Uncoated Specimens Research Articles

Effects of Cooling Conditions on Mechanical Properties and Wear Performance of JIS S45C Steel Coated by Wire Arc Spray

The study of the effects of cooling conditions on mechanical properties and wear performance by coating AISI S45C steel with Chrome Nickel Amorphous wire arc spray showed that the average surface hardness of specimens under different cooling conditions such as SCCW, SCCO, SCCS and SCCNT was 601.6 HV, while the surface hardness of HAZ of SCCS and SCCW specimens decreased to 80-90 HV. The tensile test revealed that the average ultimate tensile strength of coated specimens was 706 MPa which was slightly higher than that of uncoated specimens. This result is consistent with Tukey’s one-way ANOVA method, which found a significant difference in tensile strength values at 0.05 and 0.01 levels. For wear resistance, coated specimens showed higher wear resistance compared to uncoated specimens. Overall, the results of this study showed that wire arc spray coating could increase the strength and stress and decrease %elongation of the specimens. Therefore, this technique is suitable for maintenance work to increase the strength of steel in the industry.

Corrosion Protection of ZK60 Wrought Magnesium Alloys by Micro-Arc Oxidation

The influences of the forging process and micro-arc oxidation (MAO) coating on the corrosion behavior of ZK60 wrought magnesium alloys exposed to salt spray and constant stress corrosion conditions were investigated. The microstructure of the ZK60 Mg alloy specimens forged under different temperatures (i.e., 250, 300, and 450 °C) was characterized using metallography, EBSD, and SEM. It was demonstrated that the ZK60 alloy forged at 300 °C (i.e., ZK60EF-300) had finer grain and uniformly distributed β-phase and, thus, better corrosion resistance than the ZK60 forged at 450 °C. At the lower forging temperature (250 °C) twins formed in the ZK60 alloy, which accelerated the corrosion of the ZK60E-250 specimen. The MAO coating provided robust corrosion protection for all the ZK60 wrought Mg alloy substrates. The salt spray corrosion test results showed that when the MAO coating broke down at certain weak sites, the corrosion performance of the coated Mg alloy was predominantly determined by the alloy substrate. The stress corrosion behaviors of the uncoated and MAO-coated ZK60 alloy specimens were also investigated under a constant load of 80 MPa in 3.5 wt.% NaCl solution. The MAO coating was found to improve the stress-corrosion resistance of the ZK60 alloy pronouncedly.

Duplex surface modification of tool steel - deposition of a WN film and subsequent electron-beam modification

In this study, we demonstrate a combined treatment technique of R18 high-speed tool steel comprising deposition of a WN coating followed by electron-beam surface treatment (EBT). In order to understand the influence of the deposited WN coating on the resultant structure and properties, an uncoated specimen was directly electron-beam treated under the same EBT technological conditions. The structure of the specimens was studied by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The microhardness was also investigated. The phase composition consisted of a double phase structure of Fe and M6C carbides in both cases. The microstructure was significantly finer in the case of an EBT of the steel with WN coating, leading to a much higher microhardness in comparison with the case without WN.

Фреттинг-изнашивание наводороженного циркониевого сплава Э125, упрочненного диффузионными покрытиями

Protective coatings that improve the corrosion resistance of the E125 zirconium alloy under conditions of the combined effect of a hydrogen-containing medium and friction wear have been investigated. The formation of coatings on the surface of the samples was carried out by thermal diffusion treatment in powder saturating media with halogen activation at temperatures from 400°C to 950°C. The resulting coatings were formed as a result of the processes of oxidation, siliconization, and nitrocarburizing. Wear tests were carried out on a SRV Testsystem multifunctional testing system according to the disk-ball scheme without lubrication. Cathodic hydrogenation of the samples was carried out in an electrolyte solution containing a single normal sulfuric acid solution at room temperature. The cathodic current density was from 20 to 500 mA / cm2. The hydrogen concentration in the samples was determined on a highly sensitive G8 Galileo H gas analyzer by melting the samples in a carrier gas flow. As a result of the study, it was shown that the wear of the coated specimens after siliconizing and nitrocarburizing is three times lower than that of the original uncoated specimen. Oxidation leads to a significant, more than fivefold, increase in the amount of wear, in comparison with the same initial sample. Hydrogenation of the surface of the samples allows not only to reduce the coefficient of friction, but also to reduce the amount of wear in the process of testing samples for fretting wear. This study makes it possible to obtain modified surfaces of zirconium samples that significantly improve the mechanical properties, as well as reduce the level of hydrogenation, and increase the performance of components made of zirconium alloys under conditions of increased friction.

