Research On Hydrogen-enhanced Plasticity And Fretting Tribological Property Of Aeroengine Compressor Blades

In recent years,high-performance aero-engines have been developing towards high thrust-to-weight ratio and low energy consumption.The compressor,as one of the core engines,needs to meet its performance by greatly increasing the single-stage supercharging ratio and reducing the weight of components,which leads to higher standards for the material,structural strength and manufacturing process of the compressor blades.TiAl alloys,with their low density,high specific strength and outstandingt high-temperature performance,have shown overwhelming potential in the aviation industry.At present,most of the TiAl alloy still needs to be forged at high temperature due to the poor room temperature brittleness.However,its hot-working performance?high deformation temperature,large flow stress?and poor resistance to fretting damage performance have hindered the application of TiAl alloy in compressor blades to some extent.Some studies have shown that hydrogen processing technology can improve the hot deformation capacity of TiAl alloy.However,due to the late start and immature development of this method at home,and there are few studies on improving the characteristics of blade forming through this method.Therefore,in this paper,based on the mechanism of hydrogen-induced plasticization,the blades were treated with hydrogen to improve their thermo-mechanical forming performance and realize the accurate regulation of hydrogen on the plastic performance of the TiAl alloy.On this basis,the fretting-friction characteristics of the TiAl alloy blade and the wheel disc friction pair of the aero-engine compressor were studied,which laid a foundation for the application of the TiAl alloy material in the blade of the aero-engine.Firstly,The Ti-45Al-9Nb alloy,as the compressor blade material,was treated by hydrogen treatment technology?solid hydrogen method?,using ultra-high resolution thermal field emission scanning electron microscopy?SEM?,X-ray diffraction analysis?XRD?and digital display vickers hardness tester and other technical means to study the effects of hydrogen on the microstructure evolution and the hardness change of TiAl alloy blade at room temperature.The results showed that hydrogen could refine the laminar spacing of the alloy and promote the transformation of ?₂??phase and ?₂?B2 phase within the alloy,and the microhardness of hydrogenated alloy at room temperature was significantly higher than that of unhydrogenated alloy.Then,the mechanical behavior and microstructure evolution of unhydrogenated and hydrogenated Ti-45Al-9Nb alloys under different high temperature tensile deformation conditions were analyzed,and their constitutive equations of high temperature deformation were established respectively.The results showed that at the same strain rate and deformation temperature,the flow stress of the hydrogenated alloy decreased significantly compared with that of the unhydrogenated alloy,that is,the hydrogen-induced softening phenomenon occurred in the alloy,and the softening effect was more significant at the low strain rate and high deformation temperature.When the deformation condition was 1150?/0.0004s^-1,the maximum reduction rate of hydrogen-induced peak stress reached 16.28%.The hydrogen-induced alloy softening mechanism mainly intensifies the atomic diffusion movement through hydrogen,promotes the dislocation movement,and then promotes the bending deformation,coarsening,decomposition and fragmentation of the alloy layer,so that the dynamic recrystallization of the alloy occurs in advance.In addition,hydrogen reduced the activation energy of hot deformation of TiAl alloy,which was helpful to improve its thermo-mechanical forming performance.Subsequently,in the process of tangential fretting wear,unhydrogenated and hydrogenated Ti-45Al-9Nb alloys after tensile deformation at high temperature were taken as the research object,and the ball-disk point contact mode was used to simulate the fretting friction and wear characteristics at the contact interface between the blade tenon and the wheel tenon groove.By studying the operation behavior and surface morphology of tangential fretting wear of the specimen under different normal load ?F_n? and displacement amplitude?D?,the wear mechanism of the samples and the effect of hydrogen treatment on their fretting wear resistance were revealed.The results showed that there existed partial slip zone,mixed zone and slip zone in the fretting operation zone of both the unhydrogenated and hydrogenated alloys.Moreover,through the micrograph of the operating conditions,it was found that the mixed zone of the TiAl alloy after hydrogen deformation shifted to the direction of small normal load and large displacement amplitude,and the area of the slip zone decreased,while the area of partial slip zones increased.In addition,compared with the unhydrogenated alloy,the average friction coefficient and the maximum wear scar depth of the hydrogenated alloy were lower,and the wear mechanism was mainly adhesive wear and abrasive wear,while the oxidation wear was not obvious.In conclusion,the fretting wear resistance of TiAl alloy was significantly improved after hydrogen treatment.Finally,ANSYS Workbench was used to build a finite element analysis and calculation platform for the fluid-solid coupling simulation of the compressor blades,that is,a fluid-structure integration finite element simulation was carried out for the compressor blades under the combined action of centrifugal force and aerodynamic pressure.The results showed that the stress concentration was serious occurred at the transition connection between the blade body and the blade root,and the maximum deformation displacement occurred at the tip of the blade body,and the maximum equivalent stress and deformation displacement were357.38MPa and 9.14mm,respectively.And then,according to the simulation results,the optimum design of the blade structure was carried out,which reduced the maximum equivalent stress and deformation displacement by 37.51%and 40.04%,respectively,and there was no stress concentration on the blade surface,and the maximum deformation displacement distribution was also reduced.In addition,the natural frequencies and corresponding vibration forms of the structural modified blades were studied by means of constrained modal analysis,and it was found that the excitation frequencies of the first six orders of the blades were very good at avoiding the natural frequencies of each order,so as to avoid resonance phenomenon.