Papers by Author: Chong Hai Xu

Abstract: Based on the theory of thermodynamics, the chemical compatibility of the possible composition system of ceramic material Al2O3/Cr3C2/SiC (for short ACS) was analyzed. The results show that no chemical reaction could take place under 1800°C through Cr3C2, SiC and Al2O3. And it was tested by the fabrication of the Al2O3/Cr3C2/SiC composite with the hot pressing sintering technique. The flexural strength and fracture toughness of ACS are super than the Al2O3 ceramic.

Abstract: A new ZrO₂ nano-composite ceramic tool and die material was prepared with vacuum hot pressing technology. The friction and wear behaviors of ZrO₂ nano-composite ceramic tool and die materials in sliding against 45 chilled steel rings under dry friction were investigated by using an MMW-1A abrasion wear tester. The mechanical properties and the friction and wear properties of the composites with various compositions and contents were studied. It is indicated that the changing trends of the wear rate and the mechanical properties of the composites with the change of TiB₂ and Al₂O₃ contents are roughly the same, but the friction coefficient is not obviously. The friction and wear properties and the mechanical properties are finer when the TiB₂ and Al₂O₃ content is both 10%.

Abstract: Based on the requirements for ceramic materials of cutting tool and die and the aim of improving comprehensive mechanical properties of ceramic tool and die materials, nanocomposite ceramic tool and die materials with high mechanical properties were fabricated successfully with nanometer composite method. Friction and wear properties of the developed ZrO2/Ti(C7N3) nanocomposite ceramic tool and die materials were experimentally studied in detail. Morphologies of the worn surfaces were observed and analyzed by ESEM. Wear mechanisms of nanocomposite ceramic tool and die materials were discussed with comparison with that of single-phase ZrO2 ceramics. It indicates that wear mechanisms of ZrO2/Ti(C7N3) nanocomposite ceramic tool and die materials are mechanical cold welding, abrasive wear and adhesive wear.

Abstract: A new ZrO2 nano-composite ceramic tool and die material was prepared with vacuum hot pressing technique. The effects of sintering parameters on the nano-composite ceramic tool and die materials were studied. The results indicated that the mechanical properties of ZrO2 nano-composite ceramic tool and die material with the additions of TiB2 and Al2O3 are higher than that of the pure ZrO2 ceramic material. Sintering at 1100 for 120min could improve the density and mechanical properties of ZrO2 nano-composite ceramic material. The flexural strength, fracture toughness and hardness with the optimum sintering parameters can reach 878MPa, 9.54MPa•m1/2 and 13.48GPa, respectively, obviously higher than that with non-optimum sintering parameters.

Abstract: In recent, the development of new die materials is one of the important topics in the field of die research. In this paper, effects of nano-ZrO2 addition on the microstructure and mechanical properties of Ti(C,N)-based cermets were studied. The newly developed Ti(C,N)-based cermet die materials with different contents of nano-ZrO2 of 0~25wt% were prepared by hot pressing technique under vacuum atmosphere at 1450°C for 30min. Moreover, the microstructure of this Ti(C,N)-based cermet die materials was observed by environmental scanning electron microscope. It indicates that the comprehensive mechanical properties can reach the optimum when the weight percent of the nano-ZrO2 is 10%. The corresponding flexural strength and fracture toughness is 967 MPa and 13.62 MPa•m1/2, respectively which is approximately 65% and 110% higher than that of the cermet without nano-ZrO2 addition. It suggests that the addition of nano-ZrO2 can improve the mechanical properties especially the fracture toughness and flexural strength of Ti(C,N)-based cermet die materials.

Abstract: In this paper, back propagation neural network was used in the optimum design of the hot pressing parameters of an advanced ZrO2/TiB2/Al2O3 nanocomposite ceramic tool and die material. The BP algorithm could set up the relationship well between the hot pressing parameters and mechanical property of nanocomposite ceramic tool and die materials. After analyzed the predicted results, the best predicted results were the sintering temperature was 1420°C and the holding time was 60min. Under these hot pressing parameters, the best flexural strength and the best fracture toughness of the material could be obtained.

Abstract: In this paper, the two hybrid algorithms of back propagation artificial neural network and genetic algorithm were used in the optimum design of the hot pressing parameters of an advanced ZrO2/TiB2/Al2O3 nanocomposite ceramic tool and die material. Compared with the BP algorithm, the predicted results of hybrid algorithm indicated that the combination algorithm can offer a robust and efficient way for the fabrication process design of ceramic tool and die materials.

Abstract: Thermal stability and wear resistance of nanoceramic materials are excellent, so it is an ideal die material and has become one of the increasingly important topics in the field of die research. A new 3Y-TZP nanocomposite die material was prepared with hot pressing technique by using 3Y-TZP, CeO2, Al2O3 and nanometer sized TiC as raw materials. Effects of CeO2 on the mechanical property and microstructure of 3Y-TZP nanocomposite die material were investigated. The addition of CeO2 has obvious effect on the flexural strength and fracture toughness. When the content of CeO2 is 2mol%, the fracture toughness of the composite material reaches 11.22MPa•m1/2. With the increase of CeO2 content, the fracture toughness becomes lower, the flexural strength and hardness first increase and then decrease. When the CeO2 content is 6mol%, the maximum flexural strength reaches 866MPa. The reason for the improvement of mechanical property can be attributed to the effect of CeO2 on the phase transformation of t-ZrO2 and microstructure and the resulted phase transformation toughening mechanism.

Abstract: A computer simulation of the sintering process of two-phase ceramic tool materials has been developed using a two-dimensional hexagon lattice model mapped from the realistic microstructure. The relationship between simulation time and real duration time has been proposed. The mean grain size of simulated microstructure increases with an increase in simulation time, which is consistent with the experimental results.

Abstract: A computer simulation coupled with fabrication pressure for the sintering process of two-phase ceramic tool materials has been developed using a two-dimensional hexagon lattice model mapped from the realistic microstructure. The mean grain size of simulated microstructures by Monte Carlo Potts model integrated with pressure increases with an increase in fabrication pressure, which is consistent with the experiment results. Monte Carlo Potts model coupled with fabrication pressure is suitable for simulating the microstructure evolution at the different fabrication pressure during the fabrication of ceramic tool materials.