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AbstractAl 7075 surface composites (SCs) successfully fabricated with additive three different nano-scale particles multi-walled carbon nanotubes (MWCNTs), graphene (GNP), and titanium dioxide (TiO2) by friction stir processing (FSP). The consecutive two-pass FSP was executed under a controlled cooling environment at −20 °C with methanol pumped beneath the workpiece in a specially designed fixture. All of the SCs exhibited homogenous dispersion of filler nanoparticles in their microstructures. The grain size of SCs was remarkably reduced from that of the substrate. The enhancement in hardness and strength was ascribed fundamentally to the grain refinement and Zener (pinning) effect expedited by coolant circulation. The effect of second phase matrix on grain evolution and precipitate-intermetallics formed after FSP was characterized by scanning electron microscope (SEM) and XRD pattern. It has been recorded that there is around 95–110% increase in hardness values in SCs. The wear rate is also dropped in SCs owing to enhanced hardness and the formation of lubricating coating in the case of carbonaceous composites. [ABSTRACT FROM AUTHOR]

Al6061 alloy has become prevalent in the industrial sector because of its low density, excellent machinability, and corrosion resistance but it lacks properties like hardness and wear. Therefore, surface modifications by friction stir processing (FSP) are done with additive nanosized particles like multi-walled carbon nanotubes (MWCNT), Titanium oxide (TiO2), and Graphene nanoparticles (GNP) To perform 2-pass FSP, a uniquely engineered fixture with coolant circulated underneath the plate at sub-zero temperatures is used. Grain refinement has been observed in micrographs as a consequence of 2-pass FSP. The coolant circulated beneath carries the heat generated and enhances the heat dispersion rate, culminating in finer grains. The calculated mean grain size of the Al6061 alloy was considerably decreased in all the surface composites. There is a substantial improvement in the microhardness profile, which has increased by nearly 70–90%, as well as a significant enhancement in tensile strength of almost 20–30% in all the composites. The ductile type of failure during tensile load is revealed by SEM fractography. The process of dynamic recrystallisation is responsible for the development of equiaxed grains. The wear resistance of all the composites is also enhanced, and the COF of Al6061/GNP composite is found to be lowest at 0.23. [ABSTRACT FROM AUTHOR]

Magnesium alloy-based matrix composites are extensively used in transportation industries because of their high specific strength and low weight. Several existing technologies were utilized for preparing these composites in any proportion of constituent elements. However, friction stir processing (FSP), which employs plastic deformation with high-energy input, has proven as the most successful with proper homogenization. This study examines the microstructure and mechanical characteristics evolved by FSP of a novel magnesium alloy grade (AZ31) with Titanium dioxide (TiO2), Multi-walled carbon nanotubes (MWCNT) and Research grade Graphene nanoplatelets (GNP) that have considerable electrical, thermal and mechanical performance. At a parametric combination, tool rotation of 1200 rpm, traverse speed of 80 mm per minute, plunge depth with 0.25 mm, AZ31 alloy was processed on a specifically engineered fixture with subzero coolant circulation through it. The average size of grains of the base alloy reduced from 52.96 µm to 2.07 µm (AZ31/TiO2), 3.19 µm (AZ31/MWCNT) and 2.54 µm (AZ31/GNP) composites at this combination. The hardness and tensile strength were enhanced from 115 to 130% and 25 to 38%, respectively. Micrographs shows that the shortened grain elongation occurred due to coolant circulation resulted in restricted strengthening precipitate dissolution, which usually occur at high temperature. [ABSTRACT FROM AUTHOR]

Machining of hard materials generates high temperature in the cutting zone. Lubricants play an important role in the reduction of temperature in the cutting zone, thereby producing cooling and lubricating effects. Effective lubrication enhances the tool life thereby reducing the machining cost. Conventional lubricants are mineral-based oils that are non-biodegradable. Industries are focusing to reduce the consumption of these oils by exploring different alternatives. Dry grinding and Minimum Quantity Lubrication (MQL) technique are the alternatives of focus. Dry machining has limitations in hard to machine materials due to a steep rise in temperature. Thus, MQL is an alternative that can be applied to the machining to achieve the desired objective of lubrication and cooling. In the present work, nano-particles based nanofluids were prepared by dispersing 0.5 wt% and 1 wt% CuO nano-particles in the vegetable oils to grind Ni-Cr alloy. Surface roughness, G-ratio and Grinding Energy were evaluated under different conditions of lubrication. Due to high-pressure mist of MQL and rolling effects of nano-particles at the wheel and workpiece interface, there is significantly reduction in values of surface roughness, temperature, grinding energy with enhanced G-ratio comparatively to flood lubrication. Moreover, biodegradable oil-based Nanofluid MQL serves the purpose of environment-friendly machining. [ABSTRACT FROM AUTHOR]

