Study of Boriding Kinetics for Alloyed Ductile Irons

The boriding thermochemical treatment produces layers with high hardness, improving the tribological performance of nodular cast iron while the austempering treatment improves the mechanical performance of the substrate. In this work, samples of the nodular cast iron alloyed with copper, copper-nickel and copper-nickel-molybdenum were borided in a salt bath (borax + aluminum + alumina) at temperatures of 850, 900 and 950 ° C during 2 and 4 hours. The data of the obtained layers were used to determinate the diffusion coefficients and activation energies of this process. The results of the calculated diffusion coefficients were similar to those obtained by the direct measurements of the layer thicknesses. For the sample alloyed with Cu-Ni or Cu the obtained activation energy was 141.27 kJ / mol, and for the sample alloyed with Ni-Cu-Mo the value found was 212.98 kJ / mol. The statistical parameters and the correlation coefficients (R) showed satisfactory agreement.