Study On The Preparation Of β-Sialon Ceramics And The Influence Of Heat Treatment On Mechanical Properties

In the paper, the samples ofβ-Sialon ceramics with good mechanical properties and microstructure were prepared by pressureless sintering at 1750℃for 2h with the components of Si₃N₄, Al₂O₃, AlN, Y₂O₃ and Nd₂O₃ powder as materials, in order to find reasonable mass percentage of Y₂O₃ and Nd₂O₃, and then the standard samples were healed. SEM, XRD and three-point bending were used to investigate the character of theβ-Sialon ceramics. The following is the contents and results of the experiments.Y₂O₃ and Nd₂O₃ powder was of benefit to decreasing the sintering temperature and proving the relative density, microstructure and mechanical properties, which were found during the preparation ofβ-Sialon ceramics samples under the pressureless condition.The samples had high relative density, mechanical properties and morphologies, which were composed of 36.848%Si₃N₄, 22.372%Al₂O₃, 6.58%AlN, 2.1%Y₂O₃ and 2.1%Nd₂O₃. The bending strength and fracture toughness reached 329.4MPa and 6.058MPa·m1/2.The conclusions drew from the standard samples which were done heat treatment at 900℃, 1150℃, 1300℃and 1400℃each for 2h under vacuum condition showed that the bending toughness of the samples which were done heat treatment both 900℃and 1150℃each for 2h was higher than that of heat treatment undone, but that both 1300℃and 1400℃each for 2h decreased, and the biggest bending strength and fracture toughness of all reached 485.4MPa and 6.42MPa·m1/2, which were done heat treatment at 1150℃for 2h. The bending and fracture toughness, which were undone heat treatment, were only up to 329.4MPa and 6.058MPa·m1/2.The conclusions drew from the standard samples which were done heat-treatment at 900℃, 1150℃, 1300℃and 1400℃each for 2h under air condition showed that the bending toughness of the samples which were done heat-treatment both 900℃and 1150℃each for 2h was higher than that of heat treatment undone, but that both 1300℃and 1400℃each for 2h decreased, and the biggest bending and fracture toughness of all reached 545.9MPa and 6.51MPa·m1/2, which were done heat treatment at 1150℃for 2h.The conclusions drew from the standard samples which were done heat treatment at 900℃,1150℃,1300℃and 1400℃each for 2h, 4h,5h and 7h in air showed that the bending toughness ofβ-Sialon ceramics done heat treatment at 900℃for different time increased continuously, and at both 1150℃and 1300℃at the time from 2h to 4h it increased continuously, and then decreased from 5h to 7h, and it decreased at the time from 2h to 7h at 1400℃end to end.The bending strength was proved higher after heat treatment than that without heat treatment in air, and it reached 610.3MPa.The reason that the bending toughness increased after heat-treatment was that SiO2 was produced when Si₃N₄ reacted with O2 in air. Reasonable quantity of SiO2 producted was better for healing micro-crack, and the reasonable healing results could not make for more or less quantity of SiO2 producted.