Hi Nigel
to the Surface Engineering Forum.
I can't help with facts and figures for recent times. I think manufacturers/suppliers of equipment/consumables and coating materials would be best positioned to have this information.
Sub-sector sizes I think would be best divided by type of industry ie aerospace,oil and gas, paper, printing, textiles, anti-corrosion, automotive etc... Though some may predominantly use a particular process like HVOF or arc spray etc.. many will use more than one. It would be interesting though, to know which process is now used the most, which are in decline and whether the newer technology which no doubt will show a higher growth rate is finding new applications and markets as a posed to stealing work from the older established processes.