Investigation of wear properties of borided tungsten

In the present study, tribological properties of borides formed on pure tungsten have been investigated. The tungsten specimens were cut into Ø20x8mm dimensions, ground up to 1000 grid and polished using 1 µm Al2O3 solution. The boriding heat treatment was carried out in a solid medium containing an Ekabor-II® powder mixture placed in an electrical resistance furnace operated at the temperature of 900and 1000 ºC for 2 and 6 h under atmospheric pressure. The microstructures of polished and etched cross-sections of the specimens were observed under a Nikon MA100 optical microscope. The presence of borides formed in the coating layer was confirmed by means of X-ray diffraction equipment (Shimadzu XRD 6000) using Cu Kα radiation. The hardness measurements of the boride layer on each steel and untreated steel substrate were made on the cross-sections using a Shimadzu HMV-2 Vickers indenter with a 100 g load. X-ray diffraction analysis of boride layers on the surface of the tungsten revealed the existence of W2B5, WB, WB2, WB3 and WB4compounds. Depending on the chemical composition of substrates and boriding time, the boride layer thickness on the surface of the pure tungsten samplesranged from 18 μm to 184 μm. The hardness of the boride compounds formed on the surface of the pure tungsten samples ranged from 2182 to 4292 HV0,1, whereas Vickers hardness values of the untreated the steels was 469 HV0,1. The wear tests were carried out in a ball-disc arrangement under a dry friction condition at room temperature with an applied load of 10N and with a sliding speed of 0.3 and 0.4 m/sec at a sliding distance of 1000m. The wear surfaces of the pure tungsten were analyzed using a SEM microscopy and X-ray energy dispersive spectroscopy (EDS). It was observed that the wear rate of borided and unborided pure tungsten samples ranged from 3.86 to 42.75 mm3/Nm.