Search Results (21)

Ni-based composite coatings reinforced by high-entropy intermetallic compounds (HEICs) were prepared by detonation spraying (DS) on low alloy steel substrates. To this end, first (Ti-Nb)(V-Cr-Ni-Fe) and Al₃(TiZrNbCrHfTa) HEIC powders were fabricated by arc melting followed by ball milling. The as-milled HEIC powders were then employed as reinforcement particles to prepare Ni-7wt.% HEIC composite coatings. The average particle size of the (Ti-Nb)(V-Cr-Ni-Fe) and Al₃(TiZrNbCrHfTa) HEIC powders were 18 and 35 µm, respectively, while the average particle size of the Ni powder was 56 µm. (Ti-Nb)(V-Cr-Ni-Fe) exhibited a single hexagonal C14 Laves phase in spite of Ti and Nb segregations. The XRD pattern of Al₃(TiZrNbCrHfTa) indicated the presence of a tetragonal D0₂₂-type structure along with some minor CrTi and Cr₅Al₈ phases. The sprayed Ni-7wt.% FeNiCrV-TiNb and Ni-7wt.% Al₃(TiZrNbCrHfTa) composite coatings retained crystal structures of the powder mixtures, suggesting proper thermal stability for both powders. The coatings exhibited a dense microstructure consisting of a lamellar microstructure with low porosity and sound bonding with the substrate. The microhardness of Ni-7wt.% FeNiCrV-TiNb (450 HV) was higher than that of Al₃(TiZrNbCrHfTa) (338 HV), and it exhibited lower fluctuation than that of Ni-7wt.% Al₃(TiZrNbCrHfTa). DS is an effective method to fabricate metal matrix composites reinforced by HEICs with a low level of porosity. Full article

Thermal spray-coated components are widely used as wear-resistant coatings in many applications. However, these coatings have high levels of discontinuities that affect the corrosion resistance of the coated system. To reduce this problem, these coatings are usually sealed with liquid sealants (metals, organic or inorganic). The aim of this work is to seal the surface discontinuities of thermal-sprayed coatings using PVD and/or ALD coatings. To this end, CrN (arc deposition PVD) and TiO2 (ALD) coatings were deposited on thermal-sprayed alumina coatings. The samples produced were then analysed in both cross-sectional and planar views to detect the possible permeation of the thin film coatings into the thermal spray defects. Rf-GDOES measurements were performed to detect the very thin ALD deposit on the surface. The corrosion resistance of the sealed coatings was verified with immersion tests, wherein the OCP was monitored for 24 h, and potentiodynamic tests were performed after 15 min and 24 h immersions. The results showed that the thin films were not able to block the permeation of corrosive media, but they could reduce the permeation of corrosive media with a beneficial behaviour on corrosion resistance. Full article

Nowadays, due to the carcinogenic effects of chrome, replacing the hard chromium used for hydraulic components like rods and cylinders is becoming increasingly requested. Thermally sprayed coatings are a solution to the problem; however, proper understanding and characterisation of their tribological behaviour are essential for the successful exploitation of surface engineering. Thus, the main aim of this study is to evaluate the abrasive wear characteristics of two metal sprayed layers, tungsten carbide (WC) deposited through the high-velocity oxygen fuel coating (HVOF) method and Fe alloy coating deposited through thermal spraying with an electric arc with a wire-electrode G3Si1, and compare the results with those of an electrochemically deposited hard chromium layer. Their wear resistance is then related to their hardness. The results highlight the tribological performances of the thermally sprayed coatings. The HVOF WC10Co4Cr coating has a wear coefficient and a material wear volume that are hundreds of times lower than those of the other two coatings. Full article

