Abstract
Y2O3 ceramics samples with various grain size were tested in non-symmetric thermal shock conditions in two methods. In the first test the samples were heated in a furnace up to the predetermined temperature (530°C) and then the polished surfaces with Vickers indents were subjected to sudden temperature change using a high-velocity nitrogen jet at room temperature. The gas was channelled onto the disk centre for about 20s. In the second test samples were quickly inserted into a hot furnace (850°C). The polished surfaces with Vickers indents were sheltered by thick alumina disks. The length of surface cracks before and after thermal shocks were measured with an optical microscopy and then a parameter Rm (an indicator of thermal stress resistance) was obtained. Hence the thermal stress σT, which caused crack growth, was calculated using the value of fracture toughness KIc. These stresses were similar for both shock cases (about 50MPa) and they were not dependent on grain size of the ceramics.
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