COLD SPRAY: FUNDAMENTAL STUDIES

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Cold spray is a deceptively simple concept, in which plastically deformable powders are formed into components by 'merely' impacting on to a substrate at supersonic velocities at temperatures far from the powder melting point. The 'cold' part is particularly beguiling because it opens the way for making fascinating materials which otherwise could not be processed, e.g. materials which have very different melting points. It is a technology of particular interest to the aerospace industry as a means to manufacture and repair components. This project seeks to improve the fundamental understanding of the process, with a view to: (i) Understanding the process: Although much is known, many aspects of the metallurgy of particle bonding need to be explored more thoroughly. As well, there are many process variables connected with cold spray, but some of the more critical parameters cannot be measures during cold spray, these being powder velocity, delivery rates and temperature during cold spray. The consequences of possible variations in these parameters needs to be explored by experimentation and process modelling. Validation of the process model will be achieved with the help of a cold spray 'simulator' based on the Hopkinson bar approach. In this way, known values of 'velocity' and temperature can be physically simulated and the results can be used to help validate the model. (ii) investigating the effect of post processing thermomechanical treatments: post processing is necessary to reduce the work hardening and the porosity, as well as increase particle/particle bonding. The mechanisms controlling these will be explored in order to optimise thermomechanical treatments. (iii) exploring cold spraying of metal-metal composites: cold spraying mixtures of different metal powders could improve 'cold sprayability', create novel materials, aid post processing and bring more insight into the mechanisms of cold spraying. Mixtures of powders with different hardnesses and plastic flow properties will be initially examined, since preliminary work has revealed some promising results and interesting phenomena.