Novel Development of Corrosion Resistant Paint Using Printed Circuit Board from Modern Electronic Wastes

The growth in the industrial technology and communication sectors has enhanced the usage of electronic gadgets exponentially. Thus, it becomes highly essential to find new solution to utilize or dispose these e-wastes, in order to reduce the e-waste generation. Various reports mentioned that the major component of these e-wastes is their Printed Circuit Boards. Therefore, a new ideology is proposed to use these boards to produce a new coating with good corrosion resistance. At first the boards were separated from the discarded electronic appliances and various electrical elements were separated from these boards. Then the plain circuit boards are pulverized into fine particles and mixed with paint in 3 different proportions ranging from 1:4 to 1:2. The resulting mix was applied over the steel specimen and tested for corrosion resistance. The assessment was done in the aspects of contact angle, weight loss percentage, potentio dynamic polarization technique and electro chemical impedance spectroscopy. From the results it was clear that increase in the addition of printed circuit powder content in the corrosion proof paint coating enhanced the efficiency of the corrosion resistant behaviour 3.5 times than the specimen with uncoated steel specimens. This development of corrosion resistant behaviour of printed circuit powder was attributed from the inertness offered by the presence of silicon dioxides towards the corrosive fluids. Although, the coating of 1:2 proved to be optimum to protect the steel elements from the aggressive corrosion environment, by considering the workability aspects the 1:3 combination was suggested for the innovative development of anti-corrosion paint coating from the e-waste resources.
 HIGHLIGHTS
 
 Life cycles of every electronic wastes end with the hazardous challenging disposals
 Innovative utilizations of these electronic wastes for the corrosion resistant structural applications were detailed
 An anti corrosive coating for steel reinforcement was developed from the waste printed circuit boards
 Coating by printed circuit board powder enhanced 3.5 times more protection from the corrosion
 
 GRAPHICAL ABSTRACT

Effect of polyurea coating on the ductility of aluminum foam

The closed-cell metal foams are utilized in various industrial applications due to their impact and energy absorption capacity, noise cancelation, and lightweight properties. Additionally, the manufacturing methods of stochastic foams with blowing agents or inert gas injection are well known. However, the poor mechanical strength and high brittleness are restricting the application of these materials. A method of increasing the ductility, plastic deformation, and fracture toughness of these materials is the integration of elastomer coating. Polyurea is widely used in applications where water-proofing and high ductility are aimed. In this study, two types of polyurea coatings as MS950 and MS955 are sprayed over the aluminum foam with three densities as 0.508, 0.557, and 0.624 g/cm3 to evaluate the effect of coating on the ductility and fracture toughness of samples considering the tensile behavior and 4 densities as 0.508, 0.538, 0.557, and 0.624 g/cm3 for the flexural bending test. The MS955 polyurea coating elevated the ultimate tensile strength and elasticity modulus of all specimens with a maximum of 239% and a minimum of 70%. However, the MS950 coating did not result in a significant rise in tensile strength. The main advantage of the MS950 coating is in the amount of strain increment with 374% in maximum and 181% in minimum resulting in higher ductility and fracture toughness. Additionally, the bending characteristics of MS950 coating demonstrate a drastic increase in both load and strain which recommend the usage of this coating in bending and impact applications. Finally, an analytical evaluation of the coated and uncoated specimens in the elastic region and the elastoplastic region is provided using linear and power-law interpolation. In tensile tests, the MS955 coating resulted in higher elasticity modulus and fracture toughness. However, in bending applications, the MS950 coating demonstrated higher load strength with elevated ductility.

