Simultaneous Synchrotron X-ray Diffraction, Near-Infrared, and Visible In Situ Observation of Scuffing Process of Steel in Sliding Contact

This paper describes an in situ observation of the scuffing process of steel by means of a newly developed system that employs a combination of two-dimensional detector synchrotron X-ray diffraction (XRD), a near-infrared CCD array, and a visible CCD array. In the demonstration of the application of the system, a contact area was produced between a fixed steel pin and a rotating sapphire ring, and the XRD ring, visible image, and near-infrared image of the steel surface of the contact area were synchronously captured at 30 fps under dry conditions. The system visually captured the wear behaviour, significant instantaneous temperature increase, and variation of the grain structure of the steel within the contact area during the scuffing process. The overall wear process was observed to comprise several stages, which were identified with first micro-scuffing, normal wear, second micro-scuffing, and macro-scuffing, respectively. Intermittent plastic flow was observed to occur numerous times with instantaneous heat generation within the contact area during the micro-scuffing processes. The instantaneous heat generation produced an adiabatic boundary condition, which increased the temperature to over 1000°C. The rapid temperature increase and decrease in the contact area also caused repeated phase transformation and reversion between martensite and austenite. The in situ XRD spectrum indicated that the repeated phase transformation and reversion created a definite surface layer that initiated the macro-scuffing process, which caused catastrophic plastic flow.