P. Guiraldenq

Nitrogen implantation in tungsten carbides

In order to investigate some properties of nitrogen implantation in tungsten carbides, massive carbides WC and W2C were prepared by bulk diffusion of carbon in pure tungsten. Isothermal analysis of W-C diffusion couples was performed to determine the optimal conditions for their preparation. Nitrogen implantation was executed with an isotope separator. The samples were analysed by using the15N (p, αγ)12C nuclear reaction and were wear tested. The increase of wear resistance was shown to be effective and the importance of parameters such as fluence or loading conditions was underlined. Nitrogen migration during abrasive wear occurred on a very small scale and was dependent on the nature of the carbide.

Hardening of gold-based dental casting alloys

The ordering and precipitation phenomena responsible for hardening of gold-based alloys used in jewellery and in dentistry are complex and by no means fully understood. The authors of this article review these effects and present evidence which indicates that separation of gold-zinc intermetallic phases may contribute to such hardening in certain alloys.

Ferritic transformation of an austenitic stainless steel by hot dipping in liquid tin or tin-nickel alloys

Abstract By hot dipping 18-10 stainless steel into liquid tin at high temperatures (900–1150°C), there is a superficial ferritic transformation. Nickel additions to the liquid produce changes in the nucleation and growth kinetics and modification of the α phase morphology. The kinetics are controlled by diffusion of nickel at low temperatures and by diffusion of tin at higher temperatures. Discontinuities appear in the temperature dependence of the growth rate, corresponding to a change in the corrosion rate or the disappearance of tin-nickel compounds.

Microstructure and tribological properties of silicon-ion-implanted stainless steel

Abstract Microstructures and tribological behaviour of silicon-implanted austenitic stainless steel 304 (18 wt.% Cr, 10 wt.% Ni) have been studied for different implantation conditions. Samples were implanted with 40 keV ions and fluences were between 5 × 10 16 and 2 × 10 17 Si ions cm −2 . Transmission electron microscopy and grazing X-ray diffraction show that amorphous layers are formed by ion implantation for all fluences. At 2 × 10 17 Si ions cm −2 , some fine Fe 3 Si crystallites are also detected. Friction coefficients and wear rates are decreased if fluences are greater than 10 17 Si ions cm −2 . Transmission electron microscopy of the worn layer is carried out in order to explain the observed phenomena. It is shown that implanted layers allow surfaces to be protected from severe wear and produce changes in the workhardening behaviour of the steel.

In Vitro and in Vivo Cellular Response to Semi-Precious and Amorphous Alloys

In the last few years, a large variety of new alloys has been proposed for orthodontic applications and investigations concerning their biocompatibility have to be carried out.