Microstructure and Properties in Metals and Alloys, 4th Edition

Oxygen-free copper wires are widely required in advanced electronic and electrical systems. However, the relationship between deformation-induced microstructure evolution and property variation during severe cold drawing is not fully understood. In this study, oxygen-free copper rods with a diameter of φ20 mm were fabricated by upward continuous casting, followed by multi-pass cold drawing with deformation degrees up to 99.75%. The microstructure evolution, texture transformation, and property changes during drawing and annealing were systematically investigated. It found that increasing drawing deformation progressively elongated, fragmented, and refined the grains, reducing the average grain size from 339.18 μm to 2.12 μm. Dense dislocation cells, substructures, and nanoscale twins were generated during severe deformation, while the texture gradually evolved from random orientations to preferred <111> and <100> textures. After annealing, fine recrystallized equiaxed grains with abundant annealing twins formed together with recrystallization <101> texture. At 99.75% deformation, the tensile strength reached 486 MPa, with an electrical conductivity of 96.7% IACS (International Annealed Copper Standard). After annealing, the electrical conductivity recovered to 101.5% IACS, while the tensile strength decreased to 187 MPa. This work establishes the relationship between severe deformation microstructure evolution and property response in oxygen-free copper, providing guidance for the fabrication of high-strength and high-conductivity copper conductors. Full article

Powder Bed Fusion–Laser Based (PBF-LB) represents the most-used metal Additive Manufacturing technology thanks to its capability of producing high-complexity geometries. The need for industries to define a qualification framework of additive components drew attention to post-processing approaches that can be applied to mitigate or reduce inherent defects. Among these post-processing approaches, Hot Isostatic Pressing (HIP) is recognized as one of the most effective techniques to address these challenges. Among materials employed with PBF-LB, especially in the aerospace sector, 316L stainless steel and the AlSi10Mg aluminum alloy are the most investigated, while among innovative copper alloys, there is GRCop42. Thus, the aim of this paper is to investigate the effects of low-temperature HIP on the tensile properties and microstructure of these materials. For this reason, tensile tests, metallographic analysis and X-ray computer tomography were conducted. The results highlight the influence of low-temperature HIP treatment with respect to the as-built condition. In particular, the Yield and Ultimate Tensile Strength for 316L and GRCop42 clearly improved, while for AlSi10Mg a relevant reduction was detected. However, an unexpected result was the reduction in the GRCop42 elongation that fell from ~10% down to ~2.5%, even though the porosity of the material was reduced to close to zero. Full article

The TC11 α + β dual-phase titanium alloy exhibits limited room-temperature ductility (3.3 × 10⁻⁴ s⁻¹: elongation 13.8%) but achieves significant superplasticity at 900 °C (3.3 × 10⁻⁴ s⁻¹: elongation 314%), which correlates strongly with the mechanical response of α/β interfaces. These interfaces, which often crack at room temperature, undergo extensive sliding while preserving structural integrity during superplastic deformation. Combining microstructural analysis with first principles calculations, this study reveals how the stability of the α/β interface is dominated by the redistribution of alloying elements, thereby leading to distinct mechanical behaviors. Energy-dispersive X-ray spectroscopy results and calculated solution energies demonstrate that Mo preferentially dissolves in the β phase, whereas Al exhibits comparable solubility in both phases with a slight preference for the α phase. During high-temperature deformation, the α→β transformation drives Mo redistribution away from the interface toward newly formed β phases. This redistribution of Mo lowers the interfacial energy, strengthens the interface, suppresses stress-induced cracking, and ensures macroscopic continuity. Our study provides a theoretical perspective for Ti alloy design through interfacial engineering. Full article

