Cold spray is a solid deposition technology that utilises supersonic airflow to accelerate solid powder particles, facilitating the coating or fabrication of bulk materials through plastic deformation from high-speed impacts. During the cold spraying process, materials remain in a solid state, thus avoiding problems such as oxidation, grain growth, and phase transformation that can occur with high temperatures in thermal spraying. This makes cold spray particularly suitable for temperature-sensitive materials such as aluminium, copper, titanium, and other metals. In addition, this method can effectively deposit materials and coatings that are challenging to handle with traditional techniques including nickel-based high-temperature alloys and novel high-entropy alloys. Despite its many advantages, including its use with a wide range of materials for repairing and coating fabrication and its application to additive manufacturing, cold spray faces challenges such as low coating density, inhomogeneous microstructures, and weak adhesive coating strength. However, the microstructure and properties of coatings and materials can be effectively enhanced through the pretreatment of powders and/or post-treatment of the coatings and materials. This leads to the high-quality preparation and performance of coatings or materials. Under this context, this article provides a comprehensive review of the types, characteristics, and research advancements in post-treatment technologies for cold spraying. It covers various documented post-treatment methods, including heat treatment, laser remelting, induction remelting, hot isostatic pressing, hot rolling, friction stir, and electric pulse, applied to cold-sprayed coatings or materials, which encompass pure metals and their alloys, stainless steel, high-entropy alloys, and composite materials. Specifically, the article aims to summarize and analyze the advantages, characteristics, and existing challenges of various post-treatment technologies, while also exploring future research directions in this field.

Titanium alloys are extensively used in deep-sea exploration and resource-development equipment. The harsh environment of the deep sea hinders the performance of titanium alloys. Although titanium alloys exhibit outstanding corrosion resistance, they are susceptible to stress corrosion. This study conducted a detailed analysis of the key factors influencing titanium alloys in deep-sea environments, such as hydrostatic pressure, temperature, salinity, and trace substances. The effects of mechanical stresses such as tensile, residual, and alternating stresses on the stress corrosion of titanium alloys were also analyzed. Consequently, the influence of the compositional design and microstructure of titanium alloys on their susceptibility and sensitivity to stress corrosion were discussed. This study highlighted significant gaps, particularly in understanding the effect of microstructure on stress corrosion, stress corrosion mechanisms in titanium-welded joints, synergistic effects of multiple deep-sea environmental factors, and the effect of complex stress conditions. Current studies primarily focused on material-level analysis rather than structural-level assessments. Existing corrosion protection technologies for deep-sea applications, particularly coating technologies for such environments, remain underdeveloped. To address these limitations, this study proposed prospective research areas, including the synergistic mechanism involving multiple environmental factors, the synergistic effect between creep and stress corrosion, the effect of microstructure and residual stress in welded joints, the development of innovative protection technologies, and simulations of multi-axis stress conditions and their effect on stress corrosion.

The tundish is the final metallurgical reactor through which molten steel flows, and it significantly affects the quality of steel products. With the increasing demand for high-purity steel, the role of tundish metallurgy has attracted greater attention. This study systemically examines the causes of reoxidation in molten steel, the effects of air absorption during nonsteady-state teeming, tundish cover flux interactions, and refractory materials during the steady-state teeming process. These factors were analyzed for their influence on the chemical and inclusion composition of different steel grades. In addition, measures to mitigate the reoxidation of molten steel in tundish were analyzed. The results demonstrate that the three factors causing the reoxidation of molten steel occur simultaneously. However, in the nonsteady-state teeming stage, air absorption in the molten steel is the primary cause of reoxidation. Conversely, in the steady-state teeming stage, tundish cover flux and refractory materials are the main reasons. When reoxidation occurs due to gas absorption by molten steel, the gas absorption rates varies for different steel compositions. In the stable teeming of molten steel, the high content of SiO₂ in the rice husk ash (RHA) in the top layer of the double-layer cover flux gradually dissolves in the high-basicity cover agent in the bottom layer. At the slag-steel interface, the self-dissolution reaction (SiO₂) = [Si] + 2[O] occurs, resulting in the loss of Al, Ti, and Mn elements in the molten steel, whereas the Si content, total oxygen (T.O) content increase, and the composition, size, and number density of the inclusions change. Carbothermal reactions between Al₂O₃-SiO₂-C refractories and molten steel can generate oxidizing CO gas, which is the main cause of the reoxidation of ultra-low carbon Ti added Al-killed steel. In addition, unstable oxides such as Cr₂O₃, MnO, SiO₂, and FeO present in the gunning material and ladle filler sand can cause serious steel reoxidation. The reoxidation of steel and dissolution of SiO₂ in the underlying cover agent can be mitigated by designing a new type of tundish cover flux to replace the RHA. Nitrides can be used in the nozzle material to reduce the release of the oxidizing gas CO, preventing nozzle clogging. Microporous magnesia-refractory materials provide strong heat insulation and slag resistance.It can absorb thermal stress and reduce the initiation and expansion of cracks in refractory materials. Therefore, microporous magnesia refractories have good application prospects as tundish lining materials.

