Effects of friction stir processing on the microstructure and superplasticity of in situ nano-ZrB2/2024Al composite

In this study, in situ nano-ZrB2/2024Al composites fabricated from 2024Al–K2ZrF6–KBF4 system were processed by friction stir processing (FSP) to achieve superplasticity of the composites. And the effects of particle contents (1 wt%, 3 wt%, 5 wt%), matrix grain size (micron or sub-micron), strain rates (5×10−3 s−1, 1×10−2 s−1, 2×10−2 s−1) and deformation temperatures (400 K, 480 K, 600 K, 700 K, 750 K) on the superplasticity of the composites were investigated. After the friction stir processing, the coarse grains of the cast composites with matrix grain size of about 80–100 μm and nano-ZrB2 reinforcement size of 30–100 nm were crushed into small grains about 1 μm in size, and the uniformity of the nano-ZrB2 reinforcements was also improved. And under the same superplastic tensile testing condition at the temperature of 750 K and strain rate of 5×10−3 s−1, the FSP nano 3 wt%ZrB2/2024Al composite exhibited an superplastic elongation of 292.5%, while the elongation of the corresponding cast composite was only less than 100%. Meanwhile, the m values of the FSP composites were always higher than the cast composites, especially the FSP composites with 3 wt% particles has the m value of 0.5321 i.e., the FSP composites should had better superplastic properties than cast ones. Furthermore, the FSP composites had higher apparent deformation activation energy (Q) than that of the lattice diffusion of pure aluminium, indicating that the deformation mechanisms of the FSP composites should be grain boundary sliding mechanisms

Synergistic reinforcement of in situ ZrB2 particles and Sc on the corrosion behaviour of 7N01 alloy

In this study, the effects of in situ ZrB2 particles and rare earth element Sc on the corrosion behavior of 7N01 alloy were investigated separately, with the characteristics of their synergistic enhancement being elucidated. The introduction of Sc into the ZrB2/7N01 composites led to an enhancement in both the distribution and morphology of the in situ particles, with the size of ZrB2 particles being significantly reduced and large particle clusters almost disappearing compared to the situation without Sc addition. A decrease in the grain size of the matrix alloy 7N01 from 170 μm to 33 μm was also observed when the Sc addition was 0.5 wt%. The low corrosion susceptibility observed after the addition of Sc was attributed to the refinement of grains and the inhibition of the formation of precipitate-free zones. The addition of ZrB2 improved corrosion resistance by promoting the precipitation of Al3Sc precipitates. Importantly, it was found that the 7N01 alloy with 3 wt% ZrB2 and 0.5 wt% Sc exhibited high mechanical properties and admirable corrosion resistance, which makes it a promising material for various applications. In summary, this study highlighted the individual and combined effects of in situ ZrB2 particles and rare earth element Sc on the corrosion behavior of 7N01 alloy, with valuable insights being provided for the development of advanced structural composite materials

Effect of Resin Type on the Tribological Properties of a Three-Dimensional Self-Lubricating Composite Surface

In this paper, three kinds of polymer, of epoxy resin (EP), phenolic resin (PF), and unsaturated polyester (UP), were used as fillers to prepare the laminated composite surface, and the tribological properties of a composite surface were studied under dry sliding condition. The results showed that: (i) the composites surface without MoS2 exhibited high friction coefficient and high wear rate at 25 °C, while the friction coefficients were reduced when the temperature increases to 100 °C; (ii) with the addition of MoS2, the friction coefficient of the epoxy resin composite containing MoS2 (E1) was below 0.22 under a temperature of 25–150 °C, and the friction coefficient was increased to 0.32 as temperature increased to 150 °C, while the average friction coefficient of the unsaturated polyester composite containing MoS2 (U1) was very low and below 0.20 under a temperature of 25–150 °C. Analysis of the wear scars indicated that, for the MoS2-containing composite, the transfer films of the E1 and U1 were smooth and continuous under low temperature, while the transfer film of U1 was comparatively complete than that of E1 under 150 °C. The composites with solid lubrication had excellent high-temperature self-lubricating properties, which was attributed to the synergistic effect of the laminated structure, and the thermal expansion of the polymer, and finally a transfer film was formed on the sliding path

Microstructures and properties of in-situ (ZrB2 + Al2O3)np/AA6111 composites synthesized under magnetic and ultrasonic fields

ZrB _2 and Al _2 O _3 nanoparticle-reinforced aluminum matrix composites were successfully prepared by in situ chemical reaction of the Al-Na _2 B _4 O _7 -K _2 ZrF _6 system with magnetic field applied in the in situ reaction and ultrasonic field introduced in solidification. The results indicated that the optimized magnetic frequency was 10 Hz, and the ultrasonic power was 1.0 kW. XRD analysis showed that ZrB _2 and Al _2 O _3 nanoparticles have been obtained. The smaller clusters were evenly distributed in the matrix. ZrB _2 and Al _2 O _3 nanoparticles were dispersed and uniformly distributed. The average size of particles and grain size of (ZrB _2  + Al _2 O _3 ) _np /AA6111 composites were refined to 45 ± 10 nm and 50.4 ± 12 μ m, respectively. The maximum Vickers hardness, tensile strength, yield strength and elongation of the composites synthesized under the optimized magnetic and ultrasonic fields were 142.2 HV, 355.4 MPa, 259.4 MPa and 22.4%, which were 1.34, 1.36, 1.35 and 1.33 times higher than that of AA6111 alloy, respectively

Fabrication of diamond/aluminum composites by vacuum hot pressing: Process optimization and thermal properties

International audienc

Diamond/aluminum composites processed by vacuum hot pressing: Microstructure characteristics and thermal properties

International audienc

Enhanced thermal conductivity in diamond/aluminum composites with a tungsten interface nanolayer

International audienc

Unexpected selective alkaline periodate oxidation of chitin for the isolation of chitin nanocrystals

Periodate oxidation reaction occurring directly on chitin has been neglected in polysaccharide chemistry so far. Herein, we present the first direct alkaline periodate oxidation of chitin, which demonstrates at the same time a novel approach for the preparation of chitin nanocrystals (ChNCs). This oxidation is based on an unprecedented selective reaction of non-ordered domains of chitin by the dimeric orthoperiodate ions (H₂I₂O₁₀⁴⁻) as the major species in alkaline surroundings. Nearly 50 wt% of non-ordered regions are dissolved after sequential accelerated partial deacetylation, periodate oxidation and β-alkoxy fragmentation, which allows the isolation of up to 50 wt% of uniform anisotropic zwitterionic ChNCs