Uncoated Specimens Research Articles

Anti-icing and de-icing properties of composite superhydrophobic coating with microwave heating performance on asphalt pavement

Severe icing on asphalt pavements significantly impacts traffic safety and efficiency. Superhydrophobic coatings exhibit excellent hydrophobic and anti-icing properties, making them suitable for asphalt pavements. However, the formation of dense and hard ice limits their anti-icing effectiveness in cold regions. Within this paper, we have developed a novel composite superhydrophobic coating (CSC) with microwave heating performance by constructing a hierarchical structure using carbon nanotubes and incorporating micron-sized iron powder as a primary microwave-absorbing material. Scanning electron microscopy, 3D confocal microscopy, and contact angle tests reveal that the optimally mixed CSC possesses a complex micro-nano hierarchical structure, superhydrophobic properties (contact angle of 155.4°), and excellent anti-icing properties. Microwave heating results show that the CSC achieves a maximum heating rate of 1.108 ℃/s and an energy utilization efficiency of 47 %, representing improvements of 118.1 % and 18.3 % compared to uncoated specimens. Durability tests indicate that after wear, the CSC's contact angle decreases by 6.2 %, and the microwave heating rate drops by 13.7 %. Despite these reductions, the coating still maintains high hydrophobicity and microwave heating performance. While the friction coefficient of CSC-coated pavement decreases to μ=0.63, it still meets regulatory requirements. Overall, the application of CSC can effectively increase de-icing efficiency and mitigate the adverse effects of ice and snow on pavements.

Corrosion measurement of thermally sprayed carbide coatings on stainless steel pipes

The petrochemical industries face a formidable challenge from corrosion, which leads to high maintenance costs and lost production. Traditional corrosion monitoring methods frequently fail to provide accurate and reliable results. As a result, these components must be replaced or repaired promptly to avoid increasing costs and limiting component life, which will reduce operation efficiency. Novel techniques with demands for high surface qualities in the future will be applied to develop alloys with better performance and more diverse applications. This study examines the corrosion resistance of cermet coatings, such as tungsten carbide (WC) and Chromium carbide (Cr3C2), in acidic solution by electrochemical impedance spectroscopy and electrochemical potentiodynamic polarisation. Additionally, utilizing optical microscopy techniques, the microstructural characteristics of coatings were assessed. According to the results of the Tafel polarisation test, Cr3C2 coating exhibited a lower rate of corrosion than other coatings. The Cr3C2 coated, WC coated, and uncoated samples reported corrosion rates of 0.924, 1.122, and 2.599 mmpy respectively. The corrosion resistance of Cr3C2 and WC coatings was increased by 64% and 53%, respectively, in comparison to uncoated specimens. This suggests that the coating maximizes economy, minimizes maintenance costs, extends the structure's lifespan, and reduces down the rate of corrosion.

Enhancing corrosion resistance of T91 F/M steel in liquid lead-bismuth (LBE) by slurry FeAl coating

A FeAl coating was fabricated on T91 steel via slurry aluminizing. The corrosion behavior of coated and uncoated samples was assessed in static LBE (lead-bismuth eutectic) with two both high and low dissolved oxygen concentrations at 550 °C. The coating was mostly intact and exhibited great corrosion resistance compared to the uncoated specimens regardless of the oxygen concentration. That is because the coating can form a protective alumina film on the surface at extremely low dissolved oxygen level. This coating is of significant engineering value in enhancing the corrosion resistance of Fe base alloy in LBE.

Evaluation of titanium dioxide and tantalum pentoxide nanoparticles for coating NiTi archwires in orthodontics: An in vitro study

