Damage formation, fatigue behavior and strength properties of ZrO[2]-based ceramics

It is suggested that a non-destructive testing technique using a three-dimensional X-raytomography be applied to detecting internal structural defects and monitoring damage formation in a ceramic composite structure subjected to a bending load. Three-point bending tests are used to investigate the fatigue behavior and mechanical and physical properties of medical-grade ZrO[2]-based ceramics. The bending strength and flexural modulus are derived under static conditions at a loading rate of 2 mm/min. The fatigue strength and fatigue limit under dynamic loading are investigated at a frequency of 10 Hz in three stress ranges: 0.91-0.98, 0.8-0.83, and 0.73-0.77 MPa of the static bending strength. The average values of the bending strength and flexural modulus of sintered specimens are 43 MPa and 22 GPa, respectively. The mechanical propertiesof the ceramics are found to be similar to those of bone tissues. The testing results lead us to conclude that the fatigue limit obtained from 10{5} stress cycles is in the range 33-34 MPa, i.e. it accounts for about 75% of the static bending strength for the test material

Crystallographic analysis of rock grain orientation at meso- and microscale levels

This paper studies the results of electron backscatter diffraction analysis of naturally deformedpolycrystalline olivine. It also defines the dependence of lattice-preferred orientations of grains on their microstructural position and size. The authors detect the basic mechanisms, consequence and thermal dynamic modes of deformation. They also show that the development of a polycrystalline structure is determined by the following consecutive activation of sliding systems (010)[100] → {0kl}[100] → (100)[010] → {100}[001] → {110}[001], when dislocation sliding and diffusion creep change under the temperature decrease from 1000°C to 650°C

Influence of Interstitial Impurities (H, B, C) on Grain Boundary Cohesion in B2 Ti-based Alloys

The investigation of hydrogen, boron and carbon sorption properties at the Σ5(310) symmetrical tilt grain boundary (GB) and (310) free surface (FS) in B2 Ti-based alloys was carried out by the plane-wave pseudopotential method within density functional theory. The most preferential positions for interstitial impurities at GB were determined. It was shown that impurities sorption energies at GB depend strongly on their local environment. The analysis of electronic properties allows us to establish the microscopic na-ture of chemical bonding of all considered impurities at GB. It was shown that H decreases more signifi-cantly the surface energies than the GB energy in contrast to B and C. This results in decreasing the Grif-fith work that indicates also the decrease of the strength of grain boundary. The segregation of H at the GB makes intergranular fracture much easier because the bonding between metal atoms, which are neigh-bors of H, is weakened. The segregation behavior of hydrogen confirms it as an embrittler for B2 Ti-based alloys. At the same time boron and carbon segregation contrast to hydrogen increase the GB cohesion. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3551

A study of the influence of soft particle size and concentration on strength and strain properties of ceramic composites

In the paper a theoretical study of the influence of particle distribution of soft inclusions-agglomerates in a ceramic composite sample on its strength and deformation characteristics was carried out. A movable cellular automaton method was used to simulate a uniaxial compression test of two-dimensional rectangle composite samples. It was found that the average size of inclusions agglomerate-while maintaining the volume fraction of the particles of the soft phase has little effect on the strength and deformation properties of the simulated samples. The simulation results can help to understand the mechanical properties of such objects within any generalized model

The Study on Thermal Expansion of Ceramic Composites with Addition of ZrW[2]O]8]

The studies on structure, phase composition and thermal properties of (Al[2]O[3] - 20 wt% ZrO[2]) - ZrW[2]O[8] ceramic composites obtained using nanosized, initial powders were conducted. Homogeneously distributed white particles on the polished surface of composites were observed. Phase composition of the composites was represented with corundum, monoclinic ZrO[2] and two modifications of ZrW[2]O[8] (tetragonal and cubic). Linear thermal expansion coefficient values of the composites were determined. The difference in experimental and calculated coefficient of thermal expansion values for composites obtained may be attributed to phase transformations, features of the structure, internal stresses due to thermal expansion mismatch, which contribute significantly to thermal expansion of the ceramic composites

The impurity influence on the formation of oxide layers on TiAL surface

Using ab initio approach the segregation of 4d impurities to low index TiAl surfaces was studied. The site preference for all considered impurities was determined. We demonstrate that Y, Zr, Nb и Mo prefer to occupy the Ti-sublattice whereas other elements are located mainly on the Al-sublattice in case of their low concentration. The influence of impurities on oxygen adsorption on the stoichiometric γ-TiAl(100) surface is investigated. It is shown that the 4d impurities substituting for Ti result in decrease of oxygen adsorption energy whereas it increases if transition metal impurities occupy the Al-sublattice. The effect of some elements of V and VI groups on the adhesion at interfaces such as TiAl(001)Al/TiO2(001), TiAl(001)Ti/TiO2(001), TiAl(100)/TiO2(001), TiAl(110)Al/TiO2(100)O and TiAl(110)Ti/TiO2(100)O in dependence on their location in interfacial layers was also studied. Finally, we demonstrate that the 4d alloying elements with number of electrons from 2 to 5 lead to decrease of the relative stability of Al2O3 to TiO2 and to increase of the formation energy of O vacancy in TiO2. The latter is beneficial to the oxidation resistance of TiAl alloys

Investigation of failure mechanism of Al2O3 specimens subjected to three-point bending test

Experimental loading and FEM simulation-based approach at macroscale are utilized to investigate the failure mechanisms of Al2O3 ceramics. Experimental characterization of the microstructure is carried out using SEM. Recently the mesoscale models of a representative volume of porous alumina ceramics were built on the basis of grain and pore distribution patterns and subjected to uniaxial loading in order to determine effective mechanical characteristics which are utilized for macroscopic simulation in this work. Pre-fracture behavior of specimens undergoes the Drucker-Prager model with non-associated plastic flow rule. Experimental and numerical simulation fracture patterns show that material exhibits predominantly mode I, sometimes passing to mixed mode I+II of crack propagation. Comparison of experimental data and numerical simulation data gives a good agreement

Structure and thermal behavior of zirconium tungstate under heating

The morphology and properties of powders ZrW2O7(OH)[2]•2H[2]O and ZrW[2]O[8], obtained under the conditions of hydrothermal synthesis was studied. Using the high-temperature X-ray analysis, the mechanism of formation of zirconium tungstate was established. The influence of temperature on the structure and properties of materials was studied using shadow-casting method