Creep feed grinding induced gradient microstructures in the superficial layer of turbine blade root of single crystal nickel-based superalloy

The service performance of the turbine blade root of an aero-engine depends on the microstructures in its superficial layer.This work investigated the surface deformation structures of turbine blade root of single crystal nickel-based superalloy produced under different creep feed grinding conditions.Gradient microstructures in the superficial layer were clarified and composed of a severely deformed layer(DFL)with nano-sized grains(48–67 nm)at the topmost surface,a DFL with submicron-sized grains(66–158 nm)and micron-sized laminated structures at the subsurface,and a dislocation accumulated layer extending to the bulk material.The formation of such gradient microstructures was found to be related to the graded variations in the plastic strain and strain rate induced in the creep feed grinding process,which were as high as 6.67 and 8.17×10^(7)s^(−1),respectively.In the current study,the evolution of surface gradient microstructures was essentially a transition process from a coarse single crystal to nano-sized grains and,simultaneously,from one orientation of a single crystal to random orientations of polycrystals,during which the dislocation slips dominated the creep feed grinding induced microstructure deformation of single crystal nickel-based superalloy.

Grinding force and surface quality in creep feed profile grinding of turbine blade root of nickel-based superalloy with microcrystalline alumina abrasive wheels

Creep feed profile grinding of the fir-tree blade root forms of single crystal nickel-based superalloy was conducted using microcrystalline alumina abrasive wheels in the present study. The grinding force and the surface quality in terms of surface topography, subsurface microstructure,microhardness and residual stress obtained under different grinding conditions were evaluated comparatively. Experimental results indicated that the grinding force was influenced significantly by the competing predominance between the grinding parameters and the cross-sectional root workpiece profile. In addition, the root workpiece surface, including the root peak and valley regions, was produced with the large difference in surface quality due to the nonuniform grinding loads along the root workpiece profile in normal section. Detailed results showed that the surface roughness, subsurface plastic deformation and work hardening level of the root valley region were higher by up to25%, 20% and 7% in average than those obtained in the root peak region, respectively, in the current investigation. Finally, the superior parameters were recommended in the creep feed profile grinding of the fir-tree blade root forms. This study is helpful to provide industry guidance to optimize the machining process for the high-valued parts with complicated profiles.

Fretting wear behaviour of machined layer of nickel-based superalloy produced by creep-feed profile grinding

Fretting wear has an adverse impact on the fatigue life of turbine blade roots.The current work is to comparatively investigate the fretting wear behaviour of the nickel-based superalloy surfaces produced by polishing and creep-feed profile grinding,respectively,in terms of surface/subsurface fretting damage,the friction coefficient,wear volume and wear rate.Experimental results show that the granulated tribolayer aggravates the workpiece wear,while the flat compacted tribolayer enhances the wear resistance ability of workpiece,irrespective of whether the workpiece is processed by polishing or grinding.However,the wear behaviors of tribolayers are different.For the polished surface,when the normal load exceeds 100 N,the main defects are crack,rupture,delamination and peeling of workpiece materials;the wear mechanism changes from severe oxidative wear to fatigue wear and abrasive wear when the loads increase from 50 to 180 N.As for the ground surface,the main wear mechanism is abrasive wear.Particularly,the ground surface possesses better wear-resistant ability than the polished surface because the former has the lower values in coefficient friction(0.23),wear volume(0.06×10^(6)μm^(3))and wear rate(0.25×10^(-16)Pa^(-1)).Finally,an illustration is given to characterize the evolution of wear debris on such nickel-based superalloy on the ground surface.