Investigation On The Hot Corrosion Resistance Of Four Ni-based Superalloys

Gas turbine engine as a power plant has been widely used in the aviation field. With the development of aviation industry, the demands for the perproties of gas turbine blade have recently increased significantly. Hot corrosion in gas turbine engine in the coastal environment speeds up the failure of turbine blade due to the combined effects of fuel combustion formed Na₂SO₄ and NaCl in the ocean atmosphere Therefore, to develop a kind of blade material with high strength and good hot corrosion resistance is the demand of Aviation industry development. In order to meet the demand of aircraft engine turbine blade working along the coast, DZ68 nickel-based superalloy is developed by a new type of directional solidification.In this paper, hot corrosion behavior of four kinds of alloys, DZ68, K438, DZ125L and DZ142, is investigated. As for K438, DZ125L and DZ142, K438 with the best integrated performance is a wildly domesticly applied hot-corrision resistance superalloy; DZ125L is one of the directional solidification superalloys with the best mechanical properties in the present; DZ142 is the second generation of directional solidification nickel-based superalloy with good oxidation-resisted property.Four kinds of superalloys at the condition of 900℃and (wt75%)Na₂SO₄+(wt25%) NaCl coated salt have been analyzed by Optical Microscope, X-ray Diffraction, Scanning Electronic Microscope, Energy Dispersive X-ray analysis, Electron Probe Microanalysis. The hot-corrosion performances of these four superalloys have been investigated by the alloy composition, heat treatment structure, hot-corrosion dynamics; the products of corrosion layer and elements distribution, meanwhile, the corrosion basis mechanism of four superalloys have been discussed in this paper.Result shows that the four superalloys all represent Type I basic dissolution model at the condition of 900℃and (wt75%)Na₂SO₄+(wt25%)NaCl coated salt. As for K438 alloy, the corrosion is uneven. In the initial stage, the selective corrosion brings about and most of outcomes in the outer corrosion layer are Cr₂O₃ andα-Al₂O₃. However in the last stage, the outcomes are mainly composed by NiO. Except some parts of DZ125L where shows the selective corrosion, the rests present even corrosion and the outcomes in the outer corrosion layer mainly are NiO in the whole corrosion process. With the phenomenon of selective corrosion, the corrosion in DZ142 is uneven and most outcomes are NiO in the whole corrosion process. When it comes to DZ68 alloy, the hot corrosion is even and the corrosion front goes ahead as a plane into the substrate of alloy, the outcomes in the outer corrosion layer are mainly composed by NiO, Cr₂O₃ and (Ni,Co)Cr₂O₄ in the initial stage whereas composed by (Ni,Co)Cr₂O₄ in the last stage. The kinds of products are similar in the inner corrosion layer of the four alloys which are mainly composed by black Al₂O₃ and grey CrS. CrS distributes in the hot corrosion front near the substrate of alloy and Al₂O₃ distributes on the outer side of the inner corrosion layer. In this experimental condition, DZ142 and DZ125L alloys perform bad hot-corrosion resistance whereas K438 and DZ68 perform good hot-corrosion resistance relatively, as for the later two, the hot-corrosion resistance of DZ68 alloy seems a little better than that of K438.