Tensile creep of coarse-grained Ti3SiC2 in the 1000-1200°C temperature range

The tensile creep of coarse-grained, CG, Ti3SiC2 samples, in the 1000-1200 degreesC temperature, T, and 10 MPa to 100 MPa stress, sigma, ranges, respectively, was studied. The creep behavior is characterized by three regimes: an initial, a secondary where the creep rate is at a minimum, (epsilon)over dot(min), and a tertiary regime. In the intermediate regime (epsilon)over dot(min) is given by: (epsilon)over dot(min)(s)(-1) = epsilon(0)exp(17+/-1) (sigma/sigma(o))(2.0+/-0.1) exp(-458 +/- 12 kJ/mol/RT) where sigma(0) = 1 MPa and epsilon(0) = 1 s(-1). The times to failure are given by: t(f) (s) = exp(-2 +/- 0.3)(epsilon)over dot(min)(-1). The results presented herein confirm that: (a) dislocation creep is the dominant mechanism; (b) the high plastic anisotropy of Ti3SiC2 results in large internal stresses during creep; (c) the response is dictated by a competition between the rates of generation and dissipation of these internal stresses; (d) at higher temperatures and/or lower strain rates the internal stresses can dissipate and the behavior is more ductile. Furthermore, in the tertiary creep regime, the creep appears to occur by a combination of dislocation creep and the formation of cavities and cracks. The coarse-grained samples have lower creep rates than their fine-grained (3-5 mum) counterparts, and their times to failure are longer. The latter is partially attributable to the ability of the larger grains, whose basal planes are normal to the applied load, to form tenacious crack bridges by delamination and kink band formation, in addition to the bridges that occur when the basal planes are parallel to the applied load. (C) 2003 Elsevier B.V. All rights reserved.