MECANIQUE DE PRECISION

The purpose of this work is to study the effect of ion exchange strengthening on the erosion wear resistance of a soda lime glass exposed to sand blasting and to examine the influence of the residual stresses introduced during sand blasting. All sand blasting erosion tests were carried out in laboratory at normal incidence with a sand flux velocity of 12 m/s using incremental eroding masses up to a cumulative mass of erodent of 210 g. Three sets of glass samples were used for this study. The first set of glass samples was strengthened by ion exchange in a salt bath containing a mass of 98% KNO 3 and 2% Al 2 O 3 . Glass samples of the second set were exposed to sand blasting in their as received state whereas those of the third set were submitted to an annealing treatment after each incremental erosion test in order to eliminate any residual stresses introduced during sand blasting. After a detailed characterization of the sand used and the determination of the mechanical properties (microhardness and fracture toughness) of both the treated and untreated glasses, we compared the evolution of the mass loss, the erosion rate, the roughness and the optical transmission as a function of the eroding mass for the three sets of glass samples. The results show that the ion exchange treatment improves slightly the glass erosion resistance mainly for small eroding sand masses. The ion exchange treatment becomes less effective beyond an erodent mass of 120 g where the erosion rate for the different sets tend toward nearly the same steady state. All the mean arithmetic roughness curves show a maximum in the interval (90-120) g and tend after a slight decrease toward the same value (Ra%2.2 mm). The optical transmission decreased sharply for all glasses independently of the treatment they received after a surface degradation with a mass of 210 g. The difference in the behavior of the as received glass samples and of those annealed after each incremental test reveals the importance of the residual stresses introduced during sand blasting. They seem to effectively enhance the mass loss. #

In this work, different composites (zircon-mullite, zirconia-mullite-zirconia, mullitezirconia and alumina-zirconia-mullite) were developed by reactive sintering of a powder mixture of boehmite (AlOOH)) and zircon (ZrSiO ) 4 . These powder mixtures were mixed and ground by ball milling and then pressed in cylindrical form. Finally, the green specimens were sintered in air during 2 hours between 1400°C and 1600°C, with a heating and cooling rate of 5°C/min.

Low cost composite ceramics based on zircon-mullite-zirconia-alumina phases were prepared by reaction sintering of boehmite (AlOOH) and zircon (ZrSiO 4 ) powders. Boehmite to zircon weight ratios of the starting powders were varied (10 to 90 wt. %). The green compacts were made by uniaxial pressing at 7 MPa followed by cold isostatic pressing at 250 MPa. A reactive sintering in air of these compacts was made at different temperatures between 1400 and 1600°C during 2 hours. A quantitative evaluation of the present phases was based on XRD. Dilatometric tests on the reaction-sintered composites were carried out in order to study the zirconia phase's transformations and their thermal expansion coefficient (). In addition, the effects of both boehmite/zircon ratios and sintering conditions on the mechanical properties (Hardness Hv, Elastic modulus E and fracture toughness K IC ) of the obtained composites were characterized by Vickers indentation.