Enhanced Surface Properties Research Articles

An efficient coupled Eulerian-Lagrangian finite element model for friction stir processing

Friction stir processing (FSP) is a friction stir-based material processing method for enhancement of material microstructural and surface properties. As FSP is a multi-physics problem coupled with severe plastic deformation, material flow, heat flow, and microstructure evolution, modeling of the FSP process can be very complicated and challenging. Few research work has been reported on modeling and simulations of FSP for material modification. In this study, a computation-efficient process model is developed using ABAQUS/Explicit based on coupled Eulerian-Lagrangian (CEL) formulation to simulate FSP of aluminum alloy 5083. The three-dimensional (3D) finite element model simulates the entire process of FSP including tool plunging, dwelling, and stirring phases. Simulations are performed to evaluate the effects of tool-rotational speed and tool pin profile during the FSP process. The computational efficiency of the developed model is also evaluated in comparison with other existing models for friction stir–welding processes. FSP experiment is performed with measurements of process force and temperature for model validation. This study shows that the CEL model can be a powerful numerical tool to simulate the complex process mechanics and optimize the FSP process parameters for industrial applications.

Mechanical Properties of HVOF Sprayed CrC-NiCr Coating Exposed to Hot Corrosion Environment

Current development in power generation industry leads to search of new technologies and ways how to protect surface against aggressive corrosion environment. Suitable method leading to enhancement of surface properties is application of protective coatings on surface. This approach allows to use components composed from less quality materials. The current development in steam turbines leads to increasing operating temperatures for the purpose to enhance performance. This process results in elevation of operating temperature reaching the potential limits of commonly used materials. One of the key areas of protection in such environment is protection against hot temperature corrosion. Possible solution can be found in application of coatings based on alloys and cermets prepared by HVOF (High Velocity Oxygen Fuel) technology. This paper examines local mechanical and microstructural properties of Cr3C2-25%NiCr coating after exposition to extremely severe hot corrosion environment. Furthermore, the nanoindentation measurements of this coating were performed before and after the corrosion test. The test environment composition was based on mixture of salts 59% Na2SO4 with 34.5% KCl and 6.5% NaCl. Test temperature was 525°C and 575°C. Duration of the exposition to hot corrosion environment was 168 hours in autoclave. The results confirmed that the coating matrix is deteriorated during the exposition to such aggressive environment. The deterioration is localized at surface of coating and is characterized by creation of oxide layer which decreases the speed further speed of matrix dissolution and stabilizes the coating.

Another Approach to Characterize Particle Distribution during Surface Composite Fabrication Using Friction Stir Processing

Surface composite fabrication through Friction Stir Processing (FSP) is evolving as a useful clean process to enhance surface properties of substrate. Better particle distribution is key to the success of surface composite fabrication which is achieved through multiple passes. Multiple passes significantly increase net energy input and undermine the essence of this clean process. This study proposes a novel approach and indices to relate the particle distribution with the FSP parameters. It also proposes methodology for predicting responses and relate the response with the input parameter. Unit stirring as derived parameter consisting of tool rotation speed in revolutions per minute (rpm), traverse speed and shoulder diameter was proposed. The particle distribution was identified to be achieved in three stages and all three stages bear close relationship with unit stirring. Three discrete stages of particle distribution were identified: degree of spreading, mixing and dispersion. Surface composite on an aerospace grade aluminum alloy AA7050 was fabricated successfully using TiB2 as reinforcement particles. FSP was performed with varied shoulder diameter, rotational speed and traversing speed and constant tool tilt and plunge depth using single pass processing technique to understand the stages of distribution. Significant relationships between processing parameters and stages of particle distribution were identified and discussed.

Characterization of Al0.5FeCu0.7NiCoCr high-entropy alloy coating on aluminum alloy by laser cladding

Al0.5FeCu0.7NiCoCr high-entropy alloy (HEA) coatings were synthesized on aluminum by laser cladding, aiming at enhancing surface properties. Samples were characterized by using scanning electron microscopy with spectroscopy (SEM/EDS), X-ray diffraction, laser induced breakdown spectroscopy (LIBS), microhardness. The results showed that the HEA coatings exhibited good metallurgical bonding to the matrix by using optimized laser processing parameters. The HEA coatings were composed of fcc + bcc phases. All the composed elements can be noted in mapping through the calibration of the plasma, and the plasma of the collected Al confirmed that come from substrate dilution. The intensity change of Al-II reflected the depth variety of the cladding layer. The microstructure of clad layer was consisted of dendrite. The microhardness of HEA layer reached 750HV0.2 that was about 8 times larger than that of the substrate.

