Impact of the DC intensity and electrode distance on pulsed-DC powder-pack boride layer growth kinetics

Abstract

In this study, novel findings were obtained regarding the influence of current intensity and electrode distance on the growth of the FeB-Fe2B layer during pulsed-DC powder pack boriding (PDCPB). Boride layer formation was carried out on AISI 1018 and AISI 4140 steels at 900 °C for 2700 s, considering current intensities ranging from 2.5 to 7.5 A and electrode distances of 10, 15, and 20 mm for each current intensity. The growth of the FeB-Fe2B layer was enhanced as the current intensity/electrode distance increased. This was related to the contribution of electromigration, the amount of powder mixture (used during the PDCPB) between electrodes, and Joule heating. Analysis of variance was performed on borided steels to assess the impact of the current intensity/electrode distance on the boride layer growth. The results revealed weight coefficients of approximately 50% for current intensity, around 40% for electrode distance, and a combined contribution of both variables of no more than 3.5%. Finally, multiple regression analyses were conducted to estimate boride layer thickness expressions as a function of the independent variables. The model results demonstrated a 5% error when compared to the experimental boride layer thickness.