Search Results (556)

Pulse repetition frequency (PRF) controls pulse off-time and, therefore, the extent of thermal accumulation, melt expulsion, and dielectric recovery in finishing electrical discharge machining (EDM). This study clarifies how PRF modifies crater evolution and surface integrity in finishing EDM of 4Cr13 martensitic stainless steel, a corrosion-resistant mold steel used in precision dies and molds. A 2D axisymmetric electro-thermo-fluid model was established in COMSOL, where Gaussian current density, heat-flux, and plasma pressure were periodically imposed at PRFs of 25–100 kHz, while pulse-on time (6 μs) and peak current (8 A) were kept constant. The simulations tracked the transient pressure, heat-flux, velocity, and temperature fields over a common elapsed time of 25 μs. Finishing experiments were then carried out on flat 4Cr13 coupons at 50, 75, and 100 kHz using a copper electrode and deionized water, followed by characterization by laser confocal microscopy, SEM/EDS, and X-ray diffraction using the cosα method. Increasing PRF localized the coupled pressure-heat-flow fields near the crater rim, but shortened off-time and intensified inter-pulse heat accumulation. Accordingly, the surface roughness decreased from Ra = 1.18 μm at 50 kHz to 0.63 μm at 75 kHz, and then slightly increased to 0.71 μm at 100 kHz because of crater overlap, re-melting, and incomplete gap recovery. SEM observations confirmed large irregular craters with cracks at 50 kHz, more uniform fine craters at 75 kHz, and overlapping re-solidified traces at 100 kHz. The residual stress remained compressive for all tested conditions (−341 to −409 MPa). Overall, 75 kHz offers the best compromise between crater uniformity, roughness, and compressive stress for finishing EDM of 4Cr13 steel. Full article

For the corrosion behavior of three extruded Mg alloys (WE43, Mg10Gd, ZX10), the corrosion morphology and the resulting local stress distribution are correlated with the residual strength using µCT, Digital Image Correlation and tensile tests. Samples are corroded in HBSS at 37 °C for various exposure times to increase the extent of corrosion. They are then examined by using the gravimetric method to determine the corrosion rate. Corroded tensile samples are subjected to µCT analysis before and after tensile testing. The crack formation originating from pitting corrosion is discussed on the basis of the stress distribution around local corrosion—its extent is clearly influenced on the morphology. µCT analyses reveals that fractures occur in different ways, either at the smallest cross section, at isolated deep pitting sites, or in other critical areas with critical pitting quantity or size. Mg10Gd has a slightly higher strength compared to WE43 and ZX10. ZX10 maintains superior residual strength over time. Pitting corrosion is mainly observed in Mg10Gd and WE43, with different degrees of residual strength. This study allows for a better understanding and prediction of critical areas of non-uniform corroded Mg alloys and provides information on the bearable stress concentration. Full article

Additive manufacturing by Selective Laser Melting (SLM) or, precisely, Laser Powder Bed Fusion (L-PBF), offers new opportunities for producing electrically functional metal components with tailored geometric designs and material properties. In this study, the electrical contact resistance and related properties of 3D-printed samples made from Al5086 aluminum alloy are tested. The benefits of Al5086 include flexibility without cracking, welding ability and exceptional resistance to corrosion in saltwater and industrial environments. This makes it an excellent candidate for power electric applications due to its good electrical conductivity and corrosion resistance. In this study, an analysis is performed to assess the impact of internal volumetric properties and surface parameters on general contact resistance performance. This analysis combines advanced testing procedures and parameter identification of the electric contact resistance model. This study investigates how these parameters affect contact resistance, which is a critical factor in the reliability of electrical devices. Electrical contact resistance was measured using a dedicated test setup that applied consistent pressure and maintained directional alignment. The results show that the printing direction of the samples slightly affects resistance values due to the continuity of current paths along the build direction, likely due to homogenous inter-layer boundaries and mechanical stress distribution. These findings suggest that both print orientation and internal structure must be considered when designing 3D-printed contact elements for electrical applications. Overall, this study demonstrates the feasibility of using L-PBF-fabricated aluminum components in electric applications where both electrical and structural performances are essential. Full article

Pipelines play a vital role in transporting oil, gas, water, and other critical resources across vast distances. However, they are often exposed to harsh environmental conditions, aging, corrosion, and mechanical stresses that can lead to structural degradation or failure. Structural health monitoring (SHM) offers a proactive solution for ensuring the integrity and safety of pipeline systems through continuous or periodic assessment using advanced sensing technologies and analytical methods. This paper presents the use of Lamb waves to find surface cracks in pipelines. Finite element software, ABAQUS/CAE 2017, is used to simulate intact and damaged pipes. The Time of Flight (ToF) method is applied with two techniques. The first is based on the difference between the received waves for damaged and intact pipelines, while the second is based on the difference between two sensor reads in damaged pipelines. The effectiveness of SHM systems in detecting anomalies and guiding maintenance decisions is evaluated. The results demonstrate the potential of SHM to enhance pipeline reliability, reduce downtime, and support condition-based maintenance strategies. This research contributes to the development of smarter, safer, and more efficient pipeline monitoring systems. Full article

