Study of color change and microstructure development of Al2O3–Cr2O3/Cr3C2 nanocomposites prepared by spark plasma sintering

The densification behaviors of Al2O3–Cr2O3/Cr3C2 nanocomposites prepared by a Spark Plasma Sintering (SPS) were investigated in this work. The initial powders used for sintering were Al2O3–Cr2O3, which were prepared by metal organic chemical vapor deposition (MOCVD) in a spout bed. Different colors of the compacts such as green, purple and black were observed after densification process at different SPS temperatures from 1200 °C to 1350 °C. These changes of color were relevant to the existence of secondary phase of green Cr2O3, pink solid solution of Cr2O3–Al2O3 and black Cr3C2, which were formed under the different SPS temperature. The secondary phase of Cr2O3 retarded the processing of densification for spark plasma sintering at 1200 °C. The Cr2O3 reacted with Al2O3 to form solid solution of Cr2O3–Al2O3 and with carbon to form Cr3C2 as sintering temperature increased to 1350 °C. The characteristics of high heating rate, shorter sintering time for SPS and the formation of secondary phase of Cr3C2 effectively reduced the substrate's grain growth, making Al2O3–Cr2O3/Cr3C2 nanocomposites with small grain size.