Journal of Student Research 2014

Journal of Student Research

Metallurgical Preparation Samples were first mounted in epoxy to allow for easier handling when grinding and polishing. The polishing step allows for a mirror/micro finish of samples, which in turn allows for a clear view at high magnifications. The grinding and polishing procedure consisted of the following steps: i) Grind on 240C grit paper (speed: 100 rpm, duration: 10 min., load: 25 lb., lubricant: water) ii) Grind on Cameo Platinum II Disc (150 rpm, 10 min., 25 lb. load, lubricant: water) iii) Polish on Cameo Silver Disc (100 rpm, 10 min., abrasive: 6µm diamond paste, lubricant: isopropyl alcohol mixture) iv) Polish on Cameo White Disc (100 rpm, 10 min., abrasive: 3µm diamond paste, lubricant: isopropyl alcohol mixture) v) Polish on Cameo Grey Disc (100 rpm, 10 min., abrasive: 1µm diamond paste, lubricant: isopropyl alcohol mixture) vi) Final polish on Cameo Grey Disc (100 rpm, 10 min., abrasive: colloidal silica, no lubricant). with Knoop indenter was used with a 500 gram load. This allowed for enough of an indentation of the harder ceramics and did not overly scar the softer metals. The hardness tester was calibrated prior to testing to ensure reliability using the calibration materials provided with the tester. Samples were securely mounted in the fixture, an appropriate testing location was found using the microscope attached to the tester, the indentation was made, and the indentation size was measured and converted to the Knoop hardness number. Multiple hardness scans were made to check the reproducibility of the measurement. Microscopy The microstructures of all polished joints were examined and recorded at various magnifications (x50 to x500) using an optical microscope. Selected samples were characterized for microstructure and composition using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) at the NASA Glenn Research Center. Microhardness testing For micro-hardness testing, a Buehler Micromet-2001 tester

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