Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-09-29
2001-01-23
Diamond, Alan (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192120, C204S192160, C204S192320, C204S192350, C204S298060, C204S298120, C204S298130, C204S298310, C204S298340, C204S192220, C204S298350, C204S298230, C204S298240, C204S298250, C204S298260, C204S298210, C204S298070
Reexamination Certificate
active
06176982
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a method of applying a coating to a metallic article, particularly to a method of applying an environmental protective coating and/or a thermal barrier coating to a metallic article.
2. Description of Related Art
Environmental protective coatings include aluminide platinum coatings, chromium coatings, MCrAlY coatings (where M is one or more of Fe, Ni and Co), 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.
SUMMARY OF THE INVENTION
Accordingly the present invention seeks to provide a novel method of applying a coating to a metallic article.
Accordingly the present invention provides a method of applying a coating to a metallic article comprising providing a sputtering chamber having a first hollow cathode, the first hollow cathode comprising a material to form a protective coating, placing the metallic article within the first hollow cathode, evacuating the sputtering chamber, applying a negative voltage to the first hollow cathode to produce a plasma and such that the material of the hollow cathode is sputtered onto the metallic article to produce the protective coating, applying a positive voltage to the metallic article to attract electrons from the plasma to heat the protective coating and so inter-diffuse the elements of the metallic article and the protective coating, and applying a negative voltage to the metallic article to attract ions from the plasma to bombard the protective coating to minimise defects in the protective coating.
The hollow cathode material may comprise aluminium, platinum, yttrium, chromium, MCrAlY or an alloy mixture of any two or more of aluminium, platinum, yttrium, chromium or MCrAlY.
The hollow cathode may comprise a plurality of longitudinally arranged portions, the portions comprise different materials, passing the metallic article sequentially through the hollow cathode portions to deposit layers of different material sequentially on the metallic article.
The different materials may comprise two or more of aluminium, platinum, yttrium, chromium and MCrAlY.
The method may comprise the additional step of supplying at least one gas into the sputtering chamber and applying a negative voltage to the metallic article to produce a plasma to clean the surface of the metallic article before depositing the protective coating.
Preferably the method comprises alternately applying the positive voltage and the negative voltage to the metallic article.
The method may comprise selecting the magnitude and the duration of the positive voltage applied to the metallic article so that the elements from the protective coating diffuse into the metallic article.
Alternatively the method may comprise selecting the magnitude and the duration of the positive voltage applied to the metallic article so that the elements from the metallic article diffuse into the protective coating.
The method may comprise supplying a reactive gas into the sputtering chamber to form a dispersion strengthened protective coating.
Preferably the hollow cathode may comprise one or more projections extending from the hollow cathode towards the metallic article.
Preferably the length of the individual projections and/or the spacing between the projections is selected to produce variations in the thickness of the protective coating at predetermined regions on the metallic article.
Some of the projections may be formed from different materials to the remaining projections to produce variations in the composition of the protective coating at a predetermined region on the metallic article.
A transverse portion of the hollow cathode may be formed from different materials to the remainder of the hollow cathode to produce a variation in the composition of the protective coating at a predetermined region on the metallic article.
Preferably the method comprises the additional steps of providing a sputtering chamber having a second hollow cathode, the second hollow cathode comprising an inert material, supplying precursor gases into the sputtering chamber, the precursor gases being suitable for forming a thermal barrier coating, applying a negative voltage to the hollow cathode to produce a plasma so that the precursor gases react in the plasma and deposit a thermal barrier coating on the protective coating.
Preferably the method additionally comprises supplying at least one gas into the sputtering chamber and applying a negative voltage to the metallic article to produce a plasma to clean the surface of the protective coating before depositing the thermal barrier coating.
Preferably the reactive gases comprise zirconium chloride and yttrium chloride to deposit a yttria stabilised zirconia thermal barrier coating on the protective coating.
Preferably the metallic article comprises a nickel superalloy, a cobalt superalloy or an iron superalloy.
Preferably the metallic article comprises a turbine blade or a turbine vane.
A further method of applying a coating to a metallic article according to the present invention comprises the steps of providing a sputtering chamber having a hollow cathode, the hollow cathode comprising an inert material, supplying precursor gases into the sputtering chamber, the precursor gases being suitable for forming a thermal barrier coating, applying a negative voltage to the hollow cathode to produce a plasma so that the precursor gases react in the plasma and deposit a thermal barrier coating on the metallic article.
Preferably the method additionally comprises supplying at least one gas into the sputtering chamber and applying a negative voltage to the metallic article to produce a plasma to clean the surface of the metallic article before depositing the thermal barrier coating.
Preferably the reactive gases comprise zirconium chloride and yttrium chloride to deposit a yttria stabilised zirconia thermal barrier coating on the metallic article.
Preferably the method comprises applying different negative voltages to the hollow cathode to produce layers in the thermal barrier coating which have different structures.
Preferably the metallic article comprises a nickel superalloy, a cobalt superalloy or an iron superalloy.
Preferably the metallic article comprises a turbine blade or a turbine vane.
Preferably the method comprises depositing a bond coating on the metallic article before depositing the thermal barrier coating.
The present invention also seeks to provide a novel apparatus for applying a coating to a metallic article.
Accordingly the present invention provides an apparatus for applying a coating to a metallic article comprising a sputtering chamber having a first hollow cathode, the first hollow cathode comprising a material to form a protective coating, means to evacuate the sputtering chamber, means to apply a negative voltage to the first hollow cathode to produce a plasma and such that the material of the hollow cathode is sputtered onto the metallic article to produce the protective coating, means to apply a positive voltage to the metallic article to attract electrons from the plasma to heat the protective coating and so inter-diffuse the elements of the metallic article and
Diamond Alan
Oliff & Berridg,e PLC
Rolls-Royce plc.
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