Search Results (420)

This study investigates the mechanical, tribological, and electrochemical behaviour of a novel precipitation-hardenable martensitic alloy produced by selective laser melting (SLM). The alloy was specifically engineered with an optimised composition, free from cobalt and molybdenum, and featuring reduced nickel content (7 wt.%) and 8 wt.% chromium. It has been developed as a cost-effective and sustainable alternative to conventional maraging steels, while maintaining high mechanical strength and a refined microstructure tailored to the steep thermal gradients inherent to the SLM process. Several ageing heat treatments were assessed to evaluate their influence on microstructure, hardness, tensile strength, retained austenite content, dislocation density, as well as wear behaviour (pin-on-disc test) and corrosion resistance (polarisation curves in 3.5%NaCl). The results indicate that ageing at 540 °C for 2 h offers an optimal combination of hardness (550–560 HV), tensile strength (~1700 MPa), microstructural stability, and wear resistance, with a 90% improvement compared to the as-built condition. In contrast, ageing at 600 °C for 1 h enhances ductility and corrosion resistance (Rp = 462.2 kΩ; Ecorr = –111.8 mV), at the expense of a higher fraction of reverted austenite (~34%) and reduced hardness (450 HV). This study demonstrates that the mechanical, surface, and electrochemical performance of this novel SLM-produced alloy can be effectively tailored through controlled thermal treatments, offering promising opportunities for demanding applications requiring a customised balance of strength, durability, and corrosion behaviour. Full article

A (NiCoCr)_99.25C_0.75 medium entropy alloy (MEA) was developed via laser powder bed fusion (LPBF) using pre-alloyed powder feedstock containing 0.75 at%C, followed by a precipitation heat treatment. The as-built alloy exhibited high density (>99.9%), columnar grains, fine substructures, and strong <111> texture. Heat treatment at 700 °C for 1 h promoted the precipitation of Cr-rich carbides (Cr₂₃C₆) along grain and substructure boundaries, which stabilized the microstructure through Zener pinning and the consumption of carbon from the matrix. The heat-treated alloy achieved excellent cryogenic tensile properties at 77 K, with a yield strength of 1230 MPa and an ultimate tensile strength of 1.6 GPa. Compared to previously reported LPBF-built NiCoCr-based MEAs, this alloy exhibited superior strength at both room and cryogenic temperatures, indicating its potential for structural applications in extreme environments. Deformation mechanisms at cryogenic temperature revealed abundant deformation twinning, stacking faults, and strong dislocation–precipitate interactions. These features contributed to dislocation locking, resulting in a work hardening rate higher than that observed at room temperature. This study demonstrates that carbon addition and heat treatment can effectively tune the stacking fault energy and stabilize substructures, leading to enhanced cryogenic mechanical performance of LPBF-built NiCoCr MEAs. Full article

A Cu-11.85Al-3.2Mn-0.1Ti shape memory alloy (SMA) with excellent superelasticity and shape memory effect was successfully fabricated via selective laser melting (SLM). Increasing the energy density enhanced grain refinement, achieving a 90% refinement rate compared to cast alloy, with an average width of ~0.15 µm. Refined martensite lowered transformation temperatures and increased thermal hysteresis. Nanoscale Cu₂TiAl phases precipitated densely within the matrix, forming a dual strengthening network combining precipitation hardening and dislocation hardening. This mechanism yielded a room-temperature tensile strength of 829.07 MPa, with 6.38% fracture strain. At 200 °C, strength increased to 883.68 MPa, with 12.26% strain. The maximum tensile strength represents a nearly 30% improvement on existing laser-melted quaternary Cu-based SMAs. Full article

Enhancing damage tolerance and wear resistance in Al–Si-based alloys under thermomechanical stress remains a key challenge in lightweight structural applications. This study investigates the microstructural and tribomechanical behavior of hypoeutectic Al–Si–(Cu)–Mg alloys with varying Cu:Mg ratios (3:1 vs. 1:3) under a T6 heat treatment. Alloys A and B, with identical Si contents but differing Cu and Mg levels, were subjected to multiscale microstructural characterization and mechanical and wear testing at 25 °C, 150 °C, and 250 °C. Alloy A (Cu-rich) exhibited refined α-Al(FeMn)Si phases and homogeneously dissolved Cu in the Al matrix, promoting lattice contraction and dislocation pinning. In contrast, Alloy B (Mg-rich) retained coarse Mg₂Si and residual β-AlFeSi phases, which induced local stress concentrations and thermal instability. Under tribological testing, Alloy A showed slightly higher friction coefficients (0.38–0.43) but up to 26.4% lower wear rates across all temperatures. At 250 °C, Alloy B exhibited a 25.2% increase in the wear rate, accompanied by surface degradation such as delamination and spalling due to β-AlFeSi fragmentation and matrix softening. These results confirm that the Cu:Mg ratio critically influences the dominant hardening mechanism—the solid solution vs. precipitation—and determines the high-temperature performance. Alloy A maintained up to 14.1% higher tensile strength and 22.3% higher hardness, exhibiting greater shear resistance and interfacial stability. This work provides a compositionally guided framework for designing thermally durable Al–Si-based alloys with improved wear resistance under elevated temperature conditions. Full article

