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The tensile fractures of ultrafine-grained (UFG) Al-Mg alloy with a bimodal grain size were investigated at the micro- and macroscale using transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with focused ion beam (FIB), and optical microscopy. The nanoscale voids and crack behaviors near the tensile fracture surfaces were revealed in various scale ranges and provided the evidence to determine the underlying tensile deformation and fracture mechanisms associated with the bulk bimodal metals. The bimodal grain structures exhibit unusual deformation and fracture mechanisms similar to ductile-phase toughening of brittle materials. The ductile coarse grains in the UFG matrix effectively impede propagation of microcracks, resulting in enhanced ductility and toughness while retaining high strength. In view of the observations collected, we propose a descriptive model for tensile deformation and fracture of bimodal UFG metals.

In this study, dry sliding wear of AlSi0.75TiMnFeCux (x = 0, 0.25, 0.5) high-entropy alloy (HEA) produced through mechanical alloying (MA) and spark plasma sintering (SPS) was studied. The microstructure and phase evolution were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The wear behaviour of HEAs was assessed by reciprocating wear monitor under a dry air atmosphere. The findings demonstrated that AlSi0.75TiMnFeCux HEAs were multiphase body-centred cubic (BCC/B2) solid solution structured with complex µ-, L21, and Laves. It was discovered that the microhardness and wear behaviour of AlSi0.75TiMnFeCux were comparable to AlSi0.75TiMnFe HEA after the addition of Cu up to 0.25 molar ratio. The maximum hardness of the AlCu0-0.5FeMnTiSi0.75 HEAs reached around 1021–1035 HV. The tribology results show that an oxidative wear in AlSi0.75TiMnFe while the mixed adhesive-abrasive wear mechanism was prominent in the AlSi0.75TiMnFeCu0.25-0.5 HEAs. [ABSTRACT FROM AUTHOR]

In this study, the effects of Cu addition on AlFeMnTiSi0.75Cux (x = 0, 0.25, 0.5, 0.75, 1.00; in molar ratios) high entropy alloys (HEAs) prepared via mechanical alloying and spark plasma sintering were investigated. The structure, phase, morphology and composition of HEA powders were analysed and the results revealed that the AlFeMnTiSi0.75Cux HEAs exhibited a multiphase structure. Additionally, after sintering at 900 °C, the formation of BCC, µ and L21 phases in the densified HEAs was enhanced. The investigation of the hardness, nanoindentation and compressive properties revealed that the microstructural and mechanical properties of AlFeMnTiSi0.75Cux HEAs were improved at the optimal Cu fraction (0.25 molar ratio). The nanoindentation results revealed that the AlFeMnTiSi0.75Cux HEAs exhibited the highest hardness and elastic modulus (HIT = 19.2 GPa, EIT = 336 GPa). These results improve the current understanding of multiphase HEAs and may pave way for the development of advanced HEAs with superior mechanical properties. [ABSTRACT FROM AUTHOR]