Raman scattering study of micrometer-sized spots of magnetite and hematite formed at 18CrNiMo7-6 screw rotor surfaces due to liquid-free, unsynchronized operation

We analyze differently worn surface positions of a screw rotor's contact zone using confocal Raman spectroscopy with 2 μm spatial resolution. The Raman scattering spectra demonstrate signals from magnetite Fe₃O₄ and hematite α-Fe₂O₃ whose intensities and energy shifts are associated with the degree of wear of the surface locations. While magnetite is identified at the worn surface areas studied, excluding a possible white etching domain, scattered light signatures from hematite are only detected at surface positions, at which high temperatures and/or high pressure inputs were proposed to be present during the liquid-free wear process of the screw rotors. The findings may be used to gain a more general understanding of tribological layers and to develop microscopic indicators of wear.