Study On The Recrystallization Behavior Of Directio Nally Solidified Nickel-based Superalloy DD483 And PWA1483

Directionally solidified(DS)nickel-based superalloys are widely used in the manufacture of gas turbine blades due to their excellent high-temperature mechanical properties.The grit blasting(GB)or shot peening(SP)methods are generally adopted in the blade shell cleaning process,the cold deformation caused by these processes is basically on the surface,which makes the blade surface easily recrystallize during the later high temperature service process,the recrystallized structure formed is completely different from the original columnar structure,which will seriously reduce the endurance life and fatigue life of the blade.Therefore,it is of great significance to study the effect of GB and SP on the recrystallization(RX)of DS nickel-based superalloys.In addition,in the actual application of the blade,it was found that RX occurred under some small GB pressure or SP pressure.Therefore,in this paper,the surface of the DD483 and PWA1483 blade castings were cleaned with different GB and SP pressures and then kept at the service temperature(1100?)for 4h and 16h.The recrystallization behavior and microstructure evolution of the sample surface were studied,and the following conclusions were obtained:(1)Both alloys can get effective surface cleaning and roughness reduction after the GB and SP pressure of 0.4-0.7 MPa,and the cleaning effect is basically the same.The residual stress introduced by the two alloy surfaces after SP is smaller than that of GB.Under the same GB and SP pressure,the residual stress introduced on the surface of PWA1483 alloy is smaller than that of DD483 alloy.(2)After the two alloys after GB and SP were kept at 1100? for 4h and 16h,the diffusion of Al,Ti and other elements in the surface layer consumed the main forming elements of the?'phase,resulting in the formation of a recrystallization zone(District ?)under the oxide layer(District ?)that favors recrystallization nucleation.The two alloys after sandblasting annealing form discontinuous Al2O3 in the District ? with the formation of TiN below the District ?,this zone is called the microstructure instability zone(District ?),while shot peening sample has no District ?.(3)The longer the holding time,the greater the tendency of cellular recrystallization(CRX),and the two alloys after SP have a greater tendency to CRX than GB.After GB and SP,PWA1483 alloy has a smaller tendency to CRX after heat preservation than DD483 alloy.The two alloys after GB had incomplete ERX at 4 hours of heat preservation,at this time,small new grains had been generated,at 16 hours of heat preservation,the grains had grown and the tendency of ERX increased.(4)The thickness of the recrystallized region follows the actual stress as the GB and SP pressure changes.The longer the holding time,the greater the depth of RX.When the GB and SP pressure is 0.6MPa,the compressive stress introduced on the surface of DD483 alloy is the smallest,and the RX thickness is also relatively small.Therefore,the best surface GB and SP pressure suitable for DD483 alloy is 0.6MPa.Similarly,the best surface GB and SP pressure for PWA1483 alloy is 0.5MPa/0.6MPa.