This study delivers a comprehensive evaluation of tantalum-based coatings designed as protective surface layers for cardiovascular stents, focusing on their mechanical durability, corrosion resistance, and surface properties relevant to hemocompatibility. Coatings consisting of tantalum (Ta), tantalum oxide (Ta₂O₅), and a bilayer Ta/Ta₂O₅ system were deposited onto 316L stainless steel using plasma-assisted reactive magnetron sputtering. Structural characterization confirmed a nanocrystalline β-phase for Ta, while Ta₂O₅ exhibited an amorphous, dense, grain-boundary-free morphology that provided superior crack resistance together with enhanced corrosion protection. The bilayer configuration demonstrated the highest overall performance by combining the hardness and mechanical support of Ta with the chemical inertness and stability of Ta₂O₅. This architecture achieved the greatest hardness (861.5 HV), improved toughness proxies expressed as H/E = 0.08 and H³/E² = 0.06 GPa, and a favorable modulus gradient that effectively reduced interfacial stress and increased adhesion. Electrochemical testing in Hanks’ Body Fluid showed a dramatic 1000-fold reduction in corrosion current when compared with uncoated stainless steel, surpassing the performance of both individual monolayers. Assessments of surface properties further demonstrated that hydrophilic, oxide-rich surfaces limited protein adsorption and platelet activation, with Ta₂O₅ and Ta/Ta₂O₅ coatings performing strongly. Overall, these findings indicate that Ta/Ta₂O₅ bilayers provide a multifunctional surface solution for next-generation stents. Full article

2219 aluminum alloy is widely used in aerospace components because of its high specific strength, excellent fracture toughness, and resistance to stress corrosion cracking. Accurate characterization of its hot deformation behavior is important for the numerical simulation and process design of ring rolling. In this study, isothermal compression tests were carried out on a thermal–mechanical simulator at temperatures of 380–460 °C and strain rates of 0.01–10 s⁻¹ to investigate the hot deformation behavior of 2219 aluminum alloy. The effects of deformation temperature and strain rate on flow stress evolution were analyzed based on the experimental results. A strain-compensated Arrhenius-type constitutive model was developed to describe the flow stress behavior over a wide strain range. The material constants, including the stress exponent, stress level parameter, activation energy for hot deformation, and structure factor, were determined by regression analysis, and their strain dependence was expressed as polynomial functions of true strain. The model was evaluated by comparing predicted and experimental flow stress values, giving an average absolute error of 4.78%. The results indicate that the developed model can describe the combined effects of temperature, strain rate, and strain with good accuracy, and can be used for numerical simulation and process optimization in hot ring rolling. Full article

When a H₂S-containing gas kick occurs during drilling, the formation fluid containing hydrogen sulfide is mixed into the drilling fluid. Drilling fluid containing hydrogen sulfide is prone to causing hydrogen embrittlement when it comes into contact with the drill string during the upward return process. However, research on the risk and timing of hydrogen embrittlement in drill pipes remains limited. This study constructed a risk area and hydrogen embrittlement time analysis model. The risk area and time of hydrogen embrittlement in the drill pipe of the Jinyue 402 well in Tarim Oilfield were analyzed using the constructed model. The results indicate that the concentration of hydrogen sulfide in the Jinyue 402 well is in the area where the corrosion rate of steel increases rapidly, and the partial pressure of hydrogen sulfide is higher than the critical partial pressure at which corrosion cracking occurs. Taking into account the pH of the drilling fluid, fluid flow rate, hydrogen sulfide partial pressure, drill pipe tensile stress, hydrogen sulfide concentration, and gas partial pressure, the high-risk area for hydrogen sulfide corrosion damage in the Jinyue 402 well is 0–1680 m. The predicted highest risk point location and hydrogen embrittlement time are at a well length of 280 m and 21 h. Further predictions were made for the hydrogen embrittlement length and time of the Tazhong 83 and Zhonggu 503 wells in the Tarim Oilfield. The maximum prediction errors for the hydrogen embrittlement position and time of the drill pipe in the three wells were 4.8% and 5.2%, respectively. This indicates that the model can be applied to wells with different geological conditions and hydrogen sulfide concentrations. Full article

