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

摘要

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 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, Al_2O_3 reacted with Ta_2O_5 to form the AlTaO_4 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°C.