Radioactive isotopes reveal a non sluggish kinetics of grain boundary diffusion in high entropy alloys

High entropy alloys (HEAs) have emerged as a new class of multicomponent materials, which have potential for high temperature applications. Phase stability and creep deformation, two key selection criteria for high temperature materials, are predominantly influenced by the diffusion of constituent elements along the grain boundaries (GBs). For the first time, GB diffusion of Ni in chemically homogeneous CoCrFeNi and CoCrFeMnNi HEAs is measured by radiotracer analysis using the $^{63}$Ni isotope. Atom probe tomography confirmed the absence of elemental segregation at GBs that allowed reliable estimation of the GB width to be about 0.5 nm. Our GB diffusion measurements prove that a mere increase in number of constituent elements does not lower the diffusion rates in HEAs, but the nature of added constituents plays a more decisive role. The GB energies in both HEAs are estimated at about 0.8-0.9 J/m$^2$, they are found to increase significantly with temperature and the effect is more pronounced for the CoCrFeMnNi alloy.Comment: 11 pages, 9 figure

Extreme rejuvenation of a bulk metallic glass at the nanoscale by swift heavy ion irradiation

Swift heavy ions can be used as a tool to tune material properties by generating high aspect ratio, nanometric trails of defects, or new disordered phases. This work explores different aspects of using this tool for rejuvenating and enhancing plasticity in bulk metallic glasses. An amorphous alloy with a nominal composition of Pd40Ni40P20 was irradiated with GeV-accelerated Au ions. Irradiation-induced out-of-plane swelling steps up to approxi- mately 100 nm in height are measured at the boundary between irradiated and non-irradiated areas. Changes of the relaxation enthalpy have been investigated using differential scanning calorimetry. Low-temperature heat capacity measurements substantiate an irradiation-induced increase of the boson peak height with increasing fluences. Accompanying transport measurements using radioactive Ag atoms as tracer also revealed increased diffusion rates in the irradiated samples dependent on the total fluence. Nano-indentation measurements show enhanced plasticity in the ion-irradiated glass which can be correlated with an increased heterogeneity as indicated by variable resolution fluctuation electron microscopy. The whole volume of the derived data sub- stantiates a prominent enhancement of the excess volume in the solidified ion tracks and the irradiation-induced modifications are discussed and analyzed in the framework of strong glass rejuvenation within the nanometric ion tracks

Novel multicomponent B2-ordered aluminides: Compositional design, synthesis, characterization, and thermal stability

For the first time, multicomponent alloys belonging to a B2-ordered single phase were designed and fabricated by melting route. The design concept of high entropy alloys is applied to engineering the transition metal sublattice of binary B2 aluminide. The equiatomic substitution of transition metal elements in the Ni sublattice of binary AlNi followed to produce Al(CoNi), Al(FeNi), Al(CoFe), Al(CoFeNi), Al(CoFeMnNi), and Al(CoCuFeMnNi) multicomponent alloys. CALculation of PHAse Diagrams (CALPHAD) approach was used to predict the phases in these alloys. X-ray diffraction and transmission electron microscopy were used to confirm the B2 ordering in the alloys. Thermal stability of the B2 phase in these alloys was demonstrated by prolonged heat treatments at 1373 K and 1073 K up to 200 h. © 2020 by the author. Licensee MDPI, Basel, Switzerland