V. Gauthier-Brunet

Slip line analysis around nanoindentation imprints in Ti3SnC2: a new insight into plasticity of MAX-phase materials

The plasticity of Ti3SnC2, a recently synthesized MAX phase, was investigated. Localized deformation was induced by nanoindentation in a polycrystalline sample, and the resulting surface topography was observed by atomic force microscopy (AFM). For several grains, buckling around the indent was observed, in agreement with the kink band deformation process often reported for MAX-phase materials. For other grains, slip lines have been revealed by AFM. The corresponding slip systems have been identified through the determination of the local crystalline orientation by electron backscatter diffraction. First- and second-order pyramidal slip systems are shown to be active for some grain orientations, as well as dislocation interactions and cross slip from one system to the other.

Al-matrix composite materials reinforced by Al-Cu-Fe particles

Al-matrix material composites were produced using hot isostatic pressing technique, starting with pure Al and icosahedral (i) Al-Cu-Fe powders. Depending on the processing temperature, the final reinforcement particles are either still of the initial i-phase or transformed into the tetragonal ω-Al00.70Cu0.20Fe0.10 crystalline phase. Compression tests performed in the temperature range 293K − 823K on the two types of composite, i.e. Al/i and Al/ω, indicate that the flow stress of both composites is strongly temperature dependent and exhibit distinct regimes with increasing temperature. Differences exist between the two composites, in particul ar in yield stress values. In the low temperatureregime (T ≤ 570K), the yield stress of the Al/ω composite is nearly 75% higher than that of the Al/i composite, while for T > 570K both composites exhibit similar yield stress values. The results are interpreted in terms of load transfer contribution between the matrix and the reinforcement particles and elementary dislocation mechanisms in the Al matrix.

Evidence for Symmetry Reduction in Ti3(Al1−δCuδ)C2 MAX Phase Solid Solutions

Ti3[Al1-δCuδ]C2 MAX phase solid solutions have been synthesized by sintering compacted Ti3AlC2-Cu composites produced by mechanical milling. Using X-ray and neutron diffraction techniques, it is demonstrated that the Cu mixing into the Al site is accompanied by lattice distortion, which leads to symmetry reduction from a hexagonal to a monoclinic structure. Such symmetry reduction likely results from this mixing through deviation of the A-site position from the special (0, 0, 1/4) position within the P63/mmc space group of the original Ti3AlC2 structure. Moreover, it is demonstrated that the Cu admixture into the A site can be adjusted from the composition of the reactant mixture. The lattice parameter variation of the solid solution compounds, with 10-50 atom % Cu in the A site, is found to be consistent with Vegards law.