Evaluating composite nanomaterials to control corrosion of reinforcing steel using different tests

There is limited research on the utilization of composite nanomaterials to control corrosion of reinforcing steel in concrete. Therefore, this work was initiated to evaluate the composite nanomaterials (zinc oxide and titanium dioxide) to control corrosion deterioration in reinforced concrete using different tests. The composite nanomaterials were utilized as coating cover over the reinforcing steel surface using two methods of nanofilms and nanoparticles. Fourteen reinforced concrete prisms (100 ×100×300 mm) with central reinforcing steel coated with nanocomposite were casted using w/c ratio of 0.45. After 28 days of moist curing, the prisms were exposed to an accelerated corrosion process using an electrical current supply. The ability of nanocomposite to control corrosion was evaluated using different tests including crack width, ultrasonic pulse velocity (UPV), half-cell potential (HCP) and pullout test. The experimental results showed that nanocomposite materials coated over the reinforcing steel surface significantly reduced the corrosion level of the reinforcing steel in concrete. The non-destructive tests (UPV and HCP) showed significant difference between the nanocoated and uncoated specimens. The damage index of the UPV of the corroded uncoated prisms showed higher values than those of the corroded coated prisms. The HCP values of the nanocoated prisms after corrosion showed significantly lower negative values than those of the control uncoated prisms. Moreover, prisms coated with nanocomposite revealed less corrosion crack width and attained higher ultimate bond load compared to the uncoated prisms. The composite nanolayer coated on the reinforcing steel surface showed higher performance to control corrosion compared to the single nanolayer coated on the reinforcing steel surface. Scanning electron microscopy images showed more homogeneous filling layers of the composite nanolayer coating compared to the single nanolayer coating.

Fatigue Assessment of Twin Wire Arc Sprayed and Machine Hammer-Peened ZnAl4 Coatings on S355 JRC+C Substrate

Structural elements for applications in maritime environments, especially offshore installations, are subjected to various stresses, such as mechanical loads caused by wind or waves and corrosive attacks, e.g., by seawater, mist and weather. Thermally sprayed ZnAl coatings are often used for maritime applications, mainly due to good corrosion protection properties. Machine hammer peening (MHP) has the potential to increase fatigue and corrosion fatigue resistance of ZnAl coatings by adjusting various material properties such as hardness, porosity and roughness. This study investigates the fatigue behavior of twin wire arc sprayed and MHP post-treated ZnAl4 coatings. Unalloyed steel (S355 JRC+C) was selected as substrate material and tested as a reference. MHP achieved the desired improvements in material properties with increased hardness, decreased roughness and uniform coating thickness. Multiple and constant amplitude tests have been carried out to evaluate the fatigue capability of coating systems. In the high cycle fatigue regime, the additional MHP post-treatment led to an improvement of the lifetime in comparison to pure sandblasted specimens. The surface was identified as a crack initiation point. ZnAl coating and MHP post-treatment are suitable to improve the fatigue behavior in the high cycle fatigue regime compared to uncoated specimens.

Impact-sliding behavior of Ni-based coating prepared on tunnel boring machine disc cutter material produced using a plasma transferred arc welding process