This study systematically investigates the effects of various direct aging (DA) treatments on the residual stress, mechanical properties, and microstructure of laser powder bed fusion (LPBF) fabricated TiB₂/AlSi7Mg composites. The results demonstrate that during aging at 120 °C, the hardness exhibits a typical age-hardening behavior. The residual stress relief rate increased to 45.1% after 336 h, although the stress relief rate significantly diminished over time. Increasing the aging temperature effectively enhanced residual stress removal efficiency, with reductions of approximately 40% and 62% observed after aging at 150 °C for 4 h and 190 °C for 8 h, respectively. Regarding mechanical properties, aging at 150 °C for 4 h resulted in an optimal synergy in yield strength (YS = 358 MPa) and elongation (EL = 9.2%), followed by aging at 190 °C for 8 h with YS of 320 MPa and EL of 7.0%. Microstructural analysis revealed that low temperature aging promotes the formation of nanoscale Si precipitates, which enhance strength through the Orowan mechanism. In contrast, high temperature annealing disrupts the metastable cellular structure, leading to the loss of strengthening effects. This work provides fundamental insights for effective residual stress management and performance optimization of LPBF Al–Si–Mg alloys. Full article

Body-centered cubic (BCC) refractory high-entropy alloys (RHEAs) demonstrate significant potential as nuclear structural materials due to their exceptional mechanical properties and radiation tolerance. While Zr-containing RHEAs often develop multiphase structures through Zr-rich phase precipitation to enhance high-temperature mechanical performance, their irradiation response mechanisms remain poorly understood. This study investigated the microstructure evolution and radiation damage behavior in equiatomic MoNbTiVZr RHEA under Au-ion irradiation at fluences of 2 × 10¹⁵, 4 × 10¹⁵, and 1 × 10¹⁶ ions/cm². Microstructural characterization revealed that the annealed alloy primarily consisted of near-equiatomic BCC1 phase, Zr-rich BCC2 phase, (Mo,V)Zr Laves phase, and ordered Zr₂C phase. Post-irradiation analysis showed distinct defect evolution patterns: the BCC1 phase developed fine dislocation loops, while the Zr-rich BCC2 and Zr₂C phases exhibited dislocation clusters and dense dislocation networks, respectively. BCC1 phase exhibited the most pronounced irradiation hardening corresponding to its fine, dispersed dislocation loop characteristics. Phase separation induced by Zr precipitation reduced chemical complexity, accelerating irradiation defect evolution. These findings demonstrated that Zr-rich phase precipitation detrimentally impacted the radiation resistance of BCC-structured RHEAs, suggesting that single-phase stability should be prioritized in nuclear material design. Full article

Aluminum, boron, and titanium microalloyed into high-strength low-alloy boron steel exhibit a complex interplay, competing for nitrogen, with titanium demonstrating the highest affinity, followed by boron and aluminum. This competition affects the formation and distribution of nitrides, impacting the microstructure and mechanical properties of the steel. Titanium protects boron from forming BN and facilitates the nucleation of acicular ferrite, enhancing toughness. The segregation of boron to grain boundaries, rather than its precipitation as boron nitride, promotes the formation of martensite and thus the through-hardenability. Aluminum nitride is critical in controlling grain size through a pronounced pinning effect. In this study, we employ energy- and wavelength-dispersive X-ray spectroscopy and computer-aided particle analysis to analyze the phase content of 12 high-purity vacuum induction-melted samples. The primary objective of this study is to correctly describe the microstructural evolution in the Fe-Al-B-Ti-C-N system using the Calphad approach, with special emphasis on correctly predicting the dissolution temperatures of nitrides. A multicomponent database is constructed through the incorporation of available binary and ternary descriptions, employing the Calphad approach. The experimental findings regarding the solvus temperature of the involved nitrides are employed to validate the accuracy of the thermodynamic database. The findings offer a comprehensive understanding of the relative phase stabilities and the associated interplay among the involved elements Al, B, and Ti in the Fe-rich corner of the system. The type and size distribution of the stable nitrides in microalloyed steel have been demonstrated to exert a substantial influence on the properties of the material, thereby rendering accurate predictions of phase stabilities of considerable relevance. Full article

