Surface Engineering Techniques Research Articles

Design of Nanostructured Functional Coatings by Using Wet-Chemistry Methods

This review reports the implementation of novel nanostructured functional coatings by using different surface engineering techniques based on wet chemistry. In the first section, the theoretical fundaments of three techniques such as sol-gel process, layer-by-layer (LbL) assembly and electrospinning will be briefly described. In the second section, selected applications in different potential fields will be presented gathering relevant properties such as superhydrophobicity, biocide behavior or applications in the field of optical fiber sensors.

Evaluation of Wear on Macro-Surface Textures Generated by ns Fiber Laser

The demand for improved performance and long term reliability of mechanical systems dictate the use of advanced materials and surface engineering techniques. A small change in the surface topography can lead to substantial improvements in the tribological behaviour of the contact surfaces. One way of altering the surface topography is by surface texturing by introducing dimples or channels on the surfaces. Surface texturing is already a successful technique which finds a wide area of applications ranging from heavy industries to small scale devices. This paper reports the effect of macro texture shapes generated using a nanosecond fiber laser on wear of high carbon chromium steel used in large size bearings having rolling contacts. Circular and square shaped dimples were generated on the surface to assess the effect of sliding velocities on friction coefficient. Graphite was used as solid lubricant to minimise the effect of wear on textured surfaces. The laser parameters such as power, scan speed and passes were optimised to obtain macro circular and square dimples which was characterised using a laser confocal microscope. The friction coefficients of the circular and square dimples were observed to lie in the same range due to minimum wear on the surface. On the contrary, at medium and higher sliding velocities, square dimples exhibited lower friction coefficient values compared to circular dimples. The morphology of textured specimen was characterised using Scanning Electron Microscope.

Investigation of Mechanical, Microstructural and Corrosion behaviour of Titanium subjected to Laser Peening with and without Ablation

Present competitive world is looking for Components with high strength and fatigue resistance finding their applications in aerospace, turbine parts and especially bio-medical devices with high bio-compatibility. Advanced surface engineering techniques are required to produce parts of higher complexities and desirable surface qualities. Laser peening stood first in a row of all various surface treatments of metallic component. This paper discusses about the mechanical properties like hardness and roughness then the surface morphology and the corrosion behaviour of the laser peened titanium samples with and without coating.

Surface Functionalization and Targeting Strategies of Liposomes in Solid Tumor Therapy: A Review.

Surface functionalization of liposomes can play a key role in overcoming the current limitations of nanocarriers to treat solid tumors, i.e., biological barriers and physiological factors. The phospholipid vesicles (liposomes) containing anticancer agents produce fewer side effects than non-liposomal anticancer formulations, and can effectively target the solid tumors. This article reviews information about the strategies for targeting of liposomes to solid tumors along with the possible targets in cancer cells, i.e., extracellular and intracellular targets and targets in tumor microenvironment or vasculature. Targeting ligands for functionalization of liposomes with relevant surface engineering techniques have been described. Stimuli strategies for enhanced delivery of anticancer agents at requisite location using stimuli-responsive functionalized liposomes have been discussed. Recent approaches for enhanced delivery of anticancer agents at tumor site with relevant surface functionalization techniques have been reviewed. Finally, current challenges of functionalized liposomes and future perspective of smart functionalized liposomes have been discussed.

A review of nanostructured surfaces and materials for dental implants: surface coating, patterning and functionalization for improved performance.

The emerging field of nanostructured implants has enormous scope in the areas of medical science and dental implants. Surface nanofeatures provide significant potential solutions to medical problems by the introduction of better biomaterials, improved implant design, and surface engineering techniques such as coating, patterning, functionalization and molecular grafting at the nanoscale. This review is of an interdisciplinary nature, addressing the history and development of dental implants and the emerging area of nanotechnology in dental implants. After a brief introduction to nanotechnology in dental implants and the main classes of dental implants, an overview of different types of nanomaterials (i.e. metals, metal oxides, ceramics, polymers and hydrides) used in dental implant together with their unique properties, the influence of elemental compositions, and surface morphologies and possible applications are presented from a chemical point of view. In the core of this review, the dental implant materials, physical and chemical fabrication techniques and the role of nanotechnology in achieving ideal dental implants have been discussed. Finally, the critical parameters in dental implant design and available data on the current dental implant surfaces that use nanotopography in clinical dentistry have been discussed.

