- Text Size:
The Laser User Magazine
Issue 053 - Winter 2008
The laser-assisted cold spray process
Author: Andrew Cockburn, Matthew Bray and Bill O'Neill
Thick metal coatings are currently deposited via two well established process routes, Laser or arc based cladding, and thermal spray. A new coating technique known as Laser-assisted Cold Spray (LCS), which aims to expand on the capabilities of the two process routes currently available, is under development at the University of Cambridge in the UK. LCS is a development of the Cold Spray process (CS) in which coatings are built up from powder particles which are entrained within a gas stream and accelerated through a de Laval nozzle, impacting the substrate at supersonic speeds that exceed a material dependent critical velocity.
Above their critical velocity, metal particles undergo significant deformation on impact and bond to the substrate to form a coating. CS offers high build rates, a lack of thermally induced stresses, low oxide contents and the ability to deposit sensitive materials without the use of inert atmospheres; however, there are inherent problems associated with the ‘cold’ mechanism of deposition, which relies on a gas stream accelerating powder particles to speeds approaching 1000 ms-1. Achieving such velocities requires a large consumption of hot gas (typically nitrogen or helium) leading to high operating costs arising from the high power consumption for heating the gas and (for helium) the high price of the gas itself. Additionally, processing hard materials such as titanium alloys often results in, poor bond strengths and low coating density.