Investigation of structural and tribological properties o layers formed in SAE 5140 steel coated with boride powders

Abstract

In this study, the surface of SAE 5140 steel was coated with ferroboron using new powder bonding agent (Baybora-1) for various bonding time at 950 degrees C. The chemical composition and morphology of the phases formed in the internal structure of the bonded samples were examined by XRD, optical microscope and SEM, respectively. In addition, the mechanical properties of the boride layers formed were determined by the measurements of the subsurface hardness. In order to determine the tribological behaviour, these samples were subjected to wear testing using alumina ceramic abrasive powder at different loads. It was observed that the internal structure of unborided samples is generally formed by ferrite and pearlite phases. It has been determined that the boride layer having two different chemical compositions is formed as a result of the bonding processes made for different periods and the boride layer thickness increases with increasing bonding time. Sub-surface hardness measurements showed that three different zones were formed under the surface. In addition, the average surface hardness value of the SEA 5140 steel is 367 +/- 8.2 HV0.1, while it increased up to 1997 +/- 17.2 HV0.1 as the result of the bonding. As a result of the wear testing carried out, it was observed that the abrasion was very dependent on the phases formed in the boride layer and the most suitable balding time was determined. It has been determined that all bonded samples increase the abrasion resistance of the raw steel by about 4 times.