Genlian Fan

Enhanced Mechanical Properties of Graphene (Reduced Graphene Oxide)/Aluminum Composites with a Bioinspired Nanolaminated Structure

Bulk graphene (reduced graphene oxide)-reinforced Al matrix composites with a bioinspired nanolaminated microstructure were fabricated via a composite powder assembly approach. Compared with the unreinforced Al matrix, these composites were shown to possess significantly improved stiffness and tensile strength, and a similar or even slightly higher total elongation. These observations were interpreted by the facilitated load transfer between graphene and the Al matrix, and the extrinsic toughening effect as a result of the nanolaminated microstructure.

Uniform dispersion of graphene oxide in aluminum powder by direct electrostatic adsorption for fabrication of graphene/aluminum composites.

The excellent properties of graphene promote it as an ideal reinforcement in composites. However, dispersing graphene homogenously into metals is a key challenge that limits the development of high-performance graphene-reinforced metal matrix composites. Here, via simple electrostatic interaction between graphene oxide (GO) and Al flakes, uniform distribution of reduced graphene oxide (RGO) in an Al matrix is achieved. The adsorption process of GO on Al flakes is efficient, as it can be completed in minutes and proceeds spontaneously without any chemical agents. GO can be partially reduced by the electron interchange during the adsorption process and could be thoroughly reduced after subsequent thermal annealing. A densified RGO/Al composite can be obtained by hot pressing the RGO/Al composite powders. By employing the preceding fabrication process, a composite reinforced with only 0.3 wt.% of RGO shows an 18 and 17% increase in elastic modulus and hardness, respectively, over unreinforced Al, demonstrating RGO is a better reinforcement than most other reinforcements.

Ultrahigh damping in R-phase state of Ti–Ni–Fe alloy

Developing high damping materials with high strength is of significant technological importance, and Ti–Ni-based alloys are attracting much attention in this respect. The high damping peak in martensite state has been shown to be related to the interaction between twin boundary and hydrogen according to recent studies. In this letter the authors studied damping capacity of R phase in Ti50Ni48Fe2 alloy, which has the lowest twinning shear among known martensites (R, B19, and B19′) in Ti–Ni-based alloys. They obtained a very high internal friction Q−1=0.2 for the relaxation-type peak in R phase, much higher than that for B19 martensite or B19′ martensite. Their results suggest that choosing martensite with smallest twinning shear (thus with the highest mobility) is an important guideline for developing very high damping materials. Furthermore, avoiding introducing precipitates and dislocations is also essential for obtaining high damping.

Development of Flake Powder Metallurgy in Fabricating Metal Matrix Composites: A Review

Powder metallurgy (PM) is one of the most applied processes in the fabrication of metal matrix composites (MMCs). Recently, a novel PM strategy called flake PM was developed to fabricate MMCs with nano-laminated or hierarchical architectures. The name “flake PM” was derived from the use of flake metal powders, which could benefit the uniform dispersion of reinforcements in the metal matrices and thus result in balanced strength and ductility. Flake PM has been proved to be successful in the dispersion of nano aluminum oxides, carbon nanotubes, graphene nano-sheets, and microsized B4C particles in aluminum or copper matrix. This paper reviews the technique and mechanism developments of flake PM in previous studies, and foresees the future develop of this new fabricating method.

Damping capacity of BaTiO3/Al composites fabricated by hot extrusion

Abstract To develop new type of high damping metal matrix composites, large grain size barium titanate (BaTiO 3 ) ceramic was sintered and added into Al powder to fabricate BaTiO 3 /Al composites through the powder metallurgy method and hot extrusion. The damping properties of BaTiO 3 ceramic, Al matrix and BaTiO 3 /Al composites were examined by dynamic mechanical analysis in the temperature range from 273 K to 573 K. The results show that although BaTiO 3 exhibits high damping (tan δ =0.12) below 400 K, the damping capacity of 10%BaTiO 3 /Al (mass fraction) composites below 400 K is not increased as compared to the Al matrix. On the other hand, the damping capacity above 450 K is greatly enhanced due to the motion of dislocations at the interfaces between ceramic particles and Al matrix. The failure of exerting the intrinsic damping of BaTiO 3 particles in the composites is attributed to the poor interface bonding between the particles and the matrix. The tensile strength of the composite is 42% higher than that of the Al matrix, which indicates the possibility of obtaining high strength and high damping composites via interface improvement and the addition of high volume fraction of large grain BaTiO 3 particles.

