High temperature oxidation-sulfidation behavior of Cr-Al2O3 and Nb-Al2O3 composites densified by spark plasma sintering

The high temperature oxidation-sulfidation behavior of Cr-Al2O3 and Nb-Al2O3 composites prepared by mechanical alloying (MA) and spark plasma sintering (SPS) has been studied. These composite powders have a particular metal-ceramic interpenetrating network and excellent mechanical properties. Oxidation-sulfidation tests were carried out at 900 °C, in a 2.5%SO2 + 3.6%O2 + N2(balance) atmosphere for 48 h. The results revealed the influence of the sintering conditions on the specimens corrosion resistance, i.e. the Cr-Al2O3 and Nb-Al2O3 composite sintered at 1310 °C/4 min showed better corrosion resistance (lower weight gains) compared with those found for the 1440 °C/5 min conditions. For the former composite, a protective Cr2O3 layer immediately forms upon heating, whereas for the later pest disintegration was noted. Thus, under the same sintering conditions the Nb-Al2O3 composites showed the highest weight gains. The oxidation products were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy.