Development Of Alumina Matrix Nanocomposite Ceramic Die Material And Its Friction And Wear Behaviors

From the requirement for ceramic materials of the forming dies, nanocomposite ceramic die materials with high mechanical properties were fabricated successfully with nanometer composite method by selecting alumina ceramic as matrix which has excellent hardness, wear-resistance, high-temperature resistance, corrosion resistance and wide range raw materials. The strengthening and toughening mechanisms of the ceramic die materials were investigated from the respects of the correlations among the hot pressing process, the microstructures and mechanical properties. It reveals that the intra/inter granular microstructures and the trans/inter granular fracture modes are the main causes for improving the flexural strength and fracture toughness.Based on the stabilization mechanisms for suspensions in the colloidal chemistry, the dispersion of different nano-scale ceramic powders in liquid suspension were discussed by steric stabilization with PEG dispersant. The homogeneous and dispersing nanometer powder and its suspensions were obtained by means of adding different molecular weight PEG, adjusting PEG quality percent and pH values with ultrasonic dispersion and mechanical mixing technology.The effects of component quantity and sintering technique to microstructure and mechanical properties of nanocomposite ceramic die materials were discussed. Nanocomposite ceramic die material of Al₂O₃/Ti(C₇N₃) was fabricated successfully, its flexural strength, fracture toughness and Vickers hardness are 789MPa, 8.1 MPa·m1/2 and 16.4GPa respectively. The flexural strength and fracture toughness are much higher than that of pure micron alumina ceramic material. The nano-scale Ti(C₇N₃) particles are located between or within Al₂O₃ matrix. Thus the typical mixture granular microstructure is formed in the dense compacts, which resulted in the mixture granular fracture modes. The zigzag crack path, which is from the grain boundary into the grain and then turning to the boundary, can result in higher consumption of fracture energy and the increase of fracture toughness. Crack deflection, crack bridging, crack branching and grain pull-out reveals the improvement of the fracture toughness of the composites.The wear mechanisms of nanocomposite ceramic die materials were discussed by analyzing SEM micrographs of wear tracks on typical specimens. It is indicated that in unlubricated conditions of normal load of 50N to150N and rotational speed of 70r/min and 140r/min the friction coefficient of pure alumina is in the range of 0.58～0.8, and the friction coefficient of Al₂O₃/Ti(C₇N₃) nanocomposite ceramic die material is in the range of 0.45～0.65. The wear rate of pure alumina is in the order of 10-14m3/N·m while that of Al₂O₃/Ti(C₇N₃) nanocomposite ceramic die material is in the order of 10-15m3/N·m. The dominant wear mechanisms of pure alumina may be brittle fracture and abrasive wear. While the dominant wear mechanisms of Al₂O₃/Ti(C₇N₃) nanocomposite ceramic die material may be mechanical interlocking and plastic deformation combined with a little micro-fracture and abrasive wear.