Search

Mg-5.6Zn-0.5Zr alloy (ZK60) tends to degrade too rapid for orthopedic application, in spite of its natural degradation, suitable strength and good biocompatibility. In this study, Nd was alloyed with ZK60 via laser melting method to enhance its corrosion resistance. The microstructure features, mechanical properties and corrosion behaviors of ZK60-xNd (x = 0, 1.8, 3.6, 5.4 wt.%) were investigated. Results showed that laser melted ZK60-xNd were composed of fine ɑ-Mg grains and intermetallic phases along grain boundaries. And the precipitated intermetallic phases experienced successive changes: divorced island-like MgZn phase → honeycomb-like T phase → coarsened and agglomerated W phase with Nd increasing. It was worth noting that ZK60-3.6Nd with honeycomb-like T phase exhibited an optimal corrosion behavior with a corrosion rate of 1.56 mm year -1 . The improved corrosion behavior was ascribed to: (I) dense surface film caused by the formation of Nd 2 O 3 hindered the invasion of immersion solution; (II) the three-dimensional honeycomb structure of intermetallic phases formed a tight barrier to restrain the propagation of corrosion. Moreover, ZK60-3.6Nd exhibited good biocompatibility. It was suggested that ZK60-3.6Nd was a preferable candidate for biodegradable bone implant.

The rapid degradation rate of Magnesium (Mg) alloy limits its biomedical application even though it possesses outstanding biological performance and biomechanical compatibility. In this study, a combined method of laser rapid melting and alloying Zinc (Zn) was proposed to decrease the degradation rate of Mg-Sn alloy. The microstructure, degradation behaviors and mechanical properties of the laser-melted Mg-5Sn-xZn (x = 0, 2, 4, 6 and 8 wt.%) alloys were investigated. The results indicated that the grain size of the alloys decreased with increasing Zn content, due to the increased number of nucleation particles formed in the process of solidification. Moreover, the laser-melted Mg-Sn alloys possessed finer grains compared with traditional as-cast and as-rolled Mg-Sn alloys. The degradation rate of the alloys decreased with increasing Zn content (0-4 wt.%), which was ascribed to the grain refinement and the formation of Zn(OH) 2 protective layer. However, the degradation rate increased as the Zn content further increased (4-8 wt.%), which was caused by the galvanic corrosion between the Mg matrix and the generated Mg 7 Zn 3 phase. Besides, Zn also increased the hardness of the alloys owing to the grain refinement strengthening and solid solution strengthening.

The limited mechanical properties of Al–Si alloys hinder their application in demanding and extreme conditions. The cracking tendency of high-strength aluminum alloys and high-cost of rare-earth elements pose challenges for the large-scale application of aluminum alloys in additive manufacturing. The novel and practical high-speed scanning remelting proposed in this study enables Al–Si alloys to exhibit significant proportion of fine microstructures and nano-precipitates, surpassing the mechanical properties of aluminum alloys fabricated by normal methods with exceptional strength (496.1 ± 5.8 MPa) and plasticity (21.4 ± 0.9%). This in-situ microstructure control method opens new pathways for the application in demanding engineering contexts. [ABSTRACT FROM AUTHOR]

The high yield ratio and low strain hardening ability of titanium alloys significantly limit their engineering applications. In this work, a Ti65Zr30Cu5 (at.%) alloy with nanoscale α laths was additively manufactured and achieved a high yield strength of 1274 MPa and a high strain hardening rate up to 40% of the shear modulus. Results show that universal basal/pyramidal dislocation reactions occur during the tensile deformation process. This triggers high-density sessile 〈c 〉 dislocation junctions, which accumulate and pin other mobile dislocations. Consequently, abundant dislocation walls are induced, leading to a strong hetero-deformation-induced strain hardening effect. [ABSTRACT FROM AUTHOR]

