Search Results (41)

The short-term mechanical properties of commercial corrosion-resistant nickel alloys based on Ni-Cr (Hastelloy^® G-35^® or UNS N06035), Ni-Mo (Hastelloy^® B-3^® or UNS N10675), and Ni-Cr-Mo (VDM^® Alloy C-4 or UNS N06455, VDM^® Alloy 59 or UNS N06059, and KhN62M-VI) systems were analyzed in the as-received state and after long-term (up to 5000 h) aging at 500–700 °C. All alloys exhibited moderate strength and high ductility in the as-received state. Under the influence of high temperatures, these alloys showed a tendency toward the decomposition of Ni-based FCC solid solutions and a change in mechanical properties. It was shown that the difference in chromium and molybdenum content in Ni-Cr-Mo alloys leads to the formation of secondary phases of various composition and morphology, which had varied influence on the short-term mechanical properties of the materials. Grain boundary precipitates had a negligible effect on the strength properties of the investigated alloys, while intragranular precipitates embrittled nickel-based alloys, reducing their possible application at high temperatures. Full article

In this study, the microstructure and electrochemical and passive characteristics of NiCr_25.2−xMoAl_x (x = 0, 1.25, 2.5, and 5 mol.%) alloys were investigated. The results show that Ni-Cr-Mo-Al alloys with varying Cr:Al ratios both had a single FCC structure without any second structure precipitates, and decreases in dislocation density and grain size were observed as the Al content in NiCrMoAl alloys increased. It was found from the electrochemical results that the NiCr_23.95MoAl_1.25 alloys had the maximum radius for a semicircle and the lowest I_corr, indicating an enhanced anti-corrosion performance (R_ct: 8.08 ± 0.368 × 10⁵ Ω cm², I_corr: 1.05 ± 0.003 × 10⁻⁷ A/cm²). In this study, it was found that the anti-corrosion performance of the alloys had an approximate connection to the composition and density of passive films. Denser and more stable microstructures in NiCr_23.95MoAl_1.25 alloys were further proven by potentiostatic polarization tests and Mott–Schottky experiments, showing a lower stable current density and acceptor density (N_A: 9.79 ± 0.4 × 10⁻²⁰ cm⁻³). In addition, the results of XPS show that the Al_1.25 specimen had the highest Cr₂O₃ in the passive film’s content among the NiCrMoAl alloys. Cr₂O₃ was the main component, suggesting an enhanced protective influence of passive film. The present study can offer guidance for the application of nickel-based alloys with high anti-corrosion resistance in marine environments. Full article

Nickel-based superalloys are extensively used in high-temperature applications because of their exceptional oxidation and corrosion resistance. However, their performance in aggressive environments containing molten salts, such as Na₂SO₄ and V₂O₅, remains a critical challenge. This study investigated the hot corrosion behavior of Inconel 718, Udimet 710, Nimonic 75, and Inconel 625, focusing on the role of the alloying elements in the corrosion layers and degradation mechanisms. The superalloys were exposed to 50/50 wt.% Na₂SO₄–V₂O₅ at 900 °C for 8, 48, and 96 h, and their corrosion resistance was evaluated through weight gain measurements, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). These results indicate that Mo is a key factor in accelerating degradation, with Inconel 625 exhibiting the highest weight gain owing to the formation of thermally unstable Mo-rich phases. Fe also negatively impacted the stability of the protective scale of Inconel 718, contributing to an increased corrosion rate. In contrast, Nimonic 75 exhibited the best resistance, forming more of the NiCr₂O₄ spinel phase through the reaction of Cr₂O₃ with NiO from the high Ni and Cr contents in the corrosive layers. These findings highlight the importance of alloy composition in optimizing corrosion resistance and suggest that using superalloys with lower Mo and Fe contents and higher Cr and Ni concentrations can significantly enhance the durability of superalloys in molten salt environments. Full article

