Synthesis and mechanical properties of Ti 3GeC 2 and Ti 3(Si xGe 1− x)C 2 ( x = 0.5, 0.75) solid solutions

Abstract

In this paper we report on the synthesis and characterization of Ti 3GeC 2, Ti 3Si 0.5Ge 0.5C 2, and Ti 3Si 0.75Ge 0.25C 2 solid solutions. Polycrystalline, fully dense, predominantly single phase samples of Ti 3Si 0.5Ge 0.5C 2, Ti 3Si 0.75Ge 0.25C 2, and Ti 3GeC 2 of varying grain sizes were fabricated by reactive hot isostatic pressing (HIP) or hot pressing of Ti, C, SiC, and Ge powders. Based on the lattice parameter measurements we conclude that the extent of solid solubility in Ti 3(Si x Ge 1− x )C 2 ranges for x=0 to, at least, x=0.75. Since the hardness values of both solid solution compositions (2.5±0.2 GPa) were in between those of Ti 3SiC 2 (3.0±0.3 GPa) and Ti 3GeC 2 (2.2±0.5 GPa) we conclude that no solid solution strengthening occurs in this system. All samples explored in this work were quite damage tolerant and thermal shock resistant. A 300 N Vickers indentation in a 1.5 mm thick, four-point bend bar decreases its strengths by anywhere from 25 to 35%. Quenching in water from 1000 °C reduces the four-point flexural strength by 10 to 20%; i.e., it is not catastrophic. Notably, the post-quench flexural strength of the coarse-grained Ti 3Si 0.5Ge 0.5C 2 samples was ≈25% higher than the as-received bars. Increasing the Ge content resulted in a decrease in the compressive strengths. The ultimate compressive strengths of fine-grained Ti 3Si 0.5Ge 0.5C 2 samples, decreased monotonically from room temperature to ≈950 °C. And while failure was brittle at room temperature, above 1000 °C the loss in strength was more severe, but the deformation was more plastic.