Investigation On The Moderate Temperature Plastic Deformation Of Amorphous Ceramics

Ceramics are known to be hard and brittle. They normally exhibit little to noplastic deformation prior to fracture. This is a consequence of the strong ionic andcovalent bonds, which make the movement of dislocation through the structuredifficult. In recent years, some researchers tried to improve the plasticity bydeveloping amorphous ceramics. Because of the long-distance disordering structure,there exists none dislocation and grainboudary in the amorphous materials, whichavoids the structural limits of the crystalline ceramics. In this paper, we investigatedthe moderate temperature compressive behavior of the Al2O3-ZrO2, Al2O3-SiO2andAl2O3-MgO amorphous ceramcis. Effects of the temperature and crystallites on thecompressive behavior were also addressed. The prepatation of amorphous sampleincluded the production of amorphous powders and the hot pressing of the cyclinders.Amorphous powders were obtained through the calcination of the percursor. Thecylinders were hot pressed by using a cubic hydraulic pressing machine. Amorphoussamples were all fractured in the elastic deformation region when compressed at roomtemperature. The largest compressive strain was smaller than10%. The compressivestrains at room temperature were acributed to the compression of the possible poresand the formation of shear bands in the amorphous matrix. When the amorphousAl2O3-ZrO2samples were compressed at500-700°C, the brittle fracture transited toplastic deformation with the increasing temperature. The sample compressed at700°Cexhibited elasticity up to a strain of28%followed by a plateau region to about35%.The elastic modulus was2870MPa. The existence of nanocrystals in the amorphoussamples was found to lead to an increase of the compressive porperty. However,excess nanocrystals would induce the negative effect on the compressive behavior.When compressed at600-800°C, the amorphous Al2O3-SiO2exhibited high elasticity.The samples were still in the elastic region before unloading. The elastic modulusreduced with the increasing temperature. The elastic modulus was1922MPa whenthe sample was compressed at800°C. Amorphous Al2O3-MgO samples were facturedin the elastic region when compressed at500-600°C. During the compression test ofthe amorphous ceramics, the pores were compressed firstly. The deformation behavior of the amorphous materials was achieved through the free volume compression andshear bands formation in the amorphous structure. In the sample with strong networkstructure, higher compressive strain could be achived, which due to the major role offree volume compression. In the sample with weak network structure, the major roleof shear bands movement led to smaller compressive strain.