The working condition of the disc cutter of the tunnel boring machine (TBM) is extremely harsh and is severely worn during the rock-cutting and tunneling process. Reducing the wear rate of the cutter and extending the service life of the cutter are essential to improving the economic costs and safety of the TBM. This article explores the feasibility and effectiveness of using surface coatings to improve the wear resistance of the cutter ring. NiCrBSi/WC coatings with different current intensities were prepared on the disc surface using plasma surfacing technology. The wear performance of the coating was evaluated using a bespoke impact-sliding device that fits the actual working conditions, and the wear mechanism was studied in detail. According to the “tadpole-like” wear scar characteristics of the coating after the impact-sliding wear experiment, the wear scar zone can be divided into two regions: the impact region and the sliding region, which are consistent with the actual wear characteristics of the cutter ring. In addition, the wear behavior of the coating noticeably changed under each experiment parameter, and the evolution process of the impact-sliding wear of the gage cutter at each position can be well reproduced. When the impact angle was 45°, the wear depth and wear volume of the coating were significantly smaller than those of the uncoated samples. This is mainly due to the metallurgical bond between the Ni-based alloy zone (binder phase) and the spherical WC particles (hard phase) on the surface of each specimen. When impacted by the tribo-ball, the WC particles can undergo plastic deformation and relaxation through the Ni-based alloy zone under the applied force, thereby obtaining excellent impact and sliding resistance. When the impact angle was 60°, the impact dominates, causing the impact force to increase. Furthermore, compared with the uncoated specimens, the wear depth and wear volume of the coated specimens significantly increased, indicating that the anti-impact ability was seriously degraded in such situation. In summary, the powder composition and preparation process parameters should be reasonably selected according to the impact angle, and the impact-sliding wear experiment can effectively evaluate the impact and sliding wear performance of different coatings. This approach has an important directive function in the promotion and application of cutter ring coatings.

Impregnating Compound for Cement-Concrete Road Pavement

The paper proposes an impregnation composition for cement concrete roads used as an ice-phobic coating. The composition has been made based on keratin-containing components derived from animal waste with the addition of water-soluble polymers. The main parameter of serviceability of the coating impregnated with the developed composition was assessing the adhesion resistance of ice crust to concrete under the influence of mechanical loads. For this purpose, tests of big specimens (surface area 1925 cm2) in laboratory conditions with application of vibration and impact loads and modelling of thermal stresses were conducted. The test results showed the effectiveness of the ice-coating, as in all experiments, the uncoated specimens showed a greater resistance of the ice crust to mechanical stresses. An additional evaluation parameter was comparing the water absorption capacity of coated and uncoated concrete. The test results showed a significant difference in the water absorption capacity of the uncoated specimens, exceeding the coated specimens by 47%. Due to the results obtained, it will be possible to use the impregnation compound effectively to improve the ice resistance of cement concrete coatings.

Detection and Analysis of Corrosion and Contact Resistance Faults of TiN and CrN Coatings on 410 Stainless Steel as Bipolar Plates in PEM Fuel Cells.

Bipolar Plates (BPPs) are the most crucial component of the Polymer Electrolyte Membrane (PEM) fuel cell system. To improve fuel cell stack performance and lifetime, corrosion resistance and Interfacial Contact Resistance (ICR) enhancement are two essential factors for metallic BPPs. One of the most effective methods to achieve this purpose is adding a thin solid film of conductive coating on the surfaces of these plates. In the present study, 410 Stainless Steel (SS) was selected as a metallic bipolar plate. The coating process was performed using titanium nitride and chromium nitride by the Cathodic Arc Evaporation (CAE) method. The main focus of this study was to select the best coating among CrN and TiN on the proposed alloy as a substrate of PEM fuel cells through the comparison technique with simultaneous consideration of corrosion resistance and ICR value. After verifying the TiN and CrN coating compound, the electrochemical assessment was conducted by the potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests. The results of PDP show that all coated samples have an increase in the polarization resistance () values (ranging from 410.2 to 690.6 ) compared to substrate 410 SS (230.1). Corrosion rate values for bare 410 SS, CrN, and TiN coatings were measured as 0.096, 0.032, and 0.060 , respectively. Facilities for X-ray Diffraction (XRD), Scanning Electron Microscope (FE-SEM, TeScan-Mira III model and made in the Czech Republic), and Energy Dispersive X-ray Spectroscopy (EDXS) were utilized to perform phase, corrosion behavior, and microstructure analysis. Furthermore, ICR tests were performed on both coated and uncoated specimens. However, the ICR of the coated samples increased slightly compared to uncoated samples. Finally, according to corrosion performance results and ICR values, it can be concluded that the CrN layer is a suitable choice for deposition on 410 SS with the aim of being used in a BPP fuel cell system.