Face-centered-cubic high-entropy alloys have attracted extensive attention due to their comprehensive mechanical and other properties. However, these alloys suffer from low yield strength, making it imperative to develop alloys with high yield and tensile strengths. This study systematically investigates the microstructural characteristics and tensile mechanical properties of the Fe₅₀Mn₂₉-Co₁₀Cr₁₀Cu₁ high-entropy alloy processed by rolling at three temperatures (-196, 25, and 300 °C) followed by annealing. The aim is to elucidate the deformation mechanisms associated with different processing routes and their influences on strength and ductility. During uniaxial tensile deformation, deformation twins produced by liquid-nitrogen and room-temperature rolling along with lath-like reversed austenite impede dislocation slip, thereby improving the yield strength of the alloy. In contrast, the alloy processed by warm rolling and annealing shows few deformation twins, with dislocation slip and stacking faults dominating as the deformation mechanisms. The alloy processed by liquid-nitrogen rolling followed by 500 ^oC annealing exhibits high yield strength but poor plasticity. Conversely, alloys rolled at room temperature and 300 ^oC followed by 500 ^oC annealing demonstrate higher yield strengths and certain degree of work hardening capability, showing corresponding yield strengths of 752 and 604 MPa, tensile strengths of 917 and 784 MPa, and uniform elongations of 11.2% and 26.2%. The differing microstructures resulting from processing at varied temperatures and subsequent annealing lead to significant differences in mechanical behavior under tensile testing.

Recently, 18Ni300 maraging steel has been widely used for preparing conformal cooling molds via additive manufacturing. The requirements pertaining to the service life of these molds have become more stringent, but whether the microstructures and properties of these molds can meet the service requirements largely depends on the applied heat treatment. This paper studies the effects of two typical heat treatment processes—direct aging and solution aging—on the microstructure and tensile properties of 18Ni300 maraging steel fabricated via selective laser melting. In all prepared specimens, austenite was present and the classical Nishiyama-Wassermann orientation relationship was observed between austenite and the martensitic matrix. Elements in the as-prepared samples were evenly distributed, with obvious molten-pool and cell structures composed mainly of dislocation entanglements. In addition, a small number of long austenite strips appeared at the grain boundaries. Direct aging partially dissolved the cell and molten-pool structures and enriched Ni at some grain boundaries. The direct-aging sample exhibited relatively high austenite content. Meanwhile, the solution-aging sample exhibited a nearly complete martensite structure with evenly distributed elements. In addition, cell and molten-pool structures were almost completely removed and Ni was enriched at some grain boundaries. Further, trace amounts of austenite remained. Austenite retained in the as-prepared samples showed no obvious chemical composition segregation. Austenite present in the direct-aging and solution-aging samples was Ni enriched and confirmed to be of the reverted type. Ni at certain grain boundaries and cell walls was enriched due to cell-wall dissolution during the direct- and solution-aging treatments. Ni enrichment promoted the formation and stability of reverted austenite. Numerous round rod-shaped Ni₃Ti intermetallic compounds precipitated from the matrix after both the treatments, greatly increasing the yield strength from (1090 ± 1.5) MPa of the untreated sample to (1854 ± 13.2) MPa and (2059 ± 9.9) MPa of the direct-aging and solution-aging samples, respectively. The strength of the as-prepared samples was mainly contributed by austenite-to-martensitic phase transformation and solid-solution strengthening, while those of the direct- and solution-aging samples were mainly contributed by austenite-to-martensitic phase transformation, solid-solution strengthening, and precipitation strengthening. Moreover, the solution-aging samples exhibited greater precipitation strengthening than the direct-aging samples, mainly owing to the high density and large length-diameter ratio of their precipitates.

Variations in lower bainite and martensite phase configurations through thickness play an important role in achieving an optimum combination of strength and toughness for thick high-strength low-alloy (HSLA) steel plates. A comprehensive understanding of the hardness and microstructural evolution of tempered lower bainite and martensite (LB/M) mixtures contributes to the adjustment of the quenching and tempering parameters to further control HSLA plate deformation during manufacturing. Therefore, this study focused on the tempering behavior of the mixed LB/M microstructure and compared this behavior with those of the singular martensite and lower bainite phases. Results have shown that the hardness of LB/M microstructures follows the rule of mixtures. Hardness declines from singular martensite to the LB/M microstructure and further decreases to singular lower bainite during short-term tempering, whereas an opposite hardness decreasing trend is observed during long-term tempering. Carbide coarsening leads to a decrease in hardness during short-term tempering, where the coarsening of martensitic and lower bainitic carbides in the LB/M microstructure is consistent with that of singular martensitic and bainitic carbides. Furthermore, the coarsening of laths and carbides in the LB/M mixture is similar to that in the singular lower bainitic microstructure for long-term tempering, where lower bainitic carbides are more stable than martensitic carbides.

