Study On The Surface Laser Cladding And Tribological Properties Of A Ti-45Al Alloy

TiAl alloys have the characteristics of low density,high specific strength,and high temperature creep resistance.Its comprehensive performance indicators are superior to traditional high-temperature alloys,making it the most promising new generation of high-temperature lightweight structural materials for future aeroengine turbine blades.However,TiAl alloys have high room temperature brittleness.When used at temperatures above 800℃,their oxidation resistance is relatively low.In addition,when used for friction parts,their wear resistance is poor.Therefore,it is necessary to improve the surface properties and high-temperature oxidation resistance of TiAl alloys.The finite element analysis of the fluid-structure coupling simulation of aero turbine engine blades was constructed using ANSYS Workbench.According to the results of aerodynamic flow field simulation and blade static structure simulation,it was found that there was a stress concentration phenomenon at the transition joint between the blade tenon and the blade root,with the maximum equivalent stress of 366.69 MPa.The maximum deformation displacement occurs at the blade tip,with a deformation displacement value of6.90 mm.It is necessary to protect the stress concentration areas with laser cladding wear-resistant coatings.Laser cladding technology is a new type of special processing technology that belongs to surface additive manufacturing.It uses a laser beam to rapidly melt the cladding material and the surface of the substrate,forming a layer of high-temperature oxidation resistant and wear-resistant coating on the alloy after rapid solidification.In this paper,we used laser cladding technology to prepare NiCrAlY coatings,and studied the microstructure,hardness,and fretting resistance of the coatings after laser cladding.The fretting wear characteristics of a TiAl alloy and NiCrAlY coating were studied.The fretting wear behavior,surface morphology,and wear mechanism of substrate and coating were studied.The results show that the fretting operation conditions of the substrate and coating were slightly different under different displacement amplitudes and normal load parameters,Under the conditions of F_x=60,120,180 N,D=20,60,100μm,the fretting region of Ti-45Al alloy changed from partial slip region to mixed slip region and complete slip region.The fretting zone of the NiCrAlY coating shifted from a partial slip zone to a complete slip zone,and there was no mixed slip zone.The wear mechanisms of substrate and coating were mainly abrasive wear,adhesive wear,and oxidation wear.Under the same experimental parameters,the coefficient of friction（COF）of NiCrAlY coating is significantly smaller than that of Ti-45Al alloy,and the wear trace was smaller.Therefore,it could be explained that NiCrAlY coating had better resistance to fretting wear than Ti-45Al alloy.The corrosion resistance and oxidation resistance of the coating and substrate in the temperature range of 750℃to 1050℃were studied.It was found that the corrosion potential of NiCrAlY coating was greater than that of TiAl alloy.The corrosion current density of the coating was far less than that of the substrate,indicating that the corrosion resistance of the coating was better than that of the substrate.Under the condition of 750℃oxidation,the Ti-45Al alloy had no defects such as cracks and holes in the oxide layer,which indicated that it had certain high temperature oxidation resistance.During oxidation at 850℃to 1050℃,the TiO₂oxide on the surface of the substrate dominated.Its porous structure provided diffusion channels for external oxygen atoms,and element diffusion occurred,leading to increased oxidation of the substrate and serious damage to its high-temperature oxidation resistance.When the NiCrAlY coating was oxidized at 750℃,850℃,and 950℃,the formation of Al₂O₃and Cr₂O₃on the surface layer hindered the diffusion and entry of external oxygen atoms,and also played a heat insulating role.Therefore,the coating had good high-temperature oxidation resistance.At a high temperature of 1050℃,the high-temperature oxidation resistance of the NiCrAlY cladding layer gradually decreased,resulting in cracking and peeling of the coating.In summary,the high-temperature oxidation resistance of NiCrAlY cladding layer was superior to that of TiAl alloy matrix.