Background: This study aims to enhance the biocompatibility of Nickel–Titanium (NiTi) alloy by developing a new coating using titanium dioxide (TiO2) and titanium pentoxide (Ta2O5) through direct current (DC) reactive sputtering technology. Materials and methods: Two distinct coating materials, namely, TiO2 and Ta2O5, were used to fabricate NiTi orthodontic archwires with improved surface properties. TiO2 nanoparticles, with thickness ranging from 21.90 nm to 31.93 nm, were deposited onto NiTi alloy substrates through DC reactive sputtering deposition under different power conditions. Results: X-ray diffraction and field emission scanning electron microscopy validated the uniformity and morphology of the coatings. Immersion tests in simulated body fluid (SBF) revealed significant hydroxyapatite layer growth on TiO2-coated NiTi, especially at a sputtering power of 240 W. Reduced nickel ion release was observed on TiO2 nanoparticles with a thickness of 21.90 nm at 50 W sputtering power compared with 31.93 nm-thick nanoparticles at 240 W. Ta2O5 thin films were deposited on NiTi substrates through DC magnetron reactive sputtering at ~100 °C with a deposition power of 50 W. Structural and morphological analyses through optical microscopy and X-ray diffraction, atomic force microscopy, and scanning electron microscopy revealed the homogeneity and low roughness of the coatings. Biocompatibility assessments in artificial saliva and SBF solutions established that Ta2O5-coated NiTi alloys exhibited superior electrochemical behavior, enhanced corrosion resistance, and diminished Ni ion release compared with uncoated specimens. Conclusion: TiO2 and Ta2O5 coatings not only improved the biocompatibility of NiTi orthodontic archwires but also presented a promising path for advanced biomedical applications. These coatings have potential in improving the cellular behavior and performance of NiTi-based orthodontic devices.

Optimization of Zn-Cr proportions for hybrid multilayer electroplating of AISI 1045 steel – towards super-hydrophobicity and anti-corrosive nature

Localized corrosion in steel heat exchangers is a major concern, occurring mostly during operational shutdowns. Due to the absence of flow and moisture content availability, corrosion reduces operation efficiency. A study aimed to optimize the proportions of Zinc and Chromium (Zn-Cr) for developing a hybrid multi-layer electroplating method to inhibit corrosion in hypo-eutectoid carbon steel commonly used in heat exchangers. The Zn-Cr coating was performed using the amperometric method in an electrochemical workstation, producing coatings of varying thicknesses by varying the potential and time. The surface morphology was characterized using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) analysis. The average thickness of the Zn-Cr coating was found to be 2.5 µm using the scanning probe microscope analysis. The corrosive action of a standard 3.5% NaCl solution was investigated on both coated and uncoated specimens through open circuit potential measurement and electrochemical impedance spectroscopy. The results indicated that the Zn-Cr coating effectively resisted corrosion. Contact angle measurement of water particles with the Zn-Cr coated specimen revealed a near-super hydrophobic nature with the highest contact angle of 146.8°.

Vaterite-based in situ surface modification and process-dependent biocompatibility of laser sintered polypropylene

Polypropylene (PP) rapidly gains scientific attention as fatigue-resistant and lightweight tissue repair and implant material, while emerging laser-sintering based methods for PP processing further allow unlimited versatility of PP specimens and often reduced numbers of process steps, substituting traditional manufacturing approaches. Generally, PP is considered biocompatible for a variety of medical applications while showing superior long-term stability, however, thermoplastic processing of polypropylene may induce the formation of cytotoxic degradation products, necessitating its cytotoxicological assessment. In the present study, PP specimens have been fabricated using warm, quasi-isothermal and complementary cold, non-isothermal powder bed fusion (PBF), allowing processing PP at ambient powder bed temperature of 25 °C for minimizing thermal exposure and the formation of decomposition products. The surface of manufactured specimens has been modified with hybrid coatings consisting of mesoporous inorganic microcrystals of vaterite laden with model biomacromolecules, i.e., fluorescently labelled dextran, demonstrating the stable coating and attachment of dextran-loaded vaterite crystals independent of the applied PBF processing regime. Vaterite coating is degradable and enables the opportunity to endow the surface of PP with sustained release functionalities. Both coated and uncoated specimens demonstrated excellent biocompatibility independent of the applied processing regime, as evaluated in an ex ovo shell-less hen's egg model.

