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Abstract A novel vertically aligned carbon nanotube/dense SiC (VACNT/SiC) composite was fabricated by cyclic precursor infiltration and pyrolysis technique. It exhibits ultrahigh Young's modulus, hardness and compressive strength thanks to the dense microstructure, which surpass the values ever reported in literature. The VACNT/SiC composite is always stronger at 0° loading direction than at 90° direction with respect to CNT orientation due to the stronger axial property of individual CNT, despite that different deformation mechanisms were demonstrated at the two loading directions. Specifically, interfacial debonding occurred during fracture of the VACNT/SiC composite, which suggests a weak bonding nature of the VACNT/SiC interface. Graphical abstract Mechanical anisotropy of a novel nanostructured composite made up by high-density vertically aligned CNT arrays and dense SiC matrix. Unlabelled Image [ABSTRACT FROM AUTHOR]

Ternary diffusion behavior in Co-Al-V ternary alloys was investigated at 1373 K and 1473 K (1100 °C and 1200 °C) by the solid-state diffusion-couple technique. The extraction and interpolation of diffusion data allows the diffusion properties of Fcc Co-Al-V alloys to be mapped in the composition arrays of Al and V. A full picture of the diffusion properties was then constructed by interpolating all accessible interdiffusivities and impurity diffusivities of Co-Al binary and Co-Al-V ternary with a Redlich-Kister polynomial, in a graphic manner depicting a rapid increase of Al diffusion with increasing Al and a weak decrease with the V addition alone. Further incorporation of a nanoindentation technique enables the nanohardness property of the Co-Al-V fcc alloys to be screened in the Al and V arrays. The hardenability in the Co-Al-V alloy system has been evidenced; specifically, the alloy arrays containing higher contents of V, being solution-and-quenching processed, exhibit more effective strengthening than those with the addition of Al. The discovery of Co-Al-V alloys with comparable nanohardness but differing alloy compositions could facilitate the strengthening design of next generation Co-based alloys. [ABSTRACT FROM AUTHOR]

The effect of carbon nanotube (CNT) orientation on the mechanical properties and fracture mechanisms of a vertically aligned CNT/C composite was studied in this work by a combination of nanoindentation and micropillar compression techniques. The results suggest stronger response of the composite when loading parallel to the CNT orientation. This led to higher Young's modulus and hardness (≈34 GPa and ≈3.75 GPa) at this direction than those at perpendicular direction (≈19 GPa and ≈2.6 GPa). The mechanical anisotropy led to fracture mechanisms that were also dependent on the CNT orientation. At 0° direction, the composite was fractured into segments by splitting of the micropillar. While at 90° direction, the composite was much brittle and was fractured by dual shearing, implying a strong CNT/C interface. [ABSTRACT FROM AUTHOR]

• SiO 2 oxide scale formed inside plasma wind tunnel maintains an amorphous microstructure. • Young's modulus and hardness of SiC/SiO 2 evolved linearly with penetration depth. • Compressive residual stress in SiO 2 may increase's its nanoindentation hardness. • SiO 2 delamination has a negligible effect on the nanoindentation response of SiC/SiO 2. Mechanical strain and delamination of surface oxide from substrate are important mechanisms leading to failure of thermal protection systems in hypersonic vehicles. In this work, the deformation and fracture mechanisms of a thermally oxidized SiC/SiO 2 , formed by dynamic oxidations inside a plasma wind tunnel, are studied by nanoindentation experiments and finite element modeling. The results show an amorphous and uniform SiO 2 formation on β-SiC at 1200∼1400 °C in the plasma flow (pressure ≈6.5 kPa), after long-term single/repeated oxidations. In the plasma environment the passive oxidation of SiC is slow, as a result the as-formed SiO 2 is very thin. The SiO 2 thickness is only ≈680 nm after 8 × 500 s dynamic oxidation. SiC/SiO 2 exhibits a strong depth dependent indentation behavior, and at a critical indentation depth, delamination of SiO 2 oxide scale is triggered. Finite element modeling helps decouple the effects of SiC substrate, residual thermal stress and interfacial delamination on the nanoindentation response of SiC/SiO 2. The results evidence that delamination has a negligible effect on the nanoindentation response, and the main contributions are the SiC substrate and residual thermal stress. This work may forward the fundamental understanding of deformation and fracture mechanisms of oxide scales on thermal protection materials in response to localized loading conditions. [ABSTRACT FROM AUTHOR]