It is essential to develop the optimal hot-working process of the (CoCrNi)₉₄Al₃Ti₃ alloy, a recently developed precipitation-hardened medium-entropy alloy with promising mechanical properties, for its industrial application. In this study, the hot workability of the as-forged (CoCrNi)₉₄Al₃Ti₃ alloy was investigated over a temperature range of 1000 °C to 1150 °C and a strain rate ranging from 0.001 to 1 s⁻¹ using a Gleeble-1500D thermal simulation machine of Dynamic Systems Inc., USA. As a result, the constitutive relationship was established, and the hot deformation activation energy was calculated as 433.2 kJ/mol, suggesting its well-defined plastic flow behavior under low-energy-input conditions. Hot-processing maps were constructed to identify the stable hot-working regions. Microstructure analysis revealed that the hot-forged (CoCrNi)₉₄Al₃Ti₃ alloy exhibited continuous dynamic recrystallization (CDRX) behavior under optimal hot-working conditions. Considering the hot-processing maps and DRX characteristics, the optimal hot-working window of hot-forged (CoCrNi)₉₄Al₃Ti₃ alloy was identified as 1100 °C with a strain rate of 0.1 s⁻¹. This work offers valuable guidance for developing high-efficiency forming processes for (CoCrNi)₉₄Al₃Ti₃ medium-entropy alloy. Full article

This study systematically investigates the influence of different heat treatment processes on the microstructural evolution and mechanical properties of Cu-15Ni-3Al alloys, with particular emphasis on the synergistic strengthening mechanisms of spinodal decomposition and precipitation hardening. Two distinct aging routes—solution aging and direct aging—were designed to facilitate a comparative assessment of microstructural characteristics and their correlation with mechanical performance. Comprehensive characterization was conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and room-temperature tensile testing to elucidate the structure–property relationships. The results reveal that direct aging promotes the formation of fine, coherent L1₂-type Ni₃Al precipitates and the evolution of Ni-enriched regions initially generated through spinodal decomposition into stable Ni₃Al precipitates. These microstructural features act as effective barriers to dislocation motion, thereby significantly enhancing both strength and ductility. The findings provide valuable insights into optimizing heat treatment strategies to improve the performance of Cu-Ni-Al alloys. Full article

This review provides an overview of recent advancements in Cu-Ni-Co-Si alloys, focusing on their processing methods, microstructures, and properties. Due to their non-toxic composition, enhanced mechanical properties, and excellent electrical conductivity, Cu-Ni-Co-Si alloys have emerged as a promising alternative to traditional Cu-Be alloys in the electrical and electronics industry. This review discusses various synthesis techniques, including casting, vacuum induction melting, and additive manufacturing, and evaluates their effects on the formed microstructures. In addition, it explores the influence of different elements and thermal treatments on the alloys’ microstructures and properties, discussing strategies to enhance the properties of Cu-Ni-Co-Si alloys. Key strengthening mechanisms—including precipitation hardening, grain boundary strengthening, and solid solution hardening—are examined in detail, with particular emphasis on their synergistic effects in optimizing alloy performance. Furthermore, future research directions are highlighted, focusing on the optimization of alloying element concentrations and heat treatment protocols to achieve an enhanced balance between strength and electrical conductivity. These improvements are critical for meeting the demanding requirements of advanced applications in electronics and high-reliability components. Full article

This study focuses on cold deformation and age effects on the microhardness and electric conductivity of the Cu-4Ti (wt.%) alloys. The samples were solution treated at 900 °C, quenched in water, and aged at 450–600 °C for 1–120 min. Fifty percent cold rolling was performed before aging to analyze the impact on their microstructure and properties. Hardness and electric conductivity were examined by the Vickers microhardness and Förster testing. Hardness increased significantly while electric conductivity was maintained. The optimal hardness of 298 HV appeared following 50% cold rolling and aging for 120 min at 450 °C, and an electric conductivity of 9.4 MS/m was achieved after 120 min at 600 °C in cold-rolled materials. The deformed and solution-treated materials reached 244 HV after 120 min at 500 °C, and electric conductivity reached 7.7 MS/m. Polynomial models of regression were used to analyze the impact of aging parameters on properties. Process parameters were properly optimized by applying metaheuristic algorithms. These contributions ensure a better understanding of the relationship between the microstructure and properties in Cu-Ti alloys, as well as their application in aircraft and electronics. Full article