The morphology and microstructures of Ti-6.5Al-2Zr-1Mo-1V (TA15) samples at different stages of martensite decomposition fabricated by selective laser melting are characterized during the in situ tensile test, and the deformation and crack mechanisms are discussed. The results show that the as-deposited samples with full martensite structure, former being recognized as a state of poor plasticity, possess excellent ductility (with a maximum displacement of 0.74 mm) due to the cooperative deformation behavior of hierarchical martensites. The full-annealed sample, consisting of lamella (α + β) laths, also shows good ductility (0.65 mm) with the enhanced collaborative deformation behaviors between α and β laths. However, for samples with partially decomposed martensite structure, abrupt fracture after yielding was observed with deteriorated ductility (0.54 mm), as the slipping of dislocations is hampered by the dispersive nano-β precipitations. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (L-PBF) processed components usually exhibit reduced fatigue performance owing to unavoidable defects at multiple scales, especially when the loading direction is parallel to the building direction. In this study, hot isostatic pressing (HIP) was applied to the L-PBFed Al-4.74Mg-0.70Sc-0.32Zr (wt.%) alloy to enhance the fatigue properties with a focus on the defect (porosities and inclusions) effects, compared with the direct-aged samples. The results demonstrated that HIP induced inconspicuous microstructural effects, but it healed the porosities and promoted oxidation. Therefore, the fatigue crack initiation transformed the oxide-associated porosity into an oxide, with a significant fatigue strength improvement. This study highlights the critical importance of oxides in fatigue performance. [ABSTRACT FROM AUTHOR]

Maximization the synergistic effect of each component in transition metal-carbon complexes is expected to improve the bifunctional oxygen electrocatalysis for rechargeable Zn-air batteries but is still challenging. Herein, nucleobase guanine is employed as a supramolecular precursor to generate the core (FeCo alloy)-shell (carbon) structure embedded in ultrathin graphene-like nitrogen-doped carbon nanosheets (FeCo@NCNSs) via a confinement pyrolysis strategy. Thanks to the generated core-shell structure and bimetallic synergistic effect, the as-prepared FeCo@NCNSs exhibits excellent electrochemical performance in both oxygen reduction reaction and oxygen evolution reaction. As a result, when served as the bifunctional air electrode for a practical Zn-air battery, FeCo@NCNSs exhibits a higher open-circuit voltage (1.553 V) and peak power density (197.30 mW cm−2), as well as the greatly improved long-term cyclic stability compared to the noble metal benchmarks. This work provides a promising approach to integrate various active sites for bifunctional oxygen electrocatalysis and inspires the exploration of simple but efficient electrocatalysts for energy storage and conversion. • Guanine-derived core-shell FeCo@NCNSs were successfully synthesized via a confinement pyrolysis strategy. • Mutual synergistic effects of transition metal-carbon composites enhance reversible oxygen electrocatalysis. • The efficient noble-metal-free electrocatalyst exhibits promising performance for rechargeable Zn-air batteries. [ABSTRACT FROM AUTHOR]

Nb-Ti-Si-based in-situ composites are expected to be very promising materials for high-temperature structures seen in cutting-edge engines. However, the subpar fracture toughness and poor oxidation resistance severely limit their engineering application. To customize the microstructure and performance of directed energy deposition (DED) Nb-Ti-Si-based in-situ composite, it is important to comprehend the impact of alloying element. The present study examines the composite effect of Zr and Cr on room-temperature fracture toughness and high-temperature (1250 °C) oxidation behavior of Nb-23Ti-14Si-based in-situ composites produced by DED. With the co-alloying of Zr and Cr, (γ, α)-Nb 5 Si 3 and Cr 2 Nb phases are formed in the DED-built Nb-23Ti-14Si- x Zr- y Cr (x = 3-6 at.%Zr, y = 5-10 at.%) alloys. The formation mechanisms of the oxide scales on Nb-23Ti-14Si-based alloys during the oxidation process have been discussed. With the co-alloying of 6 at.%Zr + 12 at.%Cr, it presents the best oxidation resistance, and the weight gain at 1250 °C for 20 h has decreased to 34.67 mg/cm2. An enhancement in fracture toughness (K Q) to 14.46 MPa·m1/2 was achieved by alloying with 6 at.%Zr + 5 at.%Cr. • The microstructure evolution of DED-built Nb-23Ti-14Si-based alloys with co-alloying of Zr and Cr are studied. • The oxidation mechanism of Nb-23Ti-14Si-based alloys with co-alloying of Zr and Cr are discuss in detail. DED-built Nb-23Ti-14Si-based alloys with the co-alloying of 6 at.%Zr + 12 at.%Cr presents the best oxidation resistance. • Fracture behaviors of Nb-23Ti-14Si-based alloys with co-alloying of Zr and Cr are investigated. An improvement of K Q to 14.46 MPa·m1/2 was achieved in DED-built Nb-23Ti-14Si-based alloy with 6 at.%Zr + 5 at.%Cr alloying. [ABSTRACT FROM AUTHOR]

