A Study on the Aluminizing of Electrodeposited Nickel at 500 °c

In this research, aluminizing behavior of ultra fine-grained nickel was investigated. For this purpose,nanocrystalline nickel samples with the grain size of -25 nm were prepared via direct current electrodeposition and aluminized for different durations by pack cementation method at 500 °C. The aluminide layers were examined by means of SEM, EDS and XRD techniques. According to results, short time aluminizing resulted in the formation of a single aluminide layer whereas at long duration two distinct aluminide layers were formed. The growth kinetics of the coating was non-parabolic at short times while it obeyed the parabolic law at long duration. The parabolic growth rate constant ofsingle phase coating f ormed on electrodepos ited samples was about 30 im / hI /2 approximately 3 times greater than the data reported for coarse grained nickel (8.4 im / hIl2). Meanwhile, the overall growth rate constant was decreased to I1.7 im / hI /2, when double aluminide layers formed on nanocrystalline nickel.