The present invention relates to a titanium article having a protective coating and a method of applying a protective coating to a titanium article, particularly to a titanium aluminide article having a protective coating and a method of applying a protective coating to a titanium aluminide article.
Titanium aluminide alloys have potential for use in gas turbine engines, particularly for turbine blades and turbine vanes in the low pressure turbine and compressor blades and vanes in the high pressure compressor and the combustion chamber diffuser section. The gamma titanium aluminides provide a weight reduction compared to the alloys currently used for these purposes.
However, titanium aluminide alloys and gamma titanium aluminide alloys will require environmental protective coatings, above a certain temperature, in a similar manner to conventional nickel base alloys or cobalt base alloys.
Convention environmental protective coatings for nickel base alloys and cobalt base alloys include aluminide coatings, platinum coatings, chromium coatings, MCrAlY coatings, silicide coatings, platinum modified aluminide coatings, chromium modified aluminide coatings, platinum and chromium modified aluminide coatings, silicide modified aluminide coatings, platinum and silicide modified aluminide coatings and platinum, silicide and chromium modified aluminide coatings etc. Aluminide coatings are generally applied by the well known pack aluminising, out of pack, vapour, aluminising or slurry aluminising processes. Platinum coatings are generally applied by electroplating or sputtering. Chromium coatings are generally applied by pack chromising or vapour chromising. Silicide coatings are generally applied by slurry aluminising. MCrAlY coatings are generally applied by plasma spraying or electron beam physical vapour deposition.
Thermal barrier coatings include yttria stabilised zirconia and magnesia stabilised zirconia etc. Thermal barrier coatings are generally applied by plasma spraying or electron beam physical vapour deposition.
However, these conventional protective coatings are not as adherent to titanium aluminide alloys in particular, or titanium alloys in general, as they are to nickel base alloys or cobalt base alloys. This is due, we believe, to the titanium oxide formed on the titanium aluminide or titanium alloy.
Accordingly the present invention seeks to provide a novel protective coating for a titanium article and a novel method of applying a protective coating to a titanium article.
Accordingly the present invention provides a titanium alloy article having a protective coating on the titanium alloy article, the protective coating comprising a coating of silicate glass having a chromium oxide filler.
Preferably the protective coating comprises an oxide layer on the titanium alloy article and the coating of silicate glass having the chromium oxide filler on the oxide layer.
Preferably the titanium alloy article comprises a titanium aluminide, more preferably the titanium alloy article comprises a gamma titanium aluminide.
Preferably the oxide layer comprises titanium oxide.
Preferably the protective coating comprises a boron titanate silicate glass having a chromium oxide filler.
Preferably the titanium alloy article comprises a turbine blade, a turbine vane, a compressor blade, or a compressor vane.
The present invention also provides a method of applying a protective coating to a titanium alloy article comprising depositing a coating comprising a silicate glass having a chromium oxide filler.
Preferably the method comprises forming an oxide layer on the titanium alloy article and depositing the coating comprising silicate glass having a chromium oxide filler on the oxide layer.
Preferably the titanium alloy article comprises a titanium aluminide, more preferably the titanium alloy article comprises a gamma titanium aluminide.
Preferably the oxide layer comprises titanium oxide.
Preferably the protective coating comprises a boron titanate silicate glass having a chromium oxide filler.
Preferably the titanium alloy article comprises a turbine blade, a turbine vane, a compressor blade, or a compressor vane.
Preferably the method comprises depositing the boron titanate glass and chromium oxide filler by spraying with a binder.
Preferably the method comprises drying the protective coating, heating the protective coating at 100xc2x0 C. for 1 hour and heating the protective coating at 1030xc2x0 C. for 10 to 20 minutes to fuse the protective coating.