Bonding and oxidation protection of Ti2AlC and Cr2AlC 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 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.

Cr2AlC MAX phase as bond coat for thermal barrier coatings: Processing, testing under thermal gradient loading, and future challenges

“…However, diffusion of elements such as Co, Ti, and Mo from the substrate are detected in the carbide and Cr 2 AlC phases. Diffusion of metallic elements from the substrate has been already reported by Smialek's and Barsoum's groups under other thermal conditions and using other superalloys . Among the different tested MAX phases, Cr 2 AlC shows the lowest diffusion rate, but it is still the main problem to use these compounds in real applications at high temperature.…”

“…The first two points might be solved by improving the processing, but unfortunately diffusion cannot. Diffusion from superalloy elements to MAX phases has been already reported, although unfortunately just in a couple of other investigations. In fact, probably is one of the fields that should be explored in more details prior to the adoption of MAX phases into the market.…”

“…Finally, the self‐healing capability at high temperature of Al‐based MAX phases may play an important role in case of a crack penetrating into the bond coat layer . Nevertheless, one of the potential drawbacks for using MAX phases as bond coat is the inner diffusion of metallic elements from the superalloy substrate . In that case, Cr 2 AlC is the most promising composition since it exhibits lower diffusion rates and better compatibility with superalloys than Ti 2 AlC …”

“…Nevertheless, one of the potential drawbacks for using MAX phases as bond coat is the inner diffusion of metallic elements from the superalloy substrate . In that case, Cr 2 AlC is the most promising composition since it exhibits lower diffusion rates and better compatibility with superalloys than Ti 2 AlC …”

“…19 Nevertheless, one of the potential drawbacks for using MAX phases as bond coat is the inner diffusion of metallic elements from the superalloy substrate. 20,21 In that case, Cr 2 AlC is the most promising composition since it exhibits lower diffusion rates and better compatibility with superalloys than Ti 2 AlC. 21 Processing of bond coats is industrially carried out by thermal spray technologies instead by sputtering since thick coatings around 100 µm are required.…”