Thermal shock behaviors of functionally graded ceramic tool materials

Thermal shock resistance of Al2O3–TiC and Al2O3–(W, Ti)C functionally graded ceramic tool materials with symmetrical structures were evaluated by water quenching and subsequent three-point bending tests of strength diminution. Comparisons were made with the results from parallel experiments conducted using homogeneous Al2O3–TiC and Al2O3–(W, Ti)C ceramic tool materials. Functionally graded cutting ceramics exhibited both increased critical temperature difference and increased strength retention properties compared to homogeneous cutting ceramics, indicating their higher thermal shock resistance. The experimental results were discussed and rationalized in terms of microstructural observations and the calculations of one-dimensional transient temperature fields and transient thermal stress fields in case of surface cooling by using the perturbation method. It was concluded that higher thermal shock resistance could be achieved by means of varying the compositional distribution and hence the resultant distribution of thermo-mechanical properties of ceramic tool materials appropriately.