The Research On Wear Mechanism And Surface Shot Peening Technology Of Typical Superalloys Such As FGH96 And DD6

Nickel-based superalloys have become a key material for advanced aero-engine turbine blades and turbine discs owing to their excellent high-temperature mechanical properties.As an important component of the hot end of aero-engines,friction and wear on the alloy during service often causes material failure.In addition,with the development of aero-engines towards high thrust-to-weight ratios and low energy consumption,higher requirements have been raised for surface protection technologies and research and development of new material for turbine hot-end components.Therfore,it is important to study the friction and wear properties of typical Nickel-based superalloys used in aero-engines,surface protection technologies,and friction and wear performance of new materials.For the sliding friction and fretting wear problems of the superalloy moving parts present in the Aero-engines.Typical Ni-based superalloy such as FGH96 and DD6were selected as the objects of research in this thesis.Their sliding friction properties were investigated by changing the load and temperature.Their fretting wear mechanism were analyzed by varying the load and frequency.Then,the effect of shot peening on the friction and wear properties of the superalloys was studied and the protection mechanism was analyzed.In addition,two typical high-entropy superalloys of Ni Al Co Cr Fe Ti were prepared.Their microstructures,mechanical properties and tribological properties from 25 to 900℃were studied.The mechanism of high temperature friction and wear was analyzed by combining microstructure and mechanical properties.The main conclusions can be drawn as follows:（1）Under sliding friction conditions,load had little influence on the friction coefficient and wear rate of FGH96 and DD6,but temperature had a significant effect.With the increase of the load,the wear rate of FGH96 did not change significantly,and the wear rate of DD6 increased slightly.With the increase of the temperature,the wear rate of FGH96 and DD6 was greatly reduced.At 900℃,the wear rate of FGH96and DD6 was reduced by one order of magnitude compared to room temperature.（2）Under fretting wear conditions.With the increase of the load,the wear degree of FGH96 slightly increases,and the wear rate of DD6 was gradually decreased until stable.With the increase of the frequency,the wear resistance of FGH96 and DD6 did not change obviously.The wear properties of FGH96 and DD6 were the worst at low frequency.（3）For the wear problems of superalloy,this paper adopts the shot peening to improve its wear resistance.The results showed that the surface roughness of FGH96and DD6 increases,residual compressive stress was introduced into the alloy surface,the hardness of FGH96 and DD6 was increased in 117～151μm and 140～170μm respectively,and the wear resistance of FGH96 and DD6 was significantly improved under sliding friction and fretting wear conditions.After shot peening,the disappearance of the crack on the worn surface is mainly attributed to the improvement of the surface hardness and prevent the crack initiation and propagation,which effectively reduces the fatigue wear caused by the crack.（4）High entropy superalloy is a new type of superalloy with great potential,it has excellent mechanical properties and high temperature wear resistance.At 25℃,the yield strength,compressive strength,fracture strain and fracture toughness of the alloy are 917.8 MPa、2279.5 MPa、32.5%and 43.0 MPa·m^0.5.At 900℃,the wear rate of the alloy is 8.0×10^-6mm³/（N·m）.The great mechanical properties are attributed to the synergistic strengthening and toughening ofγphase andγ′phase.The excellent high temperature resistance is attributed to the great high temperature hardness and the oxide glazed layers on the worn surface.