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The Al–Mg–Si alloy welded structure is widely used in aerospace, marine ship, automotive and other industries. However, the mechanical properties of welded joint were seriously weakened due to the microstructure coarsening and heat affected zone (HAZ) softening, making its service life decayed. In this paper, in order to enhance the mechanical properties of Al–Mg–Si alloy welded joint, a coupled method including double pulsed Metal Inert Gas (DP-MIG) welding technology and post-weld heat treatment (PWHT) were applied on the joining process of Al–Mg–Si alloy. With the increase of DP frequency from 2 Hz to 5 Hz, the average grain size of fusion zone decreased from 113.7 μm to 88.4 μm. And the tensile strength of welded joint was at the interval of 180∼190 MPa. After a suitable heat treatment (solution treatment at 530 °C for 2 h and aging treatment at 180 °C for 8 h), the tensile strength of welded joint increased to 318.3–333.8 MPa, which exceeds 90 % of the base metal (BM). Under the comprehensive effect of solid solution strengthening, fine grain strengthening, and precipitation strengthening, the mechanical properties of Al–Mg–Si alloy welded joint were significantly improved. And the research results in this paper can provide a research basis for high quality connection of Al–Mg–Si alloys. [ABSTRACT FROM AUTHOR]

The Al–Mg–Si alloy welded structure is widely used in aerospace, marine ship, automotive and other industries. However, the mechanical properties of welded joint were seriously weakened due to the microstructure coarsening and heat affected zone (HAZ) softening, making its service life decayed. In this paper, in order to enhance the mechanical properties of Al–Mg–Si alloy welded joint, a coupled method including double pulsed Metal Inert Gas (DP-MIG) welding technology and post-weld heat treatment (PWHT) were applied on the joining process of Al–Mg–Si alloy. With the increase of DP frequency from 2 Hz to 5 Hz, the average grain size of fusion zone decreased from 113.7 μm to 88.4 μm. And the tensile strength of welded joint was at the interval of 180∼190 MPa. After a suitable heat treatment (solution treatment at 530 °C for 2 h and aging treatment at 180 °C for 8 h), the tensile strength of welded joint increased to 318.3–333.8 MPa, which exceeds 90 % of the base metal (BM). Under the comprehensive effect of solid solution strengthening, fine grain strengthening, and precipitation strengthening, the mechanical properties of Al–Mg–Si alloy welded joint were significantly improved. And the research results in this paper can provide a research basis for high quality connection of Al–Mg–Si alloys. [ABSTRACT FROM AUTHOR]

This paper investigated the microstructure and mechanical properties of AISI 430 ferritic stainless steel (FSS) after annealing in either the single-phase or two-phase region, followed by different cooling manners: water cooling, air cooling and furnace cooling. After annealing at 840 °C in the single-phase region, the sample consisted primarily of ferrite, with M 23 C 6 and M 2 (C, N) precipitates aligned mainly along the rolling direction (RD). For the water-cooled and air-cooled samples annealed at 950 °C in the double-phase region, they formed a dual-phase structure comprising ferrite and martensite, with precipitations primarily located within the martensite lath. Conversely, the sample subjected to annealing at 950 °C followed by furnace cooling displayed a single ferrite structure, owing to the decomposition of austenite. In this case, the precipitations were mainly found along the grain boundaries, with some also forming within the ferrite grain. The paper delved into the analysis of mechanical properties and strengthening mechanism through tensile experiments and fracture morphology examination. The influence of heating range and cooling manner on the yield characteristics of FSS was discussed. The results indicated that the air-cooled and furnace-cooled samples annealed at 840 °C displayed a clear yield platform in their tensile curves. Conversely, the samples treated with other heat treatments exhibited continuous yielding or no obvious yield platform. This difference may be attributed to the influence of heating temperature range and cooling manner on the distribution of dislocations and interstitial atoms within the ferrite grains. [ABSTRACT FROM AUTHOR]

Heterostructured metallic materials have drawn attention because of their superior mechanical properties compared to their homogeneous counterparts. This paper evaluates a novel and easy-to-scale approach for manufacturing gradient materials via localized impact loading and reveals the main strengthening mechanism in a high stacking-fault energy material. Impact loading caused heterogeneous strain distributions and strain hardening gradients from the surface towards the inside of the rods. The yield strength and elongation gradients of the impacted rods were 130 MPa–75 MPa and 10 %–25 %, respectively, over a depth of 0 mm–4 mm. This represents a yield strength increment of over 100 % in comparison to the homogeneous counterpart. The appearance of both microscopic and macroscopic heterostructured deformation zones was corroborated by geometrically necessary dislocation and nanoindentation profiles. In this context, the density of dislocations diminished with increasing distance from the impacted surface, leading to a concentration of dislocations in the grains adjacent to the surface. Near the impacted surface, dislocations piled up around the grain boundaries of adjoining grains, creating micro-plastic gradients that that extended into the grain interiors. The localized impact experiments resulted in a heterostructured pure Al rod with gradient properties. Specifically, 50 % of the rod's thickness achieved strengths that exceeded the as-received condition, while the remaining 50 % maintained elongations that exceeded 15 %. [ABSTRACT FROM AUTHOR]