Two-dimensional distribution of carbon nanotubes in copper flake powders

We report an approach of flake powder metallurgy to the uniform, two-dimensional (2D) distribution of carbon nanotubes (CNTs) in Cu flake powders. It consists of the preparation of Cu flakes by ball milling in an imidazoline derivative (IMD) aqueous solution, surface modification of Cu flakes with polyvinyl alcohol (PVA) hydrosol and adsorption of CNTs from a CNT aqueous suspension. During ball milling, a hydrophobic monolayer of IMD is adsorbed on the surface of the Cu flakes, on top of which a hydrophilic PVA film is adsorbed subsequently. This PVA film could further interact with the carboxyl-group functionalized CNTs and act to lock the CNTs onto the surfaces of the Cu flakes. The CNT volume fraction is controlled easily by adjusting the concentration/volume of CNT aqueous suspension and Cu flake thickness. The as-prepared CNT/Cu composite flakes will serve as suitable building blocks for the self-assembly of CNT/Cu laminated composites that enable the full potential of 2D distributed CNTs to achieve high thermal conductivity.

High content reduced graphene oxide reinforced copper with a bioinspired nano-laminated structure and large recoverable deformation ability.

By using CuO/graphene-oxide/CuO sandwich-like nanosheets as the building blocks, bulk nacre-inspired copper matrix nano-laminated composite reinforced by molecular-level dispersed and ordered reduced graphene oxide (rGO) with content as high as ∼45 vol% was fabricated via a combined process of assembly, reduction and consolidation. Thanks to nanoconfinement effect, reinforcing effect, as well as architecture effect, the nanocomposite shows increased specific strength and at least one order of magnitude greater recoverable deformation ability as compared with monolithic Cu matrix.

A Versatile Method for Uniform Dispersion of Nanocarbons in Metal Matrix Based on Electrostatic Interactions

Realizing the uniform dispersion of nanocarbons such as carbon nanotube and graphene in metals, is an essential prerequisite to fully exhibit their enhancement effect in mechanical, thermal, and electrical properties of metal matrix composites (MMCs). In this work, we propose an effective method to achieve uniform distribution of nanocarbons in various metal flakes through a slurry-based method. It relies on the electrostatic interactions between the negatively charged nanocarbons and the positively charged metal flakes when mixed in slurry. For case study, flake metal powders (Al, Mg, Ti, Fe, and Cu) were positively charged in aqueous suspension by spontaneous ionization or cationic surface modification. While nanocarbons, given examples as carboxylic multi-walled carbon nanotubes, pristine single-walled carbon nanotube, and carbon nanotube–graphene oxide hybrid were negatively charged by the ionization of oxygen-containing functional groups or anionic surfactant. It was found that through the electrostatic interaction mechanism, all kinds of nanocarbons can be spontaneously and efficiently adsorbed onto the surface of various metal flakes. The development of such a versatile method would provide us great opportunities to fabricate advanced MMCs with appealing properties.

Evolution, Control, and Effects of Interface in CNT/Al Composites: a Review

This review summarizes the work carried out in the field of interface study in carbon nanotube reinforced aluminum (CNT/Al) composites. Much research work has been conducted to reveal the evolution of CNT/Al interface in producing the composite with the purpose of achieving uniform distribution of CNTs and tight interfacial bonding. The effect and principles of coating were reviewed along with the illustration of “intermetallic interphases” design. Different roles of CNT/Al interface in structural and functional application were elucidated, and the future work that needs attention was addressed.

Back stress in strain hardening of carbon nanotube/aluminum composites

ABSTRACT As demonstrated by the loading–unloading tests and the modeling of the grain size effect and the composite effect, mainly owing to the back stress induced by CNTs, carbon nanotube/aluminum (CNT/Al) composites exhibit higher strain hardening capability than the unreinforced ultrafine-grained Al matrix. The back stress induced by CNTs should arise from the interfacial image force and the long-range interaction between statically stored dislocations and geometrically necessary dislocations around the CNT/Al interface. Therefore, this CNT-induced interfacial back stress strengthening mechanism is supposed to provide a novel route to enhancing the strain hardening capability and ductility in CNT/Al composites. IMPACT STATEMENT The present work investigates the roles and origins of back stress in the strain hardening of the carbon nanotubes/aluminum composites for the first time. GRAPHICAL ABSTRACT