The wear resistance of boride layers measured by the four-ball test

This study estimated the wear resistance of the FeB/Fe2B layers using the four-ball test. First, the boride layers were obtained at the surface of the AISI 52100 steels using the powder-pack boriding method. The treatment was carried out at a temperature of 1223 K with 1 h of exposure. Boriding the AISI 52100 steels resulted in the formation of FeB/Fe2B layers with a thickness of approximately 40 μm. Four-ball tests were performed on the borided and non-borided steel ball samples in both dry and lubricated conditions. The dry sliding four-ball tests were performed under applied loads of 49, 98 and 147 N for 150 s. In the lubricated test, only loads of 147 and 392 N were applied for 3600 s with a sliding speed of 1200 rpm. In the dry and lubricated conditions, the coefficient of friction (COF) was monitored by a full bridge load cell, in which the temperature was sensed through a thermocouple in real time. The wear scar diameter (WSD) and worn surfaces of borided and non-borided steels in both experimental conditions were characterized to understand the involved wear mechanisms. In the dry condition, the results showed that the presence of boride layers at the surface of the AISI 52100 steels has an important effect on the COF values, indicating the potential features of the solid lubricant. This effect was not visible in the COF values when the borided steels were exposed to the lubricating conditions.