The Cr₂O₃ film on the outer surface of traditional cracking furnace tubes is prone to spalling, which shortens the tube life. Fe-Ni-Cr-based austenitic stainless steel (AFA alloy) with added Al has attracted attention because it can form a more stable Al₂O₃ film on the surface. However, the alloy’s mechanical performance and the stability and oxidation resistance of the oxide film need to be improved simultaneously. This investigation examined silicon concentration variations (0–1.5 wt.%) on AFA alloy’s ambient-temperature tensile performance and oxidation response under reduced oxygen partial pressures (10⁻¹⁸–10⁻¹⁶ bar). The findings demonstrate that the alloy was composed of the FCC, B2-NiAl, and M₂₃C₆ phases. With Si addition, the B2-NiAl phase volume fraction increased. Mechanical testing demonstrated progressive elevation in tensile strength and hardness coupled with reduced elongation, attributable to combined solid-solution hardening and B2-NiAl precipitation strengthening. At low oxygen pressure, a continuous multi-layer oxide film developed on the alloy’s surface: the outermost layer was composed of a continuous Cr₂O₃ layer, with a fraction of MnCr₂O₄ spinel phase enriched on the outer surface. The middle layer was SiO₂, which evolved from a particulate to a continuous layer with increasing Si content. The innermost layer was composed of Al₂O₃. Accelerated manganese diffusion through Cr₂O₃ facilitated MnCr₂O₄ spinel layer formation. Full article

In this work, the effects of the Cu/Li ratio on the mechanical properties and corrosion behavior of Sc-containing Al-Cu-Li alloys were systematically investigated by utilizing age-hardening behavior, tensile property, corrosion behavior, and electrochemical behavior, complemented by microstructural characterization through EBSD and TEM. The results show that the peak aging strength of the alloys remained relatively consistent but slightly decreased with the decrease in Cu/Li ratio, and the yield strengths were 585 MPa, 578 MPa, and 573 MPa, respectively. The changes in the Cu/Li ratio caused different matching patterns of precipitates in the peak aging alloys. The cumulative precipitation strengthening by T₁, θ′, δ′, and S′ phases are equal within the alloys with different Cu/Li ratios. However, the strength contribution of the T₁ phase decreases from 81% to 66% with the decrease in the Cu/Li ratio. Concurrently, the precipitates of LAGBs gradually increase in number and are continuously distributed, and the precipitates of HAGBs become larger in size with lower Cu content as the Cu/Li ratio decreases, all of which leads to a weakening of the intergranular corrosion (IGC) resistance within the low Cu/Li ratio alloy. Full article

The influence of Cu content (3.10, 3.50, and 3.80 wt.%) on the precipitation behavior and mechanical properties of Al-Cu-Li alloys under two aging conditions (direct aging at 175 °C vs. 3.5% pre-stretching followed by aging at 155 °C) was systematically investigated. The alloys were characterized using hardness testing, tensile property evaluation, and transmission electron microscopy (TEM) to correlate microstructural evolution with performance. The results revealed that increased Cu content accelerated early-stage hardening kinetics and elevated peak hardness and strength. Aging at 175 °C/36 h produced T₁ phase-dominated microstructures with θ′ phases. With the increase of Cu content, the enhancement effect on the precipitation of T₁ and θ′ phases becomes more pronounced, gradually overshadowing the initial promotion effect on precipitate growth. Pre-deformation prior to 155 °C/36 h aging induced significant T₁ phase refinement and proliferation, with increasing Cu content continuously reducing T₁ phase sizes while moderately enlarging θ′ precipitates. Precipitation-strengthening analysis revealed a transition in T₁ strengthening from bypass to shearing dominance under 155 °C/36 h aging after pre-deformation, enhanced by Cu-promoted T₁ refinement, which collectively drove superior strength in high-Cu alloys. These findings provide valuable insights for the composition design and mechanical property optimization of Al-Cu-Li alloys. Full article

To enhance the mechanical properties of 6063-T4 aluminum alloy tubes, surface mechanical grinding treatment was conducted under graphene-assisted lubrication. The effects of rotational speed and cooling conditions on the mechanical properties of aluminum alloy tubes under biaxial stress were systematically explored. It was found that increasing the rotational speed and cooling rate facilitates the formation of finer lamellar grains, higher-density nano-precipitates, and a reduced dislocation density on the tube surface. These microstructural characteristics significantly contribute to an increased yield strength and sustained strain hardening capacity during bulging deformation. This study proposes an innovative approach for improving the strength and toughness of light alloy components during integral forming, providing meaningful insights for future engineering applications. Full article