Some features of formation of the structural strength of ceramic materials

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...

The Effect of Yttria Content on Microstructure, Strength, and Fracture Behavior of Yttria-Stabilized Zirconia

“…The authors showed that additions of 10–20% ZrO 2 efficiently inhibited the growth of Al 2 O 3 crystals and, thus, positively affected the mechanical behavior of the ceramics. In Reference [ 32 ], the authors have proved that the optimal mechanical properties of zirconia ceramics and alumina doped with zirconia should be determined by estimating both the fracture toughness and strength characteristics.…”

The Effect of Sintering Temperature on the Phase Composition, Microstructure, and Mechanical Properties of Yttria-Stabilized Zirconia

“…It is critically important to manufacture materials resistive to the aggressive operating environment [35][36][37][38] to avoid microstructure degradation [39][40][41][42]. Therefore, along with strength and tribology tests of materials as the most popular methods for diagnosing their load-bearing capacity, the indentation test, known as the simplest mechanical method [39,43], is widely used.…”

THE EFFECT OF ULTRA-FINE ALLOYING ELEMENTS ON THE PHASE COMPOSITION, MICROSTRUCTURE, HIGH-TEMPERATURE STRENGTH AND FRACTURE TOUGHNESS OF Ti–Si–X AND Ti–Cr–X COMPOSITES

“…The specimens were tested according to a three-point bend scheme in a temperature range 20-1000 °C. Based on the "loadflexure" dependences, the fracture stress (σf ) was calculated by the following equation [24,31,35,75]:…”

“…Besides, distinct "needle-shaped Cr2AlC phase-Ti(Cr) matrix" interfaces disappeared due to the interdiffusion of chromium, aluminum, and oxygen between the chromium oxide phase, the Cr2AlC MAX phase, and the matrix phase. This, in turn, caused a change in the fracture micromechanism [54,75]. In this composite, high-temperature fracture occurred at 800 °C (Fig.…”

“…Wear resistance and strength tests of ceramics and composites are widely used for estimating the bearing capacity of the corresponding products [54,[66][67][68]. However, to prevent the degradation of microstructure of materials in environmentally assisted harsh conditions [69][70][71][72][73], there is a need to obtain material resistive to microstructural changes in such conditions [74][75][76][77]. Microhardness and fracture toughness serve as characteristics of material for estimating its resistance to the nucleation and growth of microcracks.…”