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

Abstract

A series of high-purity Ti3(Al1−xSix)C2 solid solutions with 0<x<1 were reaction sintered from Ti, Si, Al and TiC powders using Pulsed Electric Current Sintering (PECS).11This method is commonly but inaccurately referred to as Spark Plasma Sintering (SPS). The a-lattice parameter of all sintered solid solutions remains constant at approximately 0.307nm, while the c-lattice parameter decreases from 1.858nm to 1.763nm with increasing amount of Si. The specific heat capacity of Ti3Al0.6Si0.4C2 was found to be comparable to that of end-member MAX phases, namely Ti3AlC2 and Ti3SiC2, while its coefficient of thermal expansion (CTE) was lower than that of the end members. Both Young's and shear moduli increase with increasing amount of Si. Vickers hardness (Hv) measurements demonstrate significant hardening effect in Ti3(Al1−xSix)C2 solid solutions regardless of the grain size, i.e. it changes from 4.1±0.14GPa of Ti3AlC2 and 4.2±0.37GPa of Ti3SiC2, up to 5.6±0.2GPa for Ti3(Al0.4Si0.6)C2. At room temperature, the strengthening effect was found to be marginal in the fine grained structure (grain size approximately 7 x 3 μm), 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 μm) 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°C, rather than silica that is commonly found on oxidized surfaces of Ti3SiC2.