High-temperature strength of modified Compositionally Complex Alloy Al10Co25Cr8Fe15Ni36Ti6 (in at.%)Thursday (27.09.2018) 09:45 - 10:00 S1/01 - A5 Part of:
High entropy alloys (HEA) are promising candidates for structural materials in applications at high temperatures. When the equiatomic and multicomponent system AlCoCrCuFeNi was found to exhibit a multiphase microstructure and a brittle mechanical behavior, several optimization steps were carried out to discover and explore the novel compositionally complex alloy (CCA) Al10Co25Cr8Fe15Ni36Ti6 (in at.%). After a homogenization step at 1220 °C and following annealing at 950 °C, the alloy shows a microstructure with three phases: Randomly distributed Al rich needles, a Co-Cr-Fe rich γ-matrix and Ni-Al-Ti rich γ´-precipitates. The γ´-particles have a cubic shape, a length of about 450 nm and exist to a volume fraction of about 40 %. This characteristics, even the crystal structure of the phases, are well known from Ni-based superalloys. Primary mechanical characterization showed quite good values of strength and ductility in a temperature range up to 800 °C, competitive to commercial Ni-based alloys like Alloy 800, Inconel 706 and Inconel 617. Therefor the chemical composition is adjusted with useful trace elements, known from Ni based superalloys for their special impacts, e.g. the solid solution strengthening of the matrix or the stabilization of γ´-particles. With trace elements improved initial CCA is characterized respective microstructural attributes, especially concerning shape, size and fraction of precipitations. Furthermore alloys are manufactured using induction melting under argon atmosphere and the “Bridgman process” for directional solidification. Samples for mechanical testing are prepared by electrical discharge machining (EDM) and finally high-temperature tensile tests are performed at room temperature and at elevated temperatures up to 1000 °C.