Search Results (17)

Nickel–Aluminum–Bronze (NAB) has gained significant attention in marine applications due to its excellent corrosion resistance and has shown growing potential for laser powder bed fusion (L-PBF) additive manufacturing. However, research on the fabrication of NAB alloys using L-PBF remains relatively limited. In this study, fully dense NAB samples were successfully fabricated through L-PBF process parameter optimization. The microstructural evolution and mechanical properties of both as-built and annealed L-PBF samples were systematically investigated and compared with those of traditionally cast NAB. The results reveal that the as-built L-PBF specimens primarily consist of columnar β′ grains, with the α phase distributed along the grain boundaries and a small amount of κ phase precipitated within the β′ matrix, distinctly different from the cast microstructure characterized by a columnar α-phase matrix with precipitated β′ and κ phases. After annealing at 675 °C for 6 h, the β′ phase in both methods decomposed into α + κ phases, and the original columnar structure in the L-PBF specimens transformed into a dendritic morphology. Compared to the cast samples, the L-PBF-produced NAB alloy exhibited significantly enhanced yield strength, tensile strength, and microhardness, attributable to rapid solidification during the L-PBF process. Following annealing, the yield strength and elongation increased by 12.8% and 184.4%, respectively, compared to the as-built condition, resulting from the decomposition of the martensitic phase into α + κ phases and further grain refinement. Full article

The materials used in the marine environment are generally selected for their high performances in aggressive operational media. This is also the case for marine propellers, which are mainly manufactured from cast nickel–aluminum bronze (NAB), due to their favorable mechanical properties and corrosion resistance. This study is focused on maximizing the efficiency of pulsed laser cladding through coaxial powder feeding, aiming to develop it as a sustainable reconditioning method for NAB propellers. A pulsed-wave laser (Trumpf TruPulse 556) and a cladding head (Precitec WC 50) were used for cladding of CuNi-alloyed powder on an NAB substrate. One of the main challenges was the high reflectivity of the copper matrix, present in both the base material of the propeller and in the powder, which significantly reduces laser energy absorption. However, good-quality cladded layers were obtained by optimizing the process cladding parameters. The coatings were characterized by optical and scanning electron microscopy. Microhardness values indicated transition regions within the coating layer. The results demonstrate that laser cladding with pulsed lasers is an effective and promising surface engineering method for reconditioning of damaged marine propellers. The obtained results create a path for future research aimed at extending the service life of copper-based marine components. Full article

Nickel aluminum bronze (NAB) and manganese aluminum bronze (MAB) are widely used in propulsion and seawater handling systems in naval platforms due to their attractive combination of mechanical strength, toughness, and very low susceptibility to marine corrosion. Nevertheless, it is well known that they can suffer from selective phase corrosion and erosion–corrosion, primarily caused by cavitation and sand erosion. Both alloys have a multiphase microstructure that governs their mechanical and chemical behavior. The tribocorrosion behavior of cast NAB and MAB alloys was studied in artificial seawater to analyze the effect on microstructure. The microstructure and nanohardness were evaluated and correlated with tribocorrosion test results conducted under two different loads (10 and 40 N) in a unidirectional sliding mode using a 1 M NaCl solution as the electrolyte. A significant increase in the corrosion rate due to the wear effect was observed in both alloys. MAB exhibited a slightly better tribocorrosion performance than NAB, which was attributed to significant differences in the shape, distribution, and size of the intermetallic kappa phases—rich in iron, aluminum, and nickel—within the microstructure. Pitting corrosion was observed in NAB, while selective corrosion of kappa phases occurred in MAB, highlighting the role of the protective layer in the tribocorrosion behavior of both alloys. These findings were supported by post-test solution analysis using ICP-AES and corrosion product characterization by EDX. A synergistic effect between wear and corrosion was confirmed for both alloys, as erosion removes the protective layer, exposing fresh material to continuous friction and favoring a progressive material loss over time. The practical impact of this study lies in improving the control and design of highly alloyed bronze microstructures under in-service corrosion–erosion conditions. Full article

