No abstract

On the basis of preliminary investigations of the characteristics of the crack-propagation resistance of various types of ceramic and cermet materials, we give a general evaluation of their potentialities in the context of the influence of the structural-metallurgical factor and the micromechanisms of fracture on the serviceability of the materials. We propose to evaluate the mechanical efficiency of ceramic materials by comparing their diagrams of structural strength at room and service temperatures. We found certain advantages of cermets in ensuring crack resistance under short-and long-term loading. We propose a classification of dominant and secondary micromechanisms of stress relaxation that manifest themselves in the process of crack growth in ceramics and cermets.Owing to the significant advantages of ceramic materials over traditional metallic materials with respect to the surface strength (hardness, wear resistance, erosion resistance, and resistance to corrosion fracture) at high temperatures, the former are more widely used for the production of elements of the piston-link assembly of internal-combustion engines, the nozzle-blade assembly of gas and steam turbines, the combustion chamber of rocket engines, etc.[ 1 ]. This favors an increase in serviceability, ensures particular functional properties of the components and units of certain types of equipment, and creates potentialities for the production of machines and engines whose characteristics are significantly better than the corresponding characteristics of their traditionally made analogs.However, ceramic materials are susceptible to brittle fracture due to low crack resistance under short-and longterm loading. For this reason, the problem of extension of the functional application of ceramic materials is reduced, first of all, to the development of methods for increasing the crack-growth resistance, which is important for ensuring sufficient structural strength [2].In the present work, on the basis of investigations of crack-growth resistance performed earlier, we compare potentialities of ceramic materials developed in this country in the context of the influence of the structuralmetallurgical factor and the micromechanisms of fracture on their serviceability. Materials and Methods for Evaluation of Their PropertiesTo perform comparative evaluations, we use three types of domestic ceramic materials that reflect the world trend toward the modification of structural ceramics (Table 1). They include an alumina composition (AI 2 0 3), which is a specific model of simple monophase ceramics, an alumina ceramics modified with zirconium dioxide (A12 0 3-ZrO 2 ), and a typical silicon-nitride ceramics modified with yttrium oxide (Si 3 N4-Y 2 0 3). Both modifications of ceramics were preliminarily tested for a long period of time in order to choose the optimal ratio of the components and the technological mode of sintering that allowed one to guarantee the optimal level of their structural strength [3][4][5][6][7][8]. In addition, for comparison, we con...

No abstract

No abstract

No abstract