Structural, physical and mechanical properties of Ti3(Al1-xSix)C2 solid solution with x=0-1

A series of high-purity Ti-3(Al1-x,Si-x)C-2 solid solutions with 0 < 1 were reaction sintered from Ti, Si, Al and TiC powders using Pulsed Electric Current Sintering (PECS).(1) The a-lattice parameter of all sintered solid solutions remains constant at approximately 0.307 nm, while the c-lattice parameter decreases from 1.858 nm to 1.763 nm with increasing amount of Si. The specific heat capacity of Ti(3)Al(0.)6Si(0.4)C(2) was found to be comparable to that of end-member MAX phases, namely Ti3AlC2 and Ti3SiC2, while its coefficient of thermal expansion (CFE) was lower than that of the end members. Both Young's and shear moduli increase with increasing amount of Si. Vickers hardness (H-v) measurements demonstrate significant hardening effect in Ti-3(Al1-x,Si-x)C-2 solid solutions regardless of the grain size, i.e. it changes from 4.1 +/- 0.14 GPa of Ti3AlC2 and 4.2 +/- 0.37 GPa of Ti3SiC2, up to 5.6 +/- 0.2 GPa for Ti-3(Al0.4Si0.6)C-2. At room temperature, the strengthening effect was found to be marginal in the fine grained structure (grain size approximately 7 x 3 mu m), as the compressive strength of Ti3Al0.6Si0.4C2 and Ti3Al0.4Si0.6C2 is higher for only 7.6% when compared to that of the end members. However, significant strengthening effect was observed in coarse grained structures (grain size approximately 25 x 8 jam) as the room temperature compressive strength of solid solutions exceed those of two end-members for more than 30%. Nevertheless, above brittle-to-plastic transition temperature, the solid solution strengthening effect diminishes and the strength of Ti3SiC2 is significantly higher than that of Ti3AlC2 and solid solutions. Finally, it was found that Ti3Al0.6Si0.4C2 forms protective alumina oxide layer at 1200 degrees C, rather than silica that is commonly found on oxidized surfaces of Ti3SiC2. (C) 2016 Elsevier B.V. All rights reserved.