Al–Mg–Sc–Zr alloys manufactured using selective laser melting (SLM) possess outstanding static mechanical properties and thus have great potential application in the aerospace industry. However, their fatigue performance has not been clearly investigated and understood. In this work, the high cycle fatigue properties of an Al–Mg–Sc–Zr alloy manufactured via SLM with optimised process parameters (relative density over 99%) was studied with focus on the defects, whose size, shape and distribution were determined through X-ray tomography. Microstructure analysis results show that the Al–Mg–Sc–Zr alloy produced using SLM presents a periodic, inhomogeneous structure consisting of equiaxed grains at the boundary and columnar grains at the centre of one molten pool, which causes a significant difference in deformational mismatch under the fabrication conditions. Furthermore, X ray-CT results show that the defects, mainly porosity, are randomly distributed with the critical flaw size to initiate fatigue crack, thereby reducing fatigue life. When the stress ratio (R) is 0.1, the annealed sample presents good fatigue strength (σf) reaching 100.5 MPa, which is close to that of high-strength wrought 7075Al. Finally, a fatigue crack propagation mode connected with defect microstructure characteristics was established for prediction of fatigue properties. [ABSTRACT FROM AUTHOR]

Low-temperature and short-time solution and aging heat treatment (1050 ℃, 15 min/WC + 720 ℃, 8 h/FC to 620 ℃, 8 h/AC) was proposed for laser repaired Inconel 718 components in consideration of the risks on the heat deformation and properties degradation for the forging body with long-term homogenization treatment. After this heat treatment, the as-built epitaxial columnar grains will be retained and prone to induce the anisotropy of tensile properties. Herein, the bulk sample of Inconel 718 alloy via laser directed energy deposition (LDED) was fabricated followed by heat treatment and the tensile properties were studied under different loading directions (the angle between loading direction and building direction ξ =0°, 45°, 90°) in detail. The heat-treated microstructure of Inconel 718 is composed of the epitaxial columnar grains, Laves phase and γ" phase and the tensile properties present the obvious anisotropy. When ξ =0°, alloy possesses the best strength (yield strength, YS: 1139.93±9.87 MPa; ultimate strength, UTS: 1259.56±15.77 MPa) and optimal elongation (26.23±0.96 %). When ξ =90°, the YS (1019.51±10.96 MPa), UTS (1119.54±7.17 MPa) and elongation (9.15±3.77 %) are all the worst. When ξ =45°, YS (1023.05±13.78 MPa) and UTS (1209.85±13.37 MPa) are in the middle level and the elongation reached 21.39±1.55 %. Based on in-situ tensile results, the strength difference of alloy under different loading directions is the result of the synergistic effect of geometrically necessary dislocations (GNDs) density and Laves phase, and the plasticity difference is primarily attributed to GNDs density. • Heat-treated Inconel 718 via LDED is composed of the epitaxial columnar grains, Laves phase and γ" phase. • When loading direction is parallel to building direction, Inconel 718 alloy possess the best strength and elongation. • Strength difference under different loading directions is the result of both GNDs density and Laves phase. • Elongation difference under different loading directions is attributed to GNDs density. [ABSTRACT FROM AUTHOR]

