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The bimodal-sized (micron+nano) TiC p /Al-Cu composites were successfully fabricated by adding the in situ micron-sized and nano-sized TiC p -Al master alloys into the molten Al-Cu alloy. The composites reinforced with bimodal-sized TiC p exhibited finer α-Al grains and smaller θ′ precipitates, and possessed enhanced room- and high-temperature strength and relatively high ductility compared with the Al-Cu matrix alloy and their counterparts reinforced with monomodal-sized TiC p . The improved tensile properties may be attributed to the more significant precipitation strengthening due to the smaller θ′ precipitates, grain refinement and strengthening effects of the nano-sized and micron-sized TiC p . [ABSTRACT FROM AUTHOR]

Different dendritic grain morphology of an Al-Cu alloy was obtained by adjusting the casting parameters. Compared to the equiaxed dendritic grains, the tortuous dendritic grains led to increased tensile elongation (from 10.4% to 16.8%) and work of fracture (from 11.2 J/mm 2 to 17.2 J/mm 2 ) by more than 50%, respectively. Meanwhile, the high tensile strength (∼540 MPa) and grain size (∼80 μm) were unchanged. The intergranular fracture crack zigzagged along tortuous grain boundaries, reducing the stress concentration at the crack tip and increasing the propagation resistance and path, leading to increased toughness and elongation. The zigzag morphology of grain boundaries was attributed to tortuous dendritic grains. [ABSTRACT FROM AUTHOR]

Adding various amounts of nano-sized TiC p (0.1–0.7 wt%) made a simultaneous improvement in high-temperature strength and ductility of the Al-Cu matrix alloy. The influences of temperature and strain rate on the high-temperature tensile properties and θ′ precipitate sizes in the Al-Cu matrix alloy and the nano-sized TiC p /Al-Cu composites were investigated. Theoretical calculations suggest that the yield strength increment of the composites at 453 K was primarily attributed to the strengthening effect of both the refined θ′ precipitates and TiC p , while at 493 K only the strengthening effect of TiC p was predominant due to the significant coarsening of θ′ precipitates at this temperature. [ABSTRACT FROM AUTHOR]

The creep resistance of the bimodal-sized (micron+nano) TiC p /Al-Cu composite was 10–38 times and 3–6 times higher than that of the Al-Cu matrix alloy and monomodal-sized composites, respectively, attributed to strengthening effects of nano-TiC p and larger number of finer θ′ precipitates. [ABSTRACT FROM AUTHOR]

The creep resistance of Al-Cu alloys deteriorates significantly at high temperatures owing to the coarsening of θ′ precipitates during creep, which limits their applications at elevated temperatures. We fabricated a cast Al-Cu matrix composite containing finer and denser θ′ precipitates by adding 0.3 wt% in situ nano-sized TiC p into an Al-Cu alloy. The steady creep rates of the nano-sized TiC p /Al-Cu composite were 3–17 times lower than those of the Al-Cu matrix alloy at 453–493 K under applied stresses of 120–200 MPa, respectively, which was attributed to the higher threshold stresses of the composite due to the strengthening effect of the nano-sized TiC p and the larger number of θ′ precipitates with smaller diameters. The accelerated coarsening of θ′ precipitates after higher temperature creep could contribute to the decrease of threshold stress with increasing temperature. The analysis of the true stress exponent indicates that the dislocation climb mechanism is dominant in both the matrix alloy and the composite during creep. [ABSTRACT FROM AUTHOR]

Abstract The effects of a small addition of nanosized TiC particles (TiC p) on the microstructure evolution of the Al-Mg-Si (6061) alloy throughout the entire fabrication process including casting, cold rolling and heat treatments were investigated. TiC p impeded the recrystallization and grain growth, refined the grain structure, and evidently increased the tensile strength without obvious decrease on ductility. The ultimate tensile strength and yield strength of the 1.0 wt% TiC p /6061 composite were 330 MPa and 275 MPa in T6 state and 438 MPa and 426 MPa in the as-rolled state, an increase of 42 MPa and 38 MPa, 41 MPa and 52 MPa, respectively, compared to the matrix 6061 alloy. The strength increase is attributed to strengthening effect of TiC p , dislocation accumulation and precipitate strengthening. [ABSTRACT FROM AUTHOR]

The Al2014 composites reinforced with uncoated and Ti 5 Si 3 -coated SiC P were fabricated by stir-casting. The results suggested that the Ti 5 Si 3 -coated SiC P /Al2014 composites exhibited more uniform dispersion of SiC P , higher elastic modulus and tensile properties than uncoated ones. Additionally, the nano-sized Ti 3 AlC 2 interfacial layer was detected between the Ti 5 Si 3 -coated SiC P and α-Al. [ABSTRACT FROM AUTHOR]