Mechanical performance of ceramic/ceramic nanolaminates at elevated temperatures is a main concern when they are applied as protective coatings on compressed blades of aeroengines. In this work, the deformation mechanism and mechanical properties of physical vapor deposited TiN/ZrN nanolaminates are studied by instrumented nanoindentation at 25–450 °C. The effects of layer thickness and temperature are highlighted, with the help of detailed microstructural characterizations. The results show a cracking activity of individual layers for nanolaminates with 50 nm thick layers at 25 °C, which is detrimental to the mechanical performance and arises a strong indentation size effect. In addition, due to nanocrystalline structures of both TiN and ZrN layers, reduction of layer thickness is not effective to strengthen the nanolaminate. As a result, 'the thinner, the stronger' rule that works for most nanolaminates does not hold for the specific TiN/ZrN system. The indentation cracking activity is prohibited at elevated temperature due to thermally activated plasticity of both layers. An approximate linear softening in modulus and hardness, as determined by nanoindentation, is observed. Based on the high temperature data, 'apparent' activation energy for TiN/ZrN nanolaminate is finally quantified. The work may forward the advance of novel ceramic/ceramic nanolaminates in hot-section components of aeroengines. [Display omitted] • Cracking of individual layers in TiN/ZrN is responsible for indentation pop-ins at 25 °C. • 'The thinner, the strong' rule does not hold for TiN/ZrN due to nanocrystalline structure. • TiN/ZrN experiences softening at elevated temperatures due to thermal activated plasticity. [ABSTRACT FROM AUTHOR]

This work focuses on the anisotropic deformation and fracture mechanisms of a typical physical vapor deposited TiN/ZrN multilayer, employing novel nanoindentation and micropillar compression techniques. The results highlight a stronger nanoindentation response of the multilayer when loaded perpendicular (90°) to the layer orientation, and the deformation was mainly controlled by the plasticity of ZrN layers. In comparison, at parallel (0°) orientation, the kink banding and the induced cracking may weaken the constraint beneath the indenter, thus leading to degraded hardness. By considering the anisotropic deformation mechanisms, nanoindentation finite element modeling was further performed to give reliable predictions on the strength at the inclined orientation. The modeling results suggest a dominant deformation mechanism that occurred mainly in the ZrN layers, with minor contribution from the stiff TiN layers. As a result, a minimized hardness was predicted at 45° loading direction with respect to layer orientation. Finally, the micropillar compressions show a brittle nature of both 90° and 0° oriented micropillars, and a higher fracture strain was obtained at 90°, due to the observed crack termination mechanism at this orientation. [ABSTRACT FROM AUTHOR]

Nanolaminates made up by alternative Ni and Al nanolayers are widely applied to solder structural materials, due to abundant heat releases when supplied with an energetic input. This work studies the microstructural evolution and mechanical properties of Ni/Al nanolaminates with a wide mole ratio of Ni (M Ni , 0.18–0.53), to ascertain the role of Ni x Al y intermetallic phases during heat-treatment. To this end, 3 nanolaminates with Al thickness fixed at ≈110 nm and Ni thickness varying 15–75 nm are fabricated and are heat-treated at 400 °C, to trigger formations of NiAl 3 , Ni 2 Al 3 and NiAl intermetallic phases. The results suggest an enhanced strength of Ni/Al after heat-treatment. However, their evolution with M Ni is complex. The nanolaminate with M Ni ≈0.18 is the softest after heat-treatment, due to the dominant plasticity of residual Al phases. The maximized strength is achieved when M Ni ≈0.40, in which a novel NiAl 3 /Ni 2 Al 3 nanolaminate structure is formed. Owing to the brittleness of both phases, the nanolaminate after heat-treatment is fractured by shearing upon uniaxial compression. The best strength-ductility synergy is achieved when Ni mole ratio ≈0.53. In the heat-treated nanolaminate a homogenous nanocrystalline NiAl phase is formed. As a result, the nanolaminate exhibits excellent ductility and intermediate strength among the 3 nanolaminates. [ABSTRACT FROM AUTHOR]