Cracking behavior of oxide scale formed on Ti3SiC2-based ceramic

The cyclic oxidation and acoustic emission (AE) tests were carried out for studying cracking behavior of oxide scales formed on Ti₃SiC₂-based ceramic at 1100 °C. A duplex oxide scale with an outer layer of pure TiO₂ and an inner layer of a mixture of TiO₂ and SiO₂ was formed. The oxide scale did not spall from substrate during the cyclic oxidation at 1100 °C for 360 times. However, a great number of micro-cracks penetrating whole inner oxide layer were detected. AE test showed that the oxide scale did not crack during the isothermal oxidation at 1100 °C for 1 h, however, the scale cracked during the cooling stage. Comparing the growth rate and thickness between the oxide layers formed during the isothermal oxidation and cyclic oxidation, respectively, indicated that cracks in the inner oxide layer served as paths mainly for outward diffusion of titanium and for inward diffusion of oxygen, resulting in increased growth rate of the outer oxide layer. Because of entire and compact TiO₂ consisted of outer oxide layer, and low thermal stress resulting from small mismatch of thermal expansion coefficients between the oxides and the substrate, Ti₃SiC₂ exhibited excellent cyclic oxidation resistance at 1100 °C for 360 cycles.