Ti–5V–5Mo–5Al–3Cr (Ti-5553) is a near-beta titanium alloy commonly used in aerospace applications. It is currently being explored for additive manufacturing (AM), but the fatigue behavior of this AM alloy needs to be well-understood for adoption. This paper explores the tensile and high-cycle fatigue behavior of laser powder bed (LPBF) manufactured Ti-5553 that has been post-print heat treated with a beta anneal and age (BAA), with a focus on the microstructural evolution and effects of surface roughness and print defects. Fatigue lives of as-LPBF and BAA material are nearly identical and both are far below fatigue lives of conventionally manufactured Ti-5553. As-built samples contain columnar β grains with a [001] texture in the build direction with a negligible fraction of α phase confirmed by electron backscatter diffraction (EBSD). The BAA material contains HCP alpha-phase precipitates: grain boundary α, primary α, and secondary Widmanstätten α. Fatigue samples were printed in the vertical direction and tested with an as-printed and machined surface. Both the as-LPBF and BAA samples exhibit similar fatigue strengths despite their vastly different microstructures. Machined surfaces led to an increase in tensile strength, ductility, and fatigue strength. This work emphasizes the importance of heat treatment and minimization of flaws inherent to AM processing of near-beta Ti-5553. [ABSTRACT FROM AUTHOR]

In the present paper, the effects of macrostructure and microstructure on fatigue crack growth (FCG) behavior of wire and arc additive manufacturing (WAAM) and hybrid additive manufacturing with in-situ rolling (HAMR) were investigated in three sampling directions for Ti6Al4V ELI. The results demonstrate that WAAMed samples exhibit coarse columnar grains with zigzag boundaries, interlayer heat affected band (HAB), and basketweave microstructures. The fatigue crack growth rate (FCGR) is lowest in the Y-X direction while being similar between the X–Y and X-Z directions, indicating significant anisotropy. This difference can be attributed to changes in plastic region size and internal slip characteristics near the crack tip caused by variations in macrostructure and microstructure. After applying HAMR with quasi-β heat treatment, interlayer HABs are eliminated, resulting in uniform equiaxed grains and colony microstructures. The FCGR curves in three directions significantly overlap without any observed anisotropy, which are lower than those obtained for traditionally forged materials. Therefore, the isotropic FCGR of plastic materials can be reduced by achieving a nearly flawless metallurgical quality and ensuring uniform equiaxed grain matching with the corresponding critical colony size and fine thickness lamellae. The findings suggest that the application of quasi-β heat treatment in conjunction with HAMR offers a promising high-efficiency manufacturing technique for producing isotropic titanium alloy forgings characterized by exceptional damage tolerance. [ABSTRACT FROM AUTHOR]

The aging Al–Zn–Mg–Cu alloy exhibits a significant decrease in performance after undergoing thermal shock. In order to improve the resistance of this type of alloy to thermal shocks, the influence of deep cryogenic treatment (DCT) on the high temperature mechanical properties and microstructure of thermal shocked Al–Zn–Mg–Cu alloy is investigated in this paper. It was found that the mechanical properties of Al–Zn–Mg–Cu alloys decrease significantly with the increase of electric heating temperature. The deep cryogenic treatment reduced the grain size of Al–Zn–Mg–Cu alloy, increased the density of the precipitates, and also inhibited the coarsening of the precipitates. Therefore, the deep cryogenic treatment can slow down the weakening effect of Al–Zn–Mg–Cu alloy at high temperatures. [ABSTRACT FROM AUTHOR]