Purpose: In Indian thermal power plants, the main cause of boiler tube failure is the presence of molten sulphates and vanadates, which deteriorate the tube material at high temperatures. To combat the hot corrosion failure of metals, thermal spray technology is adopted. This study aims to investigate and study the effect of hot corrosion behaviour of carbon nanotube (CNT)-reinforced ZrO2-Y2O3 composite coatings on T-91 boiler tube steel in a molten salt environment at 900 °C for 50 cycles. Design/methodology/approach: A plasma spray technique was used for development of the coatings. The samples were exposed to hot corrosion in a silicon tube furnace at 900 °C for 50 cycles. After testing, the test coupons were analysed by X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and cross-sectional analysis techniques to aid understanding the kinetics of the corrosion reaction. Findings: CNT-based reinforced coatings showed lower weight gain along with the formation of protective oxide scales during the experimentation. Improvement in protection against hot corrosion was observed with increase in CNT content in the coating matrix. Originality/value: It is pertinent to mention here that the high temperature behaviour of CNT-reinforced ZrO2-Y2O3 composite on T-91 steel at 900°C temperature in molten salt environment has never been studied. Thus, the present research was conducted to provide useful results for the application of CNT-reinforced composite coatings at elevated temperature. [ABSTRACT FROM AUTHOR]

The present work investigates the hot-corrosion behavior of carbon nanotube (CNT)-reinforced chromium oxide coatings on boiler steel in a molten salt (Na2SO4-60wt%V2O5) environment at 700°C under cyclic conditions. The coatings were deposited via the high-velocity oxygen fuel process. The uncoated and coated steel samples were subjected to hot corrosion in a silicon tube furnace at 700°C for 50 cycles. The kinetics of the corrosion behavior was analyzed through mass-gain measurements after each cycle. The corrosion products were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray analysis techniques. The results revealed that uncoated steel suffered spallation of scale because of the formation of nonprotective Fe2O3 scale. The coated steel samples exhibited lower mass gains with better adhesiveness of oxide scale with the steel alloy until the end of exposure. The CNT-reinforced coatings were concluded to provide better corrosion resistance in the hot-corrosion environment because of the uniform dispersion of CNTs in the coating matrix and the formation of protective chromium oxides in the scale. [ABSTRACT FROM AUTHOR]

Purpose Molten sulphate-vanadate induced hot corrosion is the main reason of failure of boiler tubes used at high temperatures in thermal power plants. The hot corrosion can be encountered by applying thermal spray coatings on the alloy steels. In this perspective, this paper aims to attempt to investigate the effect of carbon nanotubes reinforcement on Cr2O3 composite coatings on hot corrosion behaviour of ASTM-SA213-T22 steel in a corrosive environment of Na2SO4 – 60%V2O5 at 900°C for 50 cycles.Design/methodology/approach The coatings have been deposited with high velocity oxy fuel process. The samples were exposed to hot corrosion in a Silicon tube furnace at 900°C for 50 cycles. The kinetics of corrosion behaviour were analysed by the weight gain measurements after each cycle. Corrosion products were analysed with X-ray diffraction, scanning electron microscopy, energy dispersive and cross-sectional analysis techniques.Findings During investigations, the carbon nanotubes (CNT) reinforced Cr2O3 composite coatings on T22 steel were found to provide better corrosion resistance in the molten salt environment at 900°C. The coatings showed lower weight gain along with formation of protective oxide scales during the experiment. Improvement in protection against hot corrosion was observed with increase in CNT content in the coating matrix.Research limitations/implications The addition of CNT has resulted in reduction in porosity by filling the voids in chromium oxide coating, with interlocking of particle and has blocked the penetration of corroding species to enhance the corrosion resistance of the composite coatings. The corrosion rate was found to be decreasing with increase in CNT content in coating matrix.Originality/value It must be mentioned here that high temperature corrosion behaviour of thermally sprayed CNT-Cr2O3 composite coatings has never been studied, and it is not available in the literature. Hence, present investigation can provide valuable information for application of CNT-reinforced coatings in high temperature fuel combustion environments. [ABSTRACT FROM AUTHOR]