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.