Titanium treatment to minimize fretting

Abstract

A method for surface treating a titanium gas turbine engine component. The method includes providing a gas turbine engine component having a titanium-containing surface. The component is heated to a temperature sufficient to diffuse carbon into the titanium and below 1,000° F. The surface is contacted with a carbon-containing gas to diffuse carbon into the surface to form carbides. Thereafter, the carbide-containing surface is coated with a lubricant comprising a binder and a friction modifier. The binder preferably including titanium oxide and the friction modifier preferably including tungsten disulfide. The coefficient of friction between the surface and another titanium-containing surface is less than about 0.6 in high altitude atmospheres.

Description

FIELD OF THE INVENTION [0001] The present invention is directed to a method for surface treating titanium and titanium alloys. In particular, the invention is drawn to surface treating gas turbine engine components. BACKGROUND OF THE INVENTION [0002] A gas turbine engine generally operates by pressurizing air in a compressor and mixing the air with fuel in a combustor. The air / fuel mixture is ignited and hot combustion gasses result, which flow downstream through a turbine section. The compressor typically includes compressor disks having airfoils dovetailed into the compressor disk. The compressor may include multiple disks, each having a plurality of airfoils. [0003] Each of the compressor disk and the airfoils typically contain titanium, usually in the form of a titanium alloy. The titanium-to-titanium surface contact is susceptible to fretting wear and fretting fatigue. Fretting is the degradation of the surface usually resulting from localized adhesion between the contacting su...

AI Technical Summary

Benefits of technology

[0009] In accordance with the present invention, a metallic surface comprising titanium is carburized, under controlled conditions, using carbon-containing gases, such as methane, propane, ethylene or acetylene gas or combinations thereof as the carburizing agent in order to form stable carbides and / or interstitial carbon at a controlled, preselected distance below the surface and / or diffuse the carbon interstitially in the titanium matrix. The carbides formed in the surface harden the surface, providing a reduced coefficient of friction, and reducing fretting.

[0013] One advantage of an embodiment according to the present invention is that the method according to the present invention decreases the susceptibility of the surface to fretting.

[0014] Another advantage of an embodiment of the present invention is that the method provides a hardened surface having carbides and / or interstitial carbon, which resist corrosion.

[0016] Another advantage of an embodiment of the present invention is that the carburization takes place at a low temperature, below 1,000° F. , which reduces the cost of equipment required to produce the carburized zone.

[0017] Another advantage of an embodiment of the present invention is that the surfaces subjected to fretting wear and fatigue may be replaced less often, decreasing servicing cost and reliability.

Problems solved by technology

The titanium-to-titanium surface contact is susceptible to fretting wear and fretting fatigue.

The problem of fretting is magnified in systems having a titanium-containing surface contacting another titanium-containing surface.

For example, in a titanium compressor disk and titanium airfoil system, the fretting fatigue may result from movement of the dovetail of the airfoil within the slot in the compressor disk.

A second source of movement resulting in fretting fatigue in the dovetail system is the vibration from the airfoil.

Aerodynamic forces may result in oscillation of the airfoil within the dovetail slot.

As the airfoil vibrates, the surface of the dovetail section of the airfoil slides against the surface of the slot of the compressor disk, resulting in fretting fatigue.

However, the shot-peening process requires expensive equipment, additional processing steps and may result in surfaces having variability in roughness and dimensional accuracy.

In addition, the shot-peened surface provides insufficient resistance to fretting fatigue and wear.

The application of lubricants such as MoS2 provides some protection from localized adhesion, but the lubricants alone, without additional coating layers, fail to provide sufficient resistance to fretting fatigue and wear.

High temperature carburization methods suffer from the drawback that the method requires expensive, specialized equipment, capable of operating under high temperatures.

High-temperature thermal treatments of blade dovetails and disks preclude use of conventional carburizing practices.

Images