High-temperature tribological properties of Al2O3, Ni–20 mass% Cr and NiAl spark-plasma-sintered composites containing BaF2–CaF2 phase

Al2O3, Ni–20 mass% Cr, NiAl-based composites containing BaF2, CaF2 and SrF2 as solid lubricants were prepared by spark plasma sintering, and their microstructure and high-temperature friction and wear properties were examined. Al2O3–31BaF2–19CaF2 (mass%) composites prepared by spark plasma sintering at 1273 K contained a fine lamellar structure, which consisted of BaF2 and CaF2 phases. The Al2O3–31BaF2–19CaF2 (mass%) composites showed a low friction coefficient (0.3–0.4) at temperatures between room temperature and 1073 K, in addition that they showed the lowest wear rate at 873 K. In this study, a tentative BaF2–CaF2–SrF2 ternary phase diagram was also constructed, which clarified that the BaF2–CaF2–SrF2 ternary system has a large solid solution region at 1473 K.