Friction stir additive manufacturing (FSAM) is an advanced solid-phase forming technology based on the principle of friction stir. As no heat source is required, the FSAM process can avoid metallurgical defects during melting and solidification of the material. The FSAM also conserves energy and protects the environment. To replace the traditional forming technology with a heat source, current research aims to optimize the forming process parameters of aluminum and magnesium alloys. Similarly to the friction stir welding process, increasing the temperature in the FSAM process will dissolve part of the strengthening phase, coarsening the particles and softening the welding core area. In addition, during layer-by-layer stacking in FSAM, the stir tool will re-stir the previously formed area, introducing a new thermal cycle during the stirring process. Because the changes in the temperature and stress field are more complex in the FSAM process than in the friction stir welding process, the influence of microstructure evolution on the mechanical properties of materials in the FSAM process is worthy of investigation. In this study, a multilayer defect-free FSAM material was fabricated from 2-mm-thick 6061 aluminum alloy sheets. The microstructural evolution along the building direction was observed during the FSAM process to investigate its effect on the microhardness and tensile properties. Dynamic crystallization formed fine equiaxed grains in the stir zone, which were further refined after re-stirring in the overlapping interface regions. The tensile strength and elongation of the FSAM material were 47.7%-55.2% and 144.6%-148.8% those of the base material, respectively. Multiple thermal cycling weakens the performance of the overlapping interface regions. The spherical α-Al(MnCrFe)Si phase plays a strengthening role in the matrix. Extensive dissolution of the strengthening phase during the FSAM process is mainly responsible for the performance deterioration of the FSAM material. After heat treatment at 520 ^oC for 1 h and at 165 ^oC for 18 h of aging, the properties of the FSAM material were largely improved: the hardness slightly increased from that of the base material and the tensile strength reached 87.2%-91.9% that of the base material.

Cold dwell-fatigue failure in titanium components of gas turbine engines has been a concern for over five decades, posing a continuous threat to the safe operation of aircrafts. Owing to the complexity of influencing factors and mechanisms, there has been a lack of complete understanding and effective prevention of cold dwell effect. In this study, the effects of peak stresses on the dwell effect at room temperature were investigated, focusing on a large compressor disc manufactured from Ti6242 alloy, specifically designed for use in commercial aeroengines in China. The relationships between fatigue life and peak stress were fitted by the Basquin equation, and the stress threshold value of cold dwell effect was obtained. A detailed characterization of the fatigue failure characteristics and microscopic mechanisms was performed using OM, SEM, XCT, EBSD, and TEM techniques. The results revealed a progression of dwell fatigue-fracture characteristics in Ti6242 alloy as the peak stress increased from near-threshold value of the dwell effect to the value exceeding the yield strength. The failure characteristics included initiation of surface crack, mixed surface and subsurface crack, subsurface crack, and mixed subsurface crack and tensile dimples. Initiation facets formed due to dwell fatigue loading exhibited decreasing spatial angles with increasing peak stress levels in the range of ~20^o-44^o for the stress levels studied. However, the spatial orientations of the propagation facets formed due to dwell fatigue loading were unaffected by the peak stress and remained at less than ~20^o. Dwell fatigue stimulated the formation of dense dislocation planar slip bands, facilitating their transfer across the secondary α (α_s) lamellae and eventually resulting in long-distance slips. Increasing stress further relaxed the crystallographic conditions necessary for the crack initiation, leading to dislocation sliding and cleavage cracking in unfavorably oriented soft and hard grains. Consequently, at higher stress levels the cleavage facets exhibited a larger spatial orientation range, accompanied by the formation of more fatigue cracks. In the case of dwell fatigue, high-stress levels activated <c + a> dislocations and pyramidal slips. The size and number of fatigue cracks were related to the peak stress. Quantitative characterization of secondary cracks in the dwell fatigue specimens using XCT indirectly showed the average size of macrozones in Ti6242 compressor disc to be approximately 72 μm. The Ti6242 compressor disc exhibited a relatively strong texture, featuring a <\mathrm{11}\overline{\mathrm{2}}\mathrm{0}> partial fiber along the axial direction and a <0001> partial fiber aligned with the radial and transverse directions. Based on the spatial orientation of facets on the fracture surface, a method using EBSD data to identify a microstructural feature parameter indicative of dwell fatigue performance was proposed, i.e., the cluster size of α grains with the c-axes inclined within ~30° to the loading direction.

