Processing and mechanical properties of Ti3SiC2: I, Reaction path and microstructure evolution

Abstract

In this article, the first part of a two-part study, we report the reaction path and microstructure evolution during the reactive hot isostatic pressing of Ti3SiC2, starting with titanium, SiC, and graphite powders. A series of interrupted hot isostatic press runs have been conducted as a function of temperature (1200°-1600 °C) and time (0-24 h). Based on X-ray diffractometry and scanning electron microscopy, at 1200 °C, the intermediate phases are TiCx and Ti5Si3Cx. Fully dense, essentially single-phase samples are fabricated in the 1450°-1700 °C temperature range. The time-temperature processing envelope for fabricating microstructures with small (3-5 μm), large (approximately 200 μm), and duplex grains, in which large (100-200 μm) Ti3SiC2 grains are embedded in a much finer matrix, is delineated. The microstructure evolution is, to a large extent, determined by (i) the presence of unreacted phases, mainly TiCx, which inhibits grain growth; (ii) a large anisotropy in growth rates along the c and a directions (at 1450 °C, growth normal to the basal planes is about an order of magnitude smaller than that parallel to these planes; at 1600 °C, the ratio is 4); and (iii) the impingement of grains. Ti3SiC2 is thermally stable under vacuum and argon atmosphere at temperatures as high as 1600 °C for as long as 24 h. The influence of grain size on the mechanical properties is discussed in the second part of this study.