| Sialon ceramics become one of the most important structural ceramic because of their excellent mechanical properties, and they are widely used in automobiles, machinery and energy etc. It has two main types of crystal structure (a-Sialon and β-Sialon). The grains of β-Sialon are usually elongated, with high strength and fracture toughness, but lower hardness. The grains of a-Sialon are usually equiaxed, with high hardness, but poorer strength and fracture toughness. During the process of machining, cutting tool materials not only require good wear resistance, but also put forward higher strength and fracture toughness. Obviously, single-phase Sialon ceramic was limted as the application of cutting tool materials because of having short on the mechanical properties. Many scholars prepared the complex Sialon ceramic by means of regulating the proportion of a-Sialon and (3-Sialon. To a certain extent, it improves the fracture toughness, but it is at the expense of hardness of a-Sialon. Only by changing the proportion of the two phase could not substantially improve their comprehensive mechanical properties. Therefore, some scholars began to research on improving the micro structure of Sialon ceramics. In order to essentially improve the comprehensive mechanical properties of Sialon ceramic for making it better as cutting tool material, they attempted to prepare the elongated a-Sialon. Research shows that the elongated a-Sialon have equivalent fracture toughness with β-Sialon, but the hardness is increased by about 49%. For equiaxed a-Sialon, the fracture toughness of elongated a-Sialon is increased nearly 1 times.In order to research the thermal shock resistance of elongated a-Sialon, this study prepared the elongated a-Sialon by hot pressing firstly. Sialon is a covalent bond compound. It usually needs sintering aids to make it densification in the sintering process. In this paper, the Sialon ceramic was obtained with Y2O3 as the sintering aids and then was characterized, including the phase analysis, microstructure, density, mechanical properties and thermal shock resistance. The study found that:(1) In the experimental process, dense Sialon ceramic can be obtained by adding Y2O3 as sintering aids. The phases mainly consist of a-Sialon (Y0.5Si9.3Al2.7O0.9Ni5.1) and a small amount of grain boundary phase. It can be seen a lot of elongated grains from the SEM image of fracture surface.(2) The hardness, fracture toughness and bending strength of elongated a-Sialon were 16.68±0.33 GPa,5.39±0.09 MPa, m1/2and 597±55 MPa.(3) It was found that the critical thermal shock temperature difference of the elongated α-Sialon is about 1000℃ through rapid cooling strength method. By means of analyzing the microstructure of cross section and surface after thermal shock, it can be found that the specimen was affected by thermal stress and oxidation at the same time in the process of thermal shock damage. The residual strength of specimen experiences three stages:strength retention, strength degradation and strength rising.At the same time, this study made the elongated α-Sialon ceramic cutting tool as the research object, analyzing its cutting performance and wear mechanism. By comparing the cutting performance of commercial Sialon ceramic cutting tool to further validate the importance of the preparation of elongated α-Sialon. The study found that:(1) In the process of turning gray cast iron, the elongated α-Sialon ceramic cutting tool showed good cutting performance because of their excellent mechanical properties and thermal shock resistance. The wear morphology presented hump shape and the main wear mechanisms are adhesion.(2) The cutting performance and wear mechanism of commercial Sialon ceramic cutting tool were affected by different cutting speed. Under the same cutting parameters, the cutting performance of elongated α-Sialon cutting tool was better than commercial Sialon ceramic cutting tool because of improving the comprehensive properties of elongated α-Sialon. |
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