The relevance of the study is related to the need to join dissimilar copper and nickel alloys by laser direct energy and material deposition (LDED). The purpose of research is studying the distribution of elements, structure, and properties of contact zone of nickel-based super alloy and CuCr1 bronze obtained by direct energy and material deposition with preliminary formation of relief of contact surface. For the purposes of research, samples were made from UNS C18200 copper alloy CuCr1 without relief, with a relief of 0.5 mm depth, and with a relief of 1 mm depth. The Ni₅₀Cr₃₃W_4.5Mo_2.8TiAlNb (EP648) alloy powder was deposited onto the bronze samples with a micro-relief. The deposition was produced by direct injection of energy and material. The influence of interphase interaction of CuCr-chromium carbide system on the possibility of initiation of a crack in the area of carbide secretions is not significant and does not exceed 3.1% according to CIC criterion from the background level for CuCr1 (CIC = 1.54% for CuCr1-Al₄C₃ interface and CIC = 3.1% for CuCr1-Cr₂₃C₆ interface). An X-ray analysis revealed the presence of tensile residual macro-stresses, arising from differences in thermal expansion coefficients in the CuCr1-EP648 interface area, which may be the main cause of crack formation. Cracks are generated and run along the grain boundaries, on which traces of excretion are visible. The contact surface in the CuCr1-EP648 interface area has no visible defects, which indicates the good adhesion of materials when applying an initial layer of EP648 by LDED. The presence of a 0.5-mm micro-relief on CuCr1 has a positive effect on the strength of the connection, as it increases the surface area of the contact CuCr1-EP648 and therefore reduces the contact stress of the breakout. Full article

One of the concepts behind Generation IV reactors is a molten salt coolant system, where the materials for the reactor itself and for the primary and secondary circuit components are subjected to extreme chemical and thermal stresses. Due to the unavailability of these materials, a nickel–molybdenum alloy known as MoNiCr has been developed in the Czech Republic. This paper discusses the manufacturing process for the MoNiCr alloy, covering conventional casting technology, forming, powder atomization, additive manufacturing (AM) using the directed energy deposition (DED-LB) process, and final heat treatment. Special attention was given to the quality of the input powders for additive manufacturing, particularly regarding the optimization of the chemical composition, which significantly influenced the quality of the additively manufactured components. AM enables the realization of complex structural designs that are critical for energy applications, despite the high susceptibility of the MoNiCr alloy to solidification cracking. Through AM, a test body was successfully produced with a maximum defect rate of 0.03% and the following mechanical properties: a yield strength (YS) of 279 MPa, an ultimate tensile strength (UTS) of 602 MPa, and an elongation (El) of 51%. Full article

Rapid developments in aerospace and nuclear industries pushed forward the search for high-performance self-lubricating materials with low friction and wear characteristics under severe environment. In this paper, we investigated the influence of the Mo element on the tribological performance of nickel alloy matrix composites from room temperature to 800 °C under atmospheric conditions. The results demonstrated that composites exhibited excellent lubricating (with low friction coefficients of 0.19–0.37) and wear resistance properties (with low wear rates of 2.5–28.1 × 10⁻⁵ mm³/Nm), especially at a content of elemental Mo of 8 wt. % and 12 wt. %. The presence of soft metal Ag on the sliding surface as solid lubricant resulted in low friction and wear rate in a temperature range from 25 to 400 °C, while at elevated temperatures (600 and 800 °C), the effective lubricant contributed to the formation of a glazed layer rich in NiCr₂O₄, BaF₂/CaF₂, and Ag₂MoO₄. SEM, EDS, and the Raman spectrum indicated that abrasive and fatigue wear were the main wear mechanisms for the studied composites during sliding against the Si₃N₄ ceramic ball. The obtained results provide an insightful suggestion for future designing and fabricating solid lubricant composites with low friction and wear properties. Full article

Grain boundary engineering (GBE) was carried out on a nickel-based alloy (GH3535, Ni-16Mo-7Cr-4Fe), which intrinsically has many strings of primary molybdenum carbides. The strings induce inhomogeneous grain size distributions and increase the difficulties in achieving a GBE microstructure. In this work, the effects of the primary carbide distribution on the grain boundary network (GBN) evolution were investigated. A higher proportion of Σ3ⁿ grain boundaries (GBs) associated with extensive multiple twinning events was achieved in the specimen with more dispersive and finer primary carbides, which are the results of cross-rolling, i.e., cold rolling with a changed direction. In a starting microstructure with many strings of primary carbides, the dense and frequent occurrence of particle-stimulated nucleation (PSN) around the carbides induced more general high-angle GBs into the GBN, and the inhibition of GB migrations by the carbide strings suppressed the formation of large-sized highly twinned grain clusters. As a consequence, the Σ3ⁿ GBs could not be effectively enhanced. Full article