Production and characterization of low-density silicon nitride reinforced zinc nanocomposite coatings on mild steel for applications in marine and automotive industries

In today's automotive, marine and petrochemical industries, the desire for lightweight materials has increased. Hence, necessitating the production of components with low density. In this work, lightweight Zn–Si3N4 coatings were developed by including Si3N4 in the zinc matrix. The optimal coatings were produced on steel samples at 45 °C and varied Si3N4 particles and voltages following ASTM A53/A53M standard. The deterioration (corrosion) property i.e. corrosion rate (CR) and current density (jocorr) of the uncoated (control) and coated samples were examined in 0.5 M of sulphuric acid using a potentiodynamic polarization technique following ASTM G3/G102 standard. The microstructure of the samples was studied via the SEM micrographs and XRD patterns, while the wear performance resistance (following ASTM G99 standard) and electrical conductivity of the samples were examined with a pin-on-disc tribometer and ammeter-voltmeter. The corrosion experiment indicated that the uncoated mild steel specimen possessed a CR of 12.345 mm year−1 and jocorr of 1060 μA/cm2, while the CR and jcorr of the coated samples ranged from 2.6793 to 4.7975 mm year−1 and 231−413 μA/cm2, respectively. The lower CR and jcorr values of the coated specimens, relative to the coated sample showed that the coatings possessed superior passivation ability in the test medium. The SEM micrographs of the samples showed refined morphology, while the XRD patterns revealed high peak intensity crystals such as Zn4SiN, ZnNSi, Zn4N and Zn2NSi, which could be beneficial to the mechanical properties and corrosion resistance of the steel. Moreover, the wear resistance study indicated that the COF of the uncoated sample ranged from 0.1 to 0.5, while those for coated specimens ranged from 0.05 to 0.35. Similarly, the uncoated steel exhibited a wear volume (WV) of 0.00508 mm3, while the WV of the coated specimens ranged from 0.00266 to 0.0028 mm3, indicating the existence of high strengthening mechanisms between the interface of the protecting device and the steel. Also, the electrical conductivity of the mild steel sample reduced from 12.97 Ω−1cm−1 to 0.64 Ω−1cm−1, indicating that the electrical resistivity of the steel was enhanced by the coatings.

Zinc-Induced Liquid Metal Embrittlement in Austenitic Microstructures

The problem of liquid metal embrittlement (LME) is one of the main concerns to be addressed when developing high-strength automotive steels. Although LME has been extensively investigated over the past decade, the role of LME-induced cracking on the failure mechanism of steel substrates has not been adequately explored. This study investigates the influence of LME cracking on the tensile properties and failure mechanism of an austenitic microstructure. An in-depth analysis of the LME crack propagation path revealed that the crack propagated predominantly along highangle, random grain boundaries. The detailed failure analysis showed that the Zn-coated austenitic steel failed in an intergranular mechanism without any plastic strain being applied to the grains during deformation. The results of the study indicate that stress-assisted grain boundary diffusion is responsible for the premature failure of Zn-coated austenitic microstructures at much lower tensile stresses than that of the uncoated specimen. It was found that the application of thermomechanical conditions characterized by low stress and low temperature, combined with microstructures featuring a low Zn grain boundary diffusion rate, can effectively reduce LME cracking.

Corrosion study of CA-PVD coated perforation cutter blades of different metallurgies used for liquid shampoo packaging

Perforation cutters must tackle aggressive corrosion and wear while filling sachets/pouches containing shampoo liquids and conditioners. The present work aims to enhance the durability of the perforation cutters through the application of PVD coatings. Further, this study investigates the role of surface energy and wettability to understand the corrosion behavior of different cutter metallurgies (SS420, D2, and HSS M2) and different coatings in shampoo liquids and conditioners. Two PVD coatings, namely Titanium Nitride (TiN) and Chromium Nitride (CrN), were chosen for this work. The most popular FMCG hair shampoo and conditioner combination in South Asia was selected for the study. The coated cutters were exposed to 20% concentration by volume of different shampoo solutions and their corrosion rates were compared with uncoated cutters. The CrN-coated SS420 specimen exhibited the most significant improvement in corrosion resistance with low wettability compared to all other specimens tested in various solutions. In contrast, the uncoated M2 specimen suffered the most severe corrosion with high wettability in various solutions. An inverse correlation was observed between wettability and corrosion resistance for the various specimens. The findings of this study give a better understanding of the corrosion of perforation cutters by shampoo liquids, elucidating the impact on their longevity and providing insights into the potential benefits of PVD coatings for enhancing their durability.

