Effect of pack Al content on growth kinetics at 650 °C of Ni_2Al_3 coating layer on nickel-electroplated creep resistant ferritic steels

摘要

The hybrid Ni_2Al_3/Ni coating was formed on creep resistant ferritic steels by firstly nickel electroplating and then partially aluminising the Ni layer at 650 °C by pack cementation process using powder mixtures of Al, AlCl_3 and Al_2O_3. The effect of pack Al content (W) on growth kinetics of the outer Ni_2Al_3 layer of the coating was investigated by varying it from 2 to 10 wt% whilst keeping the pack AlCl_3 content constant at 2 wt% and aluminising conditions at 650°C/4h. It was revealed that, once W was above a minimum level, the growth of the outer Ni_2Al_3 layer thickness depended linearly on W~(1/2) . The possible reasons for such growth kinetics were discussed.