Correlation of nanoindentation-induced deformation microstructures in diamondlike carbon coatings on silicon substrates
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Phil J. Martin and Avi Bendavid CSIRO Materials Science and Engineering, Lindfield, NSW 2070 Australia (Received 24 August 2009; accepted 9 November 2009)
The effect of the presence of diamondlike carbon coatings deposited on (100) Si substrates on the deformation mechanisms operating in the silicon substrate during contact loading have been investigated by both cross-sectional transmission electron microscopy and modeling of the stresses generated beneath the indenter tip. The observed subsurface microstructures were correlated to the Tresca shear stress and the hydrostatic stress generated in the silicon substrate beneath the indenter tip. The presence of the coating altered the stresses generated in the substrate, and changed the deformation mechanism from one of principally phase transformation in uncoated Si to predominantly dislocation motion in the silicon substrate for the diamondlike C–Si system. The magnitude and distribution of the shear and hydrostatic stresses in the substrate were found to depend on both the indentation load and the thickness of the coating. Furthermore, the observed width of deformation, parallel to the interface, which was found to increase with coating thickness, was correlated to the wider distribution of the Tresca shear stress in the substrate brought about by the presence of the coating.
I. INTRODUCTION
The deformation of Si under contact loading has been widely studied1–13 and it is generally accepted that in uncoated silicon phase transformation, rather than dislocation nucleation, is the dominant deformation mechanism.4–7,10–14 Page et al.4 and Callahan and Morris5 observed that densification, or phase transformation, was the first plastic response to indentation in Si. This led to the suggestion that densification or phase transformation occurs in Si before the critical shear stress for dislocation nucleation is reached.14 Later, Bradby et al.11,12 observed slip in indented Si, regardless of whether the applied load exceeded that required to induce a discontinuity or pop-in in the load–displacement curve. Furthermore, they also observed that phase transformation occurs before the observance of pop-ins, and suggested that a pop-in occurs due to the sudden extrusion of the highly plastic transformed material beneath the indenter tip. Subsequently, Lorenz et al.15 compared the ratio of maximum hydrostatic pressure and the maximum shear stress calculated from contact theory (which for Si is 2.8 at a Poisson’s ratio, n of 0.35) with the ratio of hydrostatic a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0131
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J. Mater. Res., Vol. 25, No. 5, May 2010
pressure and the stress of homogenous dislocation nucleation in different materials. These authors concluded that since the ratio of the minimum hydrostatic stress required for phase transformation and the critical shear stress for homogeneous dislocation nucleation for Si is lower than 2.8, phase transformation is initiated before shear stress is reached and therefo
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