Post Treatment of Cold Sprayed Metallic Ti/Al to Achieve Thick Ti2AlN Coating

This investigation introduces a way of processing the cold sprayed Ti/Al to produce titanium aluminium nitride coating. This coating is to be applied as a durable protective coating on tools used in molten aluminium alloys. Ti/Al in a weight ratio of 70/30 was cold sprayed onto a specially prepared substrate using nitrogen as process and powder feeding gas. It was then alloyed in 600°C, 670°C and 900°C for 3 hours respectively so as to achieve stabilized TiAl intermetallic phase for further nitriding treatment. The nitriding was carried out in an ammonia/nitrogen atmosphere in the fluidised bed furnace for 5 hours at 900°C. The coating was fully converted to Ti₂AlN and had a web shape structure.  The nitrided layer was only limited by the thickness of the cold sprayed Ti/Al coating. Ti₂AlN coating is resistant to molten aluminium attack and can be applied to the tools used in handling molten aluminium alloys. It is well known that molten aluminium is very aggressive and addition of alloying elements such as magnesium, make it even more aggressive leading to reaction with most of the oxides. This leads to the reducing service life of the tools and productivity due to production interruption. This newly developed coating resisted the attack of molten aluminium for 1200 hours without notable chemical reaction.