Stored energy plays a crucial role in recrystallization process. One can distinguish two
contributions to this energy. The first one is the elastic energy, connected with residual
stresses, i.e., with grain-grain interaction. Another part of the stored energy is due to
dislocation density, which is mainly localized inside grains. The latter one is considered as a
main driving force of recrystallization. However, the stored energy connected with residual
stresses can also have some influence on this process. Both types of energy can be determined
experimentally and predicted by deformation models. Taking into account both types of the
stored energy, some features of recrystallization textures can be explained.
The aim of the present study was to study the interface implant-bone by synchrotron radiation, the implant has two faces the first one coated with hydroxyapatite and the second uncoated. In orthopaedic surgery, Titanium (Ti-Al-4V) implants are currently coated with hydroxyapatite (HAp), Ca10 (PO4)6 (OH)2, in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface, the new bone reconstituted after two months of implantation must have the same properties like the natural bone in order to accept the implant. Therefore we studied the residuals stresses and texture of the new bone crystals reconstituted at the interface using synchrotron radiation on ID15 at ESRF in Grenoble, France.
The aim of this study was to create a nano-structured coating using Plasma Thermal Spraying (PTS). This process consists in introducing pre-agglomerated nanosized particles in a high-temperature and high-velocity gas jet and projected them onto the substrate to form, layer by layer, a nanostructured coating. In order to retain nanometer grain sizes in the deposited coating through specific PTS technologies, a thermal field and velocity distribution in the plasma jet are analytically calculated. A finite element analysis is employed to calculate the thermal field evolution inside the agglomerated particles and the thermal induced internal stress distribution is determined. The parameters determined by the theoretical analysis are used for experimental coatings. The average crystallite size of nano-hydroxyapatite powder was 90nm. After deposit via Plasma Thermal Spraying (PTS) process and followed by a 2 hours heat treatment to reduce amorphous fraction, the experimental deposited coating shows that it retains the nanometer crystallite sizes. The substructure of nanocrystals was evaluated at about 120nm in size. Such a nanocoating may play the role of nucleation site to bone, allowing a faster stabilization of the implant.
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