Fabrication Of Nano-micro Composite Ceramic Tool Materials And Simulation Of The Fabrication Process

In order to improve the comprehensive mechanical properties of ceramic toolmaterials, a new mutli-phase and-scale Al₂O₃nanocomposite ceramic tool materialshave been fabricated with the hot pressed technology according to the chemical andphysical compatibility, the good sinterability of compsites and the multi-phase and-scale design concept. The micro-scale Al₂O₃and SiC particles as the second phase areadded into nano Al₂O₃matrix composites and with Ni, Mo, MgO, Y2O3as sinteringadditives. The relationships among sintering process, mechanical properties andmicrostructure are investigated in the thesis. Meanwhile, the friction and wear behaviorwas studied. Two dimensional and three dimensional models are developed in order tosimulate the microstructure evolution of fabrication.The mechnical properties of nano-micro composite ceramic tool materials whichare respectively fabricated at1550,1620and1690℃are investigated. The mechnicalproperteis of A03which is fabricated at1620℃has the best mechniclal properties.The vickers hardness, fracture toughness and flexural strength is16.69GPa,4.74MPa m1/2and547Mpa, respectively. Artificially made fracture surfaces of thematerials were observed with a scanning electron microscope （SEM）. By analyzing thesamples fracture surface, A02and A03have the clear crystal boundary.The material mechanical properties of different components is investigated on thesame experimental condition. When the composites contains the lower amount of nanoAl2O3, the fabricated ceramic tool materials has the better mechanical properties. Whenthe sintering temperature is1620℃，the vickers hardness, fracture toughness andflexural strength of sample A06is17.12GPa,4.55MPa m1/2and592Mpa, respectively.It is found that the main fracture modes are transgranular and intergranular and themain crack modes are crack bridging, crack deflecting and crack branching byobserving the artificailly made fracture surface and indentation cracks.The wear morphology of nano Al₂O₃matrix ceramic composite materials arestudied using a scanning electron microscope （SEM）. The friction and wearmechanisms of nano Al₂O₃matrix ceramic composite materials were studied. Adhesiveand abrasive wear is the main the form of wear. The friction coefficient and wear rateof the same material are obtained when the experimental conditions are different.When the applied load and rotational speed are300N and160r/min respectively, the wear rates of the sample A01, A02, A03, A04and A05are2.41×10^-7mm³/N m,1.19×10^-7mm³/N m,2.39×10^-7mm³/N m,6.05×10^-7mm³/N m and3.68×10^-7mm³/N m, respectively.In order to simulate microstructure of the nano-micro composite ceramic toolmaterials druing fabrication, two dimensional and three dimensional models aredeveloped. It is found that the size of matrix grain around the second particles issmaller than that of others. Compared the two dimensional and three dimensionalsimulation resultes with the microstructure of experimental ceramic tool materials, it isvalidated that adding the second phase can resist the matrix grain growth.