Method for repairing coated components using NiAl bond coats

A method for restoring adjacent airfoil to airfoil throat distance of a coated high pressure turbine blade, which has been exposed to engine operation, to restore airfoil contour dimensions of the blade comprising the sequential steps of:

• a) providing an engine run high pressure turbine blade including a base metal substrate made of a nickel-based alloy having thereon a thermal barrier coating system, the thermal barrier coating system comprising a diffusion bond coat on the base metal substrate and a top ceramic thermal barrier coating comprising a yttria stabilized zirconia material, the top ceramic thermal barrier coating having a nominal thickness t;
• wherein the component including the bond coat thereon before engine operation has a weight, w0, and the component including the bond coat and the top thermal barrier coating thereon before engine operation has a weight, w1;
• b) removing completely the thermal barrier coating system, wherein a portion of the base metal substrate also is removed, and determining thickness of the base metal substrate removed, the portion of the base metal substrate removed having a thickness, Δt;
• wherein the component has a weight, w2, after removal of the thermal barrier coating and before removal of the bond coat;
• and the component has a weight, w3, after complete removal of the thermal barrier coating system;
• c) applying a β phase NiAl overlay coating to the substrate, and determining the difference in thickness, Δx, between the β phase NiAl overlay coating and the previously removed bond coat, wherein after application of the NiAl overlay coating the component is weighed, denoted by w4, to determine a weight margin remaining, wherein a combination of at least two of w0, w1, w2, w3 and w4 is employed to determine amount of removed base metal and calculate a thickness in which to apply a top ceramic thermal barrier coating without incurring a weight penalty;
• d) reapplying the top ceramic thermal barrier coating to a nominal thickness of t+Δt−Δx, wherein Δt compensates for the portion of base metal substrate removed in b) to restore adjacent airfoil to airfoil throat distance to about the distance preceding the engine run so that the coated airfoil contour dimensions of the coated blade are restored to about the coated dimensions preceding the engine run without a weight penalty, wherein the thermal barrier coating of d) is applied at a thickness greater than the thermal barrier coating of a);
• and weight of the component having the bond coat of c) and the thermal barrier coating of d) thereon is denoted by w5, wherein w5 is less than w1.

A method for restoring adjacent airfoil to airfoil throat distance of a coated component, which has been exposed to engine operation, to restore coated airfoil contour dimensions of the component consisting essentially of the sequential steps of:

• a) providing an engine run component including a base metal substrate made of a nickel-based alloy having thereon a thermal barrier coating system, the thermal barrier coating system comprising a diffusion bond coat on the base metal substrate and a top ceramic thermal barrier coating comprising a yttria stabilized zirconia material, the top ceramic thermal barrier coating having a nominal thickness t;
• wherein the component including the bond coat thereon before engine operation has a weight, w0, and the component including the bond coat and the top thermal barrier coating thereon before engine operation has a weight w1;
• b) inspecting the component;
• c) removing completely the thermal barrier coating system by stripping, wherein a portion of the base metal substrate also is removed, the portion of the base metal substrate removed having a thickness, Δt;
• wherein the component has a weight, w2, after removal of the thermal barrier coating and before removal of the bond coat;
• and the component has a weight, w3, after complete removal of the thermal barrier coating system;
• d) applying a β phase NiAl overlay coating to the substrate and determining the difference in thickness Δx between the β phase NiAl overlay coating and the previously removed bond coat;
• and weighing the component to calculate Δt;
• wherein after application of the NiAl overlay coating the component is weighed, denoted by w4, to determine a weight margin remaining, wherein a combination of at least two of w0, w1, w2, w3 and w4 is employed to determine amount of removed base metal and calculate a thickness in which to apply a top ceramic thermal barrier coating without incurring a weight penalty;
• e) reapplying the top ceramic thermal barrier coating to a nominal thickness of t+Δt−Δx, wherein Δt compensates for the portion of base metal substrate removed in c) to restore adjacent airfoil to airfoil throat distance to about the distance preceding the engine run so that the airfoil contour dimensions of the coated component are restored to about the coated dimensions preceding the engine run without a weight penalty, wherein the thermal barrier coating of d) is applied at a thickness greater than the thermal barrier coating of a);
• and weight of the component having the bond coat of c) and the thermal barrier coating of d) thereon is denoted by w5, wherein w5 is less than W1.