A CrN coated restrike punch was made of WR-95 (similar to H-11), which was fluidized bed nitrided. The coated punch was used on hot Inconel at about 1040 deg C (1900 deg F). However, a water-soluble graphite coolant was used to maintain the punch temperature at 230 deg C (450 deg F). Visual and binocular inspection at 64+ revealed presence of cracks and complete washout of coating in the working area of the failed punch. Comparison of metallographic cross sections of used and unused punches revealed a significant microstructural transformation in case of the used punch. Presence of a yellow porous layer was clearly evident between the nitrided layer and the coating, in case of the used punch. Cracks were observed to propagate from the outer surface into the bulk. Oxidation was evident along the cracks. The microstructural transformation observed in the case of the used punch was a clear indication of high temperature exposure (due to insufficient cooling) during application. The most probable cause of failure was thermal fatigue.

TiN coated back surgery wires were made of Ti-6Al-4V. The reported failure was the presence of pits located in the uncoated area of the wires. The uncoated area of the wire is where the wire is fixtured in the coating chamber during coating. Examination and analysis of the pits using SEM/EDX detection unit revealed significant peaks of B, O, Zr and Fe. Moreover, the shape of the pits was similar to an arc crater. The formation of pits in the wire was caused during coating due to microarcing. A contaminated fixture used during the coating most likely caused the microarcing.

High temperature corrosion may occur in numerous environments and is affected by factors such as temperature, alloy or protective coating composition, time, and gas composition. This article explains a number of potential degradation processes, namely, oxidation, carburization and metal dusting, sulfidation, hot corrosion, chloridation, hydrogen interactions, molten metals, molten salts, and aging reactions including sensitization, stress-corrosion cracking, and corrosion fatigue. It concludes with a discussion on various protective coatings, such as aluminide coatings, overlay coatings, thermal barrier coatings, and ceramic coatings.

Total knee prostheses were retrieved from patients after radiographs revealed fracture of the Ti-6A1-4 VELI metal backing of the polyethylene tibial component. The components were analyzed using scanning electron microscopy. Porous coated and uncoated tibial trays were found to have failed by fatigue. Implants with porous coatings showed significant loss of the bead coating and subsequent migration of the beads to the articulating surface between the polyethylene tibial component and the femoral component, resulting in significant third-body wear and degradation of the polyethylene. The sintered porous coating exhibited multiple regions where fatigue fracture of the neck region occurred, as well as indications that the sintering process did not fully incorporate the beads onto the substrate. Better process control during sintering and use of subsequent heat treatments to ensure a bimodal microstructure were recommended.