Researchers crack recipe for ultra-strong alloys that could reshape manufacturing
Scientists have engineered a new class of high-entropy alloys that combine multiple metals into stable, magnetic materials capable of withstanding extreme temperatures. The breakthrough uses a rapid processing technique that could accelerate production of stronger, lighter components for aerospace, automotive, and defense applications.
Originaltitel: Effect of high energy ball milling, heat treatment and spark plasma sintering on structure, composition, thermal stability and magnetism in CoCrFeNiGa<sub>x</sub> (x=0.5; 1) high entropy alloys
<p>Nanocrystalline (similar to 10 nm) singe-fcc CoCrFeNiGax (x = 0.5, 1.0) high entropy alloy (HEA) particles with excellent structural and compositional homogeneity were prepared from elemental powders using single-step, short-term (190 min) high energy ball milling (HEBM) at room temperature (RT). Both HEA powders exhibit paramagnetic behaviour at RT with a small ferromagnetic contribution at low fields (saturation magnetization M-s= 4.5 - 7.5 Am-2/kg; average Curie temperature T-c = 130 K - 150 K). They are thermally stable up to 1295 K-1305 K despite the low melting temperature of Ga (302.9 K). Heat treatment up to 1000 K enhances M-s to 59.9 Am-2/kg and T-c to 740 K for the CoCrFeNiGa HEA powder due to an irreversible fcc -> bcc structural transformation, whereas the magnetic properties of CoCrFeNiGa0.5 do not show this enhancement. In-situ TEM heating reveals nanosized sigma-phase Cr-rich precipitates (< 50 nm) at 875 K only for the CoCrFeNiGa HEA powder. Spark plasma sintering (SPS) of powders produces homogeneous nanocrystalline bulk HEAs. SPS at 1073 K of the CoCrFeNiGa0.5 powder increased the crystallinity of the fcc phase. Three-dimensional local compositional mapping at atomic resolution by atom probe tomography indicates a homogeneous distribution of all elements. Bulk HEAs exhibit similar magnetic behavior as heat-treated HEA powders. Combining HEBM and SPS yields homogeneous bulk HEAs with low-melting Ga and enhanced structural, composition, and thermal stability, as well as improved magnetic properties (M-s = 55Am(2)/kg and T-c = 750 K), which is 45% and 47 K higher, respectively, compared to conventional melting approaches.</p>