In this study, first-principles calculations were employed to systematically investigate the adsorption of Cl⁻ on Al₂Cu(110) surfaces, clean Al(111)/Al₂Cu(110) interfaces, and Fe/Si-doped interfaces, as well as the influence of strain on interfacial electronic structure and corrosion activity. When Cl⁻ is adsorbed on Al sites, the bonding between Cl and Al exhibits strong ionic characteristics with localized charge transfer, while adsorption on Cu sites is characterized by more delocalized, covalent interactions. This competition dictates the site-dependent stability of adsorption. Through geometric–electronic synergy, the interface functions as both a “Cl⁻ enrichment zone” and an “activity source,” significantly favoring Cl⁻ adsorption at high-activity anodic sites such as Al-hole and Al-bridge. Conversely, Cu-top sites maintain a high work function and an inert cathodic nature, facilitating the formation of efficient micro-galvanic couples across the interface. Moreover, Fe/Si doping further modulates the interfacial electronic landscape: Si serves as an effective strengthening element due to its low substitution energy and high stability, while Fe primarily forms a solid solution on the Al side, potentially introducing galvanic corrosion risks. Stress analysis indicates that tensile strain systematically enhances surface activity by lowering the work function, while compressive strain non-monotonically influences corrosion through a three-stage mechanism involving the “densification–cracking–plastic relaxation” of the passive film. These findings elucidate the atomistic origins of corrosion initiation at Cu–Al composite interfaces and provide a theoretical foundation for enhancing corrosion resistance through alloy design and strain engineering. Full article

The corrosion behavior of hot-press-formed (HPF) B-pillar components fabricated from Al–Si-coated boron steel was investigated with an emphasis on the forming-induced crack morphology. The specimens were extracted from the inner and outer surfaces of the top, flat, and radius regions. Microstructural characteristics and coating cracks were examined using optical microscopy, as well as field-emission scanning electron microscopy (FE-SEM) in combination with energy-dispersive spectroscopy (EDS), and corrosion behavior was evaluated using cyclic corrosion immersion and potentiodynamic polarization tests in a 3.5 wt.% NaCl aqueous solution. The Al–Si coating exhibited a multilayered structure composed of alternating Al- and Fe-rich layers. The crack morphology strongly depended on the local stress state: wide macrocracks were mainly formed on the outer surface of the radius region under tensile deformation, whereas the narrow microcracks predominated on the inner surface subjected to compressive deformation. Cyclic corrosion immersion tests showed that the corrosion propagated preferentially along the coating cracks and was more severe on the inner surfaces, where narrow microcracks promoted aggressive crevice corrosion owing to chloride ion accumulation and local acidification. By contrast, wider macrocracks on the outer surface mitigated crevice corrosion by allowing electrolyte exchange. Potentiodynamic polarization tests indicated similar corrosion rates for all regions; however, the outer radius region exhibited a relatively noble corrosion potential owing to oxide film formation on the locally exposed substrate areas. These results demonstrate that the crack morphology induced by curved forming is a key factor governing the corrosion behavior of HPF B-pillar components. Full article

Stress corrosion cracking (SCC) is a critical failure mechanism that arises from the synergistic interaction between tensile stress and corrosive environments, leading to sudden and often catastrophic failures in structural components across various industries, including aerospace, nuclear energy, oil and gas, and marine engineering. This review synthesizes current understanding of SCC mechanisms, including film rupture and anodic dissolution, hydrogen embrittlement, and adsorption-induced cleavage, and evaluates material susceptibility across steels, aluminum alloys, nickel-based alloys, titanium, and emerging high-entropy alloys. Environmental factors such as aqueous chemistry, temperature, pressure, pH, and dissolved gases are examined for their roles in SCC initiation and propagation. Advanced testing methodologies, including slow strain rate testing, bent-beam configurations, electrochemical monitoring, and high-resolution microscopy, are discussed for characterizing SCC behavior. Engineering mitigation strategies are presented, encompassing material selection, stress reduction, surface treatments, and environmental control. Case studies illustrate real-world SCC failures and inform best practices. Emerging trends highlight the potential of machine learning for predictive maintenance and the development of SCC-resistant materials through additive manufacturing and microstructural engineering. This comprehensive review provides mechanical engineers with actionable insights for designing, maintaining, and safeguarding components against SCC in demanding service environments. Full article

To enhance the protection of zirconium alloys during loss-of-coolant accident conditions, the water vapor corrosion resistance of Y³⁺-stabilized zirconia coatings fabricated by plasma electrolytic oxidation on zirconium alloy was remarkably improved in this study. The corrosion resistance mechanisms of the coating were disclosed by simulating water vapor reaction processes in cubic zirconia (c-ZrO₂) and tetragonal zirconia (t-ZrO₂). The results revealed that the mass fraction of c-ZrO₂ in the coatings was increased from 9% to 32% by adjusting the Y³⁺ concentration. The mass gain and corrosion rate of the enhanced coating were approximately 60% and 37% after 3600 s water vapor corrosion at 1000 °C separately compared to those of traditional zirconia coating. This enhancement is attributed to the slower reaction rates of c-ZrO₂ with water vapor than t-ZrO₂, which suppresses corrosion and reduces the formation of Zr(OH)₄. Thus, less cracks appeared in coatings with higher c-ZrO₂ fractions, as their corrosion layers contained fewer corrosion products that induced stress concentration, which, in turn, protects the subsurface coatings from further corrosion. This study provides a viable strategy for developing coatings to protect zirconium alloys against water vapor corrosion in nuclear energy applications. Full article