Wire-arc directed energy deposition (DED) shows considerable potential for fabricating structural components from Al-Zn-Mg-Cu-Sc alloys. However, its layer-by-layer deposition nature leads to continuous grain boundary second-phase networks, grain coarsening, elemental microsegregation, and residual stress accumulation during solidification of 7075-Sc aluminum alloys, significantly compromising their mechanical properties and industrial viability. As a precipitation-strengthened alloy, 7075 can be optimized through heat treatment to control the morphology and distribution of secondary phases, thereby improving mechanical performance. Nevertheless, the inhomogeneous as-deposited microstructure proves difficult to fully homogenize using conventional heat treatment, necessitating precise temperature control and tailored aging schedules for effective thermal processing. In this study, crack-free, thick-walled Al-Zn-Mg-Cu-Sc alloy components were fabricated using custom 7075-Sc welding wire and the cold metal transfer process. Microstructural analysis revealed that the as-deposited alloy consists of fine equiaxed grains with an average diameter of approximately 14 μm and a continuous grain boundary second-phase distribution. Solution treatment at 470 ^oC results in a markedly reduced dissolution rate of the secondary phases over time, with a 4 h duration identified as optimal. Under this condition, 70.2% of the secondary phases are dissolved; the remaining phases are predominantly Al₇Cu₂Fe and Al₂Mg₃Zn₃. Subsequent artificial aging at 120 ^oC showed that an aging time of 18 h yields optimal mechanical properties. Following the combined solution and aging treatments, the alloy exhibited a yield strength of 475.2 MPa, tensile strength of 542.1 MPa, and elongation of 5.2%. These values represent increases of 52.8%, 36.5%, and 36.8%, respectively, compared to the as-deposited alloy.

Compared with α + β titanium alloys, near-β titanium alloys exhibit higher specific strength, better strength-toughness matching, superior hardenability, and greater hot and cold forming capabilities. They are widely used as main load-bearing components in advanced aviation vehicles. During the preparation of titanium alloys, the content, grain shape, and grain size of the primary α phase and secondary α phase are often controlled through thermal deformation and heat treatment, which affect the overall properties of titanium alloys. In recent years, research has revealed that the grain size and orientation within the original β phases also impact crucial properties of titanium alloys such as their strength, plasticity, and fracture toughness. This is because on the one hand, during the phase transformation of titanium alloys from β phase to α phase, the morphology, size, and orientation of the α phase are directly controlled by the β phase; on the other hand, the titanium alloy still contains residual β phase in the service state, which exerts a particularly considerable impact on near-β titanium alloys. To explore methods for preparing large β grains through the control of texture and to systematically investigate the effect of typical β phase textures on the room-temperature tensile and impact properties of titanium alloys, TC18 titanium alloy billet having {100} oriented β grain (exceeding 50 mm × 50 mm × 100 mm) was prepared using six-pass forging at α + β region, one-pass forging at quasi-β region, and high-temperature annealing. The tensile and impact toughness at 20 ^oC were measured in the <100>, <110>, and <111> directions of the large β grain, while SEM and EBSD were employed to study the microstructure and texture evolution during the preparation process. During forging at α + β region, the billet was compressed in length direction by 50% and was stretched to its original size at 30 ^oC below transformation temperature (T_β ). During forging at quasi-β region, the billet was compressed in length direction by 30% at 15 ^oC above T_β. The high temperature annealing involved holding the billet at 25 ^oC above T_β for 12 h, followed by water quenching. The results showed that the key mechanical properties of TC18 titanium alloy were considerably affected by the change in the orientation of the β phase. For the large β grains of TC18 titanium alloy, the highest values for strength, elastic modulus, and impact toughness were observed in the <111> direction and then in the <110> direction, whereas the lowest values for these properties were observed in the <100> direction. The strength, elastic modulus, and impact toughness in the <110> direction were similar to those without the β phase texture. The samples having a strong <111> β phase texture showed a 14.8% higher in tensile strength, a 12.2% higher in yield strength, a 13.6% higher in impact toughness, and only a slight decrease in plasticity than samples without an obvious β phase texture. Large {100} grains formed at the center of the billets' cross section during forging, and they gradually grew toward the surface with increasing forging times; this phenomenon was facilitated by the subgrain boundary merging of grains having a similar orientation.

