Materials Science Forum Vol. 941

Abstract: This study develops a new, facile and rapid process bioinspired on rice leaf with the aim of producing a hybrid composite coating in a first attempt to obtain a superhydrophobic coating with enhanced erosion resistance properties. Rice leaves (Oryza sativa L.) are made of hierarchical structures consisting of micropapillae and waxy nanobumps which confer to the surface a contact angle of 164° as Lotus leaf does. In particular, rice leaves accumulate amorphous silica inside and on the surface with various morphologies. This kind of silica is produced by absorbing silicates from the soil under specific conditions of temperature and pressure. The presence of biosilica in rice leaves is useful for preventing diseases or improves mechanical properties of the leaves. Single-step and two-step processes are the two strategies applied for generating a superhydrophobic coating by electrochemical deposition of ZnCl₂, α-Al₂O₃ and lauric acid (C₁₁H₂₃COOH) onto commercial pure aluminum substrate. The static contact angle measured on the coating gives values of 170° and 1° for the sliding angle conducing to a coating with superhydrophobic and self-cleaning properties. Various characterization techniques are used to determine chemical and morphological structure such as FESEM, XPS or FTIR. On one hand, in morphological analysis, flower-like structure is obtained with petals thickness of 70nm corresponding to the nanostructured contribution to the system. On the other hand, chemical analysis concludes the generation of zinc laurate (Zn (C₁₁H₂₃COO)₂) as a major compound contributing to the reduction of surface tension and increasing the superhydrophobic character of the coating as well.

Abstract: The low density and high strength/weight ratio of magnesium (Mg) and magnesium alloys make them promising candidate materials in light-weight vehicle industries, such as automobile and aerospace, where poor corrosion resistance is a major obstacle in many of their wide-spread applications. Addition of alloying elements with production of wrought Mg alloys with finer microstructure results in enhanced mechanical properties and corrosion resistance. The aim of this research is to study the changes in microstructure caused by addition of alloying elements (zinc (Zn), and tin (Sn)) to new wrought Mg-5Al alloy, and their influence on the alloy's corrosion behavior. The microstructure was investigated using optical and electron microscopy and EDS. The corrosion behavior was analyzed through electrochemical measurements and immersion test. It was found that the corrosion resistance of Mg-5Al alloy was improved by addition of alloying elements, and the amounts of these elements strongly influenced the corrosion behavior of the alloys. Nevertheless, the influence of alloying elements is different for short-term and long-term immersion periods, since the mechanisms of corrosion initiation and corrosion propagation are different.

Abstract: In the nuclear field, efforts are made to find substitutes to cobalt hardfacing alloys since these alloys have a principal drawback, the transmutation from stable ⁵⁹Co to ⁶⁰Co under neutron irradiation. In case of wear, fragments could be deposed on the surface of primary circuit and thus contaminate it, causing a real issue for deconstruction.

Abstract: Carbon fiber reinforced polymers (CFRPs) have been increasingly used in the latest generations of aircraft and helicopters for lightweight purposes, but this leaves vulnerability against lightning strike. Cold spray is one coating approach to metallize the polymers, thus making them lightning strike proof. It has been reported that direct cold spray of metals onto CFRP is difficult. However, research at McGill University has shown that tin coatings can be cold sprayed on CFRP, but the deposition efficiency is very low. In this work, aluminum and zinc powders were mixed with tin to investigate the effect of mixing on deposition efficiency of the coating. The mixed metal powders were cold sprayed on CFRP with a low-pressure cold spray system at various conditions. It was found that the addition of aluminum or zinc resulted led to increased deposition efficiencies compared to pure tin, but there are many differences in the details of the effect of Al and Zn additions on the deposition characteristics. The deposition mechanism of the mixed metal powders on CFRP is discussed, and the effect of mixing powders on the deposition efficiency is evaluated.

Abstract: The oxygen permeabilities of polycrystalline Yb₂Si₂O₇ wafers cut from sintered bodies to serve as models of environmental barrier coatings were determined at temperatures up to 1673 K under various oxygen potential gradients (dµ_O), produced by exposing the upper and lower surfaces of the wafer to atmospheres with different oxygen partial pressures (P_O2). Oxygen permeation proceeded via grain boundary (GB) diffusion of oxygen from the higher P_O2 surface to the lower P_O2 surface, concurrently with GB diffusion of ytterbium in the opposite direction. Mass transfer analysis allowed for a design guideline for selectively enhancing the structural stability of the ytterbium silicate layer with applying a dµ_O.

