Microstructure and corrosion study of Fe-based bulk metallic glass obtained by spark plasma sintering

International audienceDue to the necessity of developing new materials with better anti-corrosive properties, bulk metallic glasses are the focus of many research projects. In this study, a metallic glass with Fe48Cr15Mo14C15B6Y2 composition was produced by high-pressure atomization spray and densified by Spark Plasma Sintering. Different sintering cycles, temperatures, and pressures were carried out to conserve the amorphous structure while increasing its density. The temperatures used for this study were below the glass transition temperature, and the uniaxial force was variated between 50 and 400 MPa. Amorphous samples with nearly 98% of relative density were obtained. The effect of the sintering cycle used on the phase transformation and microstructure of the materials was studied. Additionally, the porosity and crystallinity were related to the corrosion resistance properties through electrochemical characterization

Synthesis of magnesium aluminate spinel nanopowder by sol–gel and low-temperature processing

International audienceNanospinel MgAl2O4 powder was obtained by a sol-gel method at low-temperature processing. It was synthesized using aluminum tri-sec-butoxide and magnesium nitrate hexahydrate as precursors, in an acid medium at 80 A degrees C. Heat treatments of the dried gel were performed from 200 to 1000 A degrees C (a dagger T = 100 A degrees C) and the powders were characterized by SEM, XRD, TG/DTA, FT-IR, and HR-TEM. A mixture of semispherical nanoparticles (< 50 nm) of boehmite and unreacted magnesium nitrate was found after the sol-gel reaction. According to HR-TEM and XRD results, a low-crystalline spinel MgAl2O4 started forming at 300 A degrees C, which is a lower temperature than the reported for the same phase in other works. A mechanism of reaction is proposed to explain the formation of spinel at low temperature. At 800 and 900 A degrees C a spinel mono-phase totally crystalline was observed. At 1000 A degrees C, the spinel MgAl2O4 phase is well defined but a second phase, magnesium oxide, was found to be about 6% of the final composition. The crystal sizes were 2.272 +/- 0.054, 5.222 +/- 0.030, 11.610 +/- 0.064, and 25.140 +/- 0.20 nm for the material heat treated at 700, 800, 900, and 1000 A degrees C, respectively. [GRAPHICS