MAX phases


In the 90s, the research work of Barsoum et al. from Drexel University (Philadelphia, USA) led them to focus on Ti3SiC2 (Barsoum et al., J. Am. Ceram. Soc., 1996). They showed that this compound is stiff, lightweight, machinable, made from relatively inexpensive raw materials, resistant to oxidation and thermal shock, and capable of remaining strong up to temperatures above 1,300°C in air. They synthesized about fifty compounds with the same range of promising properties. Because of their composition, Barsoum et al. called these remarkable materials M(n+1)AXn phases, where:
– M is a transition metal from the groups 3, 4, 5 or 6
– A is an element from the groups 12, 13, 14, 15 or 16
– X is carbone C and/or nitrogen N.
n is an integer from 1 to 3. Therefore the structures M2AX, M3AX2 and M4AX3 are respectively called 211, 312 and 413.

a. the three primitive cells (211, 312 and 413); b schematics of grain shape.

MAX phases have a laminated structure with a hexagonal lattice. The primitive cell can be described as a stacking of n M6X octahedron layers with one layer of A element. Furthermore measurements of lattice parameters with numerous methods reveal that MAX phases exhibit an elevated crystalline anisotropy. The c/a ratio is generally higher than 3. MAX phases synthesized by powder metallurgy are polycrystalline bulk samples with random grain orientations. It is commonly observed that during synthesis grains grow in platelet shape. Because of the high crystalline anisotropy, platelet surfaces are parallel to basal planes. Therefore projections on the surface are observed as rectangles with a high aspect ratio.

The technological impact of these ternary compounds will not derive from any single property but rather they achieve a unique combination of properties. Indeed they combine properties of both ceramics (refractory, high stiffness, low density – 4.5 g/cm3 for Ti3SiC2 –, low ductility at RT) and metals (high thermal and electric conductivity, thermal shocks resistance, low hardness, mechanical resistance).

Phases MAX are also the precursors for synthesizing one of the last largest 2D materials reported to date: MXenes. Such as graphene, these materials consist of few-atoms-thick layers. But contrary to graphene, laryers are made of transition metal carbides, nitrides or carbonitrides. Therefore, MXenes open several new promising research tracks on 2D materials.

Some of my publications on MAX phases

Dislcoation modelling in Ti2AlN MAX phase based on the Pierls-Nabarro model.
K. Gourriet, P. Carrez, P. Cordier, A. Guitton, A. Joulain, L. Thilly, C. Tromas
PHILOSOPHICAL MAGAZINE, 2015, 95 (23), 2539–2552
DOI: 10.1080/14786435.2015.1066938

Evidence of dislocation cross-slip in MAX phase deformed at high temperature.
A. Guitton, A. Joulain, L. Thilly, C. Tromas
SCIENTIFIC REPORTS, 2014, 4 (6358)
DOI: 10.1038/srep06358

Effect of microstructure anisotropy on the deformation of MAX polycrystals studied by in-situ compression combined with neutron diffraction.
A. Guitton, S. Van Petegem, C. Tromas, A. Joulain, H. Van Swygenhoven, L. Thilly
APPLIED PHYSICS LETTERS, 2014, 24 (241910)
DOI: 10.1063/1.4884601

Pressure-enforced plasticity in MAX phases: from single grain to polycrystal investigation.
G.P. Bei, A. Guitton, A. Joulain, V. Brunet, S. Dubois, L. Thilly, C. Tromas
PHILOSOPHICAL MAGAZINE, 2013, 93 (15), 1784–1801
DOI: 10.1080/14786435.2012.755272

Dislocation analysis of Ti2AlN deformed at room temperature under confining pressure.
A. Guitton, A. Joulain, L. Thilly, C. Tromas
PHILOSOPHICAL MAGAZINE, 2012, 92 (36), 4536–4546
DOI: 10.1080/14786435.2012.715250

Deformation mechanisms of MAX phases: a multiscale experimental approach.
A. Guitton
PhD Thesis, Université de Poitiers, 2013
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