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

In this article, the first part of a two-part study, me 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 degrees-1600 degrees C) and time (0-24 h), Based on X-ray diffractometry and scanning electron microscopy, at 1200 degrees C, the intermediate phases are TiCx and Ti5Si3Cx, Fully dense, essentially single-phase samples are fabricated in the 1450 degrees-1700 degrees C temperature range. The time-temperature processing envelope for fabricating microstructures with small (3-5 mu m), large (similar to 200 mu m), and duplex grains, in which large (100-200 mu m) 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 degrees C, growth normal to the basal planes is about an order of magnitude smaller than that parallel to these planes; at 1600 degrees 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 degrees 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.