Alumina forming, oxidation and thermal shock resistant MAX phases are of a high interest for high temperature applications. Herein we report, on bonding and resulting interactions between a Ni-based superalloy, NSA, and two alumina forming MAX phases. The diffusion couples Cr2AlC/Inconel-718/Ti2AlC were assembled and heated to 1000 or 1100°C in a vacuum hot press under loads corresponding to stresses of either 2 MPa or 20 MPa. The resulting interfaces were examined using X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy.Good bonding between Cr2AlC and NSA was achieved after hot pressing at 1000°C and a contact pressure of only 2 MPa; in the case of Ti2AlC a higher temperature (1100°C) and pressure (20 MPa) were needed. In both cases, a diffusion bond was realized with no evidence of interfacial damage or cracking after cooling to room temperature.Twenty thermal cycles from room temperature to 1000°C showed that Ti2AlC is a poor oxidation barrier for Inconel-718. However, in the case of Cr2AlC no cracks, delamination nor surface degradation were observed, suggesting that this material could be used to protect Inconel-718 from oxidation.
This paper reports work on the processing of functionally gradient alumina bioceramics with a continuously decreasing grain size across the thickness, with the view of ultimately utilizing high-quality nano/ultrafine powders only at the surface of an implant to provide superior wear and mechanical properties. A model of disc geometry is used to examine the feasibility of producing this brand of materials. Wet processing/ball milling and sequential slip casting procedures were used to de-agglomerate alumina powders and deposit green layers of varying particle sizes from 50 to 250 nm. Both pressure-less sintering and hot pressing were evaluated as high temperature sintering/consolidation processes. The results indicate that pressure-less sintering may not be suitable. Hot pressing, however, achieved very promising results producing near fully dense product with a grain size that gradually changes across its thickness.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.