Peritectic solidification has attracted increasing attention as a lot of important binary alloys, such as Fe–Ni, Zn–Cu, Fe–C and Ti–Al, exhibit peritectic reaction during solidification. In order to investigate the solidification behavior of Zn-rich Zn–Cu peritectic alloy containing nominally up to 7.8 wt.% Cu, a series of laser surface remelting experiments were performed. With the increase in growth velocity, Zn–Cu alloys with Cu content below 3.0wt.% showed an evolutional sequence from low-velocity η planar interface → lamellar structures → η shallow cells and finally to high-velocity η planar interface. The Zn-4.0 wt.%Cu alloy showed a similar transitional sequence except that irregular η cells appeared when low-velocity planar interface became unstable. In contrast, ε cell/dendrite was the typical microstructure of the Zn-7.8 wt.% Cu alloy within the whole scanning velocity range. Based on the maximum interface temperature criterion, a eutectic growth model under rapid solidification conditions (TMK model) and a self-consistent numerical model for the cellular and dendrite growth were applied to establish a phase and microstructure pattern selection map, which drew a clear whole picture of the relationship between phase/microstructure and solidification conditions of this series of alloys. Regarding the microstructure feature, our investigation revealed the range of the solidification velocity and chemical composition of lamellar structures as dominant microstructure and their lamellar spacing displayed a considerable range of the average value as a function of growth velocity. The relationship between the lamellar spacing and the growth velocity was further analyzed by using the TMK eutectic model, and the results showed the same overall trend as the experimental results. A phase and microstructure pattern selection map of Zn-rich Zn–Cu peritectic alloys. Regression analysis of the average spacing of lamellar structures. [ABSTRACT FROM AUTHOR]

A Ni50.8Ti49.2 alloy is fabricated by the Laser Solid Forming (LSF) technique by using prealloyed powder in this work. Characterization of the microstructure, phase transformation, and shape recovery of the as-deposited alloy are explored. Columnar grains with ⟨110⟩ preferred orientation are well aligned with the building direction, and the martensitic transformation (MT) behavior shows spatial distribution characteristics. With the increase in the deposited height, MT varies from the two-stage B2 → R → B19′ transformation to the one-stage B2 → B19′ transformation. Shape recovery properties are studied by compression tests. The as-deposited material without any further heat treatment shows a remarkably large superelastic recovery strain of 9.2% at room temperature, which is the largest value in the additive manufactured NiTi alloy. A negative adiabatic temperature change of –18.6 K induced by the elastocaloric effect during the unloading process is obtained. The shape memory effect (SME) of the as-deposited LSF Ni50.8Ti49.2 alloy is not only dependent on the detwinning of martensite but also associated with the partial superelasticity of the parent phase in the present work, demonstrating a unique two-stage yielding behavior. A residual strain up to 6% is recovered while heating, indicating an excellent SME. [ABSTRACT FROM AUTHOR]