At high temperatures, the weakened strength and decreased ductility of Al alloys limit their industrial applications. (TiB 2 –TiC)/Al–Cu–Mg–Si composites were synthesized by adding in situ dual-phased and bimodal-sized (TiB 2 –TiC)/Al master alloys to molten Al–Cu–Mg–Si alloys. The addition of minor amounts of TiB 2 and TiC particles (0.05 and 0.1 wt%, respectively) effectively refined the α-Al grains and θ′ and Q′ precipitates and increased the elevated-temperature strength and uniform elongation of the Al–Cu–Mg–Si alloys. The 0.1 wt% (TiB 2 –TiC)/Al–Cu–Mg–Si composite showed the best yield strength (279 MPa), ultimate tensile strength (366 MPa), and uniform elongation (10.6%) at 493 K, with enhancements of 9.4%, 15.1%, and 24.7% compared to the Al–Cu–Mg–Si matrix alloy (255 MPa, 318 MPa, and 8.5%). The simultaneous increases in the elevated temperature strength and ductility of the composites were attributed to the strengthening effects of the bimodal-sized TiB 2 and TiC particles, θ′ and Q′ precipitation strengthening, and the refined partial recrystallization microstructure. [ABSTRACT FROM AUTHOR]

Abstract Relatively high strength and good ductility are rarely obtained simultaneously in aluminum matrix composites. In the present work, dual-phased TiC n -Al 3 Ti m (n: nanosized TiC particles and m: micron-sized Al 3 Ti particles) particles were in situ synthesized in an Al-Ti-C system via the combustion synthesis method. Subsequently, (TiC n -Al 3 Ti m)/Al hybrid composites were readily fabricated at high addition levels (0, 1, 3, 5 and 7 vol%) via the re-melting and diluting method assisted ultrasonic vibration. Then, the isolated influences of the dual-phased TiC n -Al 3 Ti m particles on the solidification behaviors, microstructure evolution and mechanical properties, at both ambient- and elevated-temperatures, of aluminum alloys were systematically investigated. The experimental results revealed that the α-Al dendrites were substantially refined with a reduction of up to 4 times when compared with that of the unreinforced base alloy. Furthermore, at ambient temperature, 5 vol% (TiC n -Al 3 Ti m)/Al exhibited the optimum comprehensive mechanical properties, and the yield and ultimate tensile strength were 124.3% and 165.2% higher than those of the unreinforced base alloy, whilst the fracture strain was not sacrificed. Theoretical calculations suggest that thermal-mismatch and Orowan strengthening effects contributed most to the yield strength increment, whereas the favourable fracture strain was achieved mainly due to grain refinement. Moreover, at elevated temperature (453 K), the yield strength and ultimate tensile strength were improved by 327.8% and 236.1%, respectively, whilst the fracture strain was still at a relatively high level of 29.2%. The improved thermal resistance primarily resulted from the pinning effects of the TiC n -Al 3 Ti m particles on the grain boundaries and dislocations. Highlights • Novel dual-phased TiC n -Al 3 Ti m particles were in situ synthesized. • TiC n -Al 3 Ti m exerted refinement by heterogeneous nucleation and inhibited growth. • TiC n -Al 3 Ti m enhanced strength at 298 K by thermal mismatch and Orowan effects. • TiC n -Al 3 Ti m enhanced strength at 453 K by pinning and retarding effects. [ABSTRACT FROM AUTHOR]

Abstract In situ TiC p /Al-Cu-Mg-Si nanocomposites were prepared in Al-Ti-C systems with different carbon sources (pure carbon black, mixed carbon source (50 wt% CNTs + 50 wt% carbon black) and pure CNTs) via a combination of the combustion synthesis, hot press and hot extrusion methods. The in situ TiC p /Al-Cu-Mg-Si nanocomposites synthesized by the mixed carbon source obtained the most uniform distribution of nanosized TiC p , highest yield strength (σ 0.2) and tensile strength (σ UTS) and best fracture strain (ε f). The 30 vol% TiC p /Al-Cu-Mg-Si nanocomposite synthesized by the mixed carbon source showed superior σ 0.2 (217 MPa), σ UTS (251 MPa), and ε f (17.7%) at 533 K, which were respectively 4.3%, 4.1% and 136% higher than those of the nanocomposite synthesized by pure C black (208 MPa, 241 MPa and 7.5%) and respectively 3.8%, 1.6% and 88.3% higher than those of the nanocomposite synthesized by pure CNTs (209 MPa, 247 MPa and 9.4%). The superior high-temperature tensile strength and ductility of the nanocomposites prepared by the mixed carbon source were attributed to the homogeneous distribution of nanosized TiC p. The strengthening of the nanosized TiC p and θ′ precipitates was the main strengthening mechanism of the in situ TiC p /Al-Cu-Mg-Si nanocomposites at high temperatures. Highlights • In situ TiC p /Al nanocomposites are prepared in Al-Ti-C systems with various carbon sources. • Nanocomposites prepared by mixed C/CNTs show the best dispersion of nanosized TiC p. • Nanocomposites prepared by mixed C/CNTs show the best strength and ductility at 493 K and 533 K. [ABSTRACT FROM AUTHOR]