Surface Micro patterning of Aluminium Reinforced Composite for Aerospace Applications through High Energy Pulse Laser Peening

Aluminium (Al) Composites have universal engineering applications because of their higher strength to weight ratio, ductility, and formability. However, in diverse applications, mechanical properties such as hardness, corrosion, wear, and fatigue resistance are the prerequisite at closer surface regions. Such localised changes without impacting various surface treatment approaches can attempt the bulk phase. Laser shock peening is an advanced surface engineering technique, which has been successfully applied to improve the surface morphology and microstructure of the material. In this work, we are focusing on improving the surface properties of Al7075 reinforced with SiC and Zirconia through laser peening technique. The hardened layer was evaluated using surface integrity with optical microscopy, energy dispersive spectroscopy, scanning electron microscope (SEM) and analysis of microhardness. Process parameters and resulting microstructures of Aluminium composite are summarised, along with the impact of laser peening on surface properties. Research results indicated that laser peening shows a significant influence on the final condition of the surface layer of Aluminium composite.

Metal sputtered graphene based hybrid films comprising tin oxide/reduced graphene oxide/Ni as electrodes for high-voltage electrochemical capacitors

The high voltage aqueous electrochemical capacitor (EC) is a promising energy storage device because of eco-friendliness and high electrochemical performance with a wide operational voltage and high energy density. However, it typically experiences a stability problem that includes cell aging and capacitance loss. Here, to overcome the stability issue, a thin metal layer of Ni is created on one side of a SnO2/reduced graphene oxide (rGO) hybrid film to produce a binder-free film of SnO2/rGO/Ni. Due to the formation of the highly conductive metal layer of Ni, the fabricated film can be well interconnected with the current collector and have lower contact resistance and open-circuit potential compared with untreated SnO2/rGO film, which results in a remarkable enhancement of electrochemical performance, including a wide operational voltage (1.8 V), semi-permanent cycle-life (95% retention after 10k cycles), and ultrahigh volumetric energy density with a high power density, all of which are superior values compared to bare SnO2/rGO film based devices. We anticipate that the fabricated SnO2/rGO/Ni film could be utilized as a promising electrode for high voltage ECs, and our simple surface engineering technique will provide an effective electrode design for the fabrication of high performance thin-film ECs.

Oxygen Containing Functional Groups Dominate the Electrochemiluminescence of Pristine Carbon Dots

In this study, electrochemiluminescence (ECL) properties of carbon dots (CDs, less than 10 nm) have been investigated. Such CDs were fabricated via electrochemical etching strategy from graphite rods. Subsequently, a series of CDs were prepared through controlled surface engineering technique by a wet chemical method, including the oxidized-CDs (oCDs), partially reduced-CDs (rCDs), and fully reduced-CDs (F-rCDs). In-depth characterizations including UV–vis, FT-IR, Raman, XPS, etc. revealed significant differences in features of these CDs, especially the condition of surface grafted oxygen containing functional groups. ECL results suggested that all of the annihilation ECL of CDs, oCDs, and rCDs demonstrated a stable positively charged luminophore (R+•) and an unstable negatively charged luminophore (R–•) at the surface of GCE and possessed a 365 nm emission peak and consistent emission range from 550 to 850 nm. During further structural mode investigation and ECL properties simulation, the surface constru...

Controllable hierarchical micro/nano patterns on biomaterial surfaces fabricated by ultrasonic nanocrystalline surface modification

In this work, we have shown that Ultrasonic Nanocrystal Surface Modification (UNSM) cannot only improve the mechanical properties of Ti-based biomaterials but also produce surface texture with hierarchical micro/nanoscale patterns due to its high controllability. After UNSM-treatment the surface texture of Ti-based biomaterial consists of a major microscale structure with widths ranging from 4μm to 200μm, and an embedded nanoscale structure with widths as small as 120nm. With a customized cylinder tip, the average surface roughness (Ra) can be reduced to 0.03μm, comparable to the superfinishing surface. The embedded nanoscale structure originates from the formation of the pile-up, which is determined by the elastic-plastic property of materials. Such hierarchical patterns enable new functions for the treated surface. It is demonstrated that light dispersion and the alteration of wettability can be achieved by controlling surface patterns using UNSM. The capacity of improving mechanical properties, biocompatibility, and hydrophobicity simultaneously, in conjunction with its low-cost and easy-to-operate features, makes it a promising surface engineering technique for biomaterial treatment.