The descaling roller is a significant component in steel rolling production. Under harsh service conditions, the descaling roller is subjected to the dynamic impact caused by high-pressure water erosion and a high-temperature billet descaling process for a long time. Under the harsh conditions of high temperature, strong wear, multi-cycle heat, force, flow, and multi-field strong coupling, the roller surface is prone to wear and corrosion failure, which affects the production cost and efficiency. Through plasma surfacing technology, a high-performance coating can be applied on the conventional metal surface to effectively improve its surface properties. It is important to carry out experimental research on the surface plasma surfacing of the descaling roller to prolong product life, improve product quality, and save cost. At present, the research on the 42CrMo scaler matrix plasma surfacing of nickel-based alloys with different WC contents is still lacking. In this paper, 70%NiCrBSi+30%WC powder and 40%NiCrBSi+60%WC powder were used as surfacing materials; plasma surfacing experiments were carried out on the 42CrMo matrix; and SEM, XRD, microhardness, friction and wear, and corrosion tests were carried out on the surfacing layer to evaluate the feasibility of preparing an ultra-high-hardness WC-particle-reinforced nickel-based alloy plasma surfacing layer on the descaling roller surface and to explore the WC hard phase dissolution behavior and complex secondary phase formation mechanism. The results show that γ(Fe/Ni), Fe-Ni, FeSi, Fe₃C, and M₇C₃ are the main phases in the Ni/WC plasma surfacing layer. The diffusion and precipitation of elements occur in the molten pool, and complex secondary phases are formed in the surfacing layer. Compared with the 70%NiCrBSi+30%WC surfacing layer, the WC deposition phenomenon of the 40%NiCrBSi+60%WC surfacing layer has been significantly improved and has better hardness, wear resistance, and corrosion resistance. Based on the welding test, the correlation law between powder formulation, welding structure, and surfacing layer properties was revealed in this study, which lays a theoretical foundation for the preparation of high-performance coating on the descaling roller surface and has significant engineering application value and practical significance. Full article

In this study, the effect of alloying elements on the adsorption and dissociation behaviors of hydrogen molecules on the bcc-Fe (001) surface has been investigated using first-principles calculations. H₂ molecules can easily dissociate on the hollow site, and the dissociated hydrogen atoms bond with the surrounding metal atoms. Doping Cr and Mo atoms on the surface would reduce the H₂ molecule adsorption energy, which promotes the H₂ molecule adsorption and dissociation. When only one or two Ni atoms doping on the surface, it improves the adsorption energies, which in turn can hinder the H₂ molecule adsorption and dissociation. However, three or four Ni atoms doping on the surface is beneficial to the H₂ molecule adsorption and dissociation. Thus, the nickel content in Ni–Cr–Mo steel should be reasonably controlled to improve the hydrogen embrittlement resistance of the steel. Full article

In the field of aerospace, core components require excellent wear resistance, lubrication and mechanical properties over a wide temperature range. In this study, three groups of CoCrFeNi high-entropy alloy (HEA)-based self-lubricating composites were designed with the addition of Ag, Ni/MoS₂ and Cr₂O₃ using discharge-plasma-sintering technology. Their microstructure, phase composition, mechanical properties, friction and wear properties were analyzed. The results showed that, with the addition of Ag, the hardness and yield stress of HEA-Ni/MoS₂-Ag were reduced by 36 HV and 24 MPa, respectively, while the plastic strain was increased by 2%. With the addition of Cr₂O₃, the hardness (382 HV) and yield stress (430 MPa) of HEA-Ni/MoS₂-Ag-Cr₂O₃ reached their highest values, but the plastic strain reached its lowest value. HEA-Ni/MoS₂-Ag-Cr₂O₃ had the smallest friction coefficient in which the friction coefficient at 800 °C was only 0.42. Additionally, it had a small wear rate of 3.2 × 10⁻⁶ mm³/Nm over a wide temperature range. At lower temperatures, Ni/MoS₂ and Ag were conducive to lubrication, and the wear resistance was improved by the presence of Cr₂O₃. At high temperatures, a nickel oxide phase and a variety of silver molybdate phases were formed via a tribochemical reaction, which was vital to the high-temperature tribological properties. Full article

Degradation of industrial machinery through wear can be mitigated with the deposition of protective coatings to reduce maintenance costs and prolong their service lifespans. Electroless nickel-based composite coatings is one possible method used to provide this protection. The addition of Tribaloy (CoMoCrSi alloy) particles has been found to produce composite coatings with high toughness. In this work, electroless Ni-P-Tribaloy composite coatings were plated on AISI 1018 steel substrates and subjected to low-stress abrasion tests following ASTM G65 standards to investigate the abrasion of the coating. The test was performed at 10 revolution increments, with a 45 N applied load, until coating failure was observed and the measured abrasion was reported as volume loss. The two Ni-P-Tribaloy coating samples lasted for 90 and 100 revolutions, exhibiting a wear rate of 0.170 mm³ per revolution, compared to 0.135 mm³ per revolution for the Ni-P coatings. The abrasive wear mechanism in the Ni-P-Tribaloy coating was found to be plowing of the matrix around the Tribaloy particles, followed by the removal of the particles once they are protruding, which subsequently contributes to the three-body wear of the coating. The particle removal was accelerated at the coating particle-matrix interface. It is concluded that the size of the Tribaloy is a major factor, and we recommend that further studies be carried out using finer particles to improve the wear resistance of the Ni-P-Tribaloy coating. Full article