In this paper, the effects of cyclic deep cryogenic treatment (CDCT) on the mechanical properties and the precipitated phases evolution of 7B55 aluminum alloy produced by wire arc directed energy deposition (WA-DED) were systematically investigated. The findings revealed that, under both T6 and CDCT conditions, the microstructure of the 7B55 aluminum alloy exhibited fine-equiaxed grains. Under the T6 condition, the precipitated phases within the grains were primarily composed of clustered GP zones and η ′ phases. Meanwhile, the η phases were continuously distributed along the grain boundaries. Upon subjecting the material to three cycles of CDCT, a noticeable reduction in the number of GP zones within the grains was observed. Simultaneously, there was a substantial increase in the number of η ′ phases, accompanied by the occurrence of dislocation lines. The distribution of η phases along the grain boundary transitioned to an interrupted pattern. Under the CDCT-Cycle 3 (CDCT-C3) condition, the ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) achieved 658.6 ± 4.5 MPa, 624.2 ± 5.2 MPa, and 8.42 ± 0.18 %, respectively. However, with the progression to four cycles of CDCT, the GP zones within the grains disappeared and the number of η ′ phases started to decrease with the formation of a large number of η phases. The η phase along the grain boundary continuously grew by merging and absorbing solute atoms from the Al matrix near the grain boundaries. This led to the formation of coarsen and interrupted η phases and the Precipitate-Free Zone (PFZ) along the grain boundaries. Subsequently, the mechanical properties experienced a substantial decrease after the CDCT-Cycle 4 (CDCT-C4). • The effect of CDCT on the evolution of precipitated phases WA-DED Al–Zn–Mg–Cu alloy was investigated. • The number of η ′ phase and the dislocation density within grains were increased after CDCT-C3. • The η phases along grain boundaries were changed to interrupted distribution and PFZs were formed after CDCT-C4. • The UTS reached 658 MPa and a breakthrough was achieved among WA-DED aluminum alloys. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the second-stage rolling deformation of Cu–Ni–Si alloy on its stress relaxation resistance was studied, and the mechanism of the change in microstructure and properties before and after stress relaxation was explored. The results show that the tensile strength and yield strength of Two-stage rolling peak aging (TRPA) 43.7 %, TRPA68.8 %, TRPA80.3 % and TRPA96.1 % alloys at 150 °C are close. After stress relaxation, the stress relaxation rates of these alloys are 7.7 %, 11.24 %, 14.69 % and 19.4 %, respectively. It is found that the smaller the second-stage rolling deformation, the better the stress relaxation resistance of the alloy, especially the stress relaxation resistance of the TRPA43.7 % alloy, which is 60.31 % higher than that of the TRPA96.1 % alloy. According to EBSD analysis, it was found that the increase in the number of twins can improve the stress relaxation resistance of the alloy. However, the occurrence of recrystallization reduces the stress relaxation resistance. Additionally, it was determined that the precipitated phase is the δ-Ni 2 Si phase with an orthogonal structure. Before stress relaxation, the size of the precipitated phase of the alloy with TRPA96.1 % is larger than that of the alloy with TRPA43.7 %, and after stress relaxation, the precipitated phase further grows. The influence of the interface relationship between δ-Ni 2 Si phase and Cu matrix on the stress relaxation properties of TRPA43.7 % and TRPA96.1 % alloys before and after stress relaxation was investigated using the mismatch theory. In summary, this study reveals that the size of δ-Ni 2 Si phase, dislocation density and recrystallization are the key factors affecting the stress relaxation resistance of Cu–Ni–Si alloy. • In the two-stage rolling aging process, by applying a smaller deformation in the second-stage rolling and then undergoing a second-stage peak aging, the stress relaxation resistance of the alloy is improved by 60.31 % while ensuring that the hardness, strength, and electrical conductivity of the alloy undergo minimal changes. • The influence of the second-stage rolling deformation on the stress relaxation resistance of Cu–Ni–Si alloy was analyzed. Through the two-stage rolling aging process, δ-Ni 2 Si phases with sizes in the range of 5–10 nm and an orthogonal structure were obtained. Additionally, the formation of twinning effectively pinned mobile dislocations, thereby enhancing the stress relaxation resistance of the alloy. • The mechanism for enhancing stress relaxation resistance was elucidated through analysis of the morphology, size, phase interface relationships, dislocation density, twinning, recrystallization, and other factors of the second phase. • A stress relaxation dynamic regression equation was established. This equation not only predicts the residual stress and stress relaxation rate within a specific time frame but also provides a rough assessment of the alloy's stress relaxation resistance. [ABSTRACT FROM AUTHOR]

Industrial design and new product development benefit from the adaptable processing approach offered by laser direct energy deposition (LDED). In this paper, a novel Ti65 alloy was successfully prepared by LDED and subjected to thermal exposure at 650 °C and 750 °C, respectively. The results showed that the as-deposited microstructure varies in different regions due to the cooling rate. Silicide precipitation was observed at the α/β interface, and a coherent α 2 phase was generated in the matrix after thermal exposure at 650 °C. Two-scale silicides were observed at the α/β interface and inside the α laths after thermal exposure at 750 °C. The as-deposited ultimate tensile strength (UTS) was 1058 MPa and 690 MPa at room temperature and 650 °C, respectively. After thermal exposure at 650 °C, the room temperature UTS was 1135 MPa, and the elongation (EL) at 650 °C was 27.5 %. After thermal exposure at 750 °C, the room temperature EL was 11.05 %, and both UTS and EL at 650 °C showed a decrease. The quantitative analysis showed that silicide precipitation was primarily responsible for the strengthening mechanism of the specimens thermally exposed at 650 °C at room temperature. The results provide scientific data for the manufacture of Ti65 alloy with excellent mechanical properties, laying the foundation for its application in aerospace. • LDED successfully fabricated a novel near-α Ti65 titanium alloy. • Thermal exposure at 750 °C eliminates the α 2 phase coherent with the matrix. • Thermal exposure temperature has a significant effect on the size and morphology of the precipitates. • The influence of microstructure and silicides on the tensile properties was discussed. • As-deposited exhibits an optimal combination of mechanical properties at RT and 650 °C. [ABSTRACT FROM AUTHOR]

