OXIDATION BEHAVIOR OF Ta–W–Ti–Al MULTI-ALLOYS PREPARED BY SPARK PLASMA SINTERING

Abstract

In this study, Ta–W–Ti–Al multi-alloys were prepared by spark plasma sintering (SPS) as a new powder metallurgy technology based on discharge activation and thermoplastic deformation process. The oxidation behavior of the as-obtained sintered alloys were investigated under 1000 and 1200 °C in air atmosphere. Microstructures and phase compositions of alloys and oxides were analyzed using various analytical methods, such as X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), and backscatter electron microscopy (BSE). The sintered samples possessed relative densities reaching up to 98% with achievable densification. The densities of all specimens with high Ti contents exceeded 100%, suggesting the great impact of Ti addition on liquid-phase precipitation. Intermetallic compounds were formed in Ta–W–Al alloys, and samples with high Ti contents displayed grain boundary phases rich in titanium and oxygen. The addition of Ti and Al effectively improved the oxidation resistance of the resulting alloys. A protective alumina layer was formed after oxidation at 1000 °C that made oxidation kinetics of the alloys obeying pseudo-parabolic laws. At the oxidation temperature of 1200 °C, Al₂O₃ reacted with Ta₂O₅ to form the AlTaO₄ alloy with reduced protective effect. The mass gain in the alloys after oxidation at 1200 °C for 4 h was about 7 times higher compared to processing at 1000 °С.