Evidence for Symmetry Reduction in Ti(AlCu)C MAX Phase Solid Solutions.

Ti[AlCu]C MAX phase solid solutions have been synthesized by sintering compacted TiAlC-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, /) position within the P6/mmc space group of the original TiAlC structure.