Under harsh service conditions, it is very difficult to achieve multi-scale diversified synergy of the heterogeneous brazed joint. The ideal brazed joint should build a "morphology-structure-stress" synergy mode to achieve high-quality and high-reliability brazing. In this paper, the graphene nickel-based foam self-reinforcement was realized by upgrading the in-situ compression, to construct the foam-filler integrated interlayer, and then realize the filler re-optimization. The multi-interface fusion of graphene non-metallic properties and nickel-based skeleton metallic properties effectively inhibited intermetallic compounds. Micro-scale SEM and nano-scale TEM were used to jointly characterize the microstructure, and the 3D structure was thinning layer by layer in the joint fracture, which fully verified the high stability of high-density foam. The room temperature shear strength was as high as 434 MPa, and the properties were almost without damage after 200 cycles of high-low temperature life. This research could provide technical support for the microstructure-property regulation of next-generation aero engines. [ABSTRACT FROM AUTHOR]

The inhomogeneous tempered sorbite/bainite (TS/B) with various morphologies and orientations play a significant role in deformation coordination and damage evolution. In this paper, the influence of distinct morphologies and orientations of the mixed-grain structure with TS/B on the deformation heterogeneity were extensively investigated by in-situ tensile testing. Furthermore, a multi-scale model of dislocation density-based crystal plasticity (CP) coupled with the phase field method (PFM) was developed to illustrate the damage nucleation and its evolution via the representative volume element (RVE) modelling. The results shows that mixed-grain structure with TS/B exhibits non-homogeneous deformation during the tensile process, and the coarse grains bear the main plastic deformation, resulting in cross-slip traces and the wrinkling phenomenon at the grain boundary and the interior of coarse grains. Furthermore, the activation of slip systems was determined through slip trace analysis, and the slip transfer behavior between adjacent microstructure was analyzed. According to the critical resolved shear stress (CRSS), the {123}<111> slip system was determined to be the most activated slip system during the in-situ deformation. Hard-orientated lath-shaped B (M1) is more prone to accumulate low angle grain boundaries (LAGBs) than hard-orientated TS (M2) and soft-orientated granular B (M3), resulting in higher orientation rotation degree and geometrically necessary dislocations (GNDs) density of M1 than M2 and M3. The M1 exhibits the nucleation of damage during the initial deformation stage. In addition, compared with the M2 and M3, the Schmid factor (SF) of M1 dominates the transformation from hard orientation to soft orientation and the higher value of damage factor (φ) of M1 results in the more activated slip systems and local damage at high strain levels. This study provides new insights into elucidate the effects of TS/B morphologies and orientations on deformation heterogeneity and damage evolution in large-scale forged spindles for offshore wind power. • A new multi-scale model to describe the deformation heterogeneity and damage was established. • Hard-orientated lath-shaped bainite was prone to induce non-uniform deformation and a pronounced work hardening effect. • The damage heterogeneity can be attributed to the hard-oriented lath-shaped bainite. • To eliminate hard-orientated bainite and obtain uniform TS is beneficial to improve deformation uniformity and avoid local damage. [ABSTRACT FROM AUTHOR]

