TY - JOUR TI - On the use of raman spectroscopy and instrumented indentation for characterizing damage in machined carbide ceramics DO - https://doi.org/doi:10.7282/T3ZS2V52 PY - 2013 AB - Machining is a necessary post-processing step in the manufacturing of many ceramic materials. Parts are machined to meet specific dimensions, with tight tolerances, not attainable from forming alone, as well as to achieve a desired surface finish. However, the machining process is very harsh, often employing the use of high temperatures and pressures to achieve the wanted result. In the case of silicon carbide, a material with extremely high hardness and stiffness, machining is very difficult and requires machining conditions that are highly aggressive. This can leave behind residual stresses in the surface of the material, cause unwanted phase transformations, and produce sub-surface deformation that can lead to failure. This thesis seeks to determine the effect of various machining conditions on the Raman spectra and elastic properties of sintered silicon carbide materials. Sample sets examined included hot-pressed silicon carbide tiles with four different surface finishes, as well as "ideal" single crystal silicon carbide wafers. The surface finishes studied were as follows: an as-pressed finish; a grit blast finish; a harsh rotary ground finish; and a mirror polish. Each finish imparts a different amount, as well as type, of deformation to the sample and are each utilized for a specific application. The sample surfaces were evaluated using a combination of Raman spectroscopy, for phase identification and stress analysis, and nanoindentation, for obtaining elastic properties and imparting uniform controlled deformation to the samples. Raman spectroscopy was performed over each sample surface using 514- and 633-nm wavelength excitation, along with confocal and non-confocal settings to study depth variation. Surfaces stresses were determined using peak shift information extracted from Raman spectra maps, while other spectral variations were used to compare levels of machining damage. Elastic modulus, hardness, and plastic work of indentation maps were generated from load-depth curves obtained from nanoindentation with a Berkovich tip at 10mN and 30mN maximum loads. The Raman measurements were repeated on indented samples, over the indented regions. Stress-free single crystal silicon carbide wafers were used as a reference for both the Raman and nanoindentation measurements. The Raman analysis showed that stress gradients could be determined within each machined sample. Additionally, it revealed variations in the magnitude of residual stresses between machining conditions. No correlation was found between elastic properties of samples and Raman stress data. However, it was found that the 30mN indentation caused an increase in the near-surface average stress value for the mirror finish sample. The relative peak width also increased, indicating a plastic deformation resolvable by Raman. KW - Materials Science and Engineering KW - Ceramic materials--Machining KW - Raman spectroscopy LA - eng ER -