Preparation And Oxidation Behaviors Of Rhenium Doped Aluminide Coatings

Modified aluminide protective coatings are widely used in high temperature parts of aero engines and gas turbines at present.However,there are still some problems,such as the precise control of the content and distribution of the modified elements,premature spallation of the oxide scale and surface rumpling behavior during the preparation and service.It is necessary to develop new coating systems and preparation methods to meet the multi-dimensional requirements of modified aluminide coatings.This paper adoped a new preparation process combining electroplating and arc ion plating(AIP)to accurately control the content and distribution of the modified elements(Re,Pt,etc.)in the coatings.Three Re modified ?-NiAl coatings with different Re content,one RePt co-modified ?-NiAl coating and two PtReY co-modified ?-NiAl coatings were prepared to study the influence mechanism of different modified elements on the formation and growth of oxide scale,analyze the influence of modified elements on the microstructure evolution and high temperature oxidation behaviour of the coatings and its mechanism,and clarify the synergistic mechanism of multivariate modified elements.The main results are as follows:(1)Al diffusion coating was prepared by AIP Al and subsequent diffusion treatment method on DD26 Ni-based single crystal superalloy,which comprised outer layer of ?-NiAl with submicron sized ?-W precipitates and IDZ.0Re-NiAl coating was produced by electroplating pure Ni layer,AIP Al and subsequent diffusion treatment method,which included outer layer of ?-NiAl,middle layer of ?-NiAl with submicron sized ?-W precipitates and IDZ.Re doped ?-NiAl coating was fabricated by composite electroplating Ni-Re layer,AIP Al and subsequent diffusion treatment method,which was consisted of outer layer of ?-NiAl with dispersed y-Re phases,middle layer of ?-NiAl with submicron sized ?-W precipitates and IDZ.Three Re doped aluminide coatings with different Re content were prepared by controlling Re content in electroplated Ni-Re layer.After oxidation at 1100?,the phase transition from ?-Al2O3 to ?-Al2O3 could be accelerated by the addition of Re for 1Re-NiAl coating.IRe-NiAl coating had the lowest oxidation mass gain and ? phase degeneration rate after 200 h isothermal oxidation.When the content of Re was too high in 10Re-NiAl coating,on the contrary,the oxidation performance would be deteriorated.Moreover,Re-contained IDZ relieved the diffusion of Al and Nb.Electroplating Ni layer avoided the formation of W-rich phases in the outer layer after vacuum annealing,and the oxidation resistance of 0Re-NiAl coating therefore could be apparently improved comparing to A1 diffusion coating.(2)A pure Pt layer was deposited by electroplating method on the samples,followed by diffusion treatment to obtain Pt diffusion layer.RePt co-modified ?-NiAl coating,namely 1Re-(Ni,Pt)Al coating,was fabricated by composite electroplating Ni-1Re(wt.%)layer,AIP Al and subsequent diffusion treatment method on Pt diffusion layer,which was consisted of outer layer of ?-(Ni,Pt)Al with dispersed Re-rich phases,middle layer of ?-NiAl with submicron sized ?-W precipitates and IDZ.ORe-(Ni,Pt)Al coating was produced by electroplating pure Ni layer,AIP Al and subsequent diffusion treatment method on Pt diffusion layer,which included outer layer of ?-(Ni,Pt)Al,middle layer of ?-(Ni,Pt)Al with submicron sized ?-W precipitates and IDZ.PtAl diffusion coating was prepared by AIP Al and subsequent diffusion treatment method on Pt diffusion layer,which was composed outer layer of ?-(Ni,Pt)Al with submicron sized ?-W precipitates and IDZ.Results indicated that doping Re in the ?-(Ni,Pt)Al coating had advantageous effects on the morphologies,anti-spallation and rumpling behavior of TGO during oxidation.1Re-(Ni,Pt)Al coating possessed the lowest oxidation rate and level of ? to ?'phase transformation,which showed the best isothermal oxidation resistance among three coatings.Formation of NiAl2O4 spinel resulted in the weak oxidation performance of PtAl diffusion coating,and the existence of it was avoided by adding a pure Ni layer.Thus,the oxidation resistance of ORe-(Ni,Pt)Al coating could be significantly improved.(3)Two PtReY co-modified ?-NiAl coatings,namely 1Pt-NiAlReY coating and 2Pt-NiAlReY coating,were fabricated by electroplating pure Pt layer with different thickness,diffusion treatment,composite electroplating Ni-Re layer,AIP AlY and subsequent diffusion treatment method.OPt-NiAlReY coating was fabricated by composite electroplating Ni-Re layer,AIP AlY and subsequent diffusion treatment method.During isothermal and cyclic oxidation,adding Pt significantly reduced oxidation rate and enhanced the adhesion of oxide scale.Moreover,these effects were more obvious with the increase of Pt content in coating.The addition of Pt restrained the diffusion of Ti to oxide scale and formation or enlargement of voids in scale.Thus,it improved the oxidation resistance of 1Pt-NiAlReY coating and 2Pt-NiAlReY coating.Moreover,Pt,Re and Y revealed synergistic effect and jointly increased the oxidation properties during oxidation experiment.