Influence of Cr addition on tribological properties of bulk Fe₂B under dry friction and water lubrication

In the present study, friction and wear properties of bulk Fe₂B with different Cr additions were examined under dry friction and water lubrication conditions. The morphology, structure, mechanical properties and tribological properties were investigated by OM, SEM, XRD and XPS. The results show that there is no obvious new phase generated and the crystal structure has no changes with Cr addition. Cr element solubilizes in Fe₂B gains without any segregation, only bits of (Fe, Cr)₂B crystals formed. With the increasing of Cr addition, the fracture toughness increases first then decreases, and 2Cr sample has the highest toughness. Under dry friction condition, the friction coefficient and wear loss are all decrease first and then increase. 2Cr sample has the highest friction coefficient and wear loss. The tribochemical products form a lubricating film to reduce the friction coefficient and wear loss. And the wear mechanism is mainly brittle fracture. Under water lubrication condition, the friction coefficient drops remarkably, then slightly rises up. In contrast, the wear loss increases first and then decreases. 2Cr sample has the lowest friction coefficient, but the highest wear loss. The wear mechanism is mainly tribo-chemical wear in water. A comparison of the results under dry friction and water lubrication conditions, for the same sample, the friction coefficient is lower, but the wear loss is higher in water.