In good repair

Extracting maximum service life and value from intricately machined aircraft components such as turbine blades is a key consideration, given aircraft operators' need to minimise ongoing operating and replacement costs.
This is vital given that turbines have to operate at increasingly high temperatures to optimise thrust and fuel efficiency, meaning that ever more sophisticated and expensive alloys and processes are now used in turbine blade manufacture.

As a result, turbine blades and other jet engine components can be costly to replace. One way of managing these costs is to repair a component, rather than replace it, as the engine is serviced. If a repair can be made to enable continued use of the vanes at a fraction of the replacement cost, significant savings can be realised.
Various OEM or Federal Aviation Administration approved methods exist for the restoration repair of rotating and non-rotating components, where the lifecycle of the component allows.

Long-established repair techniques include brazing paste and/or TIG welding. However, these methods deliver less than satisfactory results when applied to later generation alloys. Furthermore, TIG welding, and more recently, laser welding create a heat-affected zone as a result of the rapid heating and cooling of the weld.

In these instances, post-weld heat treatment (PWHT) is required to eliminate deleterious microstructure and restore specified distributions of the Gamma-prime precipitate phase which is fundamental to the strength at extreme temperatures of modern alloys. Where welding may cause hot cracks or changes to the size and distribution of precipitates in the microstructure that cannot be restored, it cannot be undertaken. Furthermore, PWHT adds post-processing steps that translate to time and cost. Pastes are also subject to porosity or irregular build-up, either of which can lead to rework or added machine time to re-establish the OEM profile.

Other repair options include the use of paints, tapes, and plasma, but all of these methods are prone to issues such as limitation on applied thickness, dimensional control (in the case of tapes) and porosity.

A repair method that eliminates problems associated with porosity, shrinkage, and the effects of welding is the use of pre-sintered preform (PSP) braze alloys. PSPs are sintered powder metallurgy products composed of a homogeneous mixture of a superalloy base material and braze alloy powders. The method is versatile and alloys customised to the base alloy are feasible. Reduced operator skill is needed as custom preforms cut from sintered plate are tack welded to the component and then brazed onto the component under vacuum. Batch processing provides both economy of scale and uniform quality in the braze and microstructure. Distortion is also minimised through controlled heating and cooling as the whole component is subjected to the same thermal cycle. The process allows selective build-up of worn surfaces to be achieved quickly and efficiently, offering both time and cost savings. Unlike pastes and tapes, a PSP repaired component requires minimal post-braze grinding or machining to restore it to its original dimensions.

PSP shapes are available in a flat plate, cut preforms, tapered and curved preforms and made to order three-dimensional bushings, which are ideal for the restoration of worn holes and bores. Curved preforms can also eliminate the need for a second braze cycle on both convex and concave surfaces, reducing processing time.
It's these attributes which are seeing the use of PSPs increasing across a variety of both civil and military applications where the investment made in the production of a component means that disposal and manufacturing of a new product is not an attractive option. Morgan continues to invest to deliver new innovations in this area to reduce cost, improve performance and extend life.

www.morganadvancedmaterials.com