This study examines the electrochemical behavior and slow strain rate tensile (SSRT) properties of 67Si2CrNiAlMnMoCu steel featuring a multiphase nanobainitic microstructure consisting of bainitic ferrite (BF), retained austenite (RA), and martensite (M). Electrochemical measurements reveal that both the corrosion tendency and dissolution rate decrease with extended austempering time, with the sample austempered at 220 °C for 21 h showing the lowest corrosion susceptibility. SSRT results indicate that specimens with a nearly fully bainitic microstructure exhibit increased strength sensitivity to stress corrosion. Notably, the specimen austempered at 240 °C for 9 h demonstrates excellent corrosion resistance while retaining favorable overall mechanical properties, exhibiting a tensile strength-based stress corrosion cracking sensitivity coefficient as low as 4.1%. Full article

Axial cracking in threaded joints of rotary steerable tools is a critical but under-investigated failure mode that can severely disrupt shale gas drilling operations. Understanding its root cause is essential for prevention. This study aims to determine the cause of an axial cracking failure in an S35150 austenitic stainless steel threaded joint from a field operation. A comprehensive analysis was conducted, integrating physicochemical characterization of the failed joint. The stress corrosion behavior of the threaded joint in a simulated corrosive environment was evaluated via four-point bend (FPB) and double cantilever beam (DCB) stress corrosion tests. The results showed that the material exhibited high susceptibility factors: a hardness of 38.5 HRC, a yield-to-tensile ratio near 1, and a P content exceeding the standard. Fracture surface analysis revealed an intergranular morphology with substantial chlorine (0.78%) and sulfur (0.93%) contents, indicative of stress corrosion cracking (SCC). The laboratory tests results demonstrated that the threaded joint had poor crack resistance: the fracture toughness value of the specimen measured by the DCB test was 24.14 MPa·m^0.5, and all specimens fractured during the FPB. Full article

AISI 904L stainless steel (904L SS) is a promising material for nuclear power plant primary circuits due to its superior corrosion resistance, but its corrosion behavior under simulated high-temperature and high-pressure water environments with different microstructures remains poorly understood. In order to systematically investigate and clarify the electrochemical behavior and corrosion behavior under stress of 904L SS with three different microstructures (as-received, sensitized, and solution-treated) in a simulated primary circuit water environment of a nuclear power plant, experiments are conducted using dynamic polarization, electrochemical impedance spectroscopy (EIS), and U-bend immersion methods. The results show that temperature has a significant effect on corrosion resistance. As the temperature increases, the impedance of all microstructures decreases significantly, the passivation zone narrows, and the corrosion current density increases. Under high-temperature and high-pressure conditions, the corrosion resistance of the sensitized samples is the worst, while the samples treated with solution have the best overall performance. That is, microstructural optimization through solution treatment can effectively enhance the high-temperature and high-stress corrosion resistance of 904LSS in the primary circuit water environment. Full article

This study investigates the influence of vanadium–nitrogen (V-N) microalloying design on the microstructure and mechanical properties of 700 MPa grade ultra-high-strength steel bars. Through the control of the V/N ratio and cooling rate, a yield strength exceeding 700 MPa was achieved in a steel with a pearlite–ferrite matrix. Microstructural characterization via optical microscopy (OM) and scanning electron microscopy (SEM) revealed that a V/N ratio of approximately 1:10 combined with a rolling cooling rate of 1–3 °C/s resulted in the steel bar exhibiting a yield strength of 774.21 MPa and a tensile strength of 971.13 MPa. The primary microstructure of the steel consisted of ferrite and pearlite. The steel featured fine grains and favorable crystallographic orientations, which contributed to its high yield strength and good ductility. Transmission electron microscopy (TEM) analysis indicated that under hot-rolling conditions, vanadium precipitated predominantly as nano-scale V(C,N) particles. These precipitates were distributed in both the pearlite and ferrite phases, thereby enhancing the tensile and yield strength. Furthermore, the steel with an optimal nitrogen content (0.0166 wt.%) and the finest grain structure (average grain size ≈ 2.618 μm) showed the lowest stress corrosion cracking (SCC) susceptibility, characterized by an elongation loss rate (I_δ) of 12.51%, demonstrating excellent SCC resistance. Full article