Through the use of X-ray diffraction (XRD) and other diagnostics, the fundamental physical mechanisms of scuffing are becoming better understood. Peak broadening in the XRD pattern has been analyzed to determine the dislocation structure and crystallite size. Evidence from this technique has led us to conclude that scuffing is an example of adiabatic shear instability, wherein work hardening is exceeded by the thermal softening caused by the work. We are extending this research through scuff testing and XRD of nonferrous materials. For example, members of our team have recently found frictional behavior and surface morphologies consistent with scuffing in single crystals of MgO. Previous work has suggested the use of scuffing as a general method for the formation of metastable phases. Phase identification information available from the XRD data indicated the formation of austenite in scuffed SAE4340 steel, and the present work reports the discovery of a tribologically formed metastable phase in nickel. The formation of this phase was associated with surface roughening and a rapid friction increase of approximately 50%. However, the morphology of the roughened surface indicated abrasion rather than the gross plasticity typical of scuffed surfaces. X-ray diffraction identified the phase as either nickel carbide (Ni3C) or hexagonal nickel, which are similar in structure, and ruled out the presence of crystalline nickel oxides. Analysis of peak widths revealed that the dislocation density in the areas that experienced a higher friction coefficient was lower than that in low-friction areas. This finding is not consistent with dislocation density changes in scuffed steel.

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