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A gas turbine rotor blade and rotor disk arrangement is provided. The rotor blade and the rotor disk includes a coating in order to seal the gap which normally exists between the bottom part of the blade root and the bottom part of the disk slot. The coating may be applied to the blade root or to th

A gas turbine rotor blade and rotor disk arrangement is provided. The rotor blade and the rotor disk includes a coating in order to seal the gap which normally exists between the bottom part of the blade root and the bottom part of the disk slot. The coating may be applied to the blade root or to the disk itself on the bottom part of the disk slot. The coating is preferably an abradable nickel-alloy Bentonite coating. The coating may also be applied to only a portion of the areas being sealed, omitting a portion at the start of the slot or at the start of one of the lobes of the blade root, so that a lead-in is formed, whereby the blade can more easily be inserted into the slot.

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1. A rotor blade and a rotor disk for a gas-turbine engine, the rotor blade comprising: an aerofoil portion; anda root portion, the rotor disk, comprising: a slot in which the root portion is secured,wherein the root portion includes a first pair of side portions, the first pair of side portions mat

1. A rotor blade and a rotor disk for a gas-turbine engine, the rotor blade comprising: an aerofoil portion; anda root portion, the rotor disk, comprising: a slot in which the root portion is secured,wherein the root portion includes a first pair of side portions, the first pair of side portions mate with a corresponding second pair of side portions of the rotor-disk slot,wherein a first bottom portion connects the first pair of side portions,wherein a coating seals a gap between the first bottom portion and a second bottom portion of the slot,wherein the coating is on the first bottom portion and/or on the second bottom portion,wherein the rotor blade is a turbine blade driven by a working fluid, andwherein the aerofoil portion of the rotor blade includes a cooling duct for receiving a cooling fluid,wherein the first bottom portion comprises a lobe portion, andwherein the coating is on the lobe portion or on a part of the second bottom portion which lies opposite the lobe portion,wherein the first bottom portion comprises a first lobe portion and a second lobe portion, andwherein the coating is on one of the first or second lobe portions only and only on a part which is disposed closer to the other of the first or second lobe portions, or the coating is on the second bottom portion such that the coating lies opposite only the part of one of the first or second lobe portions which is disposed closer to the other of the first or second lobe portions. 2. The rotor blade and the rotor disk as claimed in claim 1, wherein the coating has a maximum thickness over its area of between 0.5 mm and 0.7 mm. 3. The rotor blade and the rotor disk as claimed in claim 1, wherein the coating is a porous metal coating. 4. The rotor blade and the rotor disk as claimed in claim 3, wherein the coating is applied by spraying on a plurality of layers of the porous metal coating, which is then compressed and shaved off during an assembly of the rotor blade in the slot. 5. The rotor blade and the rotor disk as claimed in claim 3, wherein the coating comprises nickel. 6. The rotor blade and the rotor disk as claimed in claim 3, wherein the coating comprises a nickel alloy. 7. The rotor blade and the rotor disk as claimed in claim 1, wherein the coating comprises a matrix material with an additive. 8. The rotor blade and the rotor disk as claimed in claim 7, wherein the coating is selected from the group consisting of commercially pure aluminium, an aluminium-silicon alloy, an aluminium quasicrystal alloy, a nickel graphite composite, a nickel-aluminium alloy and composite, a silicon-aluminum graphite composite, a silicon-aluminum+polyester blend, a silicon-aluminum+polyimide blend, a nickel-chrome+polyester blend, a nickel-chrome+polyurethane blend, a nickel-chrome+bentonite blend, a nickel-chrome-aluminum/bentonite blend, a nickel-chrome+boron nitride blend, a nickel-chrome+hollow spheres blend, a nickel-chrome-iron+boron nitride blend, an MCrAlY alloy, an exothermic MCrAlY alloy, and an yttria-zirconia+polyester blend. 9. The rotor blade and the rotor disk as claimed in claim 8, further comprising an MCrAlY bond coat between the rotor blade and/or rotor disk substrate and the coating. 10. The rotor blade and the rotor disk as claimed in claim 8, wherein the coating comprises a Ni4Cr4Al21 layer on a calcined Bentonite core. 11. The rotor blade and the rotor disk as claimed in claim 10, further comprising an MCrAlY bond coat between the rotor blade and/or rotor disk substrate and the coating. 12. The rotor blade and the rotor disk as claimed in claim 1, further comprising an MCrAlY bond coat between the rotor blade and/or rotor disk substrate and the coating. 13. The rotor blade and the rotor disk as claimed in claim 1, wherein the additive is selected from a group consisting of polymers, graphite, bentonite and boron nitride. 14. The rotor blade and the rotor disk as claimed in claim 13, further comprising an MCrAlY bond coat between the rotor blade and/or rotor disk substrate and the coating.