Surface modifications, including laser surface melting (LSM) and micro-shot peening (MSP), were applied to improve the fatigue performance of the Ni-Al bronze (NAB) alloy. LSM could homogenize the NAB into a uniform microstructure with refined columnar grains in the laser-melted zone but introduced residual tensile stress (RTS). The bombardment and generated heat induced by MSP could not entirely remove the granular κ_II precipitates and lamellar κ_III phase in the peened zone of the shot-peened sample (NSP sample) but introduced residual compressive stress (RCS) into the NSP sample under the peening intensity of this work. The results of fatigue tests revealed that the LSM sample had the poorest fatigue performance, but the NSP sample showed the best fatigue performance among the tested samples. The fatigue limit of the NAB alloy was about 325 MPa; meanwhile, the fatigue performance of the LSP (LSM + MSP) sample was equivalent to or a little better than that of the NAB alloy (NBM sample). The RTS and aligned columnar grains accounted for the degraded fatigue resistance of the LSM sample. By contrast, the high RCS and the refined structure were responsible for the improved fatigue strength/life of the NSP sample relative to that of the other samples. The fatigue limit of the NSP sample was as high as 450 MPa. However, the increase in fatigue strength of the NSP sample occurred in service life regions above 3 × 10⁵ cycles. Full article

The objective of this research is to enhance the mechanical and corrosion resistance properties of a cast Ni-Al bronze (NAB). To achieve this, the effect of deep cryogenic treatment (DCT), a process that has shown promise in other alloys, is initially investigated. It is demonstrated that, in the case of NAB, DCT induces only minor microstructural changes, which do not lead to any significant improvement in its properties. Consequently, it is proposed that a combined treatment be employed, involving annealing either before or after DCT. The results indicate that annealing at 675 °C for 2 h following cryogenic treatment at −180 °C increases the yield strength by approximately 11%. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in simulated seawater further confirm that this combination results in the formation of oxide layers with enhanced protective capacity. These improvements are attributed to the significant refinement and homogenization of the microstructure, including the globularization of the kI, kII, and, particularly, kIII phases, and an increase in the precipitation of the kIV phase in a finer and more homogeneous form within the alpha phase. Full article

To study the effect of aluminum and nickel elements on the microstructures and properties of the nickel–aluminum bronze (NAB) alloy, four kinds of alloys with different compositions, ZCuAl7–7–4–2, ZCuAl8-6-4-2, ZCuAl9-5-4-2, and ZCuAl10-4-4-2, are prepared by vacuum-melting technology. The effects of different Al/Ni ratios on the microstructures of NAB are investigated using a metalloscope, scanning electron microscopy, transmission electron microscopy, and XPS analysis. The mechanical property is evaluated with microhardness testing and tensile mechanical testing. The corrosion resistance is evaluated using mass-loss testing, electrochemical testing, and corrosion-product characterization. The results show that with the increase of the Al/Ni ratio, the content of precipitated phases increases, while β′ and hard κ, which have a different morphology, appear. As the Al/Ni ratio rises from 1 to 2.5, the hardness increases from 104 HV to 202 HV, and the tensile strength increases by 394 MPa from 356 MPa to 751 MPa, but the elongation decreases substantially from 50.50% to 11.00%. The best corrosion resistance is shown on ZCuAl7-7-4-2, with a corrosion rate of 0.00267 mm/a after 30 d of static immersion corrosion in 3.5 wt.% NaCl solution. Through electrochemical testing and corrosion-product characterization, it is found that ZCuAl7-7-4-2 has the largest polarization resistance R_p, and the selective corrosion of the surface is mild. Full article

Fuel cell technology has developed due to diminishing dependence on fossil fuels and carbon footprint production. This work focuses on a nickel–aluminum bronze alloy as an anode produced by additive manufacturing as bulk and porous samples, studying the effect of designed porosity and thermal treatment on mechanical and chemical stability in molten carbonate (Li₂CO₃-K₂CO₃). Micrographs showed a typical morphology of the martensite phase for all samples in as-built conditions and a spheroid structure on the surface after the heat treatment, possibly revealing the formation of molten salt deposits and corrosion products. FE-SEM analysis of the bulk samples showed some pores with a diameter near 2–5 μm in the as-built condition, which varied between 100 and −1000 μm for the porous samples. After exposure, the cross-section images of porous samples revealed a film composed principally of Cu and Fe, Al, followed by a Ni-rich zone, whose thickness was approximately 1.5 µm, which depended on the porous design but was not influenced significantly by the heat treatment. Additionally, by incorporating porosity, the corrosion rate of NAB samples increased slightly. Full article

Nickel aluminum bronze (NAB) alloys are reported to suffer accelerated local corrosion in sulfide-polluted seawater. In this work, the real-time in situ scanning vibrating electrode technique (SVET) was employed to monitor the evolution of the corrosion product film of a typical NAB alloy immersed in the clean and sulfide-polluted 3.5% NaCl solutions. In the sulfide-free condition, the corrosion current peak surged at the individual point of the NAB surface and receded to calm in 2 h. In the presence of the sulfide, however, multiple active points on the measured metal surface released high corrosion current for a long time, indicating that intense corrosion had occurred. The corrosion mass loss was more than four times the former. Global electrochemical techniques, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were adopted to perform a comprehensive analysis of the composition of the corrosion product films. The results show that a dense layer of aluminum and cuprous oxide forms on the NAB surface in the sulfide-free solution, while a loose mixture of cuprous sulfide and cuprous oxide is detected in the sulfide-contaminated solution. This finding is believed to account for the observed distinction between the corrosion behavior of NAB in the two solutions. Full article

