Indentation behavior of a Brittle Film/Brittle Substrate Composite
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abstract
AbstractSurface-film induced plasticity caused by the generation of dislocations at the film-substrate interface has been demonstrated previously for bcc metals and B2 ordered alloys deformed at low homologous temperatures. More recently, we have observed similar effects at elevated temperatures for ZrO2-coated MoSi2, which also demonstrates a film-induced reduction in hardness for microhardness tests over 25C - 1300C. In this investigation, 120 nm - 480 nm thick ZrO2 films were deposited on (001) single crystal MoSi2 by electron beam deposition. These composites were used to characterize the film-induced softening of MoSi2 at room temperature, where both MoSi2 and ZrO2 are brittle. Indents were made through the film into the substrate at 0.5 kgf loads using Vickers and Knoop indenters. Atomic Force Microscopy was employed to measure the geometry of Knoop indents after load removal, and to compare the results to the loaded indentation shapes. Increasing film thickness reduces the length of radial cracks in the substrate and lowers the composite hardness. The film also changes the relative amounts of deformation associated with material pileup at the surface near the edges of the indent, suggesting a change in deformation mechanism from pileup around the indenter edges to deformation by dislocation motion in the bulk.
