Deformation about sliding indentation in ceramics and its application to lapping
Abstract
The deformation and fracture of model brittle materials such as soda-lime glass and Ni-Zn ferrite produced by sliding indentations under lightly loaded (1-600gm) conditions has been investigated. Experiments were conducted with a pyramidal diamond indenter (Vickers) sliding against soda-lime glass and polycrystalline Ni-Zn ferrite at low velocities (1-50mm/min). In glass, when the indentation load is less than 5gm, microscopic observations of the scratch track show that it is completely plastic with no cracking. Median cracking is seen to occur when the indentation load exceeds 5gm and lateral cracking, leading to significant material removal, is observed in the load range of 80-300gm. The lateral cracks are typically formed at a shallow depth below the surface and the crack faces are parallel to the surface. At a load of $\sim$150gm in glass, a crushed zone composed of numerous microfractures begins to appear along the scratch track. Beyond an indentation load of 300gm, the lateral cracks were observed to disappear and the crushed zone was found to dominate the deformation pattern along with the median cracking. The deformation and fracture in ferrite was observed to be similar with one notable microstructural feature; above an indentation load of $\sim$100gm, the fracture become transgranular (through the grain boundary). The onset of crushed microfracturing in glass and the transition from intergranular to transgranular fracture in ferrite, were observed to coincide with a sudden, though gradual, increase in the coefficient of friction. An analytical model of sliding indentation is developed using Yoffe's characterization of the inelastic deformation around quasi-static indentations. The formation of median and lateral cracks in glass, which were observed in the experiments, are seen to be well predicted by the model. Lastly, the analysis of lapping and polishing proposed by Chauhan recently using indentation fracture as the basis for material removal is refined and made more rigorous in order to predict the surface finish of lapped surfaces and the contact loads which exist between abrasive particles and the work surface during lapping. The predictions of the model are found to be in broad agreement with a variety of experimental observations pertaining to lapping and lapped surfaces of ceramics.
Degree
Ph.D.
Advisors
Chandrasekar, Purdue University.
Subject Area
Industrial engineering|Materials science
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