The simultaneous existence of mechanical erosion and electrochemical corrosion is a common scenario for engineering alloys used in marine environments, such as pump impellers and valves. Nickel–aluminium–bronzes (NABs) are widely used alloys in these environments due to their combination of high corrosion resistance and effective mechanical properties. However, NAB alloys are increasingly cast with reduced nickel content due to its high price and low availability. In this study, we examined the tribocorrosion behaviour of two nickel–aluminium bronzes (C95500 and C95400) with different nickel contents (4.8% and 1.0%, respectively) by means of a pin-on-disk device combined with in situ electrochemistry under 1 M NaCl solution. We conducted tests for pure wear in distilled water, pure corrosion using in situ electrochemistry under 1 M NaCl solution, and a combination of wear and corrosion, called tribocorrosion, to understand the overall synergism that exists between the two. We analysed our results using gravimetric as well as volumetric analysis; in addition, we defined the friction coefficient to compare the effect of open-circuit potential (OCP). We also applied the Tafel method and compared corrosion rates for the different scenarios. We employed confocal microscopy to delimitate the impact of the surface topography of pure wear and its synergistic effect with corrosion, and used an optical microscope to study the materials’ microstructures as cast conditions. We also utilised XRD in the Bragg–Brentano configuration to determine the chemical composition of corrosion products. From the experiments conducted, we concluded that an important synergistic effect existed between the wear and corrosion of both NABs, which was associated with corrosion-induced wear. We found NAB C95400 to be more susceptible to erosion under both conditions compared with NAB C95500 due to the chemical composition and lubricant effect of corrosion products formed during the tribocorrosion tests, which were supported by the enriched Ni corrosion products, particularly the presence of nickel-rich copper chloride, 3Cu₃(CuNi)(OH)₆CuCl₂, in the C95500 alloy. We concluded that, because it increased the nickel content, the NAB alloy offered better wear and corrosion behaviour in sea water conditions due to its protective film nature. Full article

High-temperature oxidation of NH₃ on Pt alloy gauzes to NO is widely employed in industry for the production of HNO₃, which is used to obtain agricultural fertilizers. Particular attention is paid now to the investigation of the chemical composition of gauzes used in NH₃ oxidation. X-ray photoelectron and energy-dispersive X-ray spectroscopies with the depth of analysis ca. 5 nm and ca. 500 nm were applied to investigate the chemical composition of surface and subsurface layers of the new and used in NH₃ oxidation with air at T = 1133 K Pt–Pd–Rh–Ru catalytic gauzes (81, 15, 3.5, 0.5 wt.%, respectively). For all the gauzes, adsorption (OH_ad, CO_ad), graphitic (C_gr) and oxide (Rh₂O₃) films were found on the surface of the metallic alloy. Under these films, C_ab, N_ab and O_ab atoms absorbed in the subsurface layers were detected on the gauzes used in NH₃ oxidation. The obtained data testify to the penetration of O_ab and N_ab atoms into deeper layers of the alloy during etching with elevation of the catalyst temperature. O_ab atoms were accumulated predominantly on dislocations, etch pits and grain boundaries, whereas N_ab atoms intercalated mostly into interstitial sites of the alloy lattice. Full article

Corrosion is frequently viewed as a catastrophic and unavoidable disaster in marine applications. Every year, a huge cost is incurred on the maintenance and repair of corrosion-affected equipment and machinery. In the marine environment, as-cast nickel–aluminium bronze (NAB) is susceptible to selective phase corrosion. To solve this problem, chromium-reinforced nickel–aluminium bronze was fabricated using the friction stir process (FSP) with improved microstructures and surface properties. A slurry erosion–corrosion test on as-cast and FSPed composites demonstrated that the developed surfaced composite has lower erosion and corrosion rates than the as-cast NAB alloy. The erosion–corrosion rate increased with a decrease in the impact angle from 90° to 30° for both as-cast NAB and prepared composites, exhibiting a shear mode of erosion. The specimens at impact angle 30° experienced more pitting action and higher mass loss compared with those at impact angle 90°. Due to increases in the mechanical properties, the FS-processed composite showed higher erosion resistance than the as-cast NAB alloy. Furthermore, corrosion behaviour was also studied via the static immersion corrosion test and electrochemical measurements under 3.5 wt.% NaCl solution. In a static immersion corrosion test, the FSPed composite outperformed the as-cast NAB composite by a wide margin. The FSPed composite also demonstrated a reduced electrochemical corrosion rate, as revealed by the polarization curve and electrochemical impedance spectroscopic (EIS) data. This reduced rate is attributed to the formation of a Cr oxide film over its surface in the corrosive environment. Full article

