Dual-phase Nanocomposite Research Articles

Bamboo-like dual-phase nanostructured copper composite strengthened by amorphous boron framework

Grain boundary engineering is a versatile tool for strengthening materials by tuning the composition and bonding structure at the interface of neighboring crystallites, and this method holds special significance for materials composed of small nanograins where the ultimate strength is dominated by grain boundary instead of dislocation motion. Here, we report a large strengthening of a nanocolumnar copper film that comprises columnar nanograins embedded in a bamboo-like boron framework synthesized by magnetron sputtering co-deposition, reaching the high nanoindentation hardness of 10.8 GPa among copper alloys. The boron framework surrounding copper nanograins stabilizes and strengthens the nanocolumnar copper film under indentation, benefiting from the high strength of the amorphous boron framework and the constrained deformation of copper nanocolumns confined by the boron grain boundary. These findings open a new avenue for strengthening metals via construction of dual-phase nanocomposites comprising metal nanograins embedded in a strong and confining light-element grain boundary framework.

Crystalline–Amorphous Nanostructures: Microstructure, Property and Modelling

Crystalline metals generally exhibit good deformability but low strength and poor irradiation tolerance. Amorphous materials in general display poor deformability but high strength and good irradiation tolerance. Interestingly, refining characteristic size can enhance the flow strength of crystalline metals and the deformability of amorphous materials. Thus, crystalline-amorphous nanostructures can exhibit an enhanced strength and an improved plastic flow stability. In addition, high-density interfaces can trap radiation-induced defects and accommodate free volume fluctuation. In this article, we review crystalline-amorphous nanocomposites with characteristic microstructures including nanolaminates, core-shell microstructures, and crystalline/amorphous-based dual-phase nanocomposites. The focus is put on synthesis of characteristic microstructures, deformation behaviors, and multiscale materials modelling.

Dual-Phase Nanocomposite TiB2/MoS1.7B0.3: An Excellent Ultralow Friction and Ultralow Wear Self-Lubricating Material.

Proper lubrication is essential to the reliable and efficient operation of mechanical systems ranging from the industrial to the nanoscale. Self-lubricating materials that can self-generate and sustain concurrent ultralow friction and ultralow wear in harsh environments open up a unique realm that is unattainable by traditional external lubrication mechanisms, but developing such extraordinary materials has been a long-standing grand challenge. Here, we devise an unconventional strategy to construct a dual-phase nanocomposite (DPNC) that comprises a wear-resistant phase (TiB2) and an internal lubricant source (MoS1.7B0.3). Tribological tests demonstrate simultaneous ultralow friction coefficient (∼0.03) and ultralow wear rate (∼10-10 mm3·N-1·m-1) of the synthesized DPNC specimen in ambient environments; these superb properties remain intact after the specimen has been annealed at 400 °C in air. First-principles energetic and stress-strain calculations elucidate atomistic mechanisms underpinning DPNC TiB2/MoS1.7B0.3 as an ultimate self-lubricating material. This accomplishment solves the classic lubricity-durability tradeoff dilemma, enabling advances to meet the most challenging lubrication needs.

High-strength and tunable plasticity in sputtered Al–Cr alloys with multistage phase transformations

To raise mechanical strength of metallic materials, methods such as grain refinement and amorphization are usually utilized but sacrifice plasticity. Strength and plasticity are largely dictated by dislocation-defect interactions in crystalline materials and by shear banding in metallic glasses, depending significantly on the length scales of microstructural features. Here we report on the evolution of microstructures and multistage phase transformations from micro/nanocrystalline to an entirely amorphous structure, realized by tailoring the composition of Cr in co-sputtered Al100-xCrx (x = 0–25 at%) alloys. The associated Cr segregation caused the formations of different dual-phase nanocomposites. In-situ micromechanical experiments revealed that the flow stress of Al–Cr alloys can reach 2.4 GPa and the deformation behaviors varied drastically with Cr composition. This study established the mechanistic connection between the Cr composition-dependent evolution of microstructure and ultrahigh strength as well as plasticity, and revealed the benefits of building nanocomposites through a multistage phase transformation to improve the plasticity of nanocrystalline and amorphous materials.

