Study On Fabrication And Application Fundamentals Of Zirconia Matrix Composite Ceramic Materials For Spinning And Weaving Scissors

Aiming at the disadvantages of zirconia matrix ceramic materials, a new kind of zirconia matrix composite ceramic materials with high mechanical properties has been successfully developed. Under the hot-pressing technology, the zirconia matrix composite ceramic materials, ZrO₂-TiN and ZrO₂-TiN-Al₂O₃, were fabricated by adding the particles TiN and Al₂O₃ with high elastic modulus into 3Y-TZP. The mechanical properties, the low temperature degradation properties, friction and wear performance and the electrical discharge machining performance of the ziconia matrix composite ceramic materials were studied. The toughening mechanisms and the wear mechanisms were also studied. Based on the stress-induced transformation mechanism, the low temperature degradation mechanisms of the zirconia matrix composite ceramic materials were analyzed.The composite ceramic materials, ZrO₂-TiN and ZrO₂-TiN-Al₂O₃, were fabricated by the optimized hot-pressing technology, and its mechanical properties at room temperature were studied. It is shown that there is a good physical and chemical compatibility among ZrO₂, TiN and Al₂O₃. The TiN particles paly an obvious role in toughening and strengthening 3Y-TZP, and the flexural strength and fracture toughness of the composite ceramic materials are all 70% higher than those of 3Y-TZP when the addition content of TiN is 30wt%. The TiN of bigger grain size can improve the toughening effect. A small amount of Al₂O₃ can distinctly improve the density and toughness of ZrO₂-TiN composite ceramic material, but more content of Al₂O₃ is not beneficial to improving the density and the mechanical properties of the composite material. The zirconia matrix composite ceramic materials for spinning and weaving scissors, ZY30T, ZY40T andZY30T5A, were fabricated successfully. Their average flexural strength are 1410MPa, 1390MPa and 1346MPa, the average fracture toughness are 13.3MPa?m1/2, 13.8 MPa?m1/2 and 14.4 MPa?m1/2, and the average Vickers microhardness are 15.1GPa, 15.7GPa and 15.3GPa, respectively.The toughening mechanisms of ZrC^-TiN and ZrC^-TiN-AhCh were investigated. It is considered that the main toughening mechanisms are the crack shielding effect caused by dislocations and toughening effect caused by the glassy phase among the grain boundaries except the phase transformation toughening and particle toughening effect. The particles TiN and AI2O3 with high elastic modulus can increase the elastic strain energy of the matrix and the resistance of phase transformation t-m, and decrease the phase transformation toughening effect of the matrix 3 Y-TZP. There are a great deal of dislocations in TiN grains due to the face-centered cubic microstructure. The dislocations can shield the cracks when the cracks go through the TiN grains. The glassy phase can greatly improve the density and the mechanical properties.The low temperature degradation properties and the mechanisms of degradation resistance for the materials ZrC^-TiN and ZrCh-TiN-AkOa were investigated. It is shown that TiN and AI2O3 can inhibit the low temperature degradation of 3 Y-TZP, and the inhibition function of TiN is better than AI2O3. And the low temperature degradation of the composites doped by the two particles is better than that of the composite doped by the single one. ZY30T, ZY40T and ZY30T5A have an excellent low temperature degradation resistance. Based on the low temperature degradation mechanism of the stress-induced transformation, it is considered that there are two different tetragonal phase, i.e., metastable tetragonal phase with stress restriction and metastable tetragonal phase without stress restriction. It is shown that the glassy phase among the grain boundaries can prevent the nucleation of phase transformation, which is the main mechanism for improving the low temperature degradation properties of the composites.The friction and wear performance of ZrCVTiN and ZrC^-TiN-AbOs are studied. It is shown that TiN can improve the wear resistance of 3 Y-TZP, and the wear resistance ofZrO2-TiN will be improved with an increase in the content of TiN. ZY40T, ZY30T and ZY30T5Ahave a good wear resistance, among which ZY40T is the best.The wear mechanism analysis model of the zirconia matrix composite ceramic materials for spinning and weaving scissors is put forward in the present research. The layer-shape microstructure model of the friction surface for zirconia matrix composite ceramic materials is built. It is considered that the wear pattrn is slight wear when the wear depth lies in the interface between the soft covered layer and the plastic deformation layer, and the wear pattern is severity wear when the wear chipping are separated from the plastic deformation layer. The soft covered layer can decrease the friction. It is also considered that the severity wear mechanism of zirconia ceramic material is the surface fatigue wear, which is caused by the cracks originated from the surface and the subsurface of the materials. The cracks can result in spalling of friction surface.The electrical discharge machining machinability of ZrC^-TiN is experimentally studied. It is shown that the electrical discharge machining of ZY30T and ZY40T is feasible.