High- and medium-entropy alloys have attracted considerable attention because of their innovative design concepts. The VCoNi medium-entropy alloy with equiatomic ratio, a distinctive type of medium-entropy alloy, is characterized by a fcc structure. As it exhibits remarkable mechanical properties such as strength and plasticity across a broad temperature spectrum, it is suitable for versatile applications. Current research on VCoNi medium-entropy alloys predominantly focuses on the alloy design and the manipulation of heat treatment technologies to enhance mechanical properties with relatively less emphasis on elucidating plastic deformation mechanisms. A profound understanding of these mechanisms is imperative for controlling their properties. Although previous studies have revealed plastic deformation mechanisms mediated by dislocations in VCoNi medium-entropy alloys, the impact of grain orientation on dislocation movement and interaction mechanisms remains elusive. Nanoindentation technology has been widely used to assess plastic deformation behavior and dislocation evolution in materials. Grain orientation profoundly influences the mechanical properties and plastic deformation behavior of materials at the microscale. Therefore, investigating the influence of grain orientation on the plastic deformation mechanism in the VCoNi medium-entropy alloy is of great importance. A comprehensive understanding of plastic deformation and dislocation interactions can be achieved by analyzing slip steps generated by nanoindentation. This study delves into the plastic deformation behavior of VCoNi medium-entropy alloy in {101}, {111}, and {001} grains using nanoindentation. By analyzing the evolution of slip steps and load-displacement curves, it concentrates on the influence of crystal orientation on plastic deformation behavior and explores the intricate relationship among dislocation interactions, load-displacement behavior, and dislocation motion. The grain orientation in the VCoNi medium-entropy alloy dictates the activation and sequence of slip systems induced by nanoindentation, thereby substantially influencing the morphology of indentations, surrounding slip steps, and load-displacement behavior. The slip steps on the same slip plane in each grain preferentially appear on a positively inclined slip plane. On {101} grains, the slip steps appear on the (111) and (\mathrm{11}\overline{\mathrm{1}}) slip planes initially, and then on the (\mathrm{1}\overline{\mathrm{1}}\overline{\mathrm{1}}) and (\mathrm{1}\overline{\mathrm{1}}\mathrm{1}) slip planes. In {111} grains, the slip steps appear on the (\mathrm{11}\overline{\mathrm{1}}), (\mathrm{1}\overline{\mathrm{1}}\overline{\mathrm{1}}), and (\mathrm{1}\overline{\mathrm{1}}\mathrm{1}) slip planes. On {001} grains, the slip steps appear on the four {111} slip planes. {101}, {111}, and {001} grains exhibit butterfly-shaped, nested triangle-shaped, and cross-shaped overall indentation morphologies, respectively. Additionally, only a limited occurrence of double cross-slip is observed at the edges of the slip steps in {101} and {001} grains. The analysis of dislocation interactions revealed that on {101} grains, dislocation reactions tended to form Lomer-Cottrell locks and Glissile junctions, in {111} grains they tended to form Collinear junctions and Lomer-Cottrell locks, and in {001} grains they tended to form Glissile junctions. This determination influences the subsequent pop-in behavior in the load-displacement curves of different grains.

The quality of the green body is crucial for achieving excellent mechanical properties in sintered cemented carbides via the powder metallurgy process, making it necessary to explore and optimize the powder molding process. In this study, the effects of the content and solution concentration of the pressing binder, as well as the green density during the powder molding process, on the geometries, microstructures, and mechanical properties of sintered WC-12Co cemented carbides were investigated. These materials were produced using in situ synthesized ultrafine WC-Co composite powder as the raw material. The results indicated that increasing the polyethylene glycol (PEG) content as the pressing binder within a certain range led to a linear increase in the magnetic Co content of the sintered cemented carbides. The concentration of the PEG solution primarily influenced its dispersion in the powder and feedstock particle size. Both of which considerably influenced the phase constitution, density, and mechanical properties of the prepared cemented carbides. During the pressing process, as the green density increased within a certain range, the shrinkage rate of the sintered alloys exhibited a good linear relationship with it. Additionally, the density of the cemented carbides initially increased notably and then stabilized, whereas the fracture strength initially increased and then decreased. By optimizing the conditions to 1.5% PEG content, 4.1% PEG concentration, and a green density of 7.7 g/cm³, the sintered cemented carbide achieved an exceptional average transverse rupture strength of 4571 MPa with minimal fluctuations in the measured values. The formation of numerous Co-rich nanophases within the WC grains, which hinder dislocation movement, is the primary reason for the enhanced strength of the cemented carbide.