• Image

Maintenance and repair of heavy alloy components

Making high quality, fit-for-purpose repairs of Ti components using existing fusion-based methods (thermal spray, laser-DMD), continues to present a major challenge, as problems including oxidation, hot cracking, distortion, and loss of properties can be introduced. Solid state processes can overcome these difficulties.

One such process showing promise is cold spray, but to date these necessary repairs cannot be carried out either cost effectively enough, or to a high enough fitness for purpose.

Due to the hexagonal closed packed (hcp) structure, plastic deformation of Titanium (Ti) is limited and shaping processes like rolling (760-815°C) and forging (815-900°C) have either to be performed at sufficiently high temperatures nor request subsequent annealing steps in inert environments.

Therefore, less costly routes for processing more complex shapes are demanded by industries.

Cold spraying is a promising technique to produce near net shape parts. Due to the comparatively low process temperatures and short processing times, contamination by interstitial impurities like oxygen or nitrogen is avoided. Several attempts have been made to produce Ti coatings or freestanding parts by cold spraying. Due to the limited deformability of Ti, it was necessary to use costly helium in order to obtain sufficiently high impact velocities and plastic deformation.

With recent developments in cold spraying much harsher particle impact conditions can be accessed. Potentially, cold spraying using nitrogen can be tailored to manufacture titanium coatings with mechanical properties close to bulk material.