Repeated Thermal Shock Behavior of ZrB₂-SiC-Graphite Composite under Pre-Stress in Air and Ar Atmospheres

The thermo-chemo-mechanical coupling on the thermal shock resistance of 20 vol%-ZrB₂-15 vol%-SiC-graphite composite is investigated with the use of a self-developed material testing system. In each test, a specimen under prescribed constant tensile pre-stress (σ₀ = 0, 10, 20 and 30 MPa) was subjected to 60 cycles of thermal shock. In each cycle, the specimen was heated from room temperature to 2000 °C within 5 s in an air atmosphere or an Ar atmosphere. The residual flexural strength of each specimen was tested, and the fracture morphology was characterized by using scanning electron microscopy (SEM). There were three different regions in the fracture surface of a specimen tested in the air, while no such difference could be observed in the fracture surfaces of the specimens that were tested in Ar. The residual flexural strength of the composite that was tested in Ar generally decreases with the increase of σ₀. However, in the range of 0 ≤ σ₀ ≤ 10 MPa, the residual flexural strength of the composite that was tested in the air ascended with the increase of σ₀ due to the healing effect of oxidation, but it descended thereafter with a further increase of σ₀, as the effect pre-stress that became prominent.