iTSSe TSS A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 2 2 4 5 iTSSe TSS because cold-mount acrylic is fast-curing, highly viscous, and may not infiltrate the TC entirely leaving pores unsupported and subject to relief; d) a vacuum-infiltrated epoxy mount has negligible artifacts due to high internal pore support and low applied stresses. Grinding and polishing. Even when proper sectioning and mounting methods are used, minor and localized artifacts will be present near the sectioning plane, and these can be removed by proper grinding and polishing practices. For this reason, the initial planar grinding step is typically longer compared to grinding wrought materials. The grinding abrasive size is also typically finer than those used for wrought materials. One industry practice suggests a re- moval of 0.060-in. from the mount height during planar grinding of TSCs to ensure artifacts from previous steps have been removed. Of course, planar grinding uses large abrasive size and the deep abrasion forces can cause artifacts of their own. Subsequent polishing with a series of finer abrasive media can remove the planar grinding artifacts when applied for sufficient time. In this section, all samples were properly sectioned then mounted using vacuum-infiltrated slow-curing epoxy. All were planar ground using 180-grit SiC paper with water coolant, replacing the paper every 30 seconds FEATURE 11 until each sample was planar. The effect of the supplier of consumables and abrasives is not addressed in this paper, but abrasive quality and polishing surface resiliency may affect artifact formation. The post-planar polishing steps follow the ASTME 192003 Method-II[3], however, polishing times were adjusted to demonstrate how each step contributes to pore structure stabilization and removal of artifacts from the previous step. Under all polishing conditions here, the BC appears the same, exhibiting clear splat boundaries, voids, and unmelted particles. The BC is far less sensitive to artifacts than the TC under these polishing conditions, but BCs also have artifacts. The most common artifact in a BC is smearing (plastic deformation) of the metal on the polished plane that obscures these BC features. Smearing can be caused by worn consumables, dull abrasives, or improper polishing surface. Also, the BC is softer than the TC and can exhibit scratches more easily. Scratches in the BC can indicate insufficient polishing time to remove artifacts from the previous step. Scratches may also indicate contaminated or worn polishing paper. An artifact common to any polishing method is edge-rounding. It is typically identified during the optical microscopy analysis as a field of view (FOV) where all Fig. 3 — Artifacts in TBC resulting frommounting methods. Images provided by the Center for Advanced Coatings at Florida Institute of Technology. (c) (a) (d) (b)
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