The evolution and formation mechanism of microstructures in a high-entropy CoNiCr-based superalloy induced by cold-drawing deformation at cryogenic temperature were investigated. The improvement of strength while maintaining the ductility during cryogenic-drawing deformation in the CoNiCr-based high-entropy superalloy originated from the activation of multiple deformation mechanisms including deformation twins, dislocations, 9R phase and hexagonal close-packed (HCP) phase transformation. Two dominant contributions have been suggested for the increase in strength, namely, nanotwins strengthening and the existence of 9R and HCP phase. In this paper, cryogenic-deformation-induced phase transformation from face-centered cubic (FCC) to HCP in the CoNiCr-based high-entropy superalloy was found, and the atomic-scale mechanism of FCC-9R-Twin/HCP transformation was revealed. A new crystallographic model was established to explain the FCC→9R→Twin/HCP transformation. The phase transformation is significant for the comprehensive understanding of the deformation behavior of this CoNiCr-based high-entropy superalloy at cryogenic temperature, and for guiding the design of high-entropy superalloy with advanced mechanical properties. • The cryogenic-drawn samples of CoNiCr-based high-entropy superalloy exhibit superior strength while maintaining the ductility. • The strength increment originates from multiple deformation mechanisms, including deformation twins, 9R and HCP phase. • The atomic-scale mechanism of the FCC-9R-Twin/HCP transformation was revealed. • A new crystallographic model is established to explain the FCC.→9R→Twin/HCP transformation processes. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel idea of controlling microstructure and mechanical properties based on the non-equilibrium microstructure of nickel-based superalloy fabricated by laser powder bed fusion (LPBF). The network microstructures were firstly built in LPBF nickel-based superalloys by direct aging (DA) heat treatment. Thermodynamic calculations were conducted to design the DA and homogenizing + DA (HDA) heat treatments for elucidating the control mechanism. The results showed that the non-equilibrium microstructures in as-built nickel-based superalloy contributed to the network microstructure formation and recrystallization during DA heat treatment. The grains were refined and the <001> texture was eliminated after DA heat treatment. The non-equilibrium microstructures were removed and the recrystallized grains tended to coarsen after HDA heat treatment due to high temperature homogenizing treatment. The in-situ nano γ′ phase uniformly distributed in the grains of HAD-treated microstructures, which was also found inside network microstructures of DA-treated microstructures. Due to the additional strengthening effect of refined grains and network microstructures, the strength of DA-treated sample was higher than those of as-built and HAD-treated samples, while the ductility was lower than that of as-built sample, and but was close to that of HAD-treated sample. This study will provide guidance for developing a suitable heat treatment process of LPBF nickel-based superalloys. [ABSTRACT FROM AUTHOR]

Nickel-based GH3536 alloy exhibits high strength but low ductility when produced by selective laser melting (SLM), which hinders its widespread application in aerospace. This paper employed a 'two-step' method of heat treatment to optimize the microstructure of the SLM GH3536 alloy and investigated the mechanical properties. Tensile tests were conducted on SLM GH3536 alloy before and after heat treatment at 750 °C, using an in-situ high-temperature tensile stage. The relationship between the microstructural evolution and deformation behavior of the alloys was investigated by combining the in-situ tensile experiments and crystal plasticity finite element method (CPFEM). The results suggested that the elongation can be increased by 80% without a significant reduction in tensile strength. The improved elongation is attributed to the complete recrystallization, formation of annealed twins and serrated grain boundaries after heat treatment. The study also investigated the deformation behavior and fracture mode of the alloy before and after heat treatment. Discussion was done on the influence of the microstructure, particularly the twin and serrated grain boundaries on the alloy's plastic deformation. This study enhanced the understanding of plastic deformation of SLM GH3536 alloy and provided a valuable reference for the design and post-treatment of superalloy. • A two-step heat treatment method is proposed to prepare GH3536 alloy with high ductility and acceptable strength. • High-temperature microplastic deformation and damage of GH3536 alloy were observed in-situ SEM technique and its influencing factors were analyzed. • The effects of twins and serrated grain boundaries on the properties were simulated using the CPFEM model. [ABSTRACT FROM AUTHOR]

In this paper, a novel Cu-0.60Cr-0.20Nb-0.05Si-0.02Ca-0.02Ce (CCNSCC, wt.%) alloy is designed. By comparing the differences in the properties and microstructure with the Cu-0.60Cr-0.20Nb (CCN, wt.%) alloy under the same process, the effects of trace Si, Ca, and Ce elements on the CCNSCC alloy are disclosed. After undergoing cold rolling by 80% and aging at 450 °C for 60 min, the CCNSCC alloy exhibits a tensile strength of 524 MPa and a softening temperature of 600 °C. These values represent an increase of 104 MPa and 90 °C respectively compared with the CCN alloy. After a multi-stage combined thermo-mechanical treatment including preaging at 400 °C for 30 min, the tensile strength and electrical conductivity of the CCNSCC alloy reach 618 MPa and 75.2%IACS respectively. Microstructure analysis shows the existence of rod-like and polygonal Cr 8 Nb 3 Si particles, as well as globular, ellipsoidal, and crescent-shaped (Ca,Ce)Cu 5 particles. During the process of aging, the precipitation of the Cr phase occurs at the phase boundaries of Cr 8 Nb 3 Si particles. Additionally, significant quantities of fine Cr particles at the nanoscale surround the Cr 8 Nb 3 Si particles, exerting a beneficial influence on the strength and electrical conductivity of the CCNSCC alloy. Besides, the CCNSCC alloy has finer Cr particle size and lower volume fraction of recrystallized grains after aging in comparison to the CCN alloy. This indicates that the addition of trace Si, Ca, and Ce elements significantly inhibits the growth of Cr particles and occurrence of recrystallization. Plenty of dislocations are observed in different states of the CCNSCC alloy, and their interaction with the Cr precipitates is the primary factor contributing to the excellent mechanical properties of the CCNSCC alloy. The findings of this study provide valuable insights for improving the properties and microstructure of Cu–Cr–Nb alloys. • A novel Cu-0.60Cr-0.20Nb-0.05Si-0.02Ca-0.02Ce (wt.%) with excellent comprehensive properties is designed. • Cr particles and (Ca,Ce)Cu 5 particles precipitate at the boundaries of nanoscale Cr 8 Nb 3 Si particles during aging. • The addition of trace Si, Ca, and Ce significantly inhibits the growth of Cr particles and occurrence of recrystallization. [ABSTRACT FROM AUTHOR]

