Relationship between the thermal shock behavior and the cutting performance of a functionally gradient ceramic tool

Based on a deep understanding of the requirements of cutting conditions on ceramic tools, a design model for functionally gradient ceramic tool materials with symmetrical composition distribution is presented in this paper, according to which an Al2O3–TiC functionally gradient ceramic tool material FG-1 was synthesized by a powder-laminating and uniaxially hot-pressing technique. The thermal shock resistance of the Al2O3–TiC functionally gradient ceramics FG-1 was evaluated by water quenching and subsequent three-point bending tests of flexural strength diminution. Comparisons were made with results from parallel experiments conducted using a homogeneous Al2O3–TiC ceramics. The functionally gradient ceramics exhibited higher retained strength under all thermal shock temperature differences compared to the homogeneous ceramics, indicating their higher thermal shock resistance. The experimental results were supported by the calculation of the transient thermal stress field. The cutting performance of the Al2O3–TiC functionally gradient ceramic tool FG-1 was also investigated in the rough turning of the cylindrical surface of an exhaust valve of a diesel engine in comparison with that of a common Al2O3–TiC ceramic tool LT55. The results indicated that the tool life of FG-1 increased by 50% over that of LT55. The tool life of LT55 was mainly controlled by thermal shock cracking which was accompanied by mechanical shock, whilst tool life of FG-1 was mainly controlled by mechanical fatigue crack extension rather than thermal shock cracking, revealing the less thermal shock susceptibility of functionally gradient ceramics than that of common ceramics.