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Title:Dry sliding wear of metals: From subsurface microstructure to tribological behavior
Author(s):Cai, Wenjun
Director of Research:Bellon, Pascal
Doctoral Committee Chair(s):Bellon, Pascal
Doctoral Committee Member(s):Beaudoin, Armand J.; Robertson, Ian M.; Granick, Steve
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
simple shear
severe plastic deformation
electron-backscattered diffraction (EBSD)
grain reorientation
crystallographic texture
orientation mapping
Abstract:Dry sliding wear behavior of Cu-15Ni-8Sn bronze was studied by performing pin-on-disc wear tests against different counterface materials under various loads. The microstructure of the debris, worn surface and subsurface of the bronze were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). Two different types of debris particles, fine granular oxides and large flaky debris, were observed. A mechanically mixed layer, followed by a severely plastically deformed layer, formed at the sliding surface on top of the heavily deformed bulk material. The presence of the mechanically mixed layer was observed to improve significantly the wear resistance of the CuNiSn bronze. Orientation imaging microscopy was employed to analyze the severely deformed layer produced in Cu-15Ni-8Sn bronze and Ni pins by dry sliding wear under various loads and temperatures. In all cases, a nanograined layer that possesses significant crystallographic texture was observed. The dominant texture components were shear texture components. While the geometry of the pin-on-disk test imposed symmetry constraints on the possible texture components, the selection of the dominant texture components was affected by pin material's properties and by sliding conditions. In the case of the bronze pin, increasing the temperature of the wear test from room temperature to 330˚C led to an inversion of the relative intensity of texture components, while decreasing the load led to the stabilization of new texture components. These low-load texture transitions were correlated with a significant increase in friction coefficient. Grain re-orientation resulting from severe plastic deformation introduced by dry sliding wear was measured using electron-backscattered diffraction (EBSD) in Cu-15Ni-8Sn bronze. Polycrystalline samples with a large initial grain size, ≈ 150 µm, as well as single crystals were investigated. The continuous evolutions of local grain re-orientation as a function of deformation in polycrystalline and single crystalline samples were measured, up to large equivalent plastic strains, ≈ 190%. These experimental results were compared with predictions from several plasticity models, such as Sachs model, rate-dependent Taylor model with full or relaxed constraints, and an intermediate Sachs-Taylor model to gain new understanding on single-grain plasticity. Microstructural heterogeneity was observed in the vicinity of grain boundaries in polycrystal Cu-15Ni-8Sn during simple plastic deformation induced by pin-on-disc wear tests. The orientation gradient zone was measured ~ 2 – 4 µm near a 50o high angle grain boundary. The lattice curvature was studied in terms of geometrically necessary dislocations calculated from the orientation difference between neighboring points in space. Periodic microstructural instability was systematically observed at the leading edge of twin boundaries in CuNiSn pins after self-mated wear test. The dynamic response of steady sliding and the preferred orientation developed during plastic deformation were discussed on the basis of these observations.
Issue Date:2011-01-21
Rights Information:Copyright 2010 Wenjun Cai
Date Available in IDEALS:2011-01-21
Date Deposited:2010-12

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