Surface Micro Patterning of Aluminium Reinforced Composite through Laser Peening

Aluminium Composites have universal engineering applications because of their higher strength to weight ratio, ductility, and formability. However, in diverse applications, mechanical properties are the prerequisite at closer surface regions. Such localized changes without impacting various surface treatment approaches can attempt the bulk phase. Laser peening is an advanced surface engineering technique, which has been successfully applied to improve the surface morphology of the material. In this work, the authors focus on improving the surface properties of Al7075 composite through laser peening technique. The hardened layer was evaluated using surface integrity with optical microscopy, EDS, SEM and analysis of microhardness. Process parameters and resulting microstructures of Aluminium composite are summarized, along with the impact of laser peening on surface properties. Research results indicated that laser peening shows a significant influence on the final condition of the surface layer of Aluminium composite.

Boundary Tribological Behaviors of Untreated and Surface-Modified M50 Steel Lubricated by Fuel JP-10

ABSTRACTTo explore the possibility of using advanced surface engineering techniques (ASETs) to solve the wear problems caused by the poor lubricity of pure, low-viscosity aviation fuel JP-10, polished M50 bearing steel sample surfaces were treated with nitrogen ion implantation, TiAlN coating deposition, and Ta coating deposition followed by high current pulsed electron beam (HCPEB) irradiation, respectively. Boundary tribological behaviors of these ASET-treated and untreated steel samples sliding in pure JP-10 against a Si3N4 ball (ball-on-disc model) were investigated under 2.0 GPa in the atmosphere and the friction tests indicated that significant, reductions, although to different extents, in friction and wear were achieved by these modified surfaces. Simultaneously considering the tribological performance and potential pollution caused by wear debris to JP-10, HCPEB-treated Ta coating with a lowest average friction coefficient of 0.11 and a specific wear rate of around zero was the fittest to offset the inadequate lubricity of JP-10 itself under the laboratory condition.

Development of stress corrosion cracking resistant welds of 321 stainless steel by simple surface engineering

We hereby report a simple surface engineering technique to make AISI grade 321 stainless steel (SS) welds resistant to stress corrosion cracking (SCC) in chloride environment. Heat exchanger tubes of AISI 321 SS, welded either by (a) laser beam welding (LBW) or by (b) metal inert gas welding (MIG) were used for the study. The welds had high magnitude of tensile residual stresses and had undergone SCC in chloride environment while in service. The welds were characterized using field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). Subsequently, the welded surfaces were subjected to buffing operation followed by determination of residual stress distribution and surface roughness by XRD and surface profilometer measurements respectively. The susceptibility of the welds to SCC was tested in buffed and un-buffed condition as per ASTM G-36 in boiling MgCl2 for 5h and 10h, followed by microstructural characterization by using optical microscope and FESEM. The results showed that the buffed surfaces (both welds and base material) were resistant to SCC even after 10h of exposure to boiling MgCl2 whereas the un-buffed surfaces underwent severe SCC for the same exposure time. Buffing imparted high magnitude of compressive stresses on the surface of stainless steel together with reduction in its surface roughness and reduction in plastic strain on the surface which made the welded surface, resistant to chloride assisted SCC. Buffing being a very simple, portable and economic technique can be easily adapted by the designers as the last step of component fabrication to make 321 stainless steel welds resistant to chloride assisted SCC.

Structure of Micro-nano WC-10Co4Cr Coating and Cavitation Erosion Resistance in NaCl Solution

Cavitation erosion (CE) is the predominant cause for the failure of overflow components in fluid machinery. Advanced coatings have provided an effective solution to cavitation erosion due to the rapid development of surface engineering techniques. However, the influence of coating structures on CE resistance has not been systematically studied. To better understand their relationship, micro-nano and conventional WC-10Co4Cr cermet coatings are deposited by high velocity oxygen fuel spraying(HVOF), and their microstructures are analyzed by OM, SEM and XRD. Meanwhile, characterizations of mechanical and electrochemical properties of the coatings are carried out, as well as the coatings’ resistance to CE in 3.5 wt % NaCl solution, and the cavitation mechanisms are explored. Results show that micro-nano WC-10Co4Cr coating possesses dense microstructure, excellent mechanical and electrochemical properties, with very low porosity of 0.26 ± 0.07% and extraordinary fracture toughness of 5.58 ± 0.51 MPa·m1/2. Moreover, the CE resistance of micro-nano coating is enhanced above 50% than conventional coating at the steady CE period in 3.5 wt % NaCl solution. The superior CE resistance of micro-nano WC-10Co4Cr coating may originate from the unique micro-nano structure and properties, which can effectively obstruct the formation and propagation of CE crack. Thus, a new method is proposed to enhance the CE resistance of WC-10Co4Cr coating by manipulating the microstructure.