THE EFFECT OF COATING MATERIAL ON THE COLOR STABILITY OF GLASS-IONOMER-BASED RESTORATIVE MATERIALS: AN IN-VITRO STUDY

Objectives: The aim of this study was to determine the effect of coating on the color stability of different glass ionomer cements (GICs) after immersed in different children beverages. Materials and Methods: Four different GIC and a glass-ionomer coating material were used in this study. Disc shaped sixteen specimens of each GICs were done and divided into two groups, uncoated and coated (n=8). For color change, the specimens were immersed 7 day in the four solutions of cola, orange juice, chocolate milk and water. The color measurements were carried out before immersed solutions and at the end of the 1st and 7th days, using a spectrophotometer. The color change ΔE00 was calculated using the CIEDE2000 formula. Data were analyzed by Kruskall-Wallis and Wilcoxon test (p < 0.05). Results: The ΔE00 values for all coated and uncoated GICs showed an increase in all solutions after 7 days of immersion. All the ΔE00 values obtained from all the specimens immersed in cola were higher than the acceptability threshold. There was no statistical difference in terms of ΔE00 values between the coated and uncoated specimens of the same GICs at same time periods. Conclusions: Coating of GICs exhibited relatively good color stability and protect from the discoloration. The staining effect of GICs should be carefully considered when selecting dental materials in pediatric dentistry.

Effect of Zircoat-M coating on SS304L for designing high temperature process chamber in selective laser sintering

Selective laser sintering (SLS) process is one of the most useful additive manufacturing techniques used, because it has the ability to readily generate complicated structures. The quality of parts made by SLS process directly depends on controlling heat transfer to powder bed. High temperature process chamber is specially designed for high temperature plastics and metal powders (PEEK and Aluminium). With the exception of aluminium, Zircoat - M is a Zirconia-rich refractory coating compound with a high proportion (63%) of Zirconia and is best suited for ferrous and non-ferrous metals and refractories. Metals and refractories are protected by Zircoat-M from corrosion erosion and flue gases escaping from heating chambers. An attempt was made to develop a high temperature build chamber and pre-heating system to manufacture prototypes using materials having maximum melting/ fuse temperature of 800°C. PEEK and Aluminium may be used to produce light weight products for multiple sectors such as bio-medical, automobile and aerospace. A high temperature resistant stainless steel 304L grade was chosen, along with SS304L coated with Zircoat-M for Build chamber and Pre-heating system. Experimental analysis such as Thermal Expansion, Thermal Conductivity and Corrosion resistance for the coated and uncoated specimen was carried out. Coefficient of Linear Thermal Expansion of uncoated specimen is 16 × 10-6 /°C and coated specimen is 14 × 10-6 /°C. Thermal conductivity for the Ceramic coated Zircoat-M on SS304L for 100 °C is 0.280 W/mK. Thermal conductivity of SS304L at 100 °C is 16.3 W/mK. Both the specimen has very good corrosion resistance.

Study and performance analysis of graphite and aluminium oxide coating on heat spreader application

To sustain in a global Market, the electronic industries need to compete continuously in the areas such as quality, production rate and continuous improvement in manufacturing. Also Electronic devices are continuously used in day-to-day applications induce an excessive amount of heat which will indirectly affect the working condition of the system. The main issue lies in the increase in chip temperature and causes failure in performance, reliability and life span of the process. To avoid these limitations, the excessive amount of heat is to be transferred onto the outside environment. In the present situation, it is important to find the better thermal conductivity material for heat dissipation in heat spreader than the old one. Among various material, graphite and Aluminium Oxide are chosen, as they show best thermal conductivity nano materials in nature. The proposed research work analysis the heat transfer through graphite and aluminum oxide coating in electronic applications. The heat transfer rate of coated graphite and aluminum oxide were compared with uncoated material through a heat transfer measurements. Initially, graphite and aluminum oxide is mixed with the required solvents separately through a magnetic stirrer. The prepared solutions are then coated with the substrate through spin coating with two different specimens. Surface roughness measurements are also measured on the coated and uncoated specimen. The scanning electron microscopic (SEM) is captured on the specimen which confirmed the presence of graphite and aluminum oxide coating on the aluminum substrate. The overall heat transfer efficiency was improved by 30 % and 46 % respectively for Aluminium Oxide and graphite samples.