Abstract The microstructure evolution and strengthening mechanism of a γ′-strengthening superalloy prepared by induction-assisted laser solid forming (LSF) were clarified by an investigation of the LSFed IN-738LC alloy with different solution treatments (at 1070 °C, 1120 °C and 1160 °C). The results show that both the as-deposited and heat-treated deposits were dominated by the columnar grains with a width of 100–270 μm. The equiaxed grains mainly originated from the columnar-to-equiaxed transition (CET) during LSF while a small portion of the equiaxed grains originated from recrystallization during the heat treatment, due to the relatively low temperature gradient in the induction-assisted LSF. Fine grain strengthening was still working in the columnar-grains dominated LSFed IN-738LC deposits. However, γ′ strengthening was found to play a major role in the strengthening mechanism by comparing the microstructure and properties of different heat-treated deposits. The γ′ dissolution and coarsening kinetics were calculated and the interaction mechanism between the dislocation and γ′ phase in LSFed IN-738LC was clarified. The deformation of the coarse (d > 200 nm) near cubic γ′ was found to be beneficial to the increase of ultimate tensile strength (UTS) and elongation (EL), while a brittle continuous phase formed at the grain boundary (GB) which was rich in Ni, Cr, Al and Ti was found to be detrimental to the deposit's plasticity. The γ′ phase deformation and desquamating, carbide breaking and GB phase breaking are the predominant fracture failure mechanisms. On the basis of relatively high strength, the IN-738LC deposits with a lower yield strength (YS)/UTS ratio than the cast and SLMed ones were obtained when solution-treated at 1070 °C. Graphical abstract Image 1 Highlights • The microstructure evolution was quantitatively characterized. • γ′ strengthening plays a major role in the strengthening mechanism. • A modified relational map between strength and γ′ size was established. • The deformation of the coarse (d > 200 nm) near cubic γ′ was beneficial to ultimate tensile strength and elongation. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the factors influencing the fracture toughness of thin Al–Cu alloy fabricated using Arc-Direct Energy Deposition (Arc-DED). By adjusting process parameters, samples with different microstructure characteristics were obtained, including an air-cooled (AC) deposit with a high proportion of equiaxed grains, a water-cooled (WC) deposit with a high proportion of columnar grains, and a post-heat-treated air-cooled deposit (T6) with numerous nano-sized precipitates. The conditional fracture toughness (K Q)/crack tip opening displacement (CTOD) values for the AC, WC, and T6 samples were 11.7 MPa m1/2/23.27 μm,11.4 MPa m1/2/22.70 μm, and 17.6 MPa m1/2/22.39 μm, respectively. The fracture toughness of the T6 sample was 50.4% and 54.4% higher than that of the AC and WC samples, respectively. The heterogeneity of the equiaxed/columnar microstructure affected the distribution of brittle θ-Al 2 Cu phases and pores, thereby influencing crack behavior. While columnar grains exhibited a stronger capacity for accumulating geometrically necessary dislocations (GNDs) and coordinating deformation compared to equiaxed grains, cracks were more likely to propagate along grain boundaries when the loading direction was parallel to the growth direction of columnar grains. Consequently, flat crack paths were observed in columnar grains, while equiaxed grains displayed tortuous paths. Furthermore, the precipitation of nano-sized θ'-Al 2 Cu phases contributed to improved fracture toughness. By integrating microstructure characterization, fractographic observation, analysis of uneven grain deformation behavior, and examination of GNDs distribution near crack paths, the study revealed microscopic damage characteristics, fracture behavior, and toughening mechanisms. [ABSTRACT FROM AUTHOR]

Purpose As known, the wire and arc additive manufacture technique can achieve stable process control, which is represented with periodic surface waviness, when using empirical methods or feedback control system. But it is usually a tedious work to further reduce it using trial and error method. The purpose of this paper is to unveil the formation mechanism of surface waviness and develop a method to diminish it.Design/methodology/approach Two forming mechanisms, wetting and spreading and remelting, are unveiled by cross-section observation. A discriminant is established to differentiate which mechanism is valid to dominate the forming process under the given process parameters.Findings Finally, a theoretical method is developed to optimize surface waviness, even forming a smooth surface by establishing a matching relation between heat input (line energy) and materials input (the ratio of wire feed speed to travel speed).Originality/value Formation mechanisms are revealed by observing cross-section morphology. A discriminant is established to differentiate which mechanism is valid to dominate the forming process under the given process parameters. A mathematical model is developed to optimize surface waviness, even forming a smooth surface through establishing a matching relation between heat input (line energy) and materials input (the ratio of wire feed speed to travel speed). [ABSTRACT FROM AUTHOR]