With the increasing scarcity of traditional energy sources such as petroleum, the concept of sustainable development has prompted strict demands for energy-saving, economical, and environment-friendly industrial production. As the most important lightweight structural material, the requirements for aluminum alloys in modern industries are also increasing. In particular, 7xxx-series ultrahigh-strength aluminum alloy thick plates have been widely used in aerospace and other fields due to its advantages of lightweight and high specific strength. Currently, the problem of nonuniformity of microstructure and mechanical properties in the thickness direction of the thick plates is still prominent. Therefore, developing a new aging process to overcome the shortcomings of the low efficiency of traditional aging processes and difficult-to-control temperature field is urgently needed. Additionally, the research on aging heat treatment mainly focuses on the performance test and static microstructure characterization. Fewer research works have been carried out on the real-time detection of the transformation of the aging dissolution phase byin situ means. To optimize the two-stage aging process of a 7A65 aluminum alloy thick plate, this study systematically analyzed the aging precipitation behavior of the alloy by in situ electrical resistance analysis, formulated the two-stage aging process of the alloy, and explored the influence law of the aging process on the mechanical properties of the thick plate. The study also explored the strengthening and toughening mechanism of the plate through the microstructure observation and mechanical property test. The isothermal transition curve (i.e., time-temperature-transformation (TTT) curve) of the alloy shows that the “C curve” of η-phase dissolution is observed at 120-220 ^oC. According to the TTT curve, the optimal conditions for the two-stage aging process for the thick plate are determined to be as follows: heat at 121 ^oC for 6 h, and then at 152 ^oC for 19 h. After aging, the electrical conductivity of the plate is higher than 38%IACS, the yield strength is higher than 550 MPa, and the elongation reaches 9%.

An AZ31 magnesium alloy sheet with bimodal non-basal texture exhibits better rolling performance at room temperature compared with that with a typical basal texture. However, the rolling performance of bimodal non-basal texture sheets under medium temperature conditions remains unexplored. Therefore, this study aims to elucidate the rolling behavior and deformation mechanism of bimodal non-basal texture sheets at 200 ^oC. Employing EBSD characterizations, the microstructural characteristics of rolled sheets with initial basal and bimodal non-basal textures throughout a multipass rolling process were systematically investigated. Results showed that at medium temperature, the rolling performance of sheets with bimodal non-basal texture improved only slightly compared with those with basal texture. Especially, edge cracks were observed in deformed bimodal non-basal texture sheets after the fifth rolling pass, with a corresponding accumulative thickness reduction of approximately 48.0%. In contrast, sheets with basal texture exhibited edge cracks after the fourth rolling pass, with a corresponding accumulative thickness reduction of approximately 43.6%. A large number of basal <a> and non-basal dislocations (including prismatic <a> and pyramidal <c + a> dislocations) as well as a small number of {1011}-{1012} secondary twins were activated during the rolling deformation of basal texture sheets. These dislocations cause extensive dynamic recrystallization (DRX) near grain boundaries and twin interfaces, with the corresponding DRX volume fraction reaching as high as 47.9%. For bimodal non-basal textured sheets, in addition to the activation of high-density dislocations at the beginning of rolling deformation, an extensive {10\overline{\mathrm{1}}2} extension twins (ETs) were activated to carry plastic strain. With increasing rolling passes, {10\overline{\mathrm{1}}2} ET boundaries migrated toward the matrix region and absorbed a large number of dislocations, thereby reducing the dislocation density within deformed grains. This phenomenon would delay the DRX onset, resulting in a small DRX volume fraction of approximately 11.4%. The pronounced difference in the DRX behavior between bimodal non-basal texture sheets and basal texture sheets at medium temperature primarily accounts for their similar rolling performance, with mere 4.4% difference in accumulative thickness reduction.

