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

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

Structure, phase content and mechanical properties of aluminium with hard particles after shock-wave compaction

The possibilities to combine metal and metal oxide powders in various compositions open a broad range of mechanical and thermal behavior. When using in nanostructured components the resulting materials might exhibit even more interesting properties, like product effectiveness, tensile strength, wear resistance, endurance and corrosion resistance. Intermetallics like TiAl could be obtained as TiAlx in a quality similar to that obtained from melting where only eutectic mixture can be produced. Similar effects are possible when compacting nanoceramic powders whereas these can be combined with intermetallics. Currently, it is very difficult to produce wires and special shaped parts from high temperature superconducting materials. The compacting by explosives could solve this problem.The present paper uses explosion compacting of Al nanoparticles to create nanocomposite with increased physico-mechanical properties. Russian civil explosive Uglenit was chosen as high energy material (HEM) for shock-wave compaction. The different schemes and conditions were suggested to run the explosion process. Al nanoparticles as produced by electric wire explosion contain 8-10% of aluminum oxide. That aluminum oxide can serve as strengthening material in the final nanocomposite which may be generated in various compositions by explosive compacting. Further modifications of nanocomposites were obtained when including nanodiamonds into the mixture with aluminum nanoparticles with different percentages. The addition of nanodiamonds results in a substantial strengthening effect

Influence of static tensile testing on the deformation behavior of Al–4% Cu alloy containing micro- and nanoparticles

At present, aluminum alloys reinforced with nonmetallic particles are of great interest in various fields of science and technology due to their high specific strength, hardness, wear resistance, and other properties. At the same time there is a great interest in the study of processes occurring during plastic deformation of such materials under static tensile loading. Plastic flow of metals occurs through the creation and movement of linear defects (dislocations), in which there is a phenomenon of discontinuous yielding. An introduction of particles into aluminum alloy promotes a considerable increase of stiffness and specific strength of alloys, and the study of the deformation behavior of such alloys is of great interest. The objective of this research is to analyze mechanical properties and the deformation behavior of aluminum alloy with the identification of mechanisms of plastic deformation when introducing solid nonmetallic micro- and nanoparticles into the soft aluminum matrix. An analysis of the microstructure of the obtained alloys shows that the introduction of particles (Al2O3, TiB2, TiC) leads to a reduction of the alloy grain size from 350 to 170 µm while residual porosity does not exceed 2%. Tensile tests performed show that the change in the type and quantity of particles also changes characteristics of discontinuous yielding, thus resulting in an increase of yield strength (from 18 to 40 MPa), reduction of ductility (from 15 to 2%), and moreover a significant increase of tensile strength (from 77 to 130 MPa), as compared to the initial Al–4 wt % Cu alloy

Effects of transient thermal shock loadings on the structure of zirconia ceramics

In this paper the influence of thermal shock loadings on the phase composition and microstructure of ZrO[2](Y[2]O[3]) and ZrO[2](MgO) ceramics was studied. It was found that thermal shock strains were no effect on phase composition of ZrO[2](Y[2]O[3]) ceramics. Reducing the concentration of high-temperature tetragonal t-ZrO[2] and cubic c-ZrO[2] modifications and rising the content of low-temperature monoclinic m-ZrO[2] crystal system with increasing the number of thermal shock strains were observed. The values of region coherent X-ray scattering of ZrO[2](Y[2]O[3]) ceramics didn't changed, while the crystallite size of ZrO[2](MgO) ceramics decreased. The formation of block structure in all studied ceramics was observed, the sizes of the blocks formed in the ZrO[2](Y[2]O[3]) and ZrO[2](MgO) ceramics were slightly different. The formation of the blocks in ZrO[2](Y[2]O[3]) ceramics occurred on the grain boundaries, while the crystallites in ZrO[2](MgO) ceramics were crushed due to phase transformation

Rheology and porosity effect on the proliferation of preosteoblast on zirconia ceramics

It has been studied ZrO2(MexOy) based porous ceramics, obtained from the powders consisting of hollow spherical particles. It was shown that the structure is represented as a cellular carcass with a bimodal porosity, formed of a large pore close to a spherical shape and the pores that were not filled with the powder particles during the compaction. For such ceramics the increase of pore volume is accompanied by an increase in strain in an elastic area. It was also shown that the porous ZrO2 ceramics had no acute or chronic cytotoxicity. At the same time, ceramics possess the osteoconductive properties: adhesion support, spreading, proliferation and osteogenic differentiation of MSCs

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

The influence of ZrB[2]-SiC powders mechanical treatment on the structure of sintered ceramic composites

The effect of mechanical treatment by planetary ball milling on the properties of hot pressed ZrB[2] - SiC ceramics was studied. It was shown that material densification after mechanical treatment is finished at initial stages of sintering process. Addition of SiC leads to an essential increase of sample density to 99% of theoretically achievable for powder with 2% of SiC, as compared with ZrB[2] with the density less than 76%. It was demonstrated that all defects that were accumulated during mechanical treatment are annealed during hot pressing, and there are no changes of CDD values in sintered