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    ABSTRACT: Carbon nanotubes (CNT) have emerged as a very promising reinforcement for ceramics, polymers and metals. Although the CNT reinforced composites show a significant improvement in mechanical, thermal and electrical properties, there are several critical challenges to the effective use of carbon nanotube reinforce composites such as agglomeration of CNT, poor distribution and weak bond between CNT and base matrix. In this paper, mechanical alloying (MA) was applied by the authors to disperse CNT in the aluminum matrix. Both stearic acid and ethanol were used as process control agents (PCA) to control the properties of particles. Scanning electron microscope (SEM), Raman spectroscope and particle size analyzer were employed to characterize the size, shape and morphology of the CNT-Al composite. The evolutions of CNT and CNT-Al mixture as well as the effect of PCA were studied. The present research indicates that mechanical alloying is an effective way to achieve homogenous distribution of CNT in the Al matrix. Ethanol as process control agent promotes the refinement of Al particles but also increases the damage of CNT during the ball milling process.
    No preview · Article · Nov 2014 · Powder Technology
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    ABSTRACT: The high-temperature mechanical properties of precipitate-strengthened advanced alloys can be heavily influenced by adjusting chemical composition. The widely-accepted argument within the community is that, under certain temperature and loading conditions, plasticity occurs only in the matrix, and dislocations have to rely on thermally-activated climb mechanisms to overcome the barriers to glide posed by the hard precipitates. This is the case for γ′γ′-strengthened Ni-based superalloys. The presence of dilute amounts of slow-diffusing solute atoms, such as Re and W, in the softer matrix phase is thought to reduce plasticity by retarding the climb of dislocations at the interface with the hard precipitate phase. One hypothesis is that the presence of these solutes must hinder the flow of vacancies, which are essential to the climb process. In this work, density functional theory calculations are used to inform two analytical models to describe the effect of solute atoms on the diffusion of vacancies. Results suggest that slow-diffusing solute atoms are not effective at reducing the diffusion of vacancies in these systems.
    Full-text · Article · Nov 2014 · Materials Science and Engineering A
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    ABSTRACT: Co–Cr–Mo alloys are one of the most widely used metallic biomaterials for metal-on-metal joint prostheses. However, concerns over increased revision rates mainly due to nano-sized wear debris have been raised. This study was aimed at enhancing the friction, wear and load-bearing properties of Co–Cr–Mo alloys by developing a new duplex surface system combining super hard and wear-resistant S-phase layer with self-lubricating, low-friction carbon-based coating. To this end, ASTM F1537 Co–Cr–Mo alloy surface was plasma carburised (PC) at 450 °C and then coated with a carbon-based GiC coating. The microstructures of the duplex and single treated (PC or GiC coating) Co–Cr–Mo surface systems were characterized and their mechanical, tribological and corrosion properties were evaluated. The results showed that the new duplex surface system exhibited a high load bearing capacity, a low friction coefficient, excellent wear resistance and good corrosion behaviour.
    Full-text · Article · Feb 2014 · Applied Surface Science
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