TWI Industrial Member Report Summary 673/1999
T J Mursell and A J Sturgeon
There is much interest in using thermal sprayed coatings as an alternative to electrolytic hard chromium plating (EHC). This is due to recent legislation introduced to minimise the toxic waste generated by the chromium plating process. Only limited replacement has occurred to date because of difficulty in matching the combination of hardness and corrosion properties obtained with EHC. Thermal sprayed cermets such as WC-Co or Cr3C2-NiCr tend to be too abrasive against the mating material and do not always provide sufficient corrosion resistance, whilst conventional metallic alloys have difficulty in matching the hardness of chromium plating.
Recent developments in the high velocity oxyfuel (HVOF) process enable metallic coatings to be deposited, with a thickness of 0.1-2mm, that have porosity below 1% and an oxide content below 2%. The process is also particularly suited to preparing amorphous or nano-crystalline microstructures.
There is, therefore, potential in using the HVOF process to deposit amorphous and nanocrystalline metallic coatings as a more suitable alternative to hard chromium plating. These coatings may provide a more acceptable match in terms of hardness, wear characteristics and corrosion resistance.
- To review the recent literature on amorphous and nanocrystalline coatings deposited using advanced thermal spray processes, in particular the HVOF process.