The uncontrollable directional grain growth and non-equilibrium microstructure of Inconel 718 will form during laser direct energy deposition (LDED), which seriously limits the promotion and application, so it is necessary to consider the heat treatment to improve the microstructure and mechanical properties. In this paper, the effects adopting different heat treatments on the phase composition, precipitation behavior, grain structure, tensile and tribological properties of LDED Inconel 718 have been systematically investigated, with as-deposited samples compared. The results show that the number and size of γ″ phases can be significantly changed under different aging and solution conditions, and the strength and wear resistance increase while elongation decreases since the fine grain and precipitation strengthening occurring during heat treatment. By comparing the different samples, the SA1100A exhibits the highest yield and tensile strength, with 140.6% of yield strength and 83.9% of ultimate tensile strength increasing compared to as-deposited samples, also showing the narrowest wear mark width and the lowest average mass loss. [ABSTRACT FROM AUTHOR]

The influence of annealing temperature (450 °C ∼ 800 °C) on the microstructure and mechanical properties of the novel α + β titanium alloy Ti-6Al-4V-2Mo-2Fe (Ti6422) designed by the authors was investigated systematically in this paper, and the strength-plasticity enhancement mechanism was addressed comprehensively. The results showed that the microstructure of the samples annealed at 450 °C ∼ 700 °C was composed of primary α p phase and β trans structure. And as the annealing temperature increased, the size of α p and α s phase, as well as, the content of β phase gradually increased. When annealed at 750 °C and 800 °C, the microstructure consisted of equiaxed α p phase and irregular β phase without α s precipitates. As the annealing temperature increased from 450 °C to 800 °C, the yield strength of the samples climbed and subsequently declined, while the elongation after fracture kept rising. Ultrahigh strength (σ y ≥ 1340 MPa, σ b ≥ 1390 MPa) and considerable plasticity (δ ≥ 11.8%) were obtained under the annealing temperature of 500 °C and 550 °C. During deformation, annealed samples with higher content and slighter size of nanoscale α s and microscale α p phase accumulated an abundance of dislocation at the α p / β and α s / β interfaces. This resulted in notable interface strengthening and improved the strength. Moreover, the considerable plasticity was attributed to the superior coordinated deformation ability of the α p phase and certain coarse α s phase, which was conducive to delaying the reduction of the work-hardening rate and thus postponing the occurrence of necking. The microscale α p phase could withstand most of the plastic deformation. While high-density dislocation entanglement and local kink occurred in certain coarse α s phase, which alleviated the strain incompatibility in the hard β trans structure. • Ti6422 alloy exhibits an improved strength-plasticity combination through simple annealing. • Ultrahigh strength of ∼1340 MPa together with considerable plasticity of ∼12% is achieved. • Notable interface strengthening is the primary source of the ultrahigh strength. • The considerable plasticity is attributed to the superior deformation ability of the α p and coarse α s phase. [ABSTRACT FROM AUTHOR]

This paper presents a comparative analysis of microstructural and high-temperature mechanical properties of Inconel 625 (IN 625) cast Ni-based superalloy welded using two different processes, i.e. gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW). For GTAW and SMAW processes, ERNiCrMo-3 and ENiCrMo-3 filler metals were employed, respectively. The base metal exhibited a γ-matrix with a sparse distribution of the Laves phase, which was attributed to the microsegregation of Nb at the interdendritic region. After GTAW and SMAW, the fusion zone exhibited fine columnar grains resulting from rapid solidification. GTAWed and SMAWed IN 625 (G625 and S625, respectively) displayed the overmatched microhardness traverse. S625 exhibited slightly higher yield and tensile strengths than G625 at temperatures of 25, 650, 700, and 750 °C. Tensile fracture occurred at the Laves phase in the base metal, showing similar features in the two welds. However, the creep lives of G625 (8915–17044 h) were significantly longer than those of S625 (894–3125 h) at 700–750 °C, exhibiting different rupture behavior. After creep deformation, fracture occurred at the fusion line in G625, whereas in S625, the weld metal was fractured. In the crept weld metal of G625, although the Laves phase was slightly grown at the interdendritic regions, it rarely influenced creep rupture. Meanwhile, in the weld metal of S625, the Laves phase was noticeably grown despite the shorter creep time compared to that of G625. Higher contents of Fe and Si in the weld metal of S625 was responsible for the acceleration of the coarsening rate of the Laves phase, causing the short creep lives of S625 by acting as a crack initiation site. Accelerated cracking in the Laves phase can be evidenced by the low density of dislocations resulting from brittle fracture with minimal plastic deformation in the weld metal. • As-SMAWed weld metal exhibited more promoted Laves phase than of as-GTAWed weld metal. • SMAWed weld metal was vulnerable to creep compared to GTAWed weld metal at 700–750 °C. • Laves phase was promoted in the SMAWed weld metal due to its high content of Fe and Si. • Laves phase was much less developed in the GTAWed weld metal even after longer creep lives. [ABSTRACT FROM AUTHOR]