With the development of electromagnetic devices towards high-frequency, miniaturization, and high efficiency, the demand for the soft magnetic nanocrystalline alloys with high saturation magnetic flux density (B_s), excellent high-frequency performance, as well as good manufacturability is becoming increasingly urgent. In this work, the effects of B content on the melt-spun structure, thermal stability, crystallization structure, and magnetic properties of Fe_{98.5 - x} B _x Cu_1.5 (x = 12-18, atomic fraction, %) alloy ribbons were investigated; and the correlation among B content, melt-spun structure, crystallization structure, and magnetic properties was explored. The results show that the melt-spun structure of all the alloys is a dual-phase composed of α-Fe nanograins distributing in an amorphous matrix. As the x increases from 12 to 18, the number density and grain size of the α-Fe grains gradually decrease, and the structure transforms into a nearly amorphous state. After crystallization annealing under a low heating rate, the alloys with x = 12-17 have the amorphous/nanocrystalline α-Fe dual-phase structure, while the x = 18 alloy forms a amorphous/α-Fe/Fe₃B tri-phase structure. The alloys with x = 13-16 exhibit a fine nanocrystalline structure and good soft magnetic properties with the average α-Fe grain size (\overline{D}_α-Fe) of 15.8-16.3 nm, B_s of 1.80-1.91 T, and coercivity (H_c)of 18.9-22.7 A/m. Among them, the alloywith x = 15 has the \overline{D}_α-Fe, B_s, and H_c of 16.0 nm, 1.86 T, and 18.9 A/m, respectively. Based on the structure of the alloys before and after annealing, a crystallization model for the melt-spun alloys with different B contents was proposed, and the mechanism of which the strong competitive growth effect between the high-number-density pre-existing fine α-Fe nanograins in the amorphous matrix of the melt-spun alloys along with the newly-formed α-Fe grains during crystallization annealing results in the uniform and fine nanocrystalline structure of the alloys was elucidated.

Diffusion bonding has been gaining increasing attention in the manufacturing of precise and intricate structural components in aerospace and other industries. The bonding temperature is a critical factor that affects the performance of the parts produced by diffusion bonding. This study explores the impact of hot-pressing temperature on the microstructure, mechanical properties, and fracture mechanism of TC4 titanium alloy joints formed through diffusion bonding. Samples were prepared using a hot-pressing technique. The findings reveal that dynamic recrystallization occurs at the diffusion bonding interface during the process. At lower temperatures, this recrystallization results in the formation of a fine α-phase at the interface. As the hot-pressing temperature increases, the α-phase progressively coarsens. Notably, there is a substantial disparity between the size of the α-phase formed through dynamic recrystallization at the interface and that in the nondiffusion zone of the base material, leading to a crystallographic mismatch. This mismatch substantially reduces the properties at the diffusion interface and consequently leads to fracture in the diffusion-bonded joints within the bonding zone after hot pressing. In the post-heat treatment, the diffusion zone consists of primary α (α_p) phase, needle-like secondary α (α_s) phase, and β phase. Elevating the bonding temperature gradually increases the size of the α phase, thereby improving the crystallographic match at the bonding interface and facilitating interface migration. After the heat treatment at 970 ^oC, the tensile strength and elongation of the 950 ^oC diffusion-bonded TC4 Alloy joints were measured at 998.7 MPa and 17.5%, respectively, achieving the performance levels of the alloy before diffusion bonding.