Comparative study of helium bubbles in a Ti-Ta alloy and a Ti/Ta nanocomposite

ABSTRACT The size, density, and distribution of helium (He) bubbles in a Ti-Ta single-phase alloy and a Ti/Ta dual-phase nanocomposite have been investigated using transmission electron microscopy. The Ti/Ta nanocomposite was fabricated via phase separation during high-temperature annealing of the single-phase Ti-Ta alloy. He ion implantation in the Ti-Ta single-phase alloy leads to the formation of nanoscale He bubbles (∼1.7 nm in size, ∼2.6 × 105/μm3 in volumetric density). He bubbles were found to segregate to grain boundaries. Under identical implantation conditions, numerous He bubbles also formed in the Ti/Ta nanocomposite. Closer inspection revealed that the He bubbles in the Ti-rich phase are smaller and of higher volumetric density (∼1.2 nm, ∼8.4 × 105/μm3) than those in the Ta-rich phase (∼3 nm, ∼1.8 × 105/μm3) and the single-phase alloy. He bubbles were also observed to decorate phase boundaries but they were generally smaller than those on grain boundaries. These results suggest that Ti/Ta phase boundaries are less conducive to the growth of large He bubbles than grain boundaries in the Ti-Ta single-phase alloy.

Design optimization and fabrication of a wideband microwave absorber based on dual-phase dielectric semi-metallic nanocomposite

Dual-phase nanocomposites consisting of dielectric polyaniline (PA) of diameter ∼50 nm and semi-metallic expanded graphite (EG) were synthesized by in situ emulsion polymerization technique. This involved integrating EG in varied proportions of EG (0.00, 0.15, and 0.25 wt %) into PA and mixing with novolac phenolic resin (NPR) (10, 20, and 30 wt %) to tailor the microwave absorption properties ofrelative complex permittivity εr(ω) = εr′ – jεr″, where εr′ and εr″ are real and imaginary parts of complex permittivity in the X-band frequency. The measured frequency-dependent εr(ω) values showed significantly enhanced values for PA/EG–NPR nanocomposites with εr′ ∼ 14.5 εr″ ∼ 25.6, and (εr″/εr′) > 1.5 compared with PA–NPR nanocomposites with (εr″/εr′) > 0.25 and were analyzed using the principle of capacitance variation with filler concentration. Based on the Transmission Line Model, design optimization of single-layer microwave absorbers was performed for the developed nanocomposites. The fabricated absorber exhibited measured reflection loss RLm ∼32 dB at 9.7 GHz and RLm −17 dB at 10.9 GHz for 30 wt % PA/EGNPR (EG = 0.15) composite of thickness 3 mm and 20 wt % PA/EG–NPR (EG = 0.25) of thickness 2.5 mm, respectively, with −10 dB absorption bandwidth of 2.4 and 1.7 GHz in the X-band. A triangular-lattice perforated design for PA/EG composite was proposed to enhance the broad impedance matching and absorption bandwidth in the X-band.

Single crystal forms induced diverse interface structures in TiO2 (B)/anatase dual-phase nanocomposites

Two types of TiO2 (B) single crystal forms (SCF) and the induced TiO2 (B)/anatase interfaces with different orientation relationships are investigated by TEM. The dominated (001} SCF is confirmed to reveal larger nanotunnels at the interface which suggests an enhanced Li+ transport properties.

