Relationship between Thermal Shock Resistance and Cutting Performance of a Functionally Gradient Ceramic Tool

摘要

Based on the deep understanding of the requirements of cutting conditions on ceramic tools, a designrnmodel for functionally gradient ceramic tool materials with symmetrical composition distribution was presented inrnthis paper, according to which an Al_2O_3-TiC functionally gradient ceramic tool material FG-1 was synthesized byrnpowder-laminating and uniaxially hot-pressing technique. The thermal shock resistance of the Al_2O_3-TiCrnfunctionally gradient ceramics FG-1 was evaluated by water quenching and subsequent three-point bending testsrnof flexural strength diminution. Comparisons were made with results from parallel experiments conducted using arnhomogeneous Al_2O_3-TiC ceramics. Functionally gradient ceramics exhibited higher retained strength under allrnthermal shock temperature differences compared to homogeneous ceramics, indicating the higher thermal shockrnresistance. The experimental results were supported by the calculation of transient thermal stress field. The cuttingrnperformance of the Al_2O_3-TiC functionally gradient ceramic tool FG-1 was also investigated in rough turning therncylindrical surface of exhaust valve of diesel engine in comparison with that of a common Al_2O_3-TiC ceramic toolrnLT55. The results indicated that the tool life of FG-1 increased by 50 percent over that of LT55. Tool life of LT55rnwas mainly controlled by thermal shock cracking which was accompanied by mechanical shock. While tool life ofrnFG-1 was mainly controlled by mechanical fatigue crack extension rather than thermal shock cracking, revealingrnthe less thermal shock susceptibility of functionally gradient ceramics than that of common ceramics.