PetroMat

A study has been made in order to determine the transition α (h.c.p.) ⇒ β (b.c.c.) temperatures in some two-phase α-β titanium alloys for industrial use: for this aim D.T.A. tests and for comparison, specific metallographic analyses on samples specially heat treated have been carried out.

Results of a Differential Scanning Calorimetry (DSC) investigation on precipitation hardening in solubilized 6061 aluminum alloy and its composites reinforced with SiC whiskers are reported. The exothermic and endothermic effects in DSC traces of these materials (in the solubilized state) have been attributed to phase formation and reversion on the base of the 6061 AA ageing sequence described in previous TEM studies. Apparent activation energies have been calculated according to the Ozawa method in non-isothermal conditions. The ageing sequence in composites is analogous to that of 6061 AA.

Carbon free Fe-Ni alloys (12 and 20 wt.% Ni) have been analysed by X-ray diffraction and surface Mössbauer spectroscopy (CXMS and CEMS) after boriding treatment at 1273 K for 20 hours. Some (FexNil-x)2B and FexNil-xB samples, with different values of x, obtained by heating at 1073 K mixtures of elements in powder form, were used as reference. Besides (FexNil-x)2B and FexNil-xB, a third boride phase rich in boron has been detected in the outer borided layers of the alloy specimens. A third phase appears also in the corresponding X-ray patterns.

The aging response at room temperature of aluminium alloy 6061 was compared with that of its composites containing SiC whiskers or particles. Materials were solutionized for 2 h at two different temperatures (529 and 557°C), quenched in cold water and naturally aged for up to 90 days. The improvement in mechanical characteristics was checked by means of hardness measurements. The microstructural features of aged samples were studied by differential scanning calorimetry. Both aluminium alloy and its composites showed the same aging sequence.

Ageing behaviour at 180 °C of 6061 aluminium alloy-SiCw composites, drawn from bars obtained in various extruded ratios, and 6061 aluminium alloy used as matrix, have been compared. These materials were dissolved in a salt bath at 529 and 557 °C for 2 h, quenched in ice-water, and aged at 180 °C in an oil bath for increasing periods. Ageing kinetics were studied with Brinell hardness measurements and differential scanning calorimetry (DSC).

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.