In this work, three composite structures of nickel-aluminum bronze (NAB) bonded with SUS630 stainless steel with different intermediate layers were fabricated by laser deposition. The microstructure and corrosion behavior of NAB in 3.5 wt.% NaCl solution were studied. The NAB coating directly deposited on steel substrate contains a large number of Fe-rich dendrites due to the dilution by laser energy and the Cu-Fe liquid phase separation characteristics. The microstructures of NAB were independent and isolated well from the steel substrate when the nickel intermediate layer was applied. Immersion corrosion and electrochemical tests indicated that the composite structure with the nickel intermediate layer presented better corrosion resistance than direct deposited the NAB coating, especially with the NiCr alloy intermediate layer, which led to a shallower corrosion depth and formed a denser layer of protective corrosion products. Full article

Marine noise pollution generated by propellers is of wide concern. Traditional propeller materials (nickel–aluminum bronze (NAB) alloys) can no longer meet the requirements for reducing shaft vibration. However, the Mn–Cu alloy developed to solve the problem of propeller vibration is affected by seawater corrosion, which greatly limits the application of the alloy in the field of marine materials. In this study, the M2052–NAB gradient alloy was developed for the first time using LENS technology to improve the corrosion resistance while retaining the damping properties of the M2052 alloy. We hope this alloy can provide a material research basis for the development of low-noise propellers. This study shows that, after solution-aging of M2052 alloy as the matrix, the martensitic transformation temperature increased to approach the antiferromagnetic transformation temperature, which promoted twinning and martensitic transformation. The aging process also eliminated dendrite segregation, promoted the equiaxed γ-MnCu phase, and increased the crystal size to reduce the number of dislocations, resulting in obvious modulus softening of the alloy. NAB after deposition had higher hardness and good corrosion resistance than the as-cast alloy, which offers good corrosion protection for the M2052 alloy. This research provides new material options for the field of shipbuilding. Full article

Nickel Aluminum Bronze (NAB) and Manganese Aluminum Bronze (MAB) are high-alloyed bronzes that are increasingly employed in several industrial sectors, mainly related to hostile environments due to their excellent properties against corrosion, cavitation, erosion and improved mechanical properties in relation to other copper-based alloys. These materials are very sensitive against thermal treatments due to a multiphase microstructure in as-cast condition. To contribute to the knowledge of the behavior of both alloys, the effect of thermal treatments on the corrosion behavior of NAB (CuAl10Fe5Ni5) and MAB (CuMn12Al8Fe4Ni2) was studied. As-cast material was subjected to various combinations of quenching and quenching and tempering at 850 °C and 600 °C. Corrosion testing was carried out using simulated sea and fresh water. The microstructures of the as-cast and heat-treated samples were characterized by metallography using two chemical agents with FeCl₃ and NH₄OH solutions and examination by optical and scanning electron microscopy. The major effect of thermal treatments on corrosion was found in influencing the amount and distribution of β-phase, which is prone to selective corrosion in both electrolytes. Full article

There is increased interest in using nickel aluminum bronze (NAB) alloys in large-scale directed energy deposition additive manufacturing (DEDAM) processes for maritime applications, but one challenge lies in the component distortion that results from residual stress generated during fabrication. This paper describes the development and evaluation of thermo-mechanical simulations for laser hot wire (LHW) DEDAM of NAB to predict part distortion. To account for the dearth of temperature-dependent properties for NAB C95800 in open literature and public databases, temperature-dependent material and mechanical properties for NAB C95800 were experimentally measured using test specimens fabricated with a variety of DEDAM processes. Autodesk’s Netfabb Local Simulation software, a commercial finite-element based AM solver, was employed but with its heat source model modified to accommodate LHW DEDAM’s oscillating laser path and additional energy input supplied by the preheated wire feedstock. Thermo-mechanical simulations were conducted using both the acquired temperature-dependent material and mechanical properties and the constant room-temperature properties to assess the impact on simulation accuracy. The usage of constant properties in the thermo-mechanical analysis resulted in significantly different predicted distortion compared to those using the temperature-dependent properties, at times even predicting substrate displacement in an opposite direction. Full article