Predicting in service thermo-mechanical performance of ultra-high temperature ceramics
Researcher: Jianye Wang
Funding: Centre for Advanced Structural Ceramics
Ceramics such as the carbides and di‐borides of zirconium and hafnium remain solid to temperatures in excess of 3000 K, which makes these materials frontrunners for selected components in a new generation of more manoeuvrable spacecraft. Recent research has focussed on developing processing routes for these materials and improving their oxidation resistance. Very little is known about their mechanical and thermal properties at elevated temperature. There is some strength data, but it was mostly obtained in the 60’s when processing techniques and microstructures were less developed.
The project aims to investigate the variation of mechanical and thermal properties with temperature of these materials so that their performance at temperature can be predicted. Of particular interest is trying to establish the role dislocation flow might play when using these materials at very high temperatures. This year, work has focussed on mechanical characterisation. An analysis method was developed to extract the strain rate dependence of the hardness out of nano-indentation results. By measuring the strain rate dependence at a number of temperatures between room temperature and 673 K, constitutive data for the resistance to dislocation movement in ZrB2 was derived. For example, the Peierl’s stress is estimated to be 6.6±0.7 GPa. TEM investigations to determine the active slip systems are ongoing and suggest that slip occurs on both the basal planes as well as on the prism planes.
A second area of focus has been to develop the capacity of measuring hardness at very high temperatures (up to 2,273 K). At such temperatures, there are not many candidate materials for the indenter tip, and therefore an alternative technique where the material is indented against itself is used. Results to date suggest that the hardness of ZrB2 at 2273 K is 50 MPa. These hardness measurements will be contrasted with compression tests and supplemented with TEM to determine the active deformation mechanisms.