Abstract The performances of particulate–reinforced aluminum matrix composites are strongly dependent on alloying elements, precipitates and added particulates. To reveal the sole influence mechanisms of high volume fraction of nanosized particulates on the solidification behavior, microstructure and mechanical properties of aluminum alloys, nanosized SiC P (60 nm) was incorporated into commercial pure Al at different volume fractions (i.e., 0, 1, 3, 5, 7 and 9 vol%) by stir–casting assisted ultrasonic vibration. The results reveal that a fairly uniform dispersion of nanosized SiC P throughout the matrix was achieved at a volume fraction as high as 7 vol%. Average α–Al dendritic sizes were significantly refined from 270 µm for the matrix to 90 µm in the solidified microstructure of nanocomposites. Thermal analysis during solidification indicates that the presence of nanosized SiC P increased the nucleation temperature of α–Al, whilst recalescence during solidification process disappeared. Additionally, the yield and ultimate tensile strength of the nanosized SiC P /Al composites at both ambient temperature and 453 K were remarkably improved, whilst remaining suitable fracture strain. Theoretical analysis suggests that the significant strength increments induced by nanosized SiC P at ambient temperature could be attributed to thermal mismatch strengthening, Orowan strengthening and grain refinement strengthening, while the pinning effect of nanosized SiC P could predominantly account for the strengthening effect at 453 K. Highlights • Nanosized SiC P refined the microstructure via heterogeneous nucleation and inhibited growth. • SiC P enhanced strengths at 298 K mainly due to thermal mismatch and Orowan strengthening. • Pinning effects of SiC P on grain boundaries and dislocation climbing enhanced strengths at 453 K. [ABSTRACT FROM AUTHOR]

The Al-Cu-Mg-Si matrix composites reinforced with in situ hybrid-sized TiC x -TiB 2 particles with sizes ranging from 20 nm to 1.3 µm were successfully synthesized using the Al-Ti-B 4 C reaction system via a method that combined the combustion synthesis and the hot press assisted with hot extrusion. The sizes of the fabricated TiC x and TiB 2 particles increased with increasing TiC x -TiB 2 content. The hybrid-sized TiC x -TiB 2 particles improved the elevated-temperature yield strength ( σ .2 ), the tensile strength ( σ UTS ), and the fracture ductility ( ε f ) of the composites at both 493 K and 573 K. The 40 wt% (TiC x -TiB 2 )/Al-Cu-Mg-Si composite exhibited superior σ .2 (141 MPa), σ UTS (164 MPa), and ε f (31.2%) at 573 K, with enhancements of 60.2%, 72.6%, and 22.4% compared to the Al-Cu-Mg-Si matrix alloy (88 MPa, 95 MPa, and 25.5%). The improvement of the elevated-temperature mechanical properties for the in situ (TiC x -TiB 2 )/Al-Cu-Mg-Si composites was attributed primarily to the strengthening effects induced by the hybrid-sized TiC x -TiB 2 particles and the θ′ precipitation strengthening. [ABSTRACT FROM AUTHOR]

The composites reinforced with Ti 5 Si 3 -coated SiC P showed higher relative densities and mechanical properties than those of uncoated ones. It is mainly due to the translation of Ti 5 Si 3 coating layer into Al 3 Ti interfacial layer during the sintering process, increasing the interfacial bonding strength between α-Al and SiC P . [ABSTRACT FROM AUTHOR]

Abstract: Lignocellulose-to-hydrogen bioconversion is a promising technology to substitute fossil fuel-based energy. Adequate supplement of pretreatment to improve the digestibility of lignocellulose is required for effective fermentative hydrogen production. This study was conducted to evaluate the H2 production from lime pretreated cornstalk and explored the mechanisms of hydrogen yield enhancement. The accumulative hydrogen yield of 155.4 ml/g-TVS was obtained at recommend conditions of lime loading 0.10 g/g biomass, ambient temperature and residence time 96 h, which was 38.1% higher than 115.3 ml/g-TVS for the untreated sample. The enhancement of the hydrogen yield was attributed to the improvement of biodegradability of the cornstalk through lime pretreatment. Chemical composition analysis showed that 23.5% lignin, 27.4% hemicellulose and 10.2% cellulose were removed, while water-soluble substances were increased by 32.3%. Microscopy observation and FTIR and XPS analysis further confirmed that the rigid structure of lignocellulose was disrupted by lime and more cellulose exposed to the surface. [Copyright &y& Elsevier]

• Al matrix composites reinforced with different nanoparticles were investigated. • The corrosion behaviors of the composites were related to the passive film. • TiC p were beneficial for improving the corrosion behavior, but TiB 2p were not. • TiC p reduced the grain boundary phases, improving the corrosion behavior. • TiB 2p at grain boundaries form more corrosion channels, increasing the corrosion rate. Nanosized TiC and TiB 2 particles (TiC p , TiB 2p) can increase the mechanical properties of Al alloys. However, their effects on the corrosion performance of Al alloys are relatively less understood. The corrosion behavior of Al-Mg-Si alloys is improved by adding TiC p and worsened by adding TiB 2p. These changes result from i. TiC p refining the grain structure by acting as nucleants and reducing the number of grain boundary phases and ii. TiB 2p segregating at grain boundaries and accelerating the corrosion. This provides a selection criterion that can be utilized for reinforcement nanoparticles for wrought Al alloys that are applied in corrosive environments. [ABSTRACT FROM AUTHOR]