S. M. Barinov

Porous Ceramic Granules of Hydroxyapatite

A ceramic material with a structure featuring narrow intragranular and large intergranular communicating pores with a porosity of 65 vol.% has been developed. The ceramic can be used in surgery for healing bone tissue, for accretion of the alveolar bone, for correction of the abnormal occlusion, and as the vehicle for targeted drug delivery. The large communicating pores facilitate intergrowth of the bone tissue and provide communication between the implant and the surrounding tissues, whereas the narrow pores promote the proliferation of osteogenic cells or serve as the matrix for drug delivery.

Universal R-curve of Crack Propagation Resistance in Ceramic Composites

An analysis of a shape of KR-curves of subcritical crack propagation resistance in ceramic composites is performed on the basis of energy concept of fracture mechanics. Two cases of a broadening of frontal process zone and of crack bridging zone are considered. The existence of “universal K -curve” is proved which is generally described with l’ = F(K’) relationship, where l’ = 1/B is the dimensionless crack increment; F(K’) is a certain function of dimensionless increment of stress intensity factor K’; B is a factor depending on the structure and properties of a material and characterizing the extent of a subcritical crack growth. An analytical expression for F(K’) function have been derived and it is shown that as first approximation “universal K -curve” can be approximated with parabolic law. Examples are R givenfor the composites alumina - silicon carbibe whiskers and lanthanium chromite - chromium as well as for porous zirconia ceramics.

Effect of Sodium Phosphate on Sintering of Hydroxyapatite Ceramics

The effect of Na3PO4 additive introduced into hydroxyapatite ceramics in amounts of 1 and 2% on their sintering shrinkage, formation of microstructure, phase composition, and mechanical properties is considered. The conditions for maximum mechanical properties of densely sintered ceramics are determined.

Delayed fracture of borosilicate glass bonded alumina ceramics

Abstracts are not published in this journal

Dynamic fatigue of ceramics based on aluminum oxide

A comparative study of the resistance of alumina-based ceramic materials with different grain-boundary phases to delayed fracture is described. The tests were conducted by the method of dynamic fatigue in air, water, and a salt solution. It is shown that the ceramics with an alkali-free vitreous phase has a higher resistance to subcritical crack growth than the material with an alkali-containing grain-boundary phase.

Delayed Fatigue of Hydroxy- and Fluorhydroxyapatite Ceramics in Simulated Body Fluid

Ultrafine hydroxyapatite (HA) and fluorhydroxyapatite (FHA) powders were synthesized and dense bioceramic samples were fabricated thereof. The samples were treepoint bend tested in different environments, i.e. in ambient air, distilled water and simulated human saliva, in the wide deformation rate range. Weibull’ statistics test was performed under standard testing conditions but in different media. The stress velocity exponent was evaluated from the dynamic fatigue testing data. The mean strength is shown to decrease when both ceramics are exposed to water or to simulated saliva. HA ceramics is more susceptible to the environment compared to FHA ceramics, due to the later is less subjected to the stress corrosion. Fracture surface observations revealed the crack propagation is of mixed trans- and intergranular mode. Strength distribution changes from uni-modal in air environment to bimodal in harsh conditions of water and saliva, indicating slow increment of flaw size in ceramics. Crack velocity exponent values correspond to transient region from dissociative chemisorption to ion solvation mechanisms of stress corrosion in both HA and FHA ceramics. Generally, FHA ceramics is considered to be much more reliable for application in bone defects replacement or dental reconstruction.

Effect of hot isostatic pressing on the mechanical properties of aluminum oxide ceramics

The influence of the conditions of hot isostatic pressing (HIP) on the mechanical properties of presintered ceramics containing 94, 97, and 99% Al2O3 is studied. It is shown that HIP treatment provides the possibility of increasing substantially the strength, the crack resistance, and especially the modulus of the Weibull function for the statistical strength distribution. The optimum HIP parameters depend on the composition and previous technological history of the ceramics.

On the strain hardening-plastic strain relation for nickel aluminides in bending tests

Abstracts are not published in this journal

On brittle-to-ductile transition in covalent diamond-like and ionic rock salt structure solids

Abstracts are not published in this journal

Mechanical behaviour of nickel aluminide-zirconia transformation-toughened particulate composite

The fracture toughness and strength behaviour of nickel aluminide toughened by partially stabilized as well as by non-stabilized zirconia dispersoids were investigated in the range of zirconia content up to 40 vol%. The temperature dependence of the mechanical properties of the composite with an optimal zirconia content was examined. A considerable increase both in fracture toughness and in bending strength was achieved compared to the base nickel aluminide. To reveal the nature of the toughening and strengthening effects, X-ray diffraction measurements were performed before and after fracture. Residual stresses imposed on zirconia particles were evaluated. Trends in mechanical behaviour have been discussed in terms of microstructure development.