Fabrication And Properties Of Al₂O₃-Ti（C,N） Cermet Die Materials

For the lower strength, toughness, wear resistance and shorter service life of ceramic die materials, Al2O3-Ti(C,N)/Nb/Cr cermet die materials were fabricated by vacuum hot pressing method to improve the mechanical properties and wear resistance. The effects of components and hot press sintering process on the mechanical properties and microstructures of cermet die materials were investigated. The study on wear resistance of Al2O3-Ti(C,N)/Nb/Cr cermet die materials was accomplished by the friction and wear experiments. The friction and wear properties of cermet die materials were investigated, meanwhile, the wear mechanisms were also studied. The main conclusions are as following:(1) Ti(C,N) added can restrain Al2O3 grain growth and refine the microstructures, so cermet die materials are strengthened and toughened. Metals Nb and Cr added promote densification, refine hard phase grain and improve the microstructures, fracture toughness of cermet die materials. With the increasing of the sintering temperature, materials will be more dense, and the mechanical properties of them are also improved. But over high temperature will induce abnormal grain growth and reduce properties. The shorter holding time induce relatively low density and mechanical properties, and the longer holding time which easily cause excessive grain growth leads to the decline of mechanical properties.(2) The components and hot press sintering process of Al2O3-Ti(C,N)/Nb/Cr cermet die materials were designed. The content of Ti(C,N) is 30%, the content of Nb Cr is 7.5%, hot press sintering temperature is 1650℃, holding time is 20 minutes. Under these conditions, Al2O3-Ti(C,N)/Nb/Cr cermet die material prepared by hot pressing has a bending strength of 792 MPa, Vickers hardness of 20.63 GPa and fracture toughness of 7.1MPa·m1/2.(3) The main toughening mechanisms of cermet die materials are fine grain strengthening and toughening, crack deflection, crack bridging, intergranular fracture and transgranular fracture.(4) The friction coefficient decreases with the increases of the normal load and speed in unlubricated condition. Al2O3-Ti(C,N)/Nb/Cr cermet die material has a lower friction coefficient than Al2O3-Ti(C,N); under the same conditions, the wear rate of Al2O3-Ti(C,N)/Nb/Cr is also lower, it increases with the increases of the normal load and decreases when the speed get faster.(5) The dominant wear mechanisms of Al2O3-Ti(C,N) may be abrasive wear and brittle fracture accompanied by adhesive wear; the wear mechanisms of Al2O3-Ti(C,N)/Nb/Cr cermet die materials are abrasive wear, adhesive wear and fatigue wear.