Recycling of polymer waste with SiC/Al2O3 reinforcement for rapid tooling applications

In this research work an effort has been made to develop in house feed stock filament wire made up of recycled polymer waste as base matrix with SiC/Al2O3 reinforcement for sustainable development. The process starts with collection of waste polymer (high density polyethylene (HDPE) as a case study) from local industry. After manual segregation of contamination from waste polymer, initially rheological and thermal properties like: melt flow index (MFI), melting temperature, decomposition and enthalpy of the base polymer as well as reinforced with ceramic particle in different proportions, were tested. Further based upon thermal properties different proportions of HDPE, SiC and Al2O3 were prepared by using mini compounder (twin screw extruder) to ensure uniform dispersion. After this single screw extruder was used to prepare filament wire of uniform diameter for fused deposition modelling (FDM) setup. The filament wire so prepared was tested for its tensile properties by using universal testing machine (UTM) and various mechanical properties like: peak strength, break strength, percentage elongation and peak load etc. were established. Finally scanning electron micrographs (SEM) were obtained to understand the distribution of ceramic particles in filament wire. This study highlights the detailed procedure for managing the polymer waste with novel method by using recycled polymer as rapid tooling. This will enhance the sustainability and also helps to develop low cost, in-house open source FDM setup, rapid tooling (as ceramic particles in filament wire will enhance surface properties).

Non-enzymatic sensing of kidney dysfunction biomarker using pectin – MWCNT nanocomposite

Creatinine, a biomarker for kidney dysfunction, is a molecule created within skeletal muscles as a product of physical activities. The normal physiological concentration of creatinine is 40–150 μM, beyond which it will lead to kidney dysfunction. Thus monitoring of creatinine level becomes more important for normal functioning of the body. In the currently available enzymatic studies, three enzymes were required for sensing creatinine. As the enzymatic electrochemical sensing studies are tedious and have several drawbacks, non-enzymatic sensing of creatinine using a biopolymer based sensor was proposed in the present study. Pectin (PEC), a naturally occurring polysaccharide, was extracted from musk melon peels and it was used for the modification of MWCNT. The prepared bionanocomposite was characterized using UV–vis, FT-IR, XRD, RAMAN, SEM, and TGA techniques. The bionanocomposite was effectively incorporated into the carbon paste matrix (CPE) and fabricated as a working electrode (CPE/PEC-MWCNT). The enhanced surface properties like electro active surface area A (0.0329 cm2), surface concentration Γ (0.0503 × 10−6 mol cm−2), diffusion coefficient D0 (0.0964 cm2 s−1), heterogeneous rate constant ks (0.3736 s−1) of CPE/PEC-MWCNT as compared to that of GCE (Glassy Carbon electrode), CPE, CPE/PEC and CPE/MWCNT electrodes, suggested enhanced electrochemical functionalization, competent diffusion of creatinine and hence effective electron transfer at the newly fabricated electrode surface. The electrode was also effectively utilized for the sensing of creatinine in urine samples.

Use of Nanoscale Materials for the Effective Prevention and Extermination of Bacterial Biofilms

Biofilms have been shown to cause most human infections. The prevention and extermination of bacterial biofilms has always presented a major challenge in the clinic. The failure of traditional antibiotics and the development of bacterial resistance against these measures is on the rise. Nanoscale materials possess the advantage of presenting enhanced surface properties of bulk materials, and are emerging as effective agents for deterring microbial growth. This review article summarizes the fundamentals of bacterial growth, biofilm formation, mechanisms for antibacterial technologies, and usage of nanoparticles for the prevention and extermination of biofilms. Further research is required with respect to the appropriate usage of nanoparticles for the effective control of biofilms to save human lives and reduce healthcare costs.

