Positron Annihilation and EBSD Studies of Subsurface Zone Created during Friction in Vanadium

Positron lifetime and electron backscatter diffraction studies were performed on pure vanadium samples subjected to the sliding test. The changes in the microstructure produced in this test are extending even to a depth of about 450 μm. As shown by the diffraction of electron backscattering, near this surface, just after starting the sliding test, a tribolayer with refinement randomly oriented grains is formed. The thickness of this layer varies from 8 to 19 μm depending on the sliding conditions and the mean grain size is about 0.2 μm. Its source is believed to be a continuous process of dynamic recrystallization. In this layer, the formation of cracks and debris is observed as well. Below is an intermediate layer with elongated grains and serrated grain boundaries in which a geometric dynamic recrystallization process has been recognized as well.