Study On The Preparation And Crack Healing Of Al₂O₃/TiC Composite

In this paper, Al₂O₃/TiC composite was prepared by hot-press sintering with Al₂O₃ powders and TiC powders. The effects of TiC volume content and sintering temperature on mechanical properties of this composite were individually investigated using SEM, XRD and three-point bending method. A diamond-shaped indentation was introduced to the center of the tensile surface of standard Al₂O₃/TiC composite sample using Vicker's indenter method. The effect of healing temperature and time on crack healing and the mechanism of crack healing were studied. Following is the results:The effect of TiC volume content and hot-press sintering temperature on mechanical properties of composite is remarkable in the condition of keeping the same press, time and rate of temperature rising. When TiC volume content is 30% and the sintering temperature is 1750℃, the values of bending strength and the fracture toughness are maximums, 5.08MPa·m1/2 and 620MPa respectively. The fracture mode in Al₂O₃/TiC composite is mainly intergranular fracture with some transgranular fracture. The TiC particles added improve the mechanical properties of composite remarkably.The existence of cracks greatly reduce the mechanical properties of Al₂O₃/TiC composite, however, the mechanical properties of composite were significantly improved by heat treatment, but the effects of healing temperature and time to the healing results are different. Keeping the healing time for 2h, healing temperature at 800℃, 900℃, 1000℃and 1200℃, the TiC particles in composite are oxidized into TiO₂, which filling cracks as binder, so the bending strength is recover. Heat treated at 1400℃, Al₂O₃ particles begin to react with TiO₂ particles and generate Al2TiO5. The surface of samples starts crack and pull off, which lead to the serious decrease of bending strength. In this test conditions, keeping healing temperature at 900℃and healing time for 2h, the value of bending strength increases by 4.10 times and recovers to 88.65% of that of smooth sample. The bending strength value of composite and the recovery degree decrease with the increase of healing time.The mechanism of crack healing of Al₂O₃/TiC composite is that TiO₂, being oxidized by TiC in the composite, filled cracks as binder, which lead to cracks healing and bending strength recovery. The reaction of crack-healing in Al₂O₃/TiC composite surface is: 2TiC + 3O₂ = 2TiO₂ + 2CO.