Study of thermal shock resistance of flame sprayed coatings manufactured to protect molds used in glass containers industry
Molds used in glass manufacturing are subjected to continuous heating and cooling cycles, which result in their premature failure by thermal fatigue. In order to protect these molds a nickel alloy (Eutectic Castolin CPM 1205TM) was deposited as bond coat by flame spraying onto compacted graphite iron substrates and then, Al2O3-40 wt. % TiO2, ZrO2-36 wt. % Al2O3 and Al2O3, as well as a Ni-WC cermet, were sprayed as a top coatings using super oxidized and slightly oxidized flames. The effect of the flame type and the thickness of coatings on thermal shock resistance were evaluated. The results obtained indicate that coatings of Ni-WC sprayed from Eutectic Castolin 10112TM powders using a slightly oxidized flame, and ZrO2-Al2O3 coatings manufactured from nano-agglomerated Eutectic Castolin 25088TM powders with an super oxidized flame showed the best performances. The nature of Ni-WC cermets allowed increasing the thermal shock resistance due to the thermo-elastic behavior of nickel matrix and the arrest crack effect characteristic of composite materials. Likewise, in ZrO2-Al2O3 coatings, the bimodal microstructure that this kind of coatings shows contributed to increase the thermal shock resistance. The better performances of both coatings were obtained with a porosity level between 20% and 40%.