In this paper, the microstructure formation mechanism of an AlSi10Mg alloy prepared by laser directed energy deposition (DED-LB) and its influence on the mechanical properties was fully studied. The relationships between the microstructure characteristic scale, the molten pool solidification/thermal cycle conditions, and the tensile mechanical properties were established by combining the numerical simulation, theoretical calculation, and experimental validation. The as-deposited microstructure consists of the columnar α-Al dendritic array growing epitaxially along the building direction with the primary dendritic arm spacing of 18 ± 4.5 µm, the dendritic arm cell of 3 ± 1 µm surrounded by the refined eutectic network, and the Si precipitation of 17.7 ± 0.8 nm dispersed in the α-Al dendritic trunk. The feature size of the primary dendritic arm spacing and the dendritic arm cell size can be well predicted using the Kurz-Fisher and KGT dendritic growth models. The formation and size evolution of the Si precipitation was well described by the non-isothermal aging KWN model for the first time. The as-DED-LB-processed AlSi10Mg alloy exhibits a good comprehensive mechanical property with a yield strength of 187 ± 1.5 MPa and elongation to fracture of 7.4 ± 0.5%. The boundary strengthening from the eutectic phase network, the load-bearing capacity for dislocations caused by refined dendritic arms, and the precipitation strengthening of nano-Si particles play a major role in the improvement of the tensile strength and hardening ability. As a result, a quantitative relationship of the processing–microstructure–performance has been systematically investigated and established, which explores a method for the precision control and large-scale application of DED-AlSi10Mg alloys. [Display omitted] • Experiments and simulations of directed energy deposition AlSi10Mg parts. • Validity of theoretical solidification models on the microstructure. • Linking non-isothermal aging model to precipitated phase. • Quantitative relationships of processing–microstructure–performance. [ABSTRACT FROM AUTHOR]

The microstructure and microhardness of Ni-base superalloy IN-738LC fabricated by laser solid forming (LSF) with the preheating was investigated. The results showed that with the increase of the preheating temperature (T 0 ) (25 °C, 800 °C, 900 °C and 1050 °C), the total crack length decreased significantly, the segregation of Ti and Al worsened, and the volume fraction of equiaxed grain increased, as well as the size of blocky carbides, γ-γ′ eutectic and γ′ particles. The high-angle grain boundaries, at which the continuous liquid film can be easily formed, were found to be susceptible to cracking. Both the concentration of Ti and Al and the increase of dendrite spacing contribute to the growth of carbides and γ-γ′ eutectic in the interdendrite while the size of the γ′ phases was largely affected by preheating. It was interesting to find that γ′ phase exhibited a bimodal distribution in the bottom of the deposit with the preheating at 1050 °C. The average microhardness of the deposits without preheating and with preheating at 800 °C and 900 °C is about at the same level, while the deposit with preheating at 1050 °C has the lowest average value. The crack-free deposit can be obtained when T 0 was up to 1050 °C, and its room temperature tensile properties are superior to cast IN-738LC alloy. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (L-PBF) is a promising technique for fabricating high-performance complex aluminum (Al) alloy components. However, conventional high-strength wrought Al alloys that are processed using L-PBF have limited application owing to their poor cracking resistance. To investigate the cracking mechanism, L-PBF was used to fabricate a 2024Al alloy. The resultant microstructure exhibited severe hot cracking, which occurred at grain boundaries with a high angle in both solidification and liquation cracks. Increasing the scanning speed increased the susceptibility to cracking. The effect of scanning speed on the eutectics content of Al 2 Cu and Al 2 CuMg and the residual stress in as-fabricated samples are discussed. Crack elimination at a low scanning speed could be ascribed to the lower thermal stresses and adequate liquid feeding during the late stage of solidification. In addition, based on the RDG (Rappaz-Drezet-Gremaud) model, a cracking susceptibility map was produced, in which the cracking susceptibility was determined to increase with an increase in the solidification rate, in agreement with experimental observation. • Cracking mechanism in L-PBFed high-strength 2024Al alloy is determined. • Crack elimination at low scan speed is attributed to the low thermal stress and sufficient liquid feeding. • The cracking susceptibility map is established based on RDG model. [ABSTRACT FROM AUTHOR]