During laser cladding, welding, and other hot forming processes, dissimilar metals can form segregation bands. These bands often lead to solidification cracks that can directly affect the mechanical properties of the processed and formed materials. To study the formation mechanism and evolution of segregation bands during metallurgical bonding of dissimilar metal materials, a two-dimensional melting and solidification model for laser cladding of IN718 on 316L stainless steel was used. This model was established using the cellular automata method and Eulerian multiphase flow algorithm. The evolution of the temperature field, molten pool morphology, melt flow, and element distributions during laser cladding was comprehensively analyzed. The rationality of the model was confirmed by comparing the melt pool geometry and grain orientation. Additionally, the reliability of the model was confirmed by comparing the distribution of Fe element content in the x- and y-directions. The simulation results reveal that during the metallurgical bonding process of laser cladding IN718 alloy on the 316L stainless steel substrate, distinct segregation zones are observed, which are characterized by the enrichment of Fe and Ni elements and an unideal alternating distribution pattern. This finding is in high consistency with the experimental results. The Marangoni force drives more Fe elements from the bottom of the melt pool (substrate) to the rear end of the melt pool, increasing the temperature of the liquidus at that location. This solidification promotion at the rear end of the melt pool causes actual solidification liquidus temperature(T_a) to be biased toward substrate liquidus temperature(T_b), resulting in the formation of a region with a high concentration of Fe elements. The rear end of the melt pool takes on a “bulging” shape, increasing the melt flow rate within the pool. This increase rolls more Fe elements from the front end of the melt pool (powder) to the rear end of the pool. Consequently, the liquidus temperature at the rear end of the melt pool decreases, biasing T_a toward the liquidus temperature of the powder(T_p). This process hinders solidification at the rear end of the melt pool, resulting in the formation of a region with a reduced concentration of Fe elements. The rear end of the melt pool flattens gradually, decreasing the melt flow rate and drawing more elements from the front to the rear end. This change results in the formation of a segregation zone with an alternating distribution of high and low Fe element content, which is consistent with the experimental results. Through the analysis of the distribution of Fe elements in the melt pool, the morphology of the melt pool and the evolution of the melt flow state, it is evident that this segregation zone arises from the mismatch between fluid flow dynamics and the morphological changes of the melt pool during the solidification process. The rate at which the solid-liquid interface moves can be calculated by finding the difference in the solute concentration between the interface neighboring cells. Fluctuations in the molten pool flow cause the morphology of the rear end of the molten pool to constantly change, resulting in varying concentrations of Fe element after solidification. Therefore, increasing the homogeneity of element mixing in the molten pool can reduce the degree of segregation. During the experimental process, appropriate increase in the laser power and scanning rate reduction can improve the quality of the cladding layer.

Ni-based single-crystal superalloys have excellent high-temperature mechanical properties and creep properties, rendering them as preferred turbine blade materials in advanced aerospace and gas engines. Controlling competitive grain growth during directional solidification is of great substantial importance for achieving high-quality single-crystal blades. As an external physical field, a static magnetic field can be used to effectively control material forming. The use of static magnetic fields during directional solidification has evolved as an effective method for controlling microstructures and grain growth. However, the influence of static magnetic fields on competitive grain growth during the directional solidification of Ni-based superalloys requires further investigation. Therefore, this study explored the competitive growth behavior of divergent grains during the directional solidification of Ni-based superalloy using bi-crystal seeds at various withdrawal rates under a weak transverse magnetic field (0.1 and 0.7 T). Results showed that the favorably oriented grain (grain A) overgrew the unfavorably oriented grain (grain B) without the application of a magnetic field, and the overgrowth rate was independent of the withdrawal rate. The application of a magnetic field substantially changed the overgrowth rate of divergent bi-crystals, and the overgrowth rate was affected by the placed patterns of the divergent bi-crystals and the withdrawal rate. When the divergent bi-crystal seeds were placed under the magnetic field in an A-to-B pattern, with the favorably oriented grain A positioned on the left side and the unfavorably oriented grain B on the right side, the side branching of favorably oriented grain was suppressed at the grain boundary (GB), decreasing the overgrowth rate of divergent bi-crystals. However, when the divergent bi-crystal seeds were placed under the magnetic field in a B-to-A pattern, with the unfavorably oriented grain B on the left side and the favorably oriented grain A on the right side, branching from the favorably oriented grain at the GB was enhanced, increasing the overgrowth rate of divergent bi-crystals. With increasing the withdrawal rate, the effect of the magnetic field on slowing down or accelerating the grain overgrowth rate gradually diminished. In addition, a tilted interface and refined dendrites were observed under a transverse magnetic field, especially at a low withdrawal rate. The application of a magnetic field produces a thermomagnetic convective effect at the interdendrite that changes the solute distribution at the divergent bi-crystal GBs, thereby affecting the side branching behavior of dendrites at GBs. With increasing withdrawal rate, the effect of thermoelectric magnetic convection on dendrite side branching at GBs is weakened.

