Processing, microstructural characterization and mechanical properties of a Ti2AlC/nanocrystalline Mg-matrix composite

Herein we report on the processing and microstructural characterization of 50 vol.% Ti2AlC/nanocrystalline (nc) Mg-matrix composites fabricated by pressureless melt infiltration at 750 degrees C for 1 h. X-ray diffraction and transmission electron microscopy both confirmed that the Mg grain size was similar to 35 +/- 15 nm. The microstructure was also exceptionally stable; annealing for 6 h at 550 degrees C did not alter the size of the Mg-grains. Some Mg was dissolved in the Ti2AlC confirming the existence of a (Ti1-xMgx)(2)AlC solid solution, with x as high as 0.2. A small amount of Ti (3 +/- 1 at.%) was also found in the Mg matrix. At 350 40 the ultimate tensile strength is significantly greater than other pure Mg composites reported in the literature. At 700 +/- 10 MPa, the ultimate compressive stresses of these composites were approximate to 40% higher than those of a 50 vol.% Ti3SiC2-Mg or a 50 vol.% SiC-Mg, in which the Mg-matrix grains were not at the nanoscale. The Ti2AlC/nc-Mg composites are readily machinable, stiff (approximate to 70 GPa), strong, light (2.9 g/cm(3)) and exhibited exceptional damping capabilities, that increased as the square of the applied stress to stress levels of the order of approximate to 500 MPa. The energy dissipated per cycle per unit volume at such stress levels is believed to be the highest ever reported for a crystalline solid and to be due to the formation and annihilation of incipient kink bands. The technological implications of having such solids are briefly discussed. (C) 2008 Elsevier Ltd. All rights reserved.