Stronger composites
Ceramic matrix composites (CMCs) are incredibly strong materials used in jet engines, gas turbines and cutting tools for nickel superalloys. Aluminum oxide is hard and chemically inert, and tungsten carbide is used as a superhard material, but past efforts to create an Al2O3-WC CMC yielded unsatisfactory results. Recently, a study by Japanese scientists, published in Scientific Reports, shows that adding zirconium atoms results in improved Al2O3-WC CMCs.
Previously, no group had developed an Al2O3-WC CMC with a bending strength greater than 1 gigapascal (GPa), which meant that those earlier Al2O3-WC CMCs could not outperform the existing CMC materials. In an attempt to achieve a greater bending strength, a team led by scientists from Nagoya University (www.nagoya-u.jp), in collaboration with NGK Spark Plug Co. (both Nagoya, Japan), found that adding in small amounts of zirconium dioxide (ZrO2) during the creation of Al2O3-WC CMCs yielded “superhard” Al2O3-WC CMCs with bending strengths greater than 2 GPa. Notably, the investigators achieved these considerable bending strength improvements with a relatively modest addition of ZrO2. The additive represented less than 5% of the mass of the finished Al2O3-WC CMCs, which is less than the amount of additive usually present in additive-enhanced CMCs. Atomic-resolution scanning transmission electron microscopy revealed that the Zr atoms were located in thin layers between sheets of Al2O3 and WC, adding strength to the interfaces, which are generally weak points in the composites.