Iron contamination is a major concern in aluminum alloys recycling. It is considered the main deleterious contamination due to its low solubility in the aluminum matrix leading to the formation of Fe-rich intermetallic phases with platelet-like morphology, which act as stress risers deteriorating the mechanical properties. This paper investigates the effect of Fe contamination in the microstructure and mechanical properties of Al–7Si-0.7Mg-2.8Fe alloy processed by Laser Powder Bed Fusion (LPBF). Microstructure characterization was carried out by Optical Microscopy (OM), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscope (TEM). The mechanical characterization was performed by Vickers microhardness and tensile tests. The LPBF sample was analyzed in two directions, vertical and horizontal. The results show that the LPBF process provided a microstructural refinement and reduction of the aspect ratio of α-AlFeSi phase and silicon particles, leading to a strong improvement in mechanical properties when compared to the Fe-contaminated as-cast Al–7Si-0.7Mg-2.8Fe alloy. [ABSTRACT FROM AUTHOR]

To improve the mechanical properties of the pre-deformed SUS 304 ultra-thin strip by regulating its microstructure, the paper uses high energy pulsed current to treat the pre-deformed SUS 304 ultra-thin strip. Uniaxial tensile samples with different pre-deformation (10%, 30%, 50%) are prepared by tensile testing machine and used to study the changes in microstructure and mechanical properties of the pre-deformed samples before and after the electric pulse treatment. The results show that the electric pulse treatment results in a complete recovery of plasticity and a 10% increase in elongation at break for the 10% pre-deformed sample, and leads to a 6.8% decrease in yield strength, a 13.2% increase in tensile strength and a 34.4% increase in elongation at break for the 50% pre-deformed sample. The electric pulse treatment causes recovery and static recrystallization of pre-deformed samples at lower temperatures, and some annealing twins are formed within the recrystallized grains. The electric pulse treatment reduces the dislocation density, refines the deformed grains, alleviates the {111} silk texture generated during pre-tensile deformation, and improves the anisotropy. It can be seen that the electric pulse treatment can significantly improve the mechanical properties of pre-deformed samples and promote the plastic deformation capacity of the SUS 304 ultra-thin strip. [ABSTRACT FROM AUTHOR]

