Synthesis, crystal structure, microstructure and mechanical properties of (Ti_1-xZr_x)₃SiC₂ MAX phase solid solutions

Abstract

Almost pure (Ti_1-xZr_x)₃SiC₂ MAX phase solid solutions with x ranging up to 0.17 were synthesized at temperatures in the range of 1450–1750 °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 (Ti_1-xZr_x)₃SiC₂ 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 (Ti_1-xZr_x)₃SiC₂ MAX phase increases from 12.7 ± 1 GPa for Ti₃SiC₂ to 16.3 ± 1.1 GPa when x is raised from 0 to 0.17 due to an increasing amount of accompanying Ti_1-yZr_yC. The elastic moduli of (Ti_1-xZr_x)₃SiC₂ solid solutions measured by an ultrasonic pulse-echo method (325–354 GPa) are in good agreement with the predicted elastic moduli (357–342 GPa).