Start date and planned duration: January 2019, 36 months
- Investigate the use of continuous wave lasers to improve cold spray deposition using localised heating.
- Investigate the use of short pulsed lasers as a method to improve cold spray deposition for titanium and/or nickel alloys.
During cold spray, high velocity powder particles impact a substrate and undergo rapid plastic deformation. Above a critical velocity, an adiabatic shear instability forms and results in viscous flow of material outward. Material jetting occurs which helps to clear oxide layers, promoting intimate metallic contact between powder particle and substrate and forming a bond in a mechanism similar to explosion welding. The deformation behaviour of both substrate and powder as well as the breakup of the oxide layers is recognised as the key determinant of how well material can be deposited using cold spray.
Much of the cold spray community has focussed research efforts on attempting to optimise deposition parameters to increase deposit performance. However some limited studies have shown that combining cold spray with laser processing techniques can enhance both deposition behaviour and mechanical integrity of the coating.
In-line laser heating has been used to create transient regions of substrate heating ahead of the powder beam. Such effects have been used to soften the substrate and enable greater bonding with incoming powder particles. Optimum shear localisation (and hence bonding) occurs when both the impacting powder and substrate co-deform approximately equally. Tailoring laser parameters to provide local heating improves co-deformation and result in enhanced deposit properties. If the heating input can be controlled carefully, minimal microstructural changes occur in the substrate microstructure and parent properties can be maintained, while providing enhanced deposit characteristics.
TWI has investigated the potential of this technology in a number of projects. The aim of this CRP project is to produce a step-change in the quality of deposits by investigating two new approaches:
- Use of a high power laser to provide local heating, in order to minimise the region of substrate material affected and reduce both microstructural changes and potential distortion.
- Use of a short pulsed laser to ablate a small amount of material ahead of impinging cold spray particles. Removal of oxide layers in the substrate material prior to particle impact is expected to improve the metallurgical bond and lead to enhanced properties in the deposit.
Benefits to Industry
Laser assisted cold spray will open up many opportunities in the deposition of traditionally ‘difficult to spray’ alloys. Industry will from being able to develop repair procedures for components that would traditionally not have been possible to repair. The capability to trial specific applications will be available to industry via expertise and equipment at TWI.
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