Bond properties of deformed steel bars coated with quartz sand modified enamel in concrete under both monotonic and reversed cyclic loading

Reinforced concrete structures located in seismic zones require significant ductility, which is affected by the bond properties between steel and concrete. The bond may be negatively impacted by anti-corrosion coatings. Quartz sand modified enamel (QSME) enhances the bond ductility for steel rebars in concrete under monotonic loading. This study investigates the bond properties of QSME-coated deformed steel rebars under monotonic and cyclic loading. For comparison, uncoated, fusion-bonded epoxy (FBE)-coated, and unmodified enamel-coated steel rebars are also studied. In addition to the coating type, the effects of steel rebar diameter, anchorage length, and concrete strength are considered. Acoustic emission (AE) technique was utilized to capture the AE energy released during the pull-out tests. Results showed that the bond stiffness and strength properties of QSME-coated steel rebars increase when concrete strength increases, while they decrease with rebar diameter under monotonic loading. The energy dissipation capacity of QSME-coated deformed rebar specimens is in average 1.43, 2.11, and 1.56 times greater than that of uncoated, FBE- and enamel-coated specimens, respectively. Among all coating types, the QSME-coated steel rebars exhibit the highest degradation index for the residual bond strength and the most AE activity, attributed to their improved chemical bonding and interfacial friction.

Enhancing surface protection of Mg alloy concrete formwork: Magnesium carbonate-based coatings under varied pH conditions via ultrasonic-cavitated chemical conversion

Improving the anticorrosion property of Mg alloys used as concrete formwork is essential for extending their lifespan and ensuring structural integrity. Therefore, MgCO3·3H2O + MgCO3·Mg(OH)2·3H2O/MgO composite coating was prepared on AZ41 Mg alloys using an ultrasonic-cavitated chemical conversion method under different pH conditions. Electrochemical methods combined with immersion tests in the simulated concrete pore solutions containing 0.6 M NaCl were adopted to assess the anticorrosion performance of the uncoated and coated specimens. Results indicate that the improved pH benefits the densification of the composite coating, thus leading to the enhanced anticorrosion performance. The generation of dense MgCO3·Mg(OH)2·3H2O layer rather than corrosion products after immersion makes such an affordable anticorrosion coating, amenable to large-scale production, holds promise as a viable surface treatment method for Mg alloy concrete formwork.

Investigation of Garcinia kola Exudates as Corrosion Inhibitor for Mild Steel in Acidic Environment

This study investigated the performance of Garcinia kola exudates in preventing mild steel exposed to acid concentrated water and soil. The study was performed in order to find an alternative coating substance that can reduce the corrosion of mild steel pipes exposed to corrosive water and soil media. Various mild steel specimens were cut into portions and coated with the exudates at 25 - 50µm thickness. To accelerate the rate of corrosion, 0.5M hydrochloric acid (HCl) was added to tap water in a container. Also, the same concentration of HCl was equally added to soil samples. Uncoated mild steel specimens were immersed in the acid concentrated water and soil, servicing as control sample. The rate of corrosion was monitored for 30 days (720 hours). The inhibition efficiency of the exudates for both corrosive media was compared. Results showed that the weight loss and corrosion rate of mild steel decreased with increase in coating thickness. Comparatively, weight loss and corrosion rate in the uncoated specimens were higher than the coated specimens. For uncoated specimens, the corrosion rate was 0.2793mm/yr and 0.4150mm/yr for specimen immersed in water and soil respectively, but at 25µm coating thickness, it decreased to 0.01369mm/yr and 0.2870mm/yr for specimens in water and soil. Also, at 50µm coating thickness, corrosion rate decreased to 0.0052mm/yr and 0.0318mm/yr for specimens in water and soil, respectively. The inhibition efficiency increased with coating thickness, ranging from 51.00 – 98.15% for specimens immersed in water and 30.84 – 92.33% for specimens buried in soil at 25µm – 50µm coating thickness. The results demonstrated that Garcinia kola exudates can be used as corrosion inhibitor for mild steel exposed to corrosive media.

