wear behavior of MA wheel and the surface integrity of turbine blade root of single crystal nickel-based superalloy in the creep feed profile grinding process were studied.The mathematical model to predict the profile wheel wear was firstly developed and corresponded well to the experimental results.The parameters were then optimized accordingly for the blade root profile grinding from the rough workpiece to the finished part.Finally,the on-site verification was realized by grinding the turbine blade root of single crystal nickel-based superalloy DD6 of the new turboshaft aero-engine,and the high machining quality and high machining efficiency for blade root manufacture were achieved.