Diffusion of Ag, Au and Cs implants in MAX phase Ti3SiC2

MAX phases (M: early transition metal; A: elements in group 13 or 14; X: C or N), such as titanium silicon carbide (Ti3SiC2), have a unique combination of both metallic and ceramic properties, which make them attractive for potential nuclear applications. Ti3SiC2 has been considered as a possible fuel cladding material. This study reports on the diffusivities of fission product surrogates (Ag and Cs) and a noble metal Au (with diffusion behavior similar to Ag) in this ternary compound at elevated temperatures, as well as in dual-phase nanocomposite of Ti3SiC2/3C-SiC and polycrystalline CVD 3C-SiC for behavior comparisons. Samples were implanted with Ag, Au or Cs ions and characterized with various methods, including X-ray diffraction, electron backscatter diffraction, energy dispersive X-ray spectroscopy, Rutherford backscattering spectrometry, helium ion microscopy, and transmission electron microscopy. The results show that in contrast to immobile Ag in 3C-SiC, there is a significant outward diffusion of Ag in Ti3SiC2 within the dual-phase nanocomposite during Ag ion implantation at 873K. Similar behavior of Au in polycrystalline Ti3SiC2 was also observed. Cs out-diffusion and release from Ti3SiC2 occurred during post-implantation thermal annealing at 973K. This study suggests caution and further studies in consideration of Ti3SiC2 as a fuel cladding material for advanced nuclear reactors operating at very high temperatures.

Ion-induced phase transformations in nanostructural TiZrAlN films

(Ti,Zr)1−xAlxNy thin films (300nm) with Ti:Zr ratio of ~1:1 and Al content in metal sublattice up to x=0.312 were deposited at Ts=270°C using reactive unbalanced magnetron co-sputtering in Ar+N2 plasma discharges. The nitrogen content, y, was understoichiometric when x≥0.102, despite constancy of N2 partial pressure used during growth. The influence of Xe ion irradiation (180keV, 1×1015−1×1017cm−2) on the structure, phase formation and mechanical properties of the films was investigated. The increase in Al content resulted in gradual evolution of the microstructure from single-phase, nanocrystalline cubic (c) solid solution (x≤0.072) to dual-phase nanocomposite (x=0.102–0.200) and then to amorphous (x=0.312) one. Nanocrystalline and amorphous films were stable under irradiation, while crystallization occurred in nanocomposite films for a typical ion fluence of 1×1016cm−2. This phase transformation is associated with the reduction of compressive stress and eventually leads to the development of a net tensile stress inside crystallites. For all films, a decrease of the nanoindentation hardness was observed after an ion fluence of 5×1016cm−2, likely related to the incorporation of Xe impurities, as revealed by RBS data.

Enhanced high rate capability of dual-phase Li 4Ti 5O 12–TiO 2 induced by pseudocapacitive effect

The dual-phase Li 4Ti 5O 12–TiO 2 nanocomposite is successfully synthesized by a hydrothermal route with adding thiourea. The electrochemical performance of the dual-phase nanocomposite as anode for lithium-ion batteries is investigated by the galvanostatic method, cyclic voltammetry and electrochemical impedance spectra. It is demonstrated that the dual-phase Li 4Ti 5O 12–TiO 2 nanocomposite presents the improved electrochemical performance over individual single phase Li 4Ti 5O 12 and anatase TiO 2 samples. After 300 cycles at 1 C, the dual-phase Li 4Ti 5O 12–TiO 2 nanocomposite can still maintain the large discharge capacity of 116 mAh g −1. It indicates that the as-prepared nanocomposite can endure great changes of various discharge current densities to retain a good stability. The large discharge capacity of 132 mAh g −1 is also obtained at the large current density of 1600 mA g −1 upon cycling. In particular, as verified by the cyclic voltammetry, the pseudocapacitive effect is induced due to the presence of abundant phase interfaces in the dual-phase Li 4Ti 5O 12–TiO 2 nanocomposite, which is beneficial to the enhanced high rate capability and good cycle stability.

Mechanosynthesis of complex oxides with fluorite and perovskite-related structures and their sintering into nanocomposites with mixed ionic–electronic conductivity

In this paper we show that mechanochemical approach allows fast synthesis of individual phases with fluorite and perovskite structures and preparation of dual-phase nanocomposites with mixed ionic–electronic conductivity. Binary oxides obtained by mechanosynthesis are frequently metastable compounds which decompose at moderate temperatures before sintering into the dense ceramics. Complex doping provides kinetic stabilization of perovskites and fluorites and allows their sintering into dense ceramics. Moreover, complex doping of structurally different phases makes possible a preparation of compatible compounds for nanocomposites. In all 10 nanocomposites considered here, the chemical interaction (interdiffusion) was found to occur in some degree. Rules are formulated for preparation of composites from compatible compounds. All perovskites and ceria-based composites are likely to be more promising as membrane materials.