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In this work, interlayer (Cr vs amorphous CuZr) with various thicknesses ranging from 5 nm to 40 nm were utilized for 1000 nm-thick nanostructured Cu films on polyimide substrates. The effects of heterogeneous interface and interlayer thickness on the fatigue behavior of Cu/interlayer bilayers were investigated by in situ synchrotron X-ray diffraction, electrical resistance measurement, in combination with microstructural examinations. The results demonstrated that the fatigue tolerance highly depends on the thickness and constituent of interlayer. The fatigue lifetime monotonically increases as CuZr interlayer thickness increases, coupled to the yield stress. In contrast, the fatigue lifetime first increases and then decreases with increasing Cr interlayer thickness, reaching its maximum value at a thickness of 5 nm. The underlying mechanisms for this discrepancy can be elucidated in terms of heterogeneous constraint and interface voiding, both of which depend on the interlayer thickness. [ABSTRACT FROM AUTHOR]

A metastable β-titanium Ti–Al–Mo–V–Cr–Nb alloy exhibits a synergistic increasing in strength and ductility via coupling thermomechanical processing and heat treatment in present work. Synergistic effect of the thermomechanical processing and heat treatment on microstructure evolution and mechanical properties of the metastable β-Ti alloy was systematically investigated. α+β rolled sample sheet consumes less time to finish recrystallization, and leads to more uniformly distribution and smaller size of β grains than β rolled sample after same solution treatment. Primary α phase in α+β rolled sample hinders the growth of β grains during solution treatment and the spacing distance of α lamella in α+β rolled sample is smaller than β rolled sample after aging treatment, enhancing the strength significantly. The small spacing distance of α lamella is due to an increase in precipitation density. The small size and homogeneous distribution of β grains provides moderate ductility. After solution treatment at 770 °C for 2 h and aging treatment at 525 °C for 6 h, α+β rolled samples exhibit higher ultimate tensile strength (1550 MPa) and better ductility (6.5 %) than β rolled sample. The relationship between the average grain size of β grains, the average spacing distance of α lamella, and the yield strength of the alloy is quantitatively calculated using mathematical methods. The mechanisms of synergistic enhancement of strength and ductility in the alloy is qualitatively analyzed. These findings facilitate manufacturing high-performance metastable β-Ti alloys at an industry scale using commercially available thermomechanical processing. [ABSTRACT FROM AUTHOR]