Low temperature pack aluminising kinetics of nickel electroplated on creep resistant ferritic steel

A systematic study was made to determine the low temperature (< 700 °C) growth kinetics of the Ni2Al3 layer formed by the pack aluminising process on the surface of nickel electroplated on creep resistant ferritic steels. The aluminising powder packs were prepared using Al powder as a source for depositing Al, Al2O3 powder as inert filler and anhydrous AlCl3 as activator. The microstructures of the coatings formed were characterized by means of SEM/EDS and XRD. The results obtained were used to quantify the effects of aluminising temperature (T), time (t) and amount of Al powder (W) added into the pack powders on the growth kinetics of the Ni2Al3 layer (h). It was confirmed that the thickness of the Ni2Al3 layer formed can be related to the processing parameters by h = k0W1/2t1/2exp[− Ea / (RT)]. The values of the pre-exponential constant k0 and the activation energy Ea were determined. Additional experiments were made to demonstrate the effects of purity of the Al2O3 powder and amount of halide activator (AlCl3) added into the powder packs on the growth kinetics of the Ni2Al3 layer.