Method for forming a wear-resistant hard-face contact area on a workpiece, such as a gas turbine engine part

Abstract

A method for forming a wear-resistant hardfaced contact area on the shroud section of a gas turbine engine blade. A predetermined contact area of a shroud section of a gas turbine engine blade is selectively coated with a high-density hardface coating material. The hardface coating material is capable of forming a diffusion boundary between the hardface coating material and the shroud section. A hot isostatic heat treatment process is performed to form the diffusion boundary between the hardface coating material and the shroud section to form a wear-resistant hardfaced contact area diffusion bonded to the shroud section. Depending on the coating process, and the necessity for doing so, the predetermined contact area can be masked off before the step of selectively coating. A sintering heat treatment can be perfomed before the step of performing the hot isostatic heat treatment to limit the occurrence bubbles on the surface of the hardface coating material after the isostatic heat treatment step. The sintering heat treatment may be performed at a temperature substantially the same as the temperature of the hot isostatic heat treatment. The hardface coating material may comprise an alloy with substantially no oxide forming constituents so as to avoid the formation of oxide inclusions in the coating material.

Description

BACKGROUND OF THE INVENTION [0001] The present invention pertains to methods for salvaging cast articles, such as turbine engine airfoil parts. More particularly, the present invention pertains to a method for correcting the dimensional characteristics of a cast article; a method for applying a protective coating to a metal article; and a method for repairing a turbine engine airfoil part. [0002] Airfoil parts, such as blades and vanes, are critical components in the gas turbine engines that are used to power jet aircraft or for the generation of electricity. Each airfoil part is an individual unit having a root or attachment section and an airfoil section. The airfoil section has specific cordal and length dimensions that define the airfoil characteristics of the part. The root section is engaged with and held by a housing member. A plurality of the airfoil parts are thus assembled with the housing member to form a disc or ring. Blades, which during operation are rotating part, are...

AI Technical Summary

Benefits of technology

[0051] Depending on the type of casting defect, material in an area of the casting defect may be removed before the step of coating the article. For example, if the casting defect is an inclusion of an undesired composition, such as an oxide or dirt particle, the inclusion and some of the base article material can be removed by a machining or other operation. The area of the casting defect is enlarged, and may be contoured to create a better surface for holding the coating material. The casting defect may be caused, for example, by at least one of an inclusion at a surface of the article, an air bubble at the surface of the article, undercasting, a void and shrinkage. A sintering heat treatment can be performed before the step of performing the hot isostatic heat treatment to limit the occurrence of bubbles on the surface of the coating material after an isostatic heat treatment. The sintering heat treatment may be performed at a temperature substantially the same as the temperature of the hot isostatic heat treatment.

[0071] Depending on the coating process, and the necessity for doing so, the predetermined contact area can be masked off before the step of selectively coating. A sintering heat treatment can be perfomed before the step of performing the hot isostatic heat treatment to limit the occurrence of bubbles on the surface of the hardface coating material after the isostatic heat treatment step. The sintering heat treatment may be performed at a temperature substantially the same as the temperature of the hot isostatic heat treatment. The hardface coating material may comprise an alloy with substantially no oxide forming constituents so as to avoid the formation of oxide inclusions in the coating material.

Problems solved by technology

These deforming stresses cause creep rupture and fatigue problems that can result in the failure of the part.

However, like the rotating parts, these parts are subjected to other deformation such as from hot gas erosion and / or foreign particle strikes.

This deformation results in the alteration of the dimensions of the airfoil section.

The alteration of the dimensions of the airfoil section can detrimentally modify the airflow through the gas turbine engine which is critical to the engine's performance.

The repair operations that remove metal by chemical stripping, grit blasting, blending and polishing shorten the life cycle of the vane.

When certain minimum airfoil dimensions cannot be met the part is deemed non-repairable and must be retired from service.

During use, the coating at the cutting surface of the cutting tool is subjected to shearing forces resulting in flaking off the coating of the tool substrate.

The failure is likely to occur at the narrow bonding interface.

Since the coating adheres to the tool bit substrate mostly via a mechanical bond located at a boundary interface, flaking and chipping off the coating of the substrate is likely to occur during use, limiting the service life of the tool bit. FIG. 12(b) is a side view of a prior art tool bit having a fixed wear resistant cutting tip.

During extended use the tool bit is likely to fail at the relatively brittle brazed interface between the metal cutting tip and the tool substrate, and again, the useful service life of the tool bit is limited.

A cast metal component will typically have a number of imperfections caused by voids and contaminants in the cast surface structure.

The manufacture of metal components often entails costly operations to produce products with the desired surface texture, material properties and dimensional tolerances.

Metal alloy components, such as gas turbine parts such as blades and vanes, are often damaged during use.

During operation, gas turbine parts are subjected to considerable degradation from high pressure and centrifugal force in a hot corrosive atmosphere.

The gas turbine parts also sustain considerable damage due to impacts from foreign particles.

This degradation results in a limited service life for these parts.

Since they are costly to produce, various repair methods are employed to refurbish damaged gas turbine blades and vanes.

Even after sintering the coating remains attached to the substrate and weld material only by mechanical bond at an interface bonding layer making the finished piece prone to chipping and flaking.

The porosity of the coating, and the interface bonding layer, results in a structure that is prone to chipping and flaking.

Again, the conventional low-pressure plasma spray process forms a mechanical bond at an interface boundary between the coating and the substrate, resulting in a structure that is prone to failure due to chipping and flaking.

However, the root section of the blade is exposed to stress of a type different than the airfoil section, usually referred to as low cycle fatigue.

Also, the root section is subjected to metal to metal stress during rotation resulting in low cycle fatigue cracking.

None of these prior attempts provide for the effective and efficient restoration of the critical airfoil dimensions of a gas turbine engine airfoil part.

The stripping of the protective coating on the part during the repair process is a major contributing factor resulting in the discarding of the part.

Excessive wear in the area of the contact surfaces 44 can have detrimental consequences on the operation of the gas turbine engine, and thus is an area of concern.

Excessive wear in the area of the contact surfaces 44 caused by chipping and flaking can have detrimental consequences on the operation of the gas turbine engine.

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