Application of Celtis Zenkeri Exudates as Corrosion Inhibition for Galvanised Steel Exposed to Acidic Media

This study investigated the performance of Celtis zenkeri exudates in preventing galvanised steel exposed to acid concentrated water and soil. The study was performed in order to find an alternative coating substance that can reduce the corrosion of galvanised steel pipes exposed to corrosive water and soil media. Various steel specimens were cut into portions and coated with the exudates at 25 - 50µm thickness. To accelerate the rate of corrosion, 0.5M hydrochloric acid (HCl) was added to tap water in a container. Also, the same concentration of HCl was equally added to soil samples. Uncoated steel specimens were immersed in the acid concentrated water and soil, servicing as control sample. The rate of corrosion was monitored for 30 days (720 hours). The inhibition efficiency of the exudates for both corrosive media was compared. Results showed that the weight loss and corrosion rate of galvanised steel decreased with increase in coating thickness. Comparatively, the weight loss and corrosion rate in the uncoated specimens were higher than the coated specimens. With 25 - 50µm coating thickness, the decrease in corrosion rate ranged from 0.01272 to 0.0027mm/yr for specimens immersed in water and from 0.2226 to 0.0185mm/yr for specimens buried in soil, while for uncoated specimens, the corrosion rate was 0.2793mm/yr and 0.4150mm/yr for specimen immersed in water and soil respectively. The inhibition efficiency of Celtis zenkeri exudates increased with coating thickness, which ranged from 54.46 – 99.03% for specimens immersed in water and 46.36 – 95.54% for specimens buried in soil at 25µm – 50µm coating thickness. The results demonstrated that Celtis zenkeri exudates can be used as corrosion inhibitor for steel exposed to corrosive media.

Experimental investigation on the bond-slip behavior of rebars coated with epoxy and polyurethane systems: A comparative study

This study presents a comprehensive experimental investigation into the effectiveness of various rebar coating systems in mitigating corrosion and maintaining bond strength with concrete. Three coating systems were evaluated: a conventional two-component epoxy system (KC-R), a zinc-rich epoxy system (FR-R), and a moisture-cure polyurethane coating with Micaceous Iron Oxide-Enriched System (MC-R). Accelerated corrosion tests showed that uncoated rebars had a mass loss of about 3.793 ± 0.266 %, while all coated rebars exhibited negligible mass loss. However, coated rebars experienced a reduction in bond strength: KC-R and FR-R coatings resulted in 16.3 % and 48 % reductions, respectively, whereas MC-R showed the least reduction at 9.4 %. Notably, all specimens, whether coated or not, displayed a slight increase in bond strength after corrosion. Additionally, the MC-R coating reduced rebar slip at ultimate bond strength. However, the other coatings increased rebar slip compared to uncoated specimens. Overall, this study underscores the importance of proper rebar coating selection and highlights the effectiveness of the polyurethane coating system in mitigating corrosion while maintaining bond strength with concrete. Additionally, it emphasizes the significance of post-failure analysis in understanding the behavior of coated rebar specimens under different conditions.

Superhydrophobic-based corrosion mitigation systems and their effectiveness on dissimilar and similar friction stir spot-weld joint aerospace alloys

