Synthesis and mechanical properties of Ti3GeC2 and Ti3(SixGe1-x)C2 (x=0.5, 0.75) solid solutions

In this paper we report on the synthesis and characterization of Ti3GeC2, Ti3Si0.5Ge0.5C2, and Ti3Si0.75Ge0.25C2 solid solutions. Polycrystalline, fully dense, predominantly single phase samples of Ti3Si0.5Ge0.5C2, Ti3Si0.75Ge0.25C2, and Ti3GeC2 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(SixGe1-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 Ti3SiC2 (3.0 +/- 0.3 GPa) and Ti3GeC2 (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 1000degreesC 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 Ti3Si0.5Ge0.5C2 samples was approximate to25% 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 Ti3Si0.5Ge0.5C2 samples, decreased monotonically from room temperature to approximate to950degreesC. And while failure was brittle at room temperature, above 1000degreesC the loss in strength was more severe, but the deformation was more plastic. (C) 2004 Elsevier B.V. All rights reserved.