Effect of shielding gas and energy input rate on the surface geometry and microstructure of a microalloyed steel surface melted with a TIG torch

Surface engineering techniques are used to enhance surface properties, such as wear, erosion and/or corrosion of materials, by developing a functionally graded metal matrix composite layer. Recently, as an economic alternative to laser processing, a tungsten inert gas torch has been used to incorporate ceramic particles into a metal surface. This produced about 1 μm depth melted and resolidified track on the surface, which during processing, required protection by from oxygen and hydrogen environment, by a shielding gas. The present study analysed the effect of three shielding gases argon, helium, and nitrogen, on the melt zone morphology, microstructure and hardness after melting a microalloyed steel surface under different energy input conditions. The aim was to determine the optimum conditions for future research related to surface engineering, incorporating ceramic particles. The results show that when protected by argon and using energy inputs <420 J/mm, an increase of 5% in the temperature between the start and finish of the melted track was recorded, but this increased to ~25% when using energy inputs >420 J/mm. It was also found, that compared to nitrogen, using argon and helium, a re-solidified homogeneous and consistent cross- section developed along the melted track.

Combination of laser patterning and nano PTFE sputtering for the creation a super-hydrophobic surface on 304 stainless steel in medical applications

Subsequent host tissue responses to implanted biomaterials that occur immediately after implantation are highly determined by surface events between tissue-implant interfaces and in contact biological fluids. These events are directly affected by biomaterial surface features. The surface of the 304 stainless steel as a high used metallic biomaterials in blood contact medical devices need to hemocompatibility improvement. The hemocompatibility features of the surface are affected by various factors, including physical and chemical properties, particularly wettability. A high level of surface hydrophobicity helps to enhance the hemocompatibility. For this, many surface engineering techniques are used to modify and control surface wettability behavior that can be adapted to improve the hemocompatibility and overall performance of biomaterials.In the present study, a laser patterning model is applied for creation of parallel micro-grooves on the surface of 304 stainless steel in first stage. Secondly, a fluorocarbon thin film has been deposited on the inscribed surface of the steel using polytetrafluoroethylene (PTFE) sputtering. The results show that, by creating a micro-groove pattern on the steel surface, the wettability behavior of the surface will also change and the contact angle will be increased from 80° to almost 111°. Moreover, the deposition of a polymer thin film has led to a decrease in surface energy and, thereby, an increase in hydrophobicity and making a contact angle of 149°. From these finding, it can be concluded that, with simultaneous use of topography and surface chemistry changes, the wettability behavior of the surface has been increased and a high and appropriate level of hydrophobicity has been achieved consequently, that is suitable for hemocompatibilty of blood-contact devices.

Effect of laser shock peening on residual stress, microstructure and fatigue behavior of ATI 718Plus alloy

The effects of Laser Shock Peening (LSP) on the microstructure, residual stress, hardness, strength, and fatigue life of ATI 718 Plus (718Plus) alloy was investigated and the results are reported. Microstructure before and after LSP and after mechanical testing was characterized using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD)/orientation imaging microscopy (OIM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). LSP led to severe surface plastic deformation, which, in turn, led to a high magnitude of surface compressive residual stresses (∼−725MPa) and changes in the near-surface microstructure. This change was in the form of high dislocation density forming dislocation entanglements and slip bands and formation of a few near-surface sub-grains, which, in turn, caused high surface hardening (∼8.3GPa). In addition, a 16% increase in the yield strength (∼175MPa) and around 15% increase in the endurance limit (∼110MPa) occurred in corresponding tests at room temperature. The improvement in fatigue life was due to the shielding and resistance to crack initiation that the LSP treatment provided to the material through the near-surface microstructure, hardening and high compressive residual stress. This shielding also hindered crack propagation, lowering its rate to a third compared with baseline. Results of studies of stress relaxation with cycles showed how the LSP shield was affected by cycling and, in turn, the improvement in fatigue life of 718Plus. The results have demonstrated that LSP is a powerful surface engineering technique that can improve mechanical properties and fatigue performance of many important metallic materials.