In the production of critical parts for various machines and mechanisms, expensive structural steels are used alloyed with chromium, nickel, molybdenum, and vanadium. In practice, the wear resistance of parts, especially under severe operating conditions, may be insufficient due to uneven microstructure and the content of retained austenite. Therefore, increasing the operational stability of various products made of alloy steels is an important task. The purpose of this work is to investigate the effect of isothermal hardening from the intermediate (γ+α)-area and the duration of deep cryogenic treatment on the structure formation and frictional wear resistance of 38CrNi3MoV steel. The isothermal hardening promotes the formation of the required multiphase microstructure of 38CrNi3MoV steel. The influence of the duration of deep cryogenic treatment on the microhardness, amount of retained austenite, fine structure parameters, and friction wear of 38CrNi3MoV steel are established. Complex heat treatment of 38CrNi3MoV steel, according to the proposed mode, makes it possible to achieve a significant decomposition of retained austenite to martensite, which leads to an increase in frictional wear resistance of ~58%. Full article

The secondary phase, such as Ni₃Al-based L1₂ γ′, is crucially important for the precipitation strengthening of superalloys. Composition–structure–property relations provide useful insights for guided alloy design. Here we use density functional theory combined with the multiple scattering theory to compute dependencies of the structural energies and equilibrium volumes versus composition for ternary Ni₃(Al_1−xX_x) alloys with X = {Ti, Zr, Hf; V, Nb, Ta; Cr, Mo, W} in L1₂, D0₂₄, and D0₁₉ phases with a homogeneous chemical disorder on the (Al_1−xX_x) sublattice. Our results provide a better understanding of the physics in Ni₃Al-based precipitates and facilitate the design of next-generation nickel superalloys with precipitation strengthening. Full article

Oil and gas pipelines are subject to various forms of damage and degradation during their operation. Electroless Nickel (Ni-P) coatings are widely employed as protective coatings due to their ease of application and unique properties, including high wear and corrosion resistance. However, they are not ideal for protecting pipelines due to their brittleness and low toughness. Composite coatings of higher toughness can be developed through the co-deposition of second-phase particles into the Ni-P matrix. Tribaloy (CoMoCrSi) alloy possesses excellent mechanical and tribological properties making it a potential candidate for a high-toughness composite coating. In this study, Ni-P-Tribaloy composite coating consisting of 15.7 vol.% Tribaloy was successfully deposited on low-carbon steel substrates. Both the monolithic and the composite coatings were studied to evaluate the effect of the addition of Tribaloy particles. The micro-hardness of the composite coating was measured to be 6.00 GPa, 12% greater than that of the monolithic coating. Hertzian-type indentation testing was carried out to investigate the coating’s fracture toughness and toughening mechanisms. The 15.7 vol.% Tribaloy coating exhibited remarkably less severe cracking and higher toughness. The following toughening mechanisms were observed: micro-cracking, crack bridging, crack arrest, and crack deflection. The addition of the Tribaloy particles was also estimated to quadruple the fracture toughness. Scratch testing was performed to evaluate the sliding wear resistance under a constant load and a varying number of passes. The Ni-P-Tribaloy coating exhibited more ductile behavior and higher toughness, as the dominant wear mechanism was identified as material removal, as opposed to brittle fracture in the Ni-P coating. Full article

A WC-particle-reinforced nickel-based alloy surfacing layer was fabricated on 42CrMo ultra-high-strength steel. The microstructure and the mechanical and impact-damage behaviors of the surfacing layers at the evaluated temperatures were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and the Vickers hardness tester. Results showed that these WC particles gradually changed from elongated and crisscross needle-like phases to blocks with the increase in impact temperature. Numerous carbide phases (e.g., (Cr,Ni,Fe)₂₃C₆) and γ-Ni phases were formed in the substrate matrix. The surfacing layer showed a typical brittle fracture, and the impact energy decreased with the increase in temperature. Moreover, the surfacing layer showed a clear quasi-cleavage fracture morphology without dimples after a 600 °C impact test but exhibited a mixture of dimple fractures and cleavage fractures after the 200 °C and 400 °C impact tests. The Vickers fracture toughness test showed that the average hardness of the surfacing layer after a 600 °C impact test was 383 HV_1.0, which is about 0.8 times that after the 200 °C impact test. In addition, the WC particles in the surfacing layer after the 600 °C impact test showed the highest fracture toughness, but the corresponding Ni40A binder phase possessed the lowest fracture toughness. Full article