Ultrastrong nanocrystalline binary alloys discovered via high-throughput screening of the CoCr system

Nanocrystalline (nc) alloys are stronger than their coarse-grained versions. Here, we report ultrastrong alloys, discovered via high-throughput screening of the nc CoCr33-69 materials library. The nc materials library was fabricated using magnetron co-sputtering. The alloys consist of textured, columnar structures with grain size in the nanometric regime. We found that the texture and phase composition can be tailored by changing the Cr concentration. In the investigated region of the nc CoCr system, a relatively broad spectrum of yield strength, determined via micropillar compression tests, was found ranging from 1.41 GPa up to 3.64 GPa. The remarkable strength increment was caused by a chemically- and thermally-driven phase and microstructure evolution of the system. The strongest alloys were found in the regions containing the δCoCr phase, which was considered previously as metastable. Density functional calculations revealed that the δCoCr phase is more energetically favourable in Cr-rich regions compared to single-phase simple solid solutions (HCP, BCC). Experimental results showed that the range of its occurrence is wider than previously thought, i.e. after annealing the δCoCr phase was found above 44 at. % of Cr. We demonstrate that systematic screening of materials libraries can boost the discovery of new materials with outstanding properties.