Dynamic recrystallization processes are known to significantly affect both the mechanical properties and the microstructure of materials. In this paper, we investigate the influence of discontinuous dynamic recrystallization (dDRX) during deformation at high strain rates (from 10⁴ to 10⁵ s⁻¹) and elevated temperatures in pure aluminum and copper (in the range of 700–800 K for aluminum and 800–1100 K for copper). For this purpose, we propose a theoretical model in which the material is described within the framework of continuum mechanics, plastic deformations are modeled using a dislocation plasticity approach, the equation of state is represented by a neural network, and the microstructure evolution is simulated using the cellular automata method. The model is applied to uniaxial compression and tension of copper and aluminum polycrystals with an initial average grain size of 14 μm. It is shown that grain refinement occurs in all systems. The average grain size decreases from 14 μm to 4–5 μm. The distribution of plastic and total strains in the polycrystals is presented. In all considered systems, deformation localization is observed, and the localization pattern changes due to the nucleation of new grains and grain boundary surfaces during dynamic recrystallization. Full article

This study resolves the apparent breakdown of the Korringa relation in disordered liquid metals by investigating Ga-based alloys (EGaIn and Galinstan). By integrating temperature-dependent Knight shifts (K) with longitudinal (T₁) and transverse (T₂) relaxation measurements, we demonstrate that deviations from classical behavior arise from neglecting transverse spin dephasing induced by structural and electronic disorder. While solid-state alloys follow the conventional Korringa law, the liquid phase exhibits significant discrepancies between T₁ and T₂ due to enhanced electron scattering and fluctuating hyperfine fields. By explicitly incorporating T₂ into a modified framework, the proportionality between the Knight shift and nuclear relaxation is quantitatively restored. This establishes transverse relaxation as a critical parameter for describing nuclear spin dynamics in complex liquid metals, reinforcing NMR as a powerful local probe for optimizing next-generation liquid metal technologies. Full article

Cold-mercury gilding uses mercury as an adhesive to bond gold foil onto the surface of copper and silver artifacts. This technique and mercury gilding (fire gilding) both belong to the Au-Hg system and are closely related in technology. Clarifying the technical differences between them is of great significance for revealing the developmental sequence of ancient gilding technologies. On the basis of reconstructing traditional fire gilding, simulated cold-mercury-gilded samples were successfully prepared using experimental archeological methods, and multi-scale characterization was performed using SEM-EDS, XRD, and XPS. The results show that the surface of cold-mercury-gilded samples displays a micromorphology of folded and overlapped gold foil accompanied by locally dense particle aggregation. The cross-section of the gold layer exhibits a multilayer stacked structure, in which mercury is enriched at the gold layer/substrate interface and forms an AuHgCu/Ag diffusion layer. Room-temperature-stable Au-Hg and Ag-Hg phases such as Au₂Hg and AgHg are present in the gold layer, reflecting complex phase transformation behavior of the Au-Hg/Ag-Hg system at room temperature. During cold-mercury gilding, liquid mercury first adheres to the gold foil, and then interdiffusion and phase reactions occur between mercury, gold, and copper/silver atoms at room temperature. Intermetallic compounds and diffusion layers formed at the interface achieve firm bonding between the gold layer and the substrate. Both cold-mercury gilding and mercury gilding achieve metallurgical bonding through atomic interdiffusion. However, affected by differences in the initial state of mercury and operating temperature, the phase transformation and atomic diffusion behaviors of the system differ significantly, which are ultimately reflected in the cross-sectional structure of the gold layer, the composition of the interfacial diffusion layer, and the types of phases. Therefore, mercury-gilded artifacts show superior gold layer durability and bonding strength with the substrate compared with cold-mercury-gilded artifacts. Both techniques pioneered the application of mercury in metallic gilding and represent important innovations in ancient surface decoration technology. Full article

Conventional casting of 5N5 high-purity aluminum often results in coarse grains, microstructural inhomogeneity, and a low equiaxed grain area fraction. Vacuum casting in a graphite mold was integrated with multidirectional mechanical vibration to refine and homogenize the solidification microstructure. A three-factor, three-level Box–Behnken design combined with response surface methodology was employed to optimize pouring temperature (A), mold temperature (B), and vibration frequency (C), with the average grain size (Y₁) minimized and the average shape factor (Y₂) and equiaxed grain area fraction (Y₃) maximized. Analysis of variance indicated statistically significant quadratic models with a non-significant lack of fit. The predicted optimum (A ≈ 714 °C, B ≈ 363 °C, C ≈ 37 Hz) was validated experimentally, producing a refined and highly equiaxed structure (Y₁ ≈ 0.85 ± 0.02 mm, Y₂ ≈ 0.84 ± 0.04, Y₃ ≈ 88.6 ± 2.11%), consistent with model predictions. Multidirectional vibration strengthens melt convection and interfacial shear, which is considered to promote grain multiplication and increase the number of effective nuclei, thereby accelerating the columnar-to-equiaxed transition and improving microstructural uniformity. Full article

