Thermodynamic Modelling of Phase Diagrams and Interface Reactions of MAX-Phases
Final Report Abstract
MAX-phases (Mn+1AXn ternary carbides and nitrides) are promising materials for a number of applications. In particular, MAX-phase thin films are intended for use as coatings or intermediate layers in high temperature composites, where their properties could improve toughness and thermal cycling resistance. In such applications it is of critical importance that undesired reactions at the interfaces do not take place. Such reactions are generally very difficult to predict and understand. In this work the systems V–Al–C and Ti–Al–C, which contain (among others) the V2AlC and Ti2AlC MAX-phases, were modelled thermodynamically in detail using the Calphad method. The systems Al–Cr–Ni–C and Al–Ni–V–C were also modelled, but in less detail, in order to predict reactions between NiAl and Cr2AlC or V2AlC. These predictions were confirmed by differential thermal analysis and annealing experiments. The combination of NiAl and Cr2AlC leads to a decrease in melting temperature to about 1320 °C. Also the combination of NiAl and Ti 2AlC leads to a decrease in melting temperature to about 1280 °C. Therefore, Cr2AlC and Ti2AlC are unsuitable as interlayer in Al2O3/MAX-phase/NiAl composites. In contrast, the melting temperature did not decrease when V2AlC was used as interlayer and there were no further reactions. From a chemical compatibility point of view V2AlC can be used as an interlayer. In spite of this the strength of the composite was severely degraded, most probably because of thermal stresses. Although the original application in view with MAX-phases as interlayer in Al2O3/MAX-phase/NiAl composites was abandoned, there is large potential of using MAX-phases as adaptive and selfhealing coatings at high temperature. These ideas are explored in further within the SPP HAUT and the SPP Design and Generic Principles of Self-healing Materials.
Publications
- Strength degradation of NiAl coated sapphire fibres with a V2AlC interlayer, Mater. Sci. Eng. A, 525 (2009) pp. 200–206
Gebhardt, T.; Hajas, D.E.; Scholz, M.; Hallstedt, B.; Cappi, B.; Song, J.; Telle, R.; Schneider, J.M.
- Thermal and chemical stability of Cr2AlC in contact with α- Al2O3 and NiAl, Int. J. Mater. Res., 101 (2010) pp. 1519–1523
Hajas, D.E.; Scholz, M.; Ershov, S.; Hallstedt, B.; Palmquist, J.-P.; Schneider, J.M.
- Oxidation of Cr2AlC coatings in the temperature range of 1230 to 1410 °C, Surf. Coat. Technol., 206 (2011) pp. 591–598
Hajas, D.E.; to Baben, M.; Hallstedt, B.; Iskander, R.; Mayer, J.; Schneider, J.M.
- Growth and thermal stability of (V,Al)2Cx thin films, J. Mater. Res., 27 (2012) pp. 2511–2519
Jiang, Y.; Iskander, R.; to Baben, M.; Takahashi, T.; Zhang, J.; Emmerlich, J.; Mayer, J.; Polzer, C.; Polcik, P.; Schneider, J.M.
(See online at https://doi.org/10.1557/jmr.2012.202)
