Abstract
The dense (Ti1-xHfx)C ceramics with a relative density of 95-98% for x=0.2 to 0.8 were made from powder mixture of TiC and HfC at 2000°C and 32 MPa in Ar by hot-pressing. The microhardness was determined to be 2760±90kg·mm-2 (HV) for x=0.5. The formation of the mixed carbide (Ti1-xHfx)C was confirmed by X-ray diffraction.
Oxidation of (Ti0.5Hf0.5)C ceramics was performed at 1300 to 1500°C at 0.08kPa. It was assumed in the early stage that oxygen dissolves in (Ti0.5Hf0.5)C to form oxycarbide (Ti0.5Hf0.5)C1-xOx, followed by its decomposition to HfO2 and TiOx, with the microstructure of the respective gray and white stripes (subscale I). Subscale II is inherited from subscale I. At>3h, HfO2 particles of 500nm in size were formed in a matrix of TiOx containing amorphous carbon in subscale II. This scale thickens parabolically with time, which assumes that the diffusion of oxygen determines the oxidation. Faster outward diffusion of Ti from subscale II produces HfO2 scale (subscale III) as the balance. TiO2 formed already in the early stage (subscale V) is reacted with HfO2, resulting in the formation of HfTiO4 scale (subscale IV).
