Synthesis, crystal structure, microstructure and mechanical properties of (Ti1-xZrx)3SiC2 MAX phase solid solutions

Almost pure (Ti1-xZrx)(3)SiC2 MAX phase solid solutions with x ranging up to 0.17 were synthesized at temperatures in the range of 1450-1750 degrees C with reactive Spark Plasma Sintering (SPS). The zirconium partially replaces the M-element titanium of the Ti3SiC2 MAX phase up to x equals 0.17. The lattice parameters of the hexagonal (Ti1-xZrx)(3)SiC2 MAX phase are determined with X-ray diffraction using Rietveld refinement and show an anisotropic lattice expansion upon Zr insertion into Ti3SiC2. This observation is in very good agreement with density functional theory calculations where the deviation between the measured and calculated lattice parameter is less than 1%. The predicted elastic modulus reduction is only 4%. This behavior can be rationalized by considering the electronic structure, where only minute changes are observable as Zr is incorporated into Ti3SiC2. The measured nanohardness of the synthesized (Ti1-xZrx)(3)SiC2 MAX phase increases from 12.7 +/- 1 GPa for Ti3SiC2 to 16.3 +/- 1.1 GPa when xis raised from 0 to 0.17 due to an increasing amount of accompanying Ti1-yZryC. The elastic moduli of (Ti1-xZrx)(3)SiC2 solid solutions measured by an ultrasonic pulse-echo method (325-354 GPa) are in good agreement with the predicted elastic moduli (357-342 GPa).