γ-TiAl alloys are a new generation of high-temperature lightweight materials characterized by low density, high specific modulus of elasticity, excellent high-temperature strength, and creep resistance, making them highly suitable for aviation, aerospace, and automotive engine applications. A typical application of the alloys is in the low-pressure turbine blades of aero-engines, such as GEnx and Trent XWB developed by the General Electric and Rolls-Royce, respectively. Their alloy compositions are Ti-48Al-2Cr-2Nb and Ti-45Al-2Nb-2Mn-1B (atomic fraction, %), respectively. γ-TiAl alloys are required for long-term service at 600-700 ^oC; however, they react readily with oxygen to form oxide scale when exposed in air at high temperatures, compromising service safety and reliability. Thus, understanding the long-term oxidation behavior of γ-TiAl alloys during service at high temperatures is imperative. In this study, the oxide scale and microstructural evolution of cast Ti-45Al-2Nb-2Mn-1B alloy (45XD alloy) and Ti-48Al-2Nb-2Cr alloy (4822 alloy) at 700 ^oC in air for 0-2000 h were investigated using SEM and TEM. The mass gain of both alloys was measured during oxidation, and their oxidation behaviors were compared. The 4822 alloy exhibited a notably higher mass gain than the 45XD alloy. Both alloys demonstrated periodic mass gain behavior during oxidation for 0-2000 h—alternating rapid and slow gains—with stabilization in the later stages. The oxide scales formed layered structures, primarily of TiO₂ and Al₂O₃, on the surface of both alloys; the scale of 45XD alloy was continuous and dense, whereas that of the 4822 alloy was porous. Additionally, the study revealed that α₂ lamellae in the subsurface of the 45XD alloy decomposed during oxidation, forming an Al-rich and Ti-lean γ zone on the subsurface. α₂ lamellae in the bulk microstructure of the 45XD alloy were also decomposed and transformed into γ phase. The 4822 alloy experienced a significant reduction in the volume fractions of α₂ in equiaxed γ grains and α₂ + β₀ at equiaxed γ grain boundaries.