Microstructure Evaluation of Different Materials after Friction Surfacing - A Review

Friction surfacing is a solid state processing technology in the context of localized surface engineering. It is mainly used for coating applications to repair damaged or worn parts, to improve wear and corrosion resistance, to enhance surface properties at a specified area of the parts and tools and also to make metal matrix composites. This process is an environment-friendly technique in which friction between the substrate and consumable rod and the deformation of the consumable rod is the only source to generate heat. The different parameters for this process are rotational speed, pressure or force applied, tilt angle and friction time. The present study is a review of microstructructural evaluation of different materials after the friction surfacing process.

Microstructural Evolution and Phase Transformation in Laser Cladding of Cr and Mo Powder on Grey Cast Iron: Mixture Design of Experiment (DOE)

Laser cladding on grey cast iron at high power processing was investigated for microstructural evolution and phase transformation to enhance surface properties. Cladding was designed using a mixture of DOE with peak power (Pp) and pulse repetition frequency (PRF), and a mixture component of Cr and Mo ratio as factors. Microstructural findings indicated absolute elimination of graphite phase from the clad zone, in conjunction with particles evolution occurrence. Meanwhile, Cr, Mo and Fe phases were detected on the clad surface, along with M-C carbide, retained austenite and MoFe formation. The clad surface with addition of Mo exhibited a high hardness value of 945.5 HV0.1 due to carbide formation. As a result of high peak power penetration into substrate surface, the depth range of clad zone was 53 to 131 µm. From the optimisation, the highest desirability is 82.3 %. Cladding with molybdenum powder addition was found to have produced minimum surface roughness, maximum depth and hardness of 9.14 µm, 110 µm and 891.1 HV0.1, respectively.

Dimension induced intrinsic physio-electrical effects of nanostructured TiO2 on its antibacterial properties

TiO2 is one of the wonder materials that possess extraordinary engineering versatility in terms of nanostructures, shapes and morphology. TiO2 nanomaterials have shown superior antibacterial capability, it is however still unclear about the intrinsic dimensional effects on antibacterial mechanisms. This study reported a fundamental antibacterial mechanism about the intrinsic antibacterial capabilities of the engineered nanostructured TiO2 materials (ENMs) – from three aspects 1) the structures of such nanoparticles, rods, tubes, fibres and spheres; 2) sizes/diameters/length of the ENMs; 3) combined effect due to dimensions and structures. Experimental results revealed that, the 1 D nanotubular TiO2, being the smallest individual ENMs possessed the highest toxicity towards E. coli; further studies showed that 3 D dendritic nanostructure incorporated with 1 D ultrathin TiO2 nanorods had the highest antibacterial efficiency. Comparative studies have suggested that, the well-engineered 3 D TiO2 nanomaterials (microspheres) with enhanced surface properties such as evenly grown 1 D sub-structures were more aggressive than the cluster aggregated 1D nanomaterials. In-depth research concluded that with well-controlled nanorods density and length, the integrated 3 D ENMs exhibited most efficient antibacterial activities. Such results could benefit the future antibacterial applications and the agent fabrications.

Two-beam interference patterning of biodegradable magnesium alloy: Influence of number of passes and spots overlap

Laser based texturing methods provide enhanced surface properties exploitable, especially in biomedical applications. Direct writing methods allow for processing features in tens of micrometers in size due to the use of diffraction limited beams. Feature size can be further reduced exploiting the light interference combined with the pulsed laser ablation. In this work, an industrial grade single mode nanosecond-pulsed green fiber laser was used to realize two-beam direct laser interference patterning system. The system was employed on a biodegradable Mg alloy to test the feasibility of the approach for submicrometric patterning. The combination of low melting point and high thermal conductivity of Mg alloy with the use nanosecond pulses generates difficulties in terms of the machining quality. The influence of number of pulses and number of passes was evaluated on the patterned area diameter as well as the pattern periodicity. Finally, patterned regions were overlapped on a scanned line to assess the feasibility of the process on larger areas.

Mechanisms of carbon nanotube-induced pulmonary fibrosis: a physicochemical characteristic perspective.