The corrosion of steel structures in coastal areas is a major issue. Therefore, in the present study, the protection against the corrosion of structural steel is carried out by depositing 100 μm thick Al and Al-5 Mg coatings using a plasma arc thermal spray process, immersing them in 3.5 wt.% NaCl solution for 41 days (d). To deposit such metals, one of the best known processes, arc thermal spray, is frequently used, but this process has severe defects and porosity. Thus, to minimize the porosity and defects of arc thermal spray, a plasma arc thermal spray process is developed. In this process, we used normal gas to create plasma instead of argon (Ar) and nitrogen (N₂) with hydrogen (H) and helium (He). Al-5 Mg alloy coating exhibited uniform and dense morphology, where it reduced more than four times the porosity compared to Al, where Mg fills the voids of the coating, resulting in greater bond adhesion and hydrophobicity. The open circuit potential (OCP) of both coatings exhibited electropositive values due to the formation of native oxide in Al, while in the case of Al-5 Mg, the coating is dense and uniform. However, after 1 d of immersion, both coatings showed activation in OCP, owing to the dissolution of splat particles from the corner where the sharp edges are present in the Al coating, while Mg preferentially dissolved in the Al-5 Mg coating and made galvanic cells. Mg is galvanically more active than Al in the Al-5 Mg coating. Due to the capacity of the corrosion products to cover the pores and defects, both coatings stabilized the OCP after 13 d of immersion. The total impedance of the Al-5 Mg coating is gradually increased and is higher than the Al, which can be attributed to the uniform and dense coating morphology where Mg dissolves and agglomerates to form globular corrosion products and deposit over the surface, thereby causing barrier protection. The defect bearing corrosion products on Al coating led to the cause having a higher corrosion rate than the Al-5 Mg coating. A total of 5 wt.% mg in the Al coating improved the corrosion rate by a rate of 1.6 times compared to the pure Al in the 3.5 wt.% NaCl solution after 41 d of immersion. Full article

Exterior finishes protect reinforced concrete buildings against environmental factors, improve their durability, and enhance their exterior design. In this study, the influence of different metal types used in arc thermal metal spraying on the adhesion between concrete and metal coatings was analyzed. Five metals with different melting points were tested, and the differences between their melting points and surface temperatures immediately after thermal spraying were measured. The bonding strength of each metal was evaluated. Additionally, the interface between the concrete surface and metal coating was analyzed using image analysis and optical microscopy. The results demonstrated that Zn achieved the highest bonding strength (1.84 MPa), which had the lowest melting point and surface temperature immediately after spraying, while Cu/Sn achieved the lowest strength (1.38 MPa), which had the highest temperatures. The bonding strength had a closer relationship (R² = 0.9946) with the difference between the melting point and surface temperature immediately after spraying than that (R² = 0.9589) with the surface temperature immediately after spraying. The bonding strength increased as the ratio of the non-interfacial failure area to the total area increased, ensuring a stronger attachment to the concrete surface. Overall, the results showed that the bonding strength was significantly affected by the metal type. Full article

Gas metal arc welding-based additive manufacturing (GMA–AM) is a promising, low-cost approach to fabricate large-scale and complex geometry components using layer-by-layer deposition of metals. However, the low forming accuracy of GMA–AM still limits its one-off industrial application due to the strong and nonlinear interactions between arc–droplet transfer and molten pool. To fully understand the influential mechanism of this inherent interaction in the GMA–AM process to precisely control the part accuracy, the arc–droplet transfer behavior in the GMA–AM process with different current waveforms was firstly studied experimentally. The phenomena of the arc swing and the differing droplet transfer with the increase in deposited height were interpreted. The thermal force status of the molten pool and its balance boundary conditions were also theoretically analyzed. Finally, the microstructure and the hardness of the AM parts with different cooling times were tested and analyzed. The experimental results demonstrate that using the spray droplet transfer mode can generate a stable AM process under direct current application conditions, but it easily ends the AM process at the third or fourth layer deposition owing to excessive heat input. A more highly accurate deposition morphology can be obtained in one droplet per pulse mode under pulsed current application conditions, which also indicates that the AM process with a constant current welding supply is stabler and easily produces better deposition than the process with a constant voltage welding supply. With the increase in cooling time, the microstructure evolved from fine ferrite to equiaxed ferrite and to columnar ferrite combined with acicular ferrite with a lower proportion of pearlite in the vertical direction of the part, and the average hardness changed to ~168 HV (bottom), ~175 HV (middle), and ~250 HV (top). The analysis indicates that the heat accumulation of the molten pool is a critical factor that affects the deposition accuracy. To this end, a novel strategy that uses the heat accumulation to compensate for the energy formed in the molten pool is proposed to further reduce the arc heat input and weaken the heat accumulation, and its feasibility is discussed. Full article