High-speed steel typically comprises a high carbon content with an abundance of alloying elements, leading to a solidified microstructure rich in carbides. The refinement of these carbides in the microstructure is the most effective method for enhancing the mechanical properties of high-speed steel, and it remains a primary focus of the high-speed steel research. The prevalent industrial production methods for high-speed steel include traditional casting and forging, powder metallurgy, and spray forming. Traditional casting and forging methods are often constrained by segregation issues, hindering the application of high-quality cast and forged high-speed steel. Powder metallurgy high-speed steel exhibits remarkable mechanical properties; however, its high production costs have restricted its broader development. Conversely, spray forming is an advanced manufacturing method characterized by cost effectiveness, efficient production, and environmental friendliness. Although China has successfully implemented the mass production of spray-formed tool and die steel, systematic research on the microstructure and properties of such steel in actual industrial preparation is lacking. This study conducts a comparative analysis of the microstructure and mechanical properties of the M3 high-speed steel prepared via three distinct methods: electroslag remelting, spray forming, and powder metallurgy. The experimental results show that although the different preparation methods exert minimal impact on the carbide type within the annealed microstructure of the M3 high-speed steel, they considerably affect the morphology, size, and distribution of the carbides. Spray-formed and powder metallurgy high-speed steels display a dispersed, particulate carbide distribution across transverse and longitudinal sections, with spray-formed steel exhibiting coarser carbide sizes. Electroslag remelted high-speed steel exhibits a network-like distribution of carbides in the transverse sections and a distinct banded arrangement in the longitudinal sections. The mechanical properties of powder metallurgy high-speed steel were superior to those of electroslag remelted and spray-formed high-speed steels. The more uniform and finer the distribution of carbides within the steel microstructure, the higher will be their hardness, bending strength, and impact toughness. Regarding wear resistance, spray-formed high-speed steel outperforms the others, which is attributed to the presence of large-sized MC-type carbides in its microstructure. These carbides not only provide better wear resistance, but also change the formation of the oxidation layer from diffusion mechanism to sintering mechanism, thereby reducing crack propagation in the matrix and enhancing wear resistance. This study delves into the carbide precipitation behavior of the M3 high-speed steel during the spray forming process based on the microstructural characteristics of the spray-formed steel.

Compared to the conventional Rankine steam cycle, the Brayton cycle system utilizing supercritical carbon dioxide (S-CO₂) as the working fluid offers significant advantages, including higher energy conversion efficiency, a more compact structure, enhanced safety, economic benefits, and a superior overall energy efficiency ratio. Consequently, the S-CO₂ Brayton cycle system holds promise for application in thermal power generation, fourth-generation nuclear power, new gas turbines, solar power generation, and other fields. In various operating conditions, material corrosion in high-temperature CO₂ environments has consistently been identified as a primary factor leading to the degradation of superheaters and reheaters. The corrosion mechanisms of steel in CO₂, particularly the differences between ferritic and austenitic steels, are not yet fully understood. T92 ferritic steel and 316L austenitic steel are widely recognized as preferred materials and have been extensively utilized as superheater/reheater components in power stations. Enamel coating has been considered a cost-effective solution for enhancing the oxidation resistance of steels without considerably degrading their mechanical properties. Therefore, this work investigated the corrosion behaviors of T92 ferritic steel and 316L austenitic steel, and enamel-coated steels in CO₂ at 600 ^oC. Results revealed rapid oxidation and carbon invasion for both T92 and 316L steels, with 316L austenitic steel exhibiting superior oxidation resistance and slightly better carbon invasion resistance due to its higher chromium content. Meanwhile, the mass gain after 500 h of corrosion was significantly higher for T92 ferritic steel than for 316L austenitic steel, reaching 10.51 and 1.38 mg/cm², respectively. The oxidation kinetics of all samples follows an approximately parabolic trend. A double-layered structure comprising an outer Fe-rich oxide layer and an inner Cr-rich oxide layer is formed on the surface of both steels. The interface between the inward growth of the inner layer and outward growth of the outer oxide layer corresponds to the initial steel surface. In addition, rapid carbon invasion and carburization cause more metal damage than oxidation. While T92 ferritic steel and 316L austenitic steel exhibited comparable resistance to carbon invasion, differences in their structures led to variations in carbide distribution within the steels. T92 ferritic steel demonstrated homogeneous carbide formation due to its high internal diffusion channel density, resulting in an intrusion depth of 329 μm after 500 h of corrosion. In contrast, carbides primarily precipitated at the austenitic grain boundaries of 316L austenitic steel, extending up to 241 μm within the same corrosion timeframe. Enamel-coated samples exhibited excellent corrosion resistance by effectively inhibiting oxidation and carburization reactions through isolating the contact between CO₂ and the steels. Consequently, the corrosion mass gain in these samples was reduced by at least two orders of magnitude. Furthermore, the glass phase of the enamel maintained thermal stability throughout the corrosion process, while the strong bond between the enamel coating and substrate provided long-term protection against thermal stress effects.

