1992

Wear resistant hard surfaces and shock resistant cores enhance the life of mechanical components such as gears, shafts and cams. Low carbon steels can provide the core properties that such parts need while the surface characteristics can be created by the process of nitriding and nitrocarburizing. M. Rosso, G. Scavino and G. Ubertalli of the Department of Materials Science and Chemical Engineering, Polytechnic of Turin, Italy, use experimental results from research into nitrocarburizing to show the effect it has on sintered materials.

The results of the investigations of thermal behaviour of Li2ZrO3, prepared in the amorphous state by means of sol-gel technique are demonstrated. The thermal treatment was carried out in air under constant heating rate of 5 deg·min-1 and cooling rate of 2.5 deg·min-1. The methods of DTA, TG, Emanation Thermal Analysis (ETA) and dilatometry were used, for characterization of the thermal behaviour in dynamic conditions. The X-ray diffraction patterns were used for characterization of the phase changes observed by TA Methods.

Depending on the preparation temperature and the origin of the raw material, the products obtained by thermal activation of kaolinite lead, by hydrothermal treatment with sodium hydroxide at 102°C, either to zeolite 4A, or to cubic zeolite P, or to a mixture of cubic and tetragonal zeolite P.

Crystalline powders of Li2ZrO3 were prepared by gelling ZrCl4 and CH3COOLi with NH4OH at 50 °C, at different pH values (5, 7 and 8) and for different times (3, 12 and 24 h), then drying and calcining. Compacts from these powders were found sinter to higher densities than a commercial Li2ZrO3; their porosity at 1200°C was close to 3 μm and was suitable for blanket material applications. Tritium release as HTO begins at 300 °C and reaches 73% at 400 °C, a temperature much lower than that required for Li2O.

The artificial aging characteristics at 177 °C of MgAlZn (AZ80A) alloy and its composite reinforced by B4C particles were compared. The morphology and the different distributions of the hardening precipitate (Mg17Al12) were observed by optical microscopy in these two materials. The aging sequence was studied by differential scanning calorimetry. This technique coupled with X-ray diffraction analyses allowed us to evaluate both the precipitation kinetics and the amount of Mg17Al12 obtained as a function of the aging time.

Samples of titanium with a commercial purity grade 4 and of alloys Ti-6Al-4V and Ti-4Al-2Sn-4Mo were surface hardened by laser alloying with boron. This treatment was carried out by contemporaneously laser melting of the titanium alloy surface and powders containing boron which were injected on the surface of the specimens. The alloying powders were deposited on the metal surface either before or during laser treatment. Boronizing powders with different chemical compositions (B, B4C, TiB2, MoB, MoB2 and W2B5) were used to prepare surface coatings.