Repeated thermal shock behavior of the ZrB2–SiC–ZrC ultrahigh-temperature ceramic

The one thermal cycle of the heating was carried out at maximal temperature of 1800 ± 15 °C in 5 s using a resistance heating method with a large current and low voltage, and then the power supply was shut off and the specimen was naturally cooled to room temperature. According to the energy dispersive spectroscopy (EDS) analysis and scanning electron microscopy (SEM) observations, the surface microstructure of the specimen after the repeated thermal shock composed of: (1) a layer of SiO2-rich + ZrO2, (2) a layer of ZrO2 + ZrB2 and (3) unoxidized substrate. The flexural strength of the specimen after the thermal shock of 10, 20 and 30 cycles were 650 MPa, 684 MPa and 675 MPa, respectively, which were obviously higher than the flexural strength of 580 MPa before the thermal shock due to the formation of the SiO2-rich + ZrO2 layer and the compressive stress in the oxide layer. The flexural strength of the specimen after the thermal shock of 50 cycles decreased to be 427 MPa that was significantly lower than 580 MPa before the thermal shock because of the presence of a large numbers of pores in oxide layer and through holes in the surface.