This paper designed a novel (CoFeNi) 82 Ti 5 Al 5 V 8 medium entropy alloy (MEA) with "fcc + L1 2 " typical structure using JMatPro. The microstructure of the alloy, like recrystallization/non-recrystallization and L1 2 nanoparticle size, can be well controlled by thermal-mechanical processing. The result shows that the (CoFeNi) 82 Ti 5 Al 5 V 8 MEA exhibits a good combination of ultra high yield strength of ∼1500 MPa and ultimate tensile strength of ∼1747 MPa with total ductility of ∼10.8 % when the volume fraction of non-recrystallized region with high-density L1 2 nanoparticles (∼46 nm) is up to ∼91 %. Here, the high volume fraction non-recrystallization region is along with the high-density dislocations (∼6.29 × 1014 m−2). Thus, the high strength of present MEA is mainly attributed to L1 2 nanoparticle precipitation strengthening and dislocation strengthening, which contributes ∼686 MPa and ∼305 MPa to the total yield strength (accounting for ∼66 %), respectively. Therefore, the idea of combining precipitation strengthening with dislocation strengthening offers a paradigm to develop advanced structural materials for modern industrial applications. • A new L1 2 nanoparticles-strengthened (CoFeNi) 82 Ti 5 Al 5 V 8 MEA is successfully designed. • The L1 2 nanoparticle is identified as the novel (Ni,Co,Fe) 3 (Ti,Al,V) phase. • CRCA (CoFeNi) 82 Ti 5 Al 5 V 8 has an excellent property (σ s ∼1500 MPa, σ b ∼1747 MPa, δ∼10.8 %). • CRCA (CoFeNi) 82 Ti 5 Al 5 V 8 consists of N nad NR (high-density dislocations) regions. • High strength is mainly due to precipitation strengthening and dislocation strengthening. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of cold sprayed aluminum coatings on copper substrates were studied in this paper. The impact and deposition mechanisms of single and multiple particles during cold spraying were investigated using finite element modeling. The results of single particle model show that the maximum equivalent plastic strain is located at the contact surface between particle and substrate, decreasing from the jet site to the center of particles, and the equivalent plastic strain at the top of particles is almost zero. The results of multi-particle model show that the regions with large equivalent plastic strain include the contact surface between particle and substrate and the region between particles. The experimental results show that particle deposition has a significant impact on compaction during the spraying process. When the spraying distance is set to a fixed value of 30 mm, and the gas pressure is 2.2 MPa, 2.6 MPa, 3.0 MPa and 3.4 MPa, the coating porosity is always stable at about 1 %. The bonding strength of coating increases with the increase of gas pressure. When the gas pressure increases from 2.2 MPa to 3.4 MPa, the coating bonding strength has increased by 142.0 %, and the maximum value of bonding strength between the coating and the substrate is 16.9 MPa. When the gas pressure is 3.4 MPa with the gas preheating temperature of 300 °C, and the spraying distance is 20 mm, 30 mm and 40 mm, the coating porosity is 1.74 %, 0.95 % and 1.21 %, respectively. The maximum value of bonding strength between the coating and the substrate is 21.3 MPa under the spraying distance of 30 mm. • The maximum plastic strain of single particle model is located at the interface between particle and substrate. • The plastic strain of the multi-particle model is concentrated in the interface between particle and substrate. • The effect of particle deposition on compaction is very significant in the process of spraying. • The bonding strength of coating increases with the increase of gas pressure. [ABSTRACT FROM AUTHOR]

While work-hardening is typically considered in Ti as a prerogative of the β-metastable alloys, this paper introduces a novel perspective, presenting a set of alloy design rules to develop solute lean α + β titanium alloys exhibiting increased work-hardening capabilities. More specifically, reaching this goal is made possible through the development of α + α′ microstructures exhibiting Reorientation Induced Plasticity (RIP) within the α′ martensitic phase. The microstructural requirements for activating RIP and maximizing mechanical properties (i.e., combining high work-hardening, yield strength and ductility levels) are derived from an analysis of the microstructures/mechanical property relationships of various α + α′ samples. A set of design rules is provided. Emphasis is laid on the pivotal role of the chemistry of the α′ martensitic phase in RIP activation and a Molybdenum equivalent chemical criterion is proposed. The α phase is here suggested as a mean to reduce the prior β grain size and the resulting size of the martensite plates. This approach reveals that the versatile thermal treatments leading to α+α' structures broaden the mechanical property landscape, achieving large work-hardening capabilities (typically over 500 MPa) that can be combined with high yield strength (over 800 MPa). [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, the evolution of microstructure in Fe–Ni–Co–Al polycrystalline alloys and its effects on mechanical properties were systematically investigated. The results show that the proportion of high-angle grain boundaries (HAGBs) is 98.1 % with 51.2 % of Σ3 GBs during the solid solution (SS) process. The distribution of Σ3 GBs and other HAGBs (non-Σ3 HAGBs) are relatively dispersed, which prevents the formation of a specific orientation. In addition, there is no discernible anisotropy in GB migration during the SS process, ultimately resulting in the absence of texture. In contrast, during the directional recrystallization (DR) process, the directional migration of GBs is driven by the temperature gradient. Random high-angle grain boundaries (RHAGBs) with Σ values exceeding 29 possess higher GB energy and migration rate compared to low-angle grain boundaries (LAGBs) and HAGBs, making them more susceptible to GB migration. In the grain incubation area, the proportion of RHAGBs between grains oriented {111}<214> (grain 2 and grain 5) and their surrounding grains are 90 % and 75 %. These grains have the growth advantage and eventually form the main orientation {111}<214>. While the proportion of RHAGBs between grains oriented {114}<214> (grain 11) and its surrounding grains is only 65 %, characterized by lower GB energy and migration rate. Therefore, these grains eventually form the minor orientation {114}<214>. The coherent L1 2 -Ni 3 Al (γ′) precipitates were observed in both the SS-AG (SS after aging) and DR-AG (DR after aging) treatments. The DR-AG alloy, characterized by {111}<214> and {114}<214> orientations and γ′ precipitates, exhibited a 3.6 % recoverable strain and a 1.2 % superelastic strain, whereas no evident superelastic behavior was found in the SS-AG alloy, which featured a random texture and γ′ precipitates. [ABSTRACT FROM AUTHOR]