Carbon nanotubes (CNTs) are engineered nanomaterials (ENMs) with numerous beneficial applications. However, they could pose a risk to human health from occupational or consumer exposures. Rodent models demonstrate that exposure to CNTs via inhalation, instillation, or aspiration results in pulmonary fibrosis. The severity of the fibrogenic response is determined by various physicochemical properties of the nanomaterial such as residual metal catalyst content, rigidity, length, aggregation status, or surface charge. CNTs are also increasingly functionalized post-synthesis with organic or inorganic agents to modify or enhance surface properties. The mechanisms of CNT-induced fibrosis involve oxidative stress, innate immune responses of macrophages, cytokine and growth factor production, epithelial cell injury and death, expansion of the pulmonary myofibroblast population, and consequent extracellular matrix accumulation. A comprehensive understanding of how physicochemical properties affect the fibrogenic potential of various types of CNTs should be considered in combination with genetic variability and gain or loss of function of specific genes encoding secreted cytokines, enzymes, or intracellular cell signaling molecules. Here, we cover the current state of the literature on mechanisms of CNT-exposed pulmonary fibrosis in rodent models with a focus on physicochemical characteristics as principal drivers of the mechanisms leading to pulmonary fibrosis. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Respiratory Disease Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

On improving the formability of AA6061/SiCp composite synthesized using friction stir processing

AbstractFriction stir process is a potentially useful method for producing composites of enhanced surface properties. In this work, an AA6061/SiCp composite, synthesized using friction stir processing, was tested in three‐point bending and uniaxial hot tensile and bi‐axial stressing to assess its formability. Bending test results reveal an increased bending strength in the composite compared with the AA6061 alloy, subjected to friction stir processing, but without the addition of the silicon carbide particles. Based on the hot tensile tests, the biaxial stressing temperatures were fixed as 623 K and 673 K. Bi‐axial stressing reveals that a maximum bulge height of 18 mm could be obtained by forming into a cavity of 59 mm diameter at a pressure of 0.2 MPa. Based on the results, process parameters such as formed bulge height, forming time, strain rate and strain rate sensitivity index were determined. In the present experiments, the strain rate sensitivity index increased with increasing forming pressure and reached a maximum value of 0.40 at a forming pressure of 0.25, as the latter variable was increased from 0.20 MPa to 0.25 MPa. The present findings can pave the way for the commercial exploitation of friction stir process‐technology‐based, efficient processing of the AA6061/SiCp composite.

Enhancement of surface properties with influence of bath pH on electroless Ni-P-ZnO/Al2O3 nano-composite deposits for defence applications

The focus of this paper is to experimentally investigate the effect of ENi-P-ZnO/Al2O3 composite deposition on corrosion and wear resistance, surface morphology, crystallographic structure, microhardness, surface roughness (Ra) and wettability, on mild steel specimen, by maintaining bath pH at 5, 7 and 9. On investigation, it is revealed that incorporation of ZnO and Al2O3 sharply improves the corrosion resistance, microhardness, coefficient of friction, wear rate, surface roughness and morphology of the as-deposited samples as against nondeposited mild steel specimen. Incorporation of ZnO nanoparticles results in 96% reduction in corrosion rate (7.92mmpy) as against the without deposited mild steel specimen (180mmpy) and incorporation of Al2O3 nanoparticles results in 184% increase in microhardness (625Hv) as against the without deposited mild steel specimen (220Hv), under optimum operating conditions of bath pH7 and pH9 respectively, thereby enhancing applications in various defence fields like marine and aviation.

Synthesis of Nb2O5 and Ta2O5 nanopowders by means of an endo-templating method

Finding efficient templates for the nanostructuring of materials is a key point. Here, the niobium (V) - and tantalum (V) oxide ceramics nanopowders have been synthesized by a hard-templating approach by using the tricalcium phosphate biomaterial (Ca3(PO4)2.xH2O) as template agent. The oxide ceramics were investigated by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, nitrogen physisorption and Scanning Electron Microscopy (SEM). It was observed that the surface properties (specific surface areas, pore volumes) of the Nb2O5 and Ta2O5 powders were strongly dependent of the amount of the Ca3(PO4)2.xH2O template previously used in the preparation of the [oxide ceramics/template] composites. For instance, with a Ca3(PO4)2.xH2O/ceramic salt weight ratio ranging from 0 to 1, the specific surface areas of Nb2O5 and Ta2O5 were gradually enhanced of 48–166m2/g and 5–84m2/g, respectively. The pore volumes were increased as well. The use of the eco-friendly tricalcium phosphate material (Ca3(PO4)2.xH2O) as template in the hard-templating approach may be suitable and efficient in the aim of synthesizing materials with enhanced surface properties.