Laser shock peening induced residual stresses and the effect on crack propagation behavior

Laser shock peening (LSP), as a powerful surface engineering technique to improve the fatigue performance of metallic components, requires elaborately designed process pattern to maximize its benefits. In this study, a numerical method, combining finite element method (FEM) and residual stress intensity factor (SIF) analysis, was used to predict the effect of LSP pattern on the crack propagation behavior of the compact tension (CT) samples. The 3D FEM model was fully benchmarked using the mesh sensitivity study and time step calibration. The model was further validated using residual stresses data measured using the X-ray diffraction method. After that, the simulation of LSP of CT sample was conducted using five representative cases, and the corresponding residual stress fields were obtained. A mixed-mode SIF model was then applied to evaluate the effect of the residual stress field in resisting crack propagation. Based on the calculated residual SIFs from different LSP patterns, the best LSP patterns in terms slowing crack propagation speed were identified. To validate the simulation results, LSP experiments were conducted on CT samples using two identified LSP patterns and the crack growth rates were tested. The experiment results were consistent with the numerical prediction. This work demonstrates that FEM model combining residual SIF analysis can be applied to design appropriate LSP patterns on components with complex geometries.

Mimicking Neuromuscular Junctions Using Controlled Crystallization of Solvents: A Surface and Interface Engineering Technique for Polymers

Recently, crystallization engineering has become a novel processing technique for various materials, including ceramics, polymers, and composites. Herein, a novel processing technology of polymers based on controlled directional crystallization was developed for biomimetic surfaces and interfaces. Solvent was allowed to come into contact with a polymer surface for a limited time, followed by controlled crystallization of the solvent along a temperature gradient perpendicular to the surface. As a result, perpendicular pores of well-defined patterns were successfully prepared, as well as adhesive-free strong interfaces mimicking neuromuscular junctions. By increasing the temperature of the polymer or solvent contact time, the pore depth and contact angle increased. Highly hydrophobic surfaces of polycarbonate were efficiently prepared, and interfacial adhesion with polydimethylsiloxane was improved by more than 4-fold. This novel processing technique based on crystal engineering could open completely new ap...

Influence of surfactant: Using electroless ternary nanocomposite coatings to enhance the surface properties on AZ91 magnesium alloy

Magnesium (Mg) base alloy (AZ91) is widely used in various industrial, aviation, and automotive applications due to its high specific strengths. A shortcoming of Mg alloy is its poor resistance to corrosion and sub-optimal surface properties which hindered its widespread applications. Electroless Ni-P-ZnO ternary alloy nano-composite deposition is one such surface engineering technique that is likely to greatly enhance the surface properties of AZ91 magnesium alloy with addition of surfactant. Endeavour of this study is to analyze the influence of cationic surfactant (Aliquat 336) on the surface properties of electroless ternary alloy nano-composite deposits on AZ91 alloy substrate. The addition of surfactant at a concentration of 1.5g/l in the coating reveals a significant improvement in the rate of deposition, wettability, and corrosion resistance with a sharp decline in the surface roughness (Ra) as compared to the coating obtained without presence of surfactant in solution of the bath. As-deposited samples were characterized by Field Emission Scanning Electron Microscopy and Energy Dispersive X-ray Analysis (FESEM-EDAX), X-ray Diffraction (XRD).

Improvement of wear resistance of AZ91 magnesium alloy by electroless Ni-P coatings with influence of surfactant

Electroless Nickel-Phosphorus (ENi-P) coating is well-known in surface engineering techniques and is preferred in various mechanical, chemical and electronic industries view its extraordinary resistance to wear and corrosion. The paper summarizes the effect of surfactant on mechanical properties of electroless Ni-P alloy coating obtained from acidic bath. Morphology of the resultant coating was studied using scanning electron microscope and its phosphorus content was measured by EDX analyzer. Wear resistance of the coating, with and without surfactant, was evaluated by pin-on-disc tribometer wear tester machine. Endeavour of this study is to analyze the influence of Ammonium Lauryl Sulfate (ALS) surfactant on the microstructure and surface properties of ENi-P deposit on AZ91 Mg alloy substrate. The results revealed that there was a significant improvement in the wear resistance of the coated surface by addition of ALS surfactant in the chemical bath. ALS surfactant is distinctively added into the bath to reduce the surface tension forces, which binds the nickel particles to the hydrogen gas bubbles generated during the deposition process. The complete experimental details, results obtained and their analyses are presented in this paper.