Metal surface modification by plasma boronizing in a two-temperature-stage process

A two-step plasma-assisted boronizing process was performed on the AISI 1045 steel substrate to reduce the pore density introduced by a single plasma boronizing process and examine the feasibility of the process. The specimens were plasma boronized for 1 h at 650 °C and subsequently for 7 h at 800 °C. Boronizing was conducted at a pressure of 266 Pa in an atmosphere of 1.5 vol.% BCl3 (low concentration), 50 vol.% H2 and balance Ar to minimize the effect of chlorine containing compounds, such as BCl3, HCl, FeCl2 and FeCl3, on formation and growth of the boride layer. It was found that the morphology of the boride layer prepared by the two-step boronizing process was changed from a columnar to a tooth-like structure and the pores in the borided steel were eliminated completely in comparison to those synthesized by the conventional single boronizing process (25%).