Modification of Silumin Using the Electroexplosive Method

Surface modification of silumin of the grade AK12 with plasma formed during an electrical explosion of aluminum foil with a sample of yttrium oxide powder placed in the explosion region (the electroexplosive doping method) is carried out. The thermodynamic analysis of the system Al-Si-Y-O is carried out. The phases formed in this system under equilibrium conditions are revealed. Investigations of the elemental and phase composition and the defective substructure are carried out. Mechanical (microhardness) and tribological (wear resistance and friction coefficient) tests of the modified material are performed. The physical mechanisms responsible for multiple enhancement of surface properties of the modified silumin samples are revealed.

Cellulose Acetate Derived Free-Standing Electrospun Carbon Nanofibrous Mat As an Anode Material for Rechargeable Lithium-Ion Battery

Introduction Electrospun polymer derived carbon nanofibers have received attention in recent years as an anode material for energy storage devices due to their enhanced surface area, single step synthesis and shorter diffusion length.[1] Due to these enhanced surface properties, carbon nanofibers showed promising performance even at high C-rate applications.[2] More often, carbon derived from Polyacrylonitrile and its composites are explored as anode material for energy storage devices due to high carbon yield.[1,3,4] However, some other polymeric carbon precursors like polypyrrole, polyvinyl alcohol, and more recently, SU-8 negative photoresist were also explored as an electrode material for a rechargeable Lithium-ion battery. Use of SU-8 facilitates fabrication of three-dimensional electrodes as it can be patterned using photolithography, but it is an expensive source for carbon. The present study is the first report, where cellulose acetate derived carbon fibers have been used as an anode for lithium-ion battery. Cellulose acetate is an inexpensive polymeric carbon precursor. Moreover, our group has recently developed template-assisted electrospinning technique to produce patterned three-dimensional cellulose acetate nanofibrous structures [5] which can be explored further for higher surface area and enhanced performance. Experimental Cellulose acetate polymer (Mw: 29,000 g/mol; Sigma Aldrich, India) was mixed with a binary solvent (acetone and dimethylamide) and the 16 wt.% solution was electrospun to form the nanofibers. As-prepared electrospun cellulose acetate nanofibers mat was regenerated to cellulose nanofabric by deacetylation in 0.05 M NaOH in ethanol, as direct carbonization of cellulose acetate fibers results in melting. After deacetylation cellulose fiber mat was stabilized at 240 °C prior to carbonization at 900 °C in inert atmosphere. Cellulose acetate derived carbon nanofabric was then directly used as a free-standing electrode without any further modification. Electrochemical performance of mat was investigated using Swagelok cell, where lithium metal was used as counter electrode. Results and discussions: Surface morphology of the electrospun fibers was investigated with scanning electron microscope (Figure 1(a)) and deacetylation of cellulose acetate fibers was confirmed by Raman spectroscopy (Figure 1 (b)). A band near 1095 cm -1 can be clearly observed only for regenerated cellulose fiber in figure 1 (b) which corresponds to C-O ring stretching mode, and confirms the conversion of cellulose acetate nanofibers to cellulose nanofibers. Electrochemical performance of cellulose acetate derived carbon fibers was studied at 37.2 mA/g current density. Figure 1(c) shows the cyclic performance of cellulose acetate derived carbon fibers for 100 cycles of charge/discharge. The reversible capacity of these carbon nanofibers was observed to be similar to polyacrylonitrile derived carbon fibers. [3,4] Specific reversible capacity after 100 cycles was found to be ~290 mAh/g. Initial lower columbic efficiency can be attributed to faradic reactions and SEI formation, which is characteristic of carbon materials. Due to the enhanced surface area of free standing carbon fiber mat and entangled three-dimensional porous structure, initial fade was significant. This may be attributed to irreversible surface adsorption of lithium ion. However, after initial 10 cycles, more than 90% of columbic efficiency was retained. Electrochemical performance at higher current densities and detailed structural analysis will be presented in conference presentation.