Traditional rivets have been a longstanding choice for securing aircraft components as permanent fasteners. A new technique called friction stir spot welding (FSSW) is gaining popularity as a rivet replacement. Despite its advantages, dissimilar FSSW joints are susceptible to corrosion, which can lead to property degradation. This study explored the potential of superhydrophobic (SH) coating as a corrosion inhibitor for FSSW joint aerospace alloys, particularly aluminum alloy (AA). The study involved a comparison of the corrosion resistance between SH-coated dissimilar (AA2024-T3 and AA7075-T6) and similar (AA2024-T3 and AA2024-T3) FSSW joint specimens. Notably, SH-coated dissimilar FSSW joint specimens demonstrated an exceptional average water contact angle (WCA) of 156°, confirming their SH nature. The study further incorporated the design of experiments (DOE) and statistical analysis to optimize constituent parameters and enhance the performance of SH coating. Durability testing indicated that SH-coated dissimilar FSSW joint specimens exhibited high resistance to acetone without influencing the WCA of 148°. Only a slight decrease in the WCA was observed when specimens were submerged in an acidic solution, where the WCA reduced to 142° from the original WCA of 158°. Also, specimens were stable and maintained the WCA of 154° when heat-treated at the temperature of 230 ℃. Moreover, a cross-cut adhesion test revealed that less than 5 % of the coating material was lost in SH-coated dissimilar FSSW joint specimens. Additionally, the electrochemical study evaluated the anti-corrosion performance of SH-coated dissimilar FSSW joint specimens, where the specimens were immersed for 6 days in 3.5 wt% NaCl solution. After 6 days in 3.5 wt% NaCl solution, specimens remained very close to SH, maintaining the WCA above 140°. Also, the electrochemical results demonstrated that the anti-corrosion performance of the SH-coated dissimilar FSSW joint specimens was enhanced with a lower corrosion rate of 37.56 mpy and current density of 0.428 µA/cm² as compared to the uncoated specimens. The variations in corrosion rates and current densities of the SH-coated dissimilar and similar FSSW joint specimens were very minimal, which proves that the application of SH coating on the FSSW joint specimens is suitable to alleviate corrosion-related problems in FSSW joints.

Investigation of high-temperature wear behavior of Ni-Mo alloyed hardfacing coatings applied on hot strip mill vertical rolls by submerged arc welding

In this study, hot strip mill vertical rolls made of AISI 4140 steel, commonly used in the iron and steel industry's hot rolling section, were coated with ER430 and E430+EC410NiMo using the submerged arc welding (SAW) method. The coatings were characterized through scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), microhardness, and wear testing (room 24 °C, 300 °C, and 600 °C). XRD analysis showed that in the ER430 sample, the dominant phase was α-ferrite phase and a small amount of γ (austenite) phase observed, while in the ER 430+EC410NiMo sample, the α-ferrite phase was the dominant phase, but the γ (austenite) phase in the structure was more severe and additionally M6C carbide phase was formed. Coating thicknesses and microhardness values of ER430 and ER430+EC410NiMo coatings were measured as 1.5 mm and 3.75 mm thicknesses, and 533±42 HV0.1 and 473±35 HV0.1 respectively. The increase in hardness on the surface of coated specimens resulted in higher wear resistance compared to the uncoated specimens under all conditions. Regarding average friction coefficient values, coated specimens generally exhibited lower values, although in some cases, the average friction coefficient was higher. In the wear tests, the lowest wear volume losses occurred in the tests conducted at 300°C, while the highest wear volume losses were observed in the tests at 600°C. Upon evaluating the wear mechanisms, it was determined that adhesive and oxidative wear mechanisms were generally dominant in the coated specimens. At higher temperatures, oxidative wear mechanisms became more prominent. ER430+EC410NiMo coatings exhibited better wear resistance compared to ER430, which can be attributed to the toughness effect of γ (austenite) and M6C phases in these coatings. Consequently, it was concluded that applying powder deposition coatings onto hot strip mill vertical rolls made of AISI 4140 steel could enhance their wear resistance, thereby increasing productivity in manufacturing processes.

The use of POPE Phospholipid as a First-layer Coating of the Ti-6Al-4V Alloy: Preliminary Studies

Phospholipids emerge as a powerful tool to be used as a coating for biomaterials, as they can increase the biocompatibility of the material and inhibit the growth of bacterial cells. Here, POPE phospholipid was deposited on the Ti-6Al-4V alloy surfaces by using a simple method, seeking to improve the corrosion resistance of the base material. Results show that the electrochemical potential of the Ti-6Al-4V/POPE is more positive than that observed in the base material, which could indicate a lower susceptibility to corrosion. Two EECs were used to explain the corrosion mechanisms of the coated and uncoated specimens, demonstrating the base material displays an oxide layer about 1.86 nm in the beginning of the corrosion tests and 2.59 nm after 24 h of immersion. Due to the complexity of the system containing lipids deposited on the metallic matrix, the corrosion behaviour of Ti-6Al-4V/POPE was evaluated considering only the evolution of the CPEs with immersion times. This work shows that the use of POPE for coating the Ti-6Al-4V alloy increased the corrosion resistance of the base material, expanding the range of advantages in the use of this surface treatment in the development of new biomaterials.