Wear resistance study on HVOF based SiC and TiB2 ceramic coating for AH36 steel for marine based thermal applications

ASTM AH36 steel has been a primary material used for marine-based construction and applications. It is also a primary material employed in boilers and thermal-based equipment. The material is known for versatility and reliability in marine environments. However, the steel has an inherent limitation for wear resistance when subjected to adverse conditions during operation by the marine ecology as well as abrasive materials when being in thermal operation. This has been a major reason for services and these problems can be mitigated by improving the hardness, chemical inertness and adhesion to the substrate. Silicon Carbide (SiC) and Titanium Diboride (TiB2) are noted for their hardness and ecologically inert behaviour. The steel surface has been coated with these ceramic materials to improve the wear resistance. The coating is provided by the High-Velocity Oxy-Fuel (HVOF) technique. A microstructural, mechanical and wear analysis is performed on SiC, TiB2 and Mixture of 80 %SiC-20 %TiB2 coated specimens to analyze the surface modifications. Based on the pin on disc test results it can be observed that the application of Silicon Carbide and Titanium Diboride coatings has shown an improvement in wear resistance by reducing a wear loss by 1/8th, 1/6th and 1/10th respectively against the uncoated specimen. This increase in wear resistance is attributed to the improvement in the hardness of the surface by formation of harder compounds and additional phases during HVOF process. This indicates that inert material-based surface modifications can be an ecofriendly and effective way to improve the wear resistance in marine steels.

Studija mehaničkih svojstva Inconel 625 i Incoloi 800H sa istopljenim solima na bazi nitrata

Energy storage is the most indispensable technology in the recent days with augmented power demand, which helps in balancing the energy demand and production time. Among the broad spread of energy storage types, molten salts technology in concentrated solar plants is most economical, highly efficient with excellent duration on the storage timings. In this current effort, Inconel 625 and Incoloy 800H nickel based super alloys have been taken and heated with sodium nitrate and potassium nitrate molten salts. The super alloy substrates were coated with Yttria stabilized zirconia as thermal barrier coating which could enhances the heat resistance and corrosion resistance property of the base substrates. Both layered and non-coated super alloy samples were intense to a fairly accurate temperature of 1000 o C for different duration as 9, 12 and 15 hours. The mechanical properties of both unheated and heated specimens were compared with the results obtained from tensile test, compression test, hardness test, and impact test. The changes in the micro-structural properties were investigated with the support of SEM images and by XRD analysis. The mechanical properties of YSZ coated specimens are found to be better than the uncoated specimens; which increases the sustainability of the super alloys with the molten salts.

Investigation on Hot Corrosion Behaviour of Inconel 625 and Incoloy 800H Superalloys with YSZ‐Thermal Barrier Coating Under High‐Temperature Environment for Bioreactor Applications

Thermal energy storage is one of the promising technologies in the modern era for balancing the peak power demand without emitting much emission. Molten‐salt technology plays a dominant role among the varieties of thermal energy storage systems. The difficulty in storing the molten‐salt technology requires a storage material with high temperature, corrosion, and oxidation resistance properties. The nickel‐based superalloys such as Inconel 625 and Incoloy 800H possess the desired properties to be used as a storage material for the molten salts. In this present work, the Incoloy 800H and Inconel 625 superalloy specimens were taken up for investigation. The specimens were coated with yttria‐stabilized zirconia as a thermal barrier coating using a plasma spray process. The sodium chloride and potassium chloride molten salts with a weight fraction of 7 : 3 have been taken with both uncoated and YSZ‐coated specimens, and specimens were heated up to 1000°C approximately. The specimens were heated for different hours such as 8, 12, and 16 hours, respectively. The increase in heating time also results in the increase in the tensile property of the specimens. The mechanical testing, such as tensile test and hardness test, was performed to comprehend the mechanical properties. Scanning electron microscope images and X‐ray diffraction analysis were made to study the microstructural properties and the corrosion resistance property. From the test results, YSZ‐coated specimens possess high corrosion resistance and high mechanical strength compared to the uncoated specimens.

