The Isothermal Oxidation Behavior of a Ti3Al-Nb-V-Mo Alloy
The isothermal oxidation behavior of Ti-24Al-14Nb-3V-0.5Mo alloy in synthetic air from 700°C to 1000°C was studied. The main emphasis was focused on the effect of microstructure obtained by different processes of melting and hot rolling, i.e. large and duplex of 2+B2, on the oxidation resistance. Regardless of the microstructure, the overall oxidation process of the specimens exposed at 700°C was dominantly controlled by the beneficial effect of Nb-addition due to the formation of a continuous -Al2O3 layer in the scale. However, both specimens showed poor oxidation resistance above 900°C, especially for the as-rolled specimen, because of higher volume fraction of the 2-phase. The spallation occurred in both specimens at 1000°C, which was probably relative to the formation of Ti2AlN between the thick scale and the substrate except for the TiO2 and -Al2O3.
Mechanical properties and oxidation behavior of the Ti–24Al–14Nb–3V–0.5Mo alloy sheet
Abstract Tensile properties of the Ti–24Al–14Nb–3V–0.5Mo alloy (at.%) solution treated at 1000 °C after hot-rolling was studied in the temperature range between room temperature and 700 °C. The tensile strength was sensitive to the test temperature and was decreased as the temperature increased from 200 to 500 °C. Tensile strength of the alloy at room temperature initially increased gradually with an increase in the strain rate from 8.3 × 10−4 to 0.33 s−1 followed by a slow hardening with increasing the strain rate to 8.3 × 10−1 s−1. The alloy exposed at 700 °C showed the best oxidation resistance due to the formation of a continuous α-Al2O3 layer in the scale. However, the beneficial doping effect of Nb addition on the oxidation resistance above 700 °C was probably overlaid by fast internal diffusion of oxygen, which was proved by a thick transitional layer beneath the scale in the specimen exposed at 800 °C.
TEM observation of the alpha(2)/O interface in a Ti3Al-Nb alloy
A study of the microstructures of a Ti-24Al-14Nb-3V-0.5Mo (at%) alloy was carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), anc high-resolution electron microscopy (HREM). The results indicate that the O-phase is directly derived from the alpha(2)-phase and is distributed all over the primary alpha(2)-grains with fine plate-like form. Transformation of the alpha(2) to the O-phase is explained by a diffusional growth mechanism, and the interface between the alpha(2) and O-phases is completely coherent. (C) 1997 Elsevier Science B.V.