Powder metal rotating components for turbine engines and process therefor

Abstract

A process for producing turbine rotors and other large rotating components of power-generating gas turbine engines using powder metallurgy techniques. The process involves forming a powder of a gamma prime or gamma double prime precipitation-strengthened nickel-based superalloy whose particles are about 0.100 mm in diameter or smaller. The powder is placed in a can and consolidated to produce an essentially fully dense consolidation, which is then hot worked to produce a billet of a size sufficient to form a forging of at least 2300 kg. The billet is forged at a temperature and strain rate to produce a forging with a uniform fine grain of ASTM 10 or finer. Thereafter, the forging may undergo a heat treatment to achieve a desired balance of mechanical properties while retaining a uniform grain size of ASTM 10 or finer.

Description

BACKGROUND OF THE INVENTION [0001] This invention relates to processes for producing large forgings using metal powders as the starting material. More particularly, this invention is directed to a process for producing turbine rotors and other large rotating components of turbine engines using powder metallurgy techniques. [0002] Rotor components for certain advanced land-based gas turbine engines used in the power-generating industry, such as the H and FB class gas turbines of the assignee of this invention, are currently formed from gamma double-prime (γ″) precipitation-strengthened nickel-based superalloys, such as Alloy 718 and Alloy 706. For example, wheels and spacers have been formed from triple-melted (vacuum induction melting (VIM) / electroslag remelting (ESR) / vacuum arc remelting (VAR)) ingots with diameters of about 27 to 36 inches (about 70 to about 90 cm), which are then billetized and forged. Due to potential chemical or microstructural segregation and anticipated hot w...

AI Technical Summary

Benefits of technology

[0005] The present invention provides a process for producing turbine rotors and other large rotating components of power-generating gas turbine engines using powder metallurgy techniques. The method significantly reduces the ratio of input weight to final forging weight by eliminating yield losses during conversion from large grained ingot to a fine grained forging. The method also virtually eliminates chemical and microstructural segregation, and results in a fine, uniform grain size (ASTM 10 or finer) that advantageously reduces the required sonic shape envelope and therefore further reduces the finish forging weight. Additionally, the use of fine grain PM billet has the capability of reducing the press forces required to produce finish forgings, thereby reducing capital equipment cost and expanding the potential supplier base.

[0007] As a result of the above process, very large rotor components that were previously limited to processing by conventional cast and wrought techniques may now be formed by powder metallurgy techniques with reduced material losses, as well as microstructural, compositional, and mechanical property advantages that can be achieved with powder metallurgy processes.

Problems solved by technology

In addition to these substantial material losses, the best current processing practices typically result in nonuniform and relatively coarse-grained microstructures in the billet (e.g., ASTM 00 or larger) and the finish forgings (e.g., ASTM 8.0 or larger) (reference throughout to ASTM grain sizes is in accordance with the standard scale established by the American Society for Testing and Materials).

The billet grain size is too large to permit any adequate ultrasonic inspection to identify potential life limiting defects and is consequently not performed on currently used billet.

While powder metal nickel-based superalloys have been processed for use in aircraft engine turbine rotor forgings, whose forgings are typically less than 2000 pounds (about 900 kg), powder metal techniques have not been used to produce the significantly larger forgings required by gas turbines used in the power-generating industry, which can weigh in excess of 5000 pounds (about 2300 kg).

However, as more complex alloys such as Alloy 718 and beyond become preferred and the size of forgings continues to increase, the concerns of chemical and microstructure segregation, high material losses associated with converting large grained ingots to finish forgings, and limited industry capacity to process large, high strength forgings make the higher base cost PM alloys potentially more cost effective.