Macroporous biphasic calcium phosphate bioceramics, for use as bone substitutes, have been fabricated by cold isostatic pressing and conventional sintering, using naphtalen particles as a porogen to produce macropores. The resulting ceramics, composite materials made of hydroxyapatite and β-tricalcium phosphate (TCP) containing ∼45% macropores and with various microporosities, have been submitted to compression and three-point bending tests, toughness tests by single-edge-notched-bending (SENB), and spherical indentation tests. By combining two approaches at two different scales, one for closed porosity and one for open porosity, a model is established to describe mechanical properties as a function of the amount and morphology of porosity. The model assumes a quasi-continuous matrix containing macropores, the matrix being itself microporous, and considers that fracture always initiates on a macropore. The preliminary mechanical tests performed on the sintered ceramics tend to validate the modelling approach.

Modelling the mechanical properties of microporous and macroporous biphasic calcium phosphate bioceramics

Mechanism and microstructural evolution of combustion synthesis of ZrB2–Al2O3 composite powders

A detailed investigation of the effect of alumina diluent on the Al2O3-TiB2/ZrB2 composite by self propagating high temperature synthesis (SHS) dynamic compaction was carried out. A dense composite could be obtained and microstructure could be tailored and controlled by adding alumina as diluent during the SHS reaction. The microhardness values decreased for 5 and 10 wt pct additions of alumna but increased for 15 and 20 wt pct additions. Hardness is influenced by the different phases present and the grain size.

Effect of alumina diluent on the fabrication of in-situ Al2O3-Ti/ZrB2 composite by self propagating high temperature synthesis dynamic compaction

Discrepancies have been noted between the predictions of classical mechanics for dense bodies and the Vickers indentation cracking behaviour of porous YBa2Cu3O7- x ceramics, and in particular a shift in the ‘universal’ indentation diagram of Niihara et al. The hydrostatic constraint factor is measured as the ratio of hardness to yield stress on porous sintered steels. Its introduction into the universal indentation diagram of porous ceramics allows retrieval of the behaviour predicted for dense materials. The question of whether the evolution of the constraint factor with porosity could be common to all porous materials densifying under constrained compression is addressed.

F. Tancret

Papers

Influence of porosity on the hydrostatic constraint factor for evaluating toughness from Vickers indentation cracks in brittle materials