Turbine blade tip with optimized abrasive

Abstract

A new abrasive blade tip treatment is disclosed with the potential to provide improved blade tip clearance control in the turbine section of modern industrial gas turbines (IGT's). This blade tip treatment is composed of a unique combination of abrasive compounds that result in improved resistance to thermal degradation while retaining desirable initial cutting capacity.

Description

FIELD OF THE INVENTION [0001] This invention is directed generally to coatings for turbine blades, and more particularly to turbine blade tip coatings for tip clearance control. BACKGROUND OF THE INVENTION [0002] Typically, gas turbine engines are formed from a combustor positioned upstream from a turbine blade assembly. The turbine blade assembly is formed from a plurality of turbine blade stages coupled to discs that are capable of rotating about a longitudinal axis. Each turbine blade stage is formed from a plurality of blades extending radially about the circumference of the disc. Each stage is spaced apart from each other a sufficient distance to allow turbine vanes to be positioned between each stage. The turbine vanes are typically coupled to the shroud and remain stationary during operation of the turbine engine. [0003] The tips of the turbine blades are located in close proximity to an inner surface defined by ring segments. There typically exists a gap between each of the ...

AI Technical Summary

Benefits of technology

[0007] It is an object of the invention to provide improved blade tip clearance control, and thus increased engine efficiency, by maintaining abrasion characteristics of an abrasive tipped blade while providing resistance to thermal degradation of the abrasive. It is another object of the invention to provide an abrasive blade tip coating that increases the effective lifetime of abrasive blades in the engine. It is a further object of the invention to reduced the risk of blade tip wear due to rubbing.

[0009] The abrasives can be placed, such as by electroplating or other deposition technique, on the blade tip and be included in a super alloy matrix that is preferably nickel and / or cobalt-based. The super alloy can be CoNiCrAlY and may have other added elements for enhanced oxidation life.

Problems solved by technology

However, operational experience has shown that the abradability of this blade tip clearance control system is insufficient.

While cBN abrasives exhibit excellent cutting ability when new, thermal decomposition of the cBN particles in an elevated temperature oxidizing environment produces effectively bare blade tips, which have been shown to have very limited cutting ability and which result in unacceptable blade tip wear.

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