Residual stress analysis of plasma sprayed coatings through the weak magnetic field testing method

A proposed technique for swiftly evaluating coating stress variations involves utilizing weak magnetic detection under geomagnetic field conditions. This method examines the surface magnetic induction strength on uncoated test specimens, analyzing the magnetic induction change pre- and post-spraying. Employing the Almen test method, the assessment of specimen deflection and residual stress magnitude affirms the viability of weak magnetic detection for assessing coating residual stress. The experimental findings establish a direct link between the rate of magnetic induction intensity change and residual stress magnitude through polynomial fitting, suggesting that weak magnetic detection can preliminarily analyze coating stress variation.

Investigation of mechanical properties in thin spray-on liner coated sandstone: Comparative study of unfilled and filled flaws

Thin spray-on liners (TSLs) are increasingly recognized as a potent skin support technology in underground engineering applications, particularly in mining. To better understand the coating and filling effects of TSL on the mechanical properties of the flawed specimens, a series of uniaxial compression tests were conducted on TSL-coated sandstone with unfilled and filled flaws. The experimental results showed that compared with the flawed specimen, the strength and peak strain of the TSL-coated and filled specimens increased, and the degree of improvement was more evident for the filled specimen coated with TSL. The specimens coated with TSL exhibited higher total, elastic, and dissipation energies compared to the uncoated specimens. Additionally, a greater proportion of the total input energy was transformed into dissipation energy after coating. For the filled specimens, more dissipation energy was generated during the failure process owing to the friction of the flaw surface provided by the filling effect. Moreover, the crack initiation and propagation behaviors of the flawed and filled sandstone specimens coated with TSL were analyzed by numerical simulation. For the specimens with an inclination angle of 45°, the TSL provided confinement to inhibit the initiation and propagation of tensile cracks, resulting in delayed crack initiation. The TSL filling plays a role in sharing part of the stress on the flaw surface, which weakens the stress concentration at the flaw tip. The effect of the TSL on the stress at the flaw tip was analyzed using a theoretical solution. The variation in SIF KII of the specimens with different flaw inclination angles was studied using a theoretical solution. Compared with the flawed specimens, the stress concentration in the filled flawed specimen was lower and the confinement effect could enhance the decrease in the flaw tip stress.

Deposition of nickel-titanium coating on stainless steel 316L by direct current sputtering for bio-implants: Electrochemical, microstructural, and morphological investigations

In general, the application of coatings provides vital protection for medical devices with a host of beneficial properties such as biostability and biocompatibility, chemical barrier, and micro-encapsulation. In the current work, a nickel-titanium (NiTi) system was deposited on stainless steel (SS316L) by the direct current sputtering (DCS) technique to estimate the corrosion behavior in the simulated body fluid (SBF) at 37 °C. The characterization of the coating layer was done using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDX) techniques to know the phases, elemental composition, and structure of the coating that indicated the formation of the Ni3Ti phase as a flake-shaped structure with 2.6 and 0.4 wt% of Ni and Ti, respectively. The results of atomic force microscopy (AFM) showed a decrease in surface roughness from 25.2 to 11.05 nm after coating due to a decrease in the mean diameter of particles from 710.8 to 579.9 nm after coating. The data corrosion test showed the change of corrosion potential to a more noble value with minimizing the corrosion current density as well as the improvement of resistance after coating from 6.91 × 103 to 25.49 × 103 Ω.cm2 to get protection efficiency equal to 73.9 %. In a cyclic polarization test, it can be seen that the passivity region shifts to lower current density values. Microhardness was also measured to show an increase from 187 to 366 HV due to the selected technique of coating that gives more hardness; the measured wettability did not change the contact angle of the uncoated specimen to keep it at 90°; and finally, the histological analysis did not show any severe infection or inflammation. All these observations can suggest the NiTi coating for bio-applications.