Abstract: The In Situ composites with microstructurally different types of intermetallic matrix such as nearly γ (TiAl) (composite A), multiphase with high amount of lamellar α₂(Ti₃Al) + γ (TiAl) regions (composite B) and fully lamellar α₂ + γ (composite C) were prepared by centrifugal casting and consecutive heat treatments of Ti-44.5Al-8Nb-0.8Mo-3.6C-0.1B, Ti-37Al-7Nb-0.8Mo-5.9C-0.1B and Ti-46.4Al-5Nb-1C-0.2B (at.%) alloys, respectively. The centrifugal casting results in a uniform distribution of coarse primary carbide particles in the as-cast samples. Hot isostatic pressing (HIP) and heat treatments have no effect on the Vickers hardness of the in-situ composite B but lead to a significant softening of the in-situ composites A and C. The in-situ composite C with a coarse-grained fully lamellar matrix shows a higher flow stress at 1000 °C and improved creep resistance at 800 °C compared to those of the in-situ composites A and B.

Abstract: Architectured copper clad aluminium composites processed by a restacking drawing method at room temperature are reported in this work. Wires were drawn to severe plastic strain without any intermediate annealing. Three different diameters were studied in order to examine the influence of a different plastic deformation level on the structure of the different wires. Thanks to image processing it has been shown that independently of the plastic deformation, inserted fibers remain continuous and are homogeneous in size and shape. Furthermore, XRD and TEM characterizations confirm that there is no significant intermetallic growth during the deformation. Thus, the improvement and/or degradation of the functional properties of the wires can be well controlled by performing an appropriate post-processing annealing treatment. Keywords: Cu/Al composite, architectured wire, drawing, microscopy, image processing

Abstract: In this work, a commercial MMC (A359-20% SiC_P) was remelted, diluted to different particle contents (5 to 20 vol. %), and foamed at a fixed temperature using titanium hydride. In general, excellent foamability could be obtained for all SiC contents. Foam stability (retention of expansion), on the other hand, depended on SiC content. Remelting and diluting procedures also influenced the foam stability on account of varied oxide contents generated upon impeller stirring. The foam quality, in terms of cell wall integrity, improved with increasing SiC content. Despite the defect levels, good compression properties were obtained in these foams, which are close to model predictions. Overall, this system is very promising for producing good quality foams by melt processing technique.

Abstract: Competitive reactions and formation mechanism of microstructures in Mg/Cu super-laminate composites (SLCs) during initial hydrogenation were studied. During initial hydrogenation of Mg/Cu SLCs, hydrogenation of Mg and alloying of Mg with Cu followed by hydrogenation of Mg₂Cu are competitive. It is found that microstructures of Mg/Cu SLCs during initial hydrogenation have changed drastically depending on the order of hydrogenation of Mg and Mg₂Cu. The microstructures of Mg/Cu SLCs after initial hydrogenation can be categorized in 3 types.

Abstract: Strength and ductility are the two most important mechanical properties of a structural material. However, they are often mutually exclusive. In this study, a 6 wt. % TiB₂ nanoparticle reinforced 7075Al (i.e. TiB₂/7075Al) composite was designed and produced by the processing route combining casting, friction stir processing, hot extrusion and T6 heat treatment. The result of tensile testing demonstrates that the as-processed composite sample presents an ultimate tensile strength of 677 MPa and a total elongation to failure of around 15 %, being higher than any Al or Al based materials ever reported. The typical microstructure contains the TiB₂ reinforcement nanoparticles uniformly distributed in the equiaxed Al grain matrix (2 μm in average grain size). In addition to the dispersed nanoprecipitates of the 7075Al (Al-Zn-Mg-Cu) matrix, the integrated TiB₂ nanoparticles are systematically decorated by a shell corresponding to (Zn_1.5Cu_0.5)Mg. This finding challenges our understanding and opens a door for further enhancing strength and ductility being easily scalable for industrial applications.