Search

• Mechanical properties and microstructure evolution of Ti2448 alloy in micro-to nanoscale are investigated. • Invalidity of the "Smaller is stronger" size effect was discovered in Ti2448 sub-micron pillars uniaxial compression tests. • Improving work hardening and plastic stability is achieved by stress-induced nanoscale α" and ω phase transformations. The nanoscale phase transitions (α″ and ω of 2–5 nm size) are induced by high-level flow stress (∼1GPa) during Ti-24Nb-4Zr-8Sn pillar deformation, leading to the invalidity of the "Smaller is stronger" size effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • Partially-recrystallized β structure with abundant substructures and defects was characterized. • Microstructural hierarchies were obtained in β + α microstructure. • Excellent strength-ductility synergy could be achieved no matter in β or α + β phased condition. • Enhanced strain-hardening rate postponed the occurrence of plastic instability. Microstructural hierarchies of a fine-grained (∼6μm) Ti-10Mo-8 V-1Fe-3.5Al alloy fabricated by hot working process were investigated in β-phased and (α + β)-phased condition respectively. The β-phased microstructure was characterized by a fraction (∼24%) of recrystallized β-grains distributed randomly in the matrix, including subgrains with abundant substructures and defects. After aging, the consequent precipitation behavior of α featured by heterogeneous and insular areas with coarse α(∼0.9 μm) embedded in the ultrafine α(∼0.13 μm). It was clarified that excellent strength-ductility synergy can be achieved by hierarchical microstructure no matter in β or α + β phased condition, in sharp contrast to their coarse-grained counterparts. The microstructural dependence of mechanical properties was discussed in terms of the strain-hardening rate arising from the formation of dislocation pile-up influenced by a dispersion of precipitates, and by grain size (GS). [ABSTRACT FROM AUTHOR]

Abstract: Novel continuous freestanding β-SiC/SiO x C y /Cfree nanocomposite films, namely, β-SiC nano-crystals in amorphous SiO x C y and free C cluster matrix material, were fabricated by melt spinning the polycarbosilane (PCS) precursor. Effects of oxidation curing time and sintering temperatures on the photoluminescence (PL) properties of nanocomposite films were investigated. The PL spectra show two strong blue emissions at 416nm and 435nm, which are unchanged neither with oxygen content nor with β-SiC crystallite size. The PL intensity of the films is enhanced by increasing curing time when sintered at 1200°C. However, a reversed trend is identified after the films were sintered at 1300°C. Spectroscopy and microscopy studies indicate that the radiative recombination of carriers is ascribed to the oxygen mono- and di-vacancy from SiO x C y at the surfaces of β-SiC nano-crystals, whereas the photogeneration of carriers occurs in the β-SiC nano-crystals cores. The obtained results are expected to have important applications in advanced optoelectronic devices. [ABSTRACT FROM AUTHOR]

Quasi-static tensile deformation behaviors at room temperature (RT) and 77 K of Ti-3Al-2Zr-1.5Mo alloy with lamellar microstructure were systematically investigated in this study. The experimental results indicated the excellent cryogenic mechanical properties of Ti-3Al-2Zr-1.5Mo alloy with lamellar microstructure. The strength and elongation of the Ti-3Al-2Zr-1.5Mo alloy at 77 K are much larger than those of RT specimen. It demonstrated that the strength, plasticity and strain-hardening rate were improved simultaneously at cryogenic temperature. Microstructural analysis indicated that strong cryogenic twinning induced plasticity (TWIP) effect occurs in the Ti-3Al-2Zr-1.5Mo alloy with lamellar microstructure. The intersection between the substructure and the α/β interface is one of factors to the nucleation of twins at cryogenic temperature. The optimization of the properties of Ti-3Al-2Zr-1.5Mo alloy should be attributed to the significant TWIP effect at cryogenic temperature. In addition, the cryogenic environment weakens the hindering effect of the interfaces on crack propagation. [Display omitted] [ABSTRACT FROM AUTHOR]