Gear transmission is a prevalent method in mechanical transmission; however, its effectiveness is often compromised by excessive wear on the meshing surfaces, primarily attributed to inadequate lubrication. This wear substantially hampers the overall service life of gears. In this study, a chemically deposited FeS coating, boasting favorable lubricating characteristics, was applied to 20CrMnTi gear steel to enhance the tribological performance of gear surfaces. The wear morphology and composition of the FeS coatings were analyzed using SEM, EDS, XRD, white light interferometry, and Raman spectroscopy. The tribological properties of the FeS coatings under dry friction conditions were examined. The FeS coating, with a thickness of about 5.4 μm, exhibited commendable purity, featuring an abundance of aggregated micron-sized sheets on its surface. Results revealed that the FeS-coated samples demonstrated reduced wear levels and friction coefficients compared with the gear steel substrate. Furthermore, the friction coefficient and wear volume of the FeS coating exhibited a noticeable decrease with increasing applied load. Although the friction coefficient of the FeS coating remained relatively stable with increasing rotational speed, wear volume increased. Microscopic analysis revealed that higher loads facilitated the spreading of the lubricating film, whereas elevated rotational speeds intensified oxidative and adhesive wear of the material. Throughout the experiment, the lubricating film transferred to the counterpart surface, forming a transfer film that impeded direct contact between the microasperities of the frictional pair. Even after the coating layer was fully worn, the transfer film can still maintain the long-lasting lubricating performance between the friction pairs and reduce the material wear.

Fe-based amorphous composite coatings have attracted great attention because their specific properties can be enhanced by introducing other metallic or ceramic particles. This work introduces a novel approach, distinct from traditional methods, by designing a composite coating with dual amorphous phases. The composite coating (named FH) was fabricated using high-velocity oxygen-fuel spraying of a blended amorphous powder. This powder comprised well-established Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Y₂ (named FM) and Fe₅₉Cr₁₂Nb₅B₂₀Si₄ (named FN) amorphous powders. This study focuses on investigating the corrosion and wear behaviors of the FH coating in comparison with those of monolithic amorphous coatings. The findings reveal that the FH coating possesses a high amorphous content and a compact structure. It features a uniform distribution of two types of amorphous splats, with no evident element diffusion. In 3.5%NaCl solution, the FH coating exhibits passivation behavior, similar to the two monolithic amorphous coatings, and yields a lower corrosion current and higher polarization resistance, indicating enhanced its corrosion resistance. This improved corrosion resistance of the FH coating is attributed to a harmonious balance between beneficial alloy elements and its compact structure, addressing the limitations of monolithic amorphous coatings. Furthermore, the FH coating displays a high friction coefficient under dry friction conditions and maintains a low wear rate, comparable to those of the FN coating. The wear mechanisms of the three amorphous coatings under dry friction primarily involve fatigue wear, supplemented by minor abrasive and oxidative wear. Compared to the monolithic amorphous coating, the FH coating shows enhanced interfacial bonding of splats and a balanced combination of strengthening and toughening, which effectively inhibit crack propagation caused by fatigue wear, thereby endowing the coating with superior wear resistance. Therefore, the composite coating with dual amorphous phases achieves a balance in cost efficiency, corrosion resistance, and wear resistance.