Montmorillonite/poly(urethane-siloxane) nanocomposites: Morphological, thermal, mechanical and surface properties

The aim of this work was to prepare and characterize the series of segmented polyurethane nanocomposites (PUNC) modified with poly(dimethylsiloxane) and based on montmorillonite (Mt) as a nano-filler. α,ω-Dihydroxy-poly(propylene oxide)-b-poly(dimethylsiloxane)-b-poly(propylene oxide) macrodiol was used as the soft segment component, while 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) were selected as the hard segment components. PUNC were synthesized with different ratio of hard/soft segments. PUNC were morphologically, structurally, thermally, mechanically and surface characterized by XRD, TEM, FTIR, AFM, TGA, DMTA, tensile test, XPS, contact angle, surface free energy (SFE) and water absorption measurements. Added Mt (1wt%) was completely delaminated and well dispersed in the form of mixed exfoliated/intercalated layers in the polymer matrix, and that PUNC have more pronounced microphase separated morphology, higher thermal stability, superior mechanical features, enhanced surface properties, as well as outstanding hydrophobicity. Due to the improved features, developed polymers can be considered as candidates for materials with specific biomedical applications or as waterproof coatings.

Enhancing surface properties of breast implants by using electrospun silk fibroin.

In the present study, a new electrospun silk fibroin coating of silicone breast implants with improved biocompatibility and mechanical properties was obtained. Fibrous scaffolds were produced by electrospinning a solution containing silk fibroin, derived from Bombyx mori cocoons, and polyethylene oxide (PEO) to be used as a coating of breast implants. A randomly oriented structure of fibroin/PEO was electrospun on implants as assessed by SEM analysis, roughness measurements and ATR-FTIR spectroscopy. The scaffold showed 0.25 µm diameter fibres, 0.76 µm size superficial pores, arithmetic roughness of 0.632 ± 0.12 µm and texture aspect ratio of 0.893 ± 0.04. ATR-FTIR spectroscopy demonstrates the presence of PEO and fibroin in the coating. The mechanical characterisation of the implants before and after being coated with fibroin/PEO demonstrated that the fibroin/PEO scaffold contributes to the increase in the elastic modulus from 0.392 ± 0.02 to 0.560 ± 0.03 MPa and to a more elastic behaviour of the breast implants. Using the fibroin/PEO coating, human fibroblasts seeded on this matrix increased viability up to 30% compared to conventional breast implants. Electrospun silk fibroin could represent a clinically compatible, viable form to coat breast implants. Low cytotoxicity by the fibroin coating and its physico-chemical and mechanical properties may find application in improving breast implants biocompatibility. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1655-1661, 2018.

Metallomacrocyclic–carbon complex: A study of bifunctional electrocatalytic activity for oxygen reduction and oxygen evolution reactions and their lithium-oxygen battery applications

A metallophthalocyanine – carbon complex is designed by a simple approach to achieve superior, bifunctional catalytic activity. A simple and cost-effective technique is utilized to prepare carbon_iron phthalocyanine composites. Furthermore, to investigate ball milling effects, iron phthalocyanine is ball milled, which is used to prepare the carbon_ball-milled iron phthalocyanine composites. All the prepared composites exhibit better catalytic activity in both oxygen reduction and oxygen evolution reactions than Pt/C, indicating carbon support significantly improves the stability, conductivity, and surface properties of iron phthalocyanine. The ball-milling improves specific surface area, which in turn enhances the oxygen evolution reaction activity of the composites. When the carbon-iron phthalocyanine composites were applied to an air-cathode catalyst in a lithium-oxygen battery, high reversibility and low over-potential were attained. Among all the synthesized catalysts, the reduced graphene oxide_ball-milled iron phthalocyanine composite exhibits superior bifunctional electrocatalytic activity with high reversibility (92%) and low over-potential (0.7V) due to enhanced surface properties.