Bonding and oxidation protection of Ti${}_2$AlC and Cr${}_2$AlC for a Ni-based Superalloy

Abstract

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 Cr${}_2$AlC/Inconel-718/Ti${}_2$AlC 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 Cr${}_2$AlC and NSA was achieved after hot pressing at 1000°C and a contact pressure of only 2 MPa; in the case of Ti${}_2$AlC 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 Ti${}_2$AlC is a poor oxidation barrier for Inconel-718. However, in the case of Cr${}_2$AlC no cracks, delamination nor surface degradation were observed, suggesting that this material could be used to protect Inconel-718 from oxidation.