The development of lightweight materials presents challenges to constitutive modeling and numerical analysis of lightweight components. The hardening of lightweight materials varies more under different stress states than with inherent anisotropy. Although anisotropy is an intrinsic property of rolled sheets, accurate numerical analysis of lightweight components necessitates precise modeling of complex hardening under different loading conditions and anisotropy. This study characterizes the yield evolution of 5182-O aluminum alloy and employs crystal plasticity simulations to understand its plastic deformation characteristics. The mechanical properties of the 5182-O aluminum alloy were examined under different complex stress states through uniaxial tensile, plane-strain tensile, and shear experiments. Initially, the hardening behavior was accurately calibrated using inverse engineering, and plastic deformation characteristics were described analytically using the pDrucker yield equation. The pDrucker yield function was then extended to an analytical anisotropic form using an improved linear transformation tensor. The parameters of the yield function can be analyzed to model differential hardening across various stress states and anisotropic hardening along different loading directions. In addition, the evolution of voids under different stress states and grain orientations was analyzed using crystal plasticity finite element simulations combined with representative volume element (RVE) modeling. Void growth in polycrystalline materials strongly depends on the surrounding microstructure, such as grain morphology and crystallographic orientation. The RVE of single and polycrystalline aggregates containing voids was constructed using a three-dimensional Voronoi mosaic. Crystal plasticity finite element simulations were conducted to perform several simulation experiments with different combinations of grain morphology and crystallographic orientation. Results demonstrated that the anisotropic strength difference of the 5182-O aluminum alloy was < 1%, whereas the maximum strength difference between different stress states was approximately 8%, highlighting the importance of accurately modeling hardening differences due to anisotropy and stress state. The comparison of the calibrated pDrucker yield function with the experimental values under the uncorrelated flow criterion demonstrated relatively high prediction accuracy for different loading directions. The proposed yield function accurately characterized the differential and anisotropic hardening of the 5182-O aluminum alloy under various stress states. Crystal plasticity simulations revealed a strong correlation between stress triaxiality and grain orientation with evolution based on cumulative plastic slip and normalized void volume fraction.

Forming limit diagram (FLD) is a crucial tool for assessing the formability of sheet metals under various forming conditions. However, conducting FLD experiments can be challenging and time-consuming requiring numerical determination of FLDs. Marciniak-Kuczyński (M-K) theory is one of the most well-known instability criteria for calculating forming limits, and the rapid development of crystal plasticity models provides a feasible framework for better understanding the relation between flow localization and material microstructure. Therefore, integrating the M-K theory with advanced crystal plasticity models offers a potential approach to precisely predict forming limits and explore the complex interaction between material behavior and microstructural characteristics. In this study, a crystal plasticity finite element (CPFE) model considering damage evolution was developed based on the microstructure and crystal orientation of a TA32 titanium alloy sheet. The material parameters for the proposed model were calibrated through uniaxial tensile tests and microstructure characterization. The internal correlation between damage evolution and the dislocation slip mechanism under different strain paths was analyzed at the grain scale. Additionally, the FLD of the TA32 sheet at 750 ^oC was predicted by coupling the CPFE model with the M-K theory. The results show that the proposed CPFE model accurately predicts the macroscopic mechanical response, microscopic inhomogeneous deformation, and damage evolution behavior of the TA32 sheet under different strain rates at 750 ^oC. The difference in the deformation behavior and damage propagation was mainly attributed to the anisotropic activation of various slip systems. The basal and prismatic slip systems of the basal bimodal texture in the original sheet were difficult to be activated under different strain paths, making it easier to induce damage than the transverse texture. The FLD predicted by the CPFE-M-K coupling model agrees well with the Nakazima test results, accurately capturing the decrease in the limit of major strain near the equibiaxial tensile region. This decrease is closely related to the anisotropy of the mechanical properties of the material. Furthermore, the change in the initial inclination angle of the groove in the CPFE-M-K coupling model considerably affects the prediction accuracy of the forming limits of the TA32 sheet. The critical initial inclination angles within the strain increment ratio ranges of -0.5-0.5 and 0.6-1.0 are 0° and 90°, respectively.