The surface treatment of concrete enhances the bonding of its metal coatings. Therefore, in the present study, on the concrete surface, prior to the deposit of an 85Zn-15Al coating via an arc thermal spraying process, different surface treatments were considered for the effective electromagnetic pulse (EMP) shielding properties of the concrete. However, the direct coating on a concrete surface possesses lower bond adhesion, therefore it is of the utmost importance to treat the concrete surface prior to the deposition of the metal coating. Moreover, to obtain better bond adhesion and fill the defects of the coating, the concrete surface is treated by applying a surface hardener (SH), as well as a surface roughening agent (SRA) and a sealing agent (SA), respectively. The metal spraying efficiency, adhesion performance, and bonding strength under different concrete surface treatment conditions were evaluated. The EMP shielding effect was evaluated under the optimal surface treatment condition. The proposed method for EMP shielding exhibited over 60% of spraying efficiency on the treated surface and a bonding strength of up to 3.9 MPa for the SH–SRA–SA (combining surface roughening and pores/defects filling agents) specimen compared to the control one, i.e., 0.8 MPa. The EMP shielding values of the surface-treated concrete with surface hardener, surface roughening agent, and sealing agent, i.e., SH–SRA–SA specimens, exhibited 96.6 dB at 1000 MHz. This was about 12 times higher than without coated concrete. Full article

The steel making processes involves extreme and harsh operating conditions; hence, the production hardware is exposed to degradation mechanisms under high temperature oxidation, erosion, wear, impact, and corrosive environments. These adverse factors affect the product quality and efficiency of the steel making industry, which contributes to production downtime and maintenance costs. Thermal spray technologies that circumvent surface degradation mechanisms are also attractive for their environmental safety, effectiveness and ease of use. The need of thermal spray coatings and advancement in terms of materials and spray processes are reviewed in this article. Application and development of thermal spray coatings for steel making hardware from the molten metal processing stages such as electric arc and basic oxygen furnaces, through to continuous casting, annealing, and the galvanizing line; to the final shaping process such as cold and hot rolling of the steel strips are highlighted. Specifically, thermal spray feedstock materials and processes that have potential to replace hazardous hard chrome plating are discussed. It is projected that novel coating solutions will be incorporated as awareness and acceptance of thermal spray technology grows in the steel making sectors, which will improve the productivity of the industry. Full article

Using a concrete surface, the ingress of aggressive ions and the initiation of the corrosion reaction of an embedded steel rebar were studied. To reduce the corrosion reaction of the embedded steel rebar, either a coating on the steel rebar or a repair material was used on the concrete surface. Therefore, in the present study, 200 µm thick Cu, Ti, and 85Zn-15Al were used as repair materials, and their coatings were deposited on the concrete surface using a twin-wire arc thermal spray process. Different experiments such as bond adhesion, water permeability, immersion in a 5 wt.% NaCl solution, and accelerated carbonation were performed to assess the durability of the coatings, and the characterization of the coatings was performed by using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The Cu and 85Zn-15Al coatings exhibited severe defects and porosity; therefore, these coatings exhibited very low bond adhesion, whereas the Ti coating showed a dense and compact morphology, and its bond adhesion value was 11 times greater than that of the Cu coating. The NaCl immersion results can be used to determine the extent of the deterioration of different coatings in coastal areas; based on these results, the Cu coating exhibited delamination, while 85Zn-15Al showed white rust deposition. By contrast, there was no detrimental effect of NaCl immersion on the Ti coating during the 28 days under study, and the coating exhibited characteristics identical to those observed after deposition. The Ti coating reduced the carbonation depth by 1.5–2 times that of the Cu and 85Zn-15Al coatings after four and eight weeks of exposure. The present study suggests that Ti can be the potential metal used as a repair material for concrete to enhance the durability of buildings and infrastructure. Full article