We report the electrochemical dissolution behavior of Ti-based alloys prepared by two different processing methods including laser solid foming (LSF) additive manufacturing and forging in a 15 wt % NaCl solution. The corrosion resistance of the forged Ti6Al4V alloy is slightly better than that of the LSFed state, and is ascribed to the dominant galvanic effect of fine α/β lamellae accelerating the corrosion dissolution rate of the LSFed sample. The size, morphology, and content of the α/β phase and Al segregation affect the anodic dissolution behavior by promoting/inhibiting the galvanic effect. The galvanic effect of duplex Ti-based alloys is the key factor determining the anodic dissolution performance and dissolved surface quality. The distinction in electrochemical dissolution behavior on Ti6Al4V alloy produced by LSF and forging provides a mechanism support on their difference of electrochemical machining machinability. • Effect of processing method on electrochemical dissolution performance of Ti6Al4V were revealed. • Fine basketwave microstructure has inferior corrosion resistance but better roughness than coarse equiaxed α phase. • Galvanic effect determines the corrosion resistance and dissolved surface quality of Ti6Al4V alloy. [ABSTRACT FROM AUTHOR]

Al-Mn-Sc based alloys present potential in manufacturing high-performance aluminum alloy by selective laser melting (SLM) technology. However, the solidification and solid-state phase transformation behaviors induced by SLM layer-by-layer deposition and the interaction between the Al-Mn and Al-Sc systems result in complexity in the precipitation of Mn-bearing phases and Al 3 Sc. In this work, ternary Al-5Mn-xSc (x = 0, 0.7, 1.5 wt%) alloys were fabricated via SLM, and their microstructure and mechanical behavior were investigated. The results indicated that the Sc/Mn ratio and the precipitation sequence were critical in controlling the grain and precipitate characteristics of the Al-Mn-Sc alloy deposits. The precipitation of primary Al 3 Sc was inhibited by the pre-precipitated Mn-bearing particles in Al-5Mn-0.7Sc alloy, resulting in columnar grain structure similar to that of Al-5Mn. In the case of Al-5Mn-1.5Sc alloy, the preferentially precipitated Al 3 Sc induced a bimodal grain structure. However, with the mismatch in plastic deformation capacity between different grain regions, micron-sized Al 6 (Mn,Fe) particles formed around the equiaxed/columnar grain region interface tended to induce cracking. [Display omitted] • The effect of Sc content on the microstructure of Al-Mn-Sc alloy is analyzed. • A high-strength SLM-ed Al-Mn-Sc alloy and its strengthening mechanism is revealed. • The discordant deformation cracking mechanism of Al-5Mn-1.5Sc alloy is revealed. • The interaction between Mn and Sc makes Sc/Mn ratio critical for Al-Mn-Sc alloys. [ABSTRACT FROM AUTHOR]

The application of laser powder bed fusion (L-PBF) in conventional high-strength wrought aluminum alloys is a significant challenge due to its high cracking sensitivity. In this study, 2024Al and 1.3-wt% Zr-modified 2024Al alloy deposits were prepared by L-PBF using pre-alloyed powder. The solidification cracking susceptibility of the 1.3-wt% Zr-modified 2024Al alloy was reduced to ∼0.4 of that of the 2024Al alloy. Compared to the complete columnar α-Al grain microstructure in the 2024Al deposit, the crack-free Zr-modified 2024Al deposit exhibited a heterogeneous grain structure having columnar α-Al grains in the inner region of the molten pool and ultrafine α-Al equiaxed grains at the fusion boundary. Based on the time-dependent nucleation theory and constitutional undercooling analysis ahead of solidification interface, the precipitation behavior of primary Al 3 Zr nanoparticles is analyzed, and it is deduced that the high intensity of effective nucleation sites by nanosized primary Al 3 Zr at the fusion boundary of molten pool leads to the formation of equiaxed grains at the beginning of the solidification of molten pool. The as-deposited Zr-modified 2024Al exhibited a yield strength (YS) of ∼376 ± 7 MPa and an ultimate tensile strength (UTS) of 441 ± 7 MPa with an elongation of 14.1 ± 1.6%. The YS and UTS increased to 402 ± 9 MPa and 483 ± 37 MPa after T6 heat treatment, respectively. Both the tensile properties of the as-deposited and T6-treated Zr-modified 2024Al were comparable to the wrought 2024-T651 alloy and higher than most of the previous L-PBFed Al–Cu–Mg alloys. [ABSTRACT FROM AUTHOR]