Tensile behavior of basalt textile-reinforced mortar (BTRM)

This research aims to evaluate the tensile properties of basalt textile-reinforced mortar. The tension test was carried out on nineteen sets of pin action specimens. The variables studied in the current research are textile mesh size, number of plies, and mortar type, as well as coating some of the textiles with epoxy. The results indicated that increasing the number of plies resulted in an increase in the ductility and the ultimate load of specimens. The polymer modified cementitious mortar reinforced with glass fibers is the most efficient in enhancing the strength and ductility among the different types of mortars used in the study. Moreover, coating textiles with epoxy enhanced the ultimate load by about 25% compared to the uncoated specimens. The experimental results were compared with the corresponding values predicted by a model reported in the literature. The experimental results were in good agreement with those predicted using the model.

Influence of twin wire arc spraying and machine hammer peening on the corrosion fatigue of ZnAl4 coatings on S355 J2C + C substrate

ZnAl-based coatings are used as corrosion protection for offshore application, e.g., offshore wind turbines. These applications are subjected to superimposed mechanical and corrosive stresses, e.g., wind, tide, seawater and mist. Thermally sprayed coatings processed by twin wire arc spray process and the mechanical post-treatment process machine hammer peening (MHP) were investigated. The coating consisting of ZnAl4 was deposited on a S355 J2C + C substrate. In addition to two conditions produced with different process parameters during MHP post-treatment, uncoated and as-sprayed conditions were evaluated as reference. The aim was to determine the effect of the coating and its properties, such as hardness, porosity and roughness, on the corrosion and corrosion fatigue behavior. In this study, potentiodynamic polarization tests and instrumented corrosion fatigue tests using a self-designed corrosion cell were performed in 3.5% NaCl solution. Mechanical and electrochemical measurement techniques in combination with fractographic and microstructural analyses were used to characterize corrosion fatigue damage mechanisms.MHP resulted in a uniform coating thickness with lower roughness and porosity in comparison to the as-sprayed coatings, which were further reduced by adjusting the process parameters of MHP. The electrochemical potential of the ZnAl coating provides passive corrosion protection for the substrate. The coating system improved corrosion fatigue resistance at high cycle fatigue regime. While as-sprayed and MHP post-treated specimens run out at 280 MPa, uncoated specimens run out at 240 MPa. The open circuit potential (OCP) curves plotted during the corrosion fatigue tests can be correlated with the damage mechanisms. Crack initiation and propagation in the coating and crack propagation in the substrate can be identified from the OCP curves.

Thin TiO2 Nanocoating of Porous Titanium through Radio Frequency Magnetron Sputtering to Improve the Biological Response of Orthopedic Implants

: The present study applied a TiO2 nanocoating on a titanium foam substrate produced by powder metallurgy through magnetron sputtering. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were employed to investigate the surface morphologies of the porous specimens and pre- and post-coating phases, respectively. Also, the growth and proliferation of MG-63 cells (osteoblasts) and their attachment and proliferation on the coated porous titanium specimen (relative to the uncoated specimens) were studied using in vitro and methyl thiazol tetrazolium (MTT) cytotoxicity tests. Considering the porous macrostructure of the coated titanium specimen and the nanostructure of the TiO2 coating on the porous surface and macro-pore walls, the coated specimen was found to be effective in the biocompatibility improvement of dental and orthopedic implants.