An investigation of tribological properties plasma paste boronizing of AISI 8620 steel by using different gas mixtures

In this research, AISI 8620 steel was boronized by using borax and B2O3 based paste mixtures (in addition to SiC and B4C) in plasma at different temperatures and times and at various gas mixtures.In this study, cross-sections of boronized steels were prepared metallographically to observe morphological details using optical microscope and the thickness of the layers formed on the steels was measured by an optical micrometer attached to it. The analysis of phases formed on the steels were obtained in X-ray diffractometer using CuK? ( ? =1,5418 A°). The hardness of the layers was measured on the cross-sections using Micro-Vickers indenter (Shimadzu HMV-2) with 50 g loads. Tribological tests were carried out on ball-on-disc tribometer in dry environment at the speed of 330 rpm and load of 10 N.The results of microstructure analysis showed that the boride layer thickness increased as the boriding temperatures and times increased. The boride layer on the steel consists of FeB and Fe2B phases for Ar/H2 gas mixtures. Fe3N and B25N phases have been found on the steel as well as FeB and Fe2B borides for Ar/H2/N2 gas mixtures.It was observed that the surface hardness of the steels boronized using borax and B2O3 paste increased with increase in plasma paste boronizing temperatures and times. Furthermore, the surface of the steel boronized using borax and B2O3 paste with SiC had lower hardness than that of the steel boronized using paste added B4C.Dry tribological tests showed that the wear rates of the plasma paste boronized steel surface decreased as the boronizing temperatures increased. The wear resistance of the steels boronized using borax paste was higher when compared with the steels boronized using B2O3 paste. The friction coefficient was found 0,34-0,71 for the steels boronized in Ar/H2/N2 plasma.