The influence of thermally sprayed aluminum coatings (Al99%; arc spraying) on the fatigue strength of gas metal arc welded (GMAW) non-alloyed structural steel specimens with respect to foundations for offshore wind turbines was investigated. Additionally, the corrosion protection effect of such coatings for water conditions similar to the Baltic Sea was determined. Wöhler tests were carried out on test specimens with different weld details in the as-welded condition as well as in the thermal spray coat under the consideration of different kinds of surface preparation (blast cleaning with corundum and grit). Substrate and coating were characterized by scanning electron microscopy and the influence on the residual stress states was determined. Corrosion rate monitoring via LPR measurements was carried out as well as the monitoring of the galvanic current between coated and uncoated steel to characterize the coatings’ sacrificial capability for minor defects. Fatigue strength was significantly increased through thermal spraying, especially for test specimens with welded transverse stiffeners (Δσ_c,var = 127 MPa after coating compared to Δσ_c,var = 89 MPa as welded). With a characteristic value of the stress range of Δσ_c,var = 153 MPa, the welded butt joint specimens already exhibited a high fatigue strength in the as-welded condition. The corrosion studies demonstrated that thermally sprayed Al99% coatings have a high resistance to corrosion in seawater environments and are suitable as planar sacrificial anodes sufficiently polarizing bare steel below 0.8 V. The combination of fatigue strength improvement and corrosion protection makes the thermally sprayed Al coatings promising for design and operation of e.g., offshore structures. Full article

Wear of the working surfaces of machinery parts is a phenomenon that cannot be fully countered, only postponed. Among surface lifecycle elongation techniques, hardfacing is one which is most often used in heavy load applications. Hardfaced coating can be applied using different welding approaches or thermal spraying technologies, which differ when it comes to weld bead dimensional precision, layer thickness, process efficiency and material. In this study the authors examine the geometrical behavior and hardness properties of two distinctive chromium-based Gas Metal Arc Welding (GMAW) cored wires. The stringer beads are applied numerically with five levels of linear energy, being a resultant of typical values of welding speed and wire feed, ranging between 250 mm/s to 1250 mm/s (welding speed) and 2 m/min to 10 m/min (wire feed). The samples were cut, etched and measured using a digital microscope and Vickers indenter, additionally the chemical composition was also examined. Hardness was measured at five points in each cutout, giving 40 measurements per sample. The values were analyzed using an ANOVA test as a statistical background in order to emphasize the divergent behavior of the cored wires. It appeared that, despite having less chromium in its chemical composition, wire DO*351 exhibits higher hardness values; however, DO*332 tends to have a more stable geometry across all of the heat input levels. Full article

Antibacterial agents derived from classic organic compounds have been frequently employed for a number of years as a protective layer for biofilms. On the other hand, these agents often comprise dangerous components that, due to their interaction with toxic compounds, may be damaging to human beings. This hazard may be caused by the agents’ proximity to the toxic substances. Over the course of the past three decades, a variety of approaches, such as the utilization of a broad spectrum of metallic and oxide materials, have been the subject of research in order to develop a diverse selection of antibacterial coating layers that are acceptable. One of these approaches is the use of silver nanoparticles. It has been established that the cold spray technique, a solid-state method compatible with nanopowders, has shown higher performance and is the most effective strategy for coating materials. This has been proven via testing. It is possible to produce one-of-a-kind material coatings in ways that are not even remotely imaginable with any other thermal coating method, which is the primary reason for its prominence in contemporary production. The capacity to do so is what provides it with an advantage over its rivals in the market. This current study was conducted, in part, to investigate the effects of Cu-alloying elements on the antibacterial behavior of metallic glassy alloys on Ni₅₀TM₅₀ (TM; Ti, Zr) and Cu₅₀TM₄₀Ni₁₀ (TM; Ti, Zr) systems prepared by the mechanical disordering technique, in conjunction with the cold spray method. These alloys were created by combining the mechanical disordering technique with the cold spray method. The arc melting process was employed to generate master alloys consisting of Ni₅₀Ti₅₀, Ni₅₀Zr₅₀, Cu₅₀Ti₄₀Ni₁₀, and Cu₅₀Zr₄₀Ni₁₀ for the purpose of this investigation. The master alloys were then used as feedstock materials for the creation of metallic glassy powders. Following the pulverization of the alloys of each system into a powdered form, the mixtures were charged through a high-energy ball milling operation for a duration of 50 h. Using the cold spray technique, the as-milled powders, which were metallic glasses, were applied singly in order to coat SUS304 sheets. The method was employed for this purpose. After the addition of Cu to the two binary Ni₅₀TM₅₀ (TM; Ti, Zr) alloys, the antibacterial properties of their corresponding metallic glassy phases were found to be significantly enhanced. This was shown by the fact that they were successful in preventing the development of biofilm by E. coli in contrast to the other systems that were evaluated. Full article

