Study On The Internal Friction Of Al₂O₃ Ceramic And Al₂O₃ Composite Ceramics Prepared By Microwave Sintering

Alumina composite ceramics materials have been widely used in various fields due to its excellent comprehensive properties and low cost. However, it's hard to avoid the introduction of various defects and other micro-mechanism in preparation process, which will greatly reduce its properties and application field; At the same time, alumina ceramic is often used in engine parts, bearing and so on. When applied to a specific environment, it may require specific damping performance. Internal friction, as an indicator of damping performance characterization of materials, is also a sensitive tool when studying different kinds of microstructure defects of materials. A variety of qualitative and quantitative information in various microscopic processes of materials can be obtained through the research. It can also provide theoretical guidance for the application of alumina ceramics, and further expand the range of application and reducing loss. In this paper, alumina composite ceramics samples were prepared by microwave sintering, and the internal friction was tested by multi-functional internal friction machine under different conditions. By means of XRD?DSC?SEM?EDS?TEM and so on, the formation mechanism of internal friction peak of alumina ceramic was analyzed and cause of internal friction peaks was discussed.The result shows that alumina ceramic appeared an internal friction peak in the low temperature range, about 200?, due to the influence of the density and grain size of the materials during processing. In the high temperature period, the internal friction of alumina ceramics is associated with grain boundaries. ZrO₂/Al₂O₃ composite ceramics, appeared internal friction peak around 50?, were mainly affected by stress and density of matrix. The internal friction peak around 130 ? was caused by interfacial order parameter and density of matrix. The internal friction peaks appeared around 400? may be related to the porosity of the substrate; The ceramic samples appeared an internal friction peak, called transition peak, when insulated for 7.5 min in sintering process around 600 ?. Another kind of internal friction peak also appeared, which is the superposition of grain boundary internal friction peak and phase transition peak, when the insulation time is 30 min and annealing temperature is500 ?. The internal friction peak of Nb₂O₅-7.5La₂O₃-Al₂O₃ composite ceramics appeared about 150 ? when the Nb2O5 content was 2.5vol.%. When the Nb2O5 content was 15 vol.%, it appeared about 175?, which was attributed to the interaction between the Al3+ vacancies and the domain wall. The internal friction peak near 325?was mainly related to the appearance of Al₂O₃ columnar crystal. The internal friction of Al₂O₃ composite ceramics with the addition of graphene did not change with temperature ranging from room temperature to 600?, the matrix were similar to the pure alumina after annealing, so there was no internal friction peak appeared. While the internal friction over 600? is mainly affected by grain boundary and various interface. Through the comparison of the internal friction of pure Al₂O₃ ceramics and ceramic composite analysis, the addition of ZrO₂ greatly improved the damping property of Al₂O₃ ceramics. In Nb₂O₅-7.5La₂O₃-Al₂O₃ composite ceramics, when Nb2O5 content was higher, the damping property was lower. The addition of graphene had little effect on the damping properties of Al₂O₃ ceramics.