For the failure issue of the weak part of the safety end of the nuclear power pressure vessel connection, the J-integral method was used to test the fracture toughness of the weak part at the bottom of the dissimilar metal welded joints (DMWJs) of SA508-III and 316L in the temperature range of 25 °C to 320 °C, and the mechanism of temperature-induced crack instability and propagation was studied. The research results indicate that at all test temperatures, the position of the weld near the 316L steel is the failure site of the welded joint. The fracture toughness of the joint decreases with increasing temperature, with a maximum decrease of 42.0%. Analysis shows that as the temperature increases, the dislocation density decreases, the tensile strength decreases, and the yield strength ratio decreases, making it easier for secondary cracks to initiate near the crack tip, thereby accelerating the unstable propagation of cracks. At the same time, as the temperature increases, the number of twin crystals that can promote crack turning and prolong the crack propagation path decreases, the energy absorbed before fracture decreases, and the fracture toughness value decreases accordingly, further accelerating the unstable propagation of cracks. Full article

AISI 1045 steel often undergoes premature failure under combined corrosive-wear conditions due to its insufficient surface durability. To address this, a hot-dip aluminum (HDA) coating was deposited on the steel substrate. The microstructure, corrosion behavior, and tribological properties of the coating were systematically characterized using scanning electron microscopy (SEM), electrochemical techniques, and tribometry. The results reveal that the coating exhibits a continuous triple-layer structure, consisting of the steel substrate, an intermediate Fe-Al intermetallic compound layer, and an outer aluminum-rich layer. In a 3.5 wt.% NaCl solution, the coating formed a protective Al₂O₃ film, demonstrating clear passivation behavior. It significantly enhanced the substrate’s performance, achieving an approximately 90% reduction in wear rate and a substantial increase in charge transfer resistance. The coated sample showed a lower friction coefficient (0.24) compared to the bare substrate (0.34). Herein, this work demonstrates that a straightforward and industrially viable hot-dip aluminizing process can effectively improve the corrosion and wear resistance of medium-carbon steel. The findings provide a practical surface-hardening strategy for such steels operating in aggressive environments. Full article

Structural applications that use High-Strength Low-Alloy (HSLA) steels require detailed microstructural analysis to manufacture welded components that combine strength and weldability. The balance of these properties depends on both the chemical composition and the welding parameters. Moreover, in multi-pass welds, thermal cycling results in a complex Heat-Affected Zone (HAZ), characterized by sub-regions with a multitude of microstructural constituents, including brittle phases. This study investigates the influence of Vanadium addition on the microstructure and performance of the HAZ. Multi-pass welded joints were manufactured on 15 mm thick S355 steels with different Vanadium contents using a robotic GMAW process. A steel variant containing both Vanadium and Niobium was also considered, and the results were compared to those of standard S355 steel. Moving through the different sub-regions of the welded joints, the results show a heterogeneous microstructure characterized by ferrite, bainite and martensite/austenite (M/A) islands. The presence of Vanadium reduces carbon solubility during the phase transformations involved in the welding process. This results in the formation of very fine (average size 11 ± 4 nm) and dispersed precipitates, as well as a lower percentage of the brittle M/A phase, in the variant with a high Vanadium content (0.1 wt.%), compared to the standard S355 steel. Despite the presence of the brittle phase, the micro-alloyed variants exhibit strengthening without loss of ductility. The combined presence of both hard and soft phases in the HAZ provides stress-damping behavior, which, together with the very fine precipitates, promises improved resistance to crack propagation under different loading conditions. Full article