Due to their outstanding stiffness-to-weight ratio, fiber-reinforced plastics are established materials for weight reduction in the aerospace and automotive industries. To improve certain properties, such as their low thermal and electrical conductivity, metallic coatings can be applied to the polymer surface. One of the methods used for this purpose is thermal spraying. Studies have shown that the adhesion strength of metallic coatings on polymer surfaces is low. To improve the adhesion strength, the surface of the fiber-reinforced plastics was pretreated with pulsed laser-based methods. This study describes in detail the process chain, the resulting surface conditions and their effect on the adhesion strength of wire arc sprayed copper coatings in pull-off and shear tensile testing. The results show up to ~200% increase in adhesion strength for the laser-structured samples compared to the grit-blasted reference samples in the pull-off test. Full article

Advancement in electronic and communication technologies bring us up to date, but it causes electromagnetic interference (EMI) resulting in failure of building and infrastructure, hospital, military base, nuclear plant, and sensitive electronics. Therefore, it is of the utmost importance to prevent the failure of structures and electronic components from EMI using conducting coating. In the present study, Cu, Cu-Zn, and Cu-Ni coating was deposited in different thicknesses and their morphology, composition, conductivity, and EMI shielding effectiveness are assessed. The scanning electron microscopy (SEM) results show that 100 µm coating possesses severe defects and porosity but once the thickness is increased to 500 µm, the porosity and electrical conductivity is gradually decreased and increased, respectively. Cu-Zn coating exhibited lowest in porosity, dense, and compact morphology. As the thickness of coating is increased, the EMI shielding effectiveness is increased. Moreover, 100 µm Cu-Zn coating shows 80 dB EMI shielding effectiveness at 1 GHz but Cu and Cu-Ni are found to be 68 and 12 dB, respectively. EMI shielding effectiveness results reveal that 100 µm Cu-Zn coating satisfy the minimum requirement for EMI shielding while Cu and Cu-Ni required higher thickness. Full article

High-strength aluminum alloy fabricated using spray deposition technology possesses many advantages, such as fine crystal grains, low component segregation, uniform microstructure, and small internal stress. In this study, spray-deposited 2195 Al-Cu-Li alloy in forged state was used and welded using the gas tungsten arc welding (GTAW) process to test and verify the features of the fusion joint. Quantitative analysis was carried out to evaluate the relationship between the local microstructures and performances of the fusion joint, which was composed of four zones: weld metal, fusion zone, heat-affected zone, and base metal. The characteristic quantities of each zone, including recrystallized grain fraction, grain sizes, grain misorientation angle, and Vickers hardness, and their distributions were considered as the key factors affecting the performance of the joint because of welding thermal cycle impact on the fusion joint. To recognize the metallurgical characteristics of spray-deposited alloy 2195, a statistical algorithm based on the concept of the Hall–Petch relationship was proposed to validate the actual test results, which include the correlation effects of both the filler wire and welding process. The correlation between the microstructures and performances of several characteristic quantities were evaluated by integrating the above characteristic information of the fusion joint under the strong coupling of multiple factors. Thus, the advantages of weldability of spray-deposited alloy 2195 using GTAW could be understood in detail. Full article