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Metallic alloys are critical to essentially all advanced technologies and engineered systems. The well-documented impact of corrosion (and oxidation) of alloys, remains a significant industrial and economic challenge, year on year. Recent activity in the field of metallurgy has revealed a class of metallic alloys, termed multi principal element alloys (MPEAs) that present unique physical properties. Such MPEAs have in many instances also demonstrated a high resistance to corrosion – which may permit the broader use of MPEAs as corrosion resistant alloys (CRAs) in harsh environments. Herein, the progress in MPEA research to date, along with prospects and challenges, are concisely reviewed—with potential future lines of research elaborated.

Voltage-activated adhesion is a relatively new discovery that relies on direct currents for initiation of crosslinking. Previous investigations have found that direct currents are linearly correlated to the migration rates of electrocuring, but this is limited by high voltages exceeding 100 V with instances of incomplete curing of voltage-activated adhesives on semiconducting substrates. Practical applications of electrocuring would benefit from lower voltages to mitigate high voltage risks, especially with regard to potential medical applications. Alternative electrocuring strategies based on alternating current (AC), electrolyte ionic radius, and temperature are evaluated herein. Square waveform AC electric fields are hypothesized to initiate a two-sided curing progression of voltage-activated adhesive (PAMAM-g-diazirine aka Voltaglue), where initiation occurs at the cathode terminal. Structure-activity relationships of AC frequency at currents of 1-3 mA are evaluated against direct currents, migration rate, storage modulus, and lap shear adhesion on ex-vivo tissue mimics. Numerous improvements in electrocuring are observed with AC stimulation versus DC, including a 35 % decrease in maximum voltage, 180 % improvement in kinetic rates, and 100 % increase in lap shear adhesion at 2 mA. Li + ion electrolytes and curing at 4 o C shift curing kinetics by +104 % and -22 % with respect to the control ion (Na + ion at 24 o C), suggesting electrolyte migration is the rate limiting step. Li + ion electrolytes and curing at 50 o C improves storage modulus by 110% and 470 % respectively. Further evaluations of electrocured matrices with 19 F NMR, solid-state NMR and infrared spectroscopy provide insights into the probable crosslinking mechanisms.

Fiber reinforced composites, though relatively new, have already become important engineering materials. So far the main emphasis of research has been on the development of materials, but nowadays more attention is being paid to the industrial manufacture of products made of composites. Conventional machining methods and some unconventional machining methods like laser beam machining (LBM) and water jet machining (WJM) cannot be effectively applied for machining of composites due to the resulting problems of air borne dust, tool wear, and thermal damage. Recently electrochemical spark machining (ECSM) has been applied for the cutting and drilling of holes in composites. The success achieved in the application of ECSM for cutting of composites has stimulated interest in exploring the prospects of use of traveling wire electrochemical spark machining (TW-ECSM) process for cutting of composites. An apparatus for TW-ECSM is designed and fabricated in the laboratory. The results about the feasibility of the process and its performance during machining of composites are presented in this paper. Experiments are carried out on glass-epoxy and kevlar-epoxy composites, using sodium hydroxide (NaOH) as electrolyte. The wire and the workpiece were kept in physical contact with each other by the use of a gravity feed mechanism. The effects of voltage and concentration of the electrolyte on material removal rate, average diametral overcut, tool wear rate, and wire erosion ratio are reported. The theoretical analysis of the mechanism of the process identifies the thermo-mechanical phenomena as the main source of material removal in ECSM.

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We report on tip induced doping in local tunnel spectra of single layer graphene (SLG) with tunable back-gate using room temperature scanning tunneling microscopy and spectroscopy (STM/S). The SLG samples, prepared on silicon dioxide surface by exfoliation method and verified by Raman spectra, show atomically resolved honeycomb lattice. Local tunnel spectra show two minima with a clear evolution in the position of both with doping by the back gate. A similar variation in spectra is also observed spatially due to charge inhomogeneity. With doping the two minima move in opposite directions with one showing nearly a square root dependence and the other a linear dependence on gate voltage. We explain these features as arising from the STM tip induced and bias voltage dependent doping in SLG.

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Tribological studies of the 2D nanoadditives such as MoS2 and graphene are mostly performed in base oils such as SN500, SN150, or paraffin. We have focused on their effect in lubrication properties of industrial oils (e.g., axle, transmission, and compressor oils) along with SN500 oil employing a four-ball tester. Two types of graphene powders (GpowA with fewer defects than GpowC), MoS2 powder, and their physical mixtures are chosen as nanoadditives. The tribology performance for 0.05 wt% of additives in various industrial oils is evaluated by monitoring the coefficient of friction (COF) during rubbing and wear scar diameter (WSD) of the steel balls after rubbing. Elemental analysis and electron microscopy have been performed on the wear surfaces for evidence of any tribofilm formation. GpowA favors antifriction for axle and transmission oils with 40% reduction in axle oil, whereas it improved antiwear properties in most of the oils. GpowC shows a COF decrement by 12% only for compressor oil, but contribute to wear reduction in all oils. The observed COF reduction is attributed to the compatibility of nonfunctionalized GpowA with nonpolar axle oil and functionalized GpowC with polar compressor oil. MoS2 shows a decrease in the COF and WSD in most industrial oils; the best being 60% COF and 7% WSD reduction in axle oil. For additives in oils that favor antiwear, flakes or particles are observed on the wear surface supported by the higher elemental contribution of the constituents from the wear region. The mixtures of GpowA or C with MoS2, however, does not seem to favor improvement in the COF or WSD in industrial oils. With assistance from oleylamine surfactants, the lubrication properties of most additives are improved, particularly for the mixtures with 12–15% COF reduction and 4–7% WSD reduction in compressor oil. The study indicates that a large sheet size of high-quality graphene aids antifriction and addition of surfactant molecules facilitates a co-operative effect between MoS2 and graphene for improved tribology.