A solution entropy model was developed for the undercooled binary eutectic alloy systems. As an extension of Taylor and Fidler et al.'s model, the present model considered the change of phase composition with the increase of undercooling. Furthermore, the sub-regular solution model and the interaction parameter (lAB) were also introduced.. In this paper, the extended model is used to calculate the solution entropy for binary eutectic phases under the undercooled condition, and the application scope of the model is also extended. Not only the growth manner of eutectic phases, but also the transition of morphologies may be predicted and explained by calculating the solution entropy of eutectic phases under the non-equilibrium condition with the developed model. Experimental results show that the developed model is valid for the undercooled Ni-Si and Ni-Sn eutectic alloy systems. [ABSTRACT FROM AUTHOR]

Eutectic high entropy alloys (EHEAs) have attracted considerable interest because of their excellent casting fluidity and outstanding mechanical properties. In this study, a novel system of EHEAs, namely CrFeNi x V 0.64 Ta 0.36 (1.3 ≤ x ≤ 1.9) was designed and prepared. The microstructure evolution and mechanical properties of CrFeNi x V 0.64 Ta 0.36 EHEAs were investigated in as-cast state. The results showed that the alloy was composed of σ-phase, Fe 7 Ta 3 -type intermetallic compounds (IMC), and a small amount of the eutectic phase when x = 1.3. A rare bimodal eutectic microstructure [face-centered-cubic (FCC) structure /σ + Fe 7 Ta 3 -type IMC] was observed in EHEAs, even in high entropy alloys when x = 1.6, 1.7, 1.8, and 1.84. The typical hypo-eutectic microstructure was acquired when x was increased to 1.9. The fully eutectic composition, i.e., CrFeNi 1.85 V 0.64 Ta 0.36 with alternatingly lamellar FCC and Fe 7 Ta 3 -type IMC structures exhibited the best mechanical properties, with the compressive yield strength, fracture strength, and engineering strain being 1475.9 MPa, 2799 MPa, and 38.095%, respectively. [Display omitted] • A rare bimodal eutectic microstructure was observed in EHEAs, even in HEAs and conventional alloys. • The fully eutectic Ni1.85 gained best mechanical properties with σ s and ε being 1475.3 MPa and 38.095%, respectively. [ABSTRACT FROM AUTHOR]

A laboratory study was carried out, using Pb–15 wt.% Sn alloy on self-made apparatus, to determine the solidification behavior of the semi-solid slurry with the solid fraction beyond 0.6. It is found that the solid–liquid separation is obvious in the samples with the solid fraction beyond 0.6. According to this character of semi-solid processing, a kind of single-crystal powder coated with Pb–Sn eutectic was made during continuous stirring and cooling processes. The analysis and discussion indicated that this approach can reduce the content of oxide and impurity in the powder. [ABSTRACT FROM AUTHOR]

For most safety-critical applications, the achievement of both high strength and high toughness is one of the key requirements for structural materials. However, strength and toughness are generally mutually exclusive. Here, we report a selective-laser-melted Al–Mg–Sc–Zr alloy with a good combination of strength and toughness, which is comparable to those of 7075-T651 high-strength wrought Al alloy. Despite the brittle crack associated with order-induced planar slip due to secondary Al 3 (Sc,Zr) nano-precipitates, the fracture toughness was effectively improved via diverse intrinsic/extrinsic toughening mechanisms associated with its ultrafine and heterogeneous microstructure. The present work provides a potent strategy for fabricating high-strength and high-toughness Al-based alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, bulk deposits of a Sc modified Al-Mn-Fe-Si alloy were prepared by selective laser melting (SLM), and the microstructural characteristics and tensile properties of the deposits were analyzed. The as-deposited sample presented a multiscale microstructure consisting of epitaxial columnar grains with width of 30–140 μm, in which there exist α-Al dendrite arrays with average primary dendrite arm spacing of 0.34 μm, and interdendritic nanoscale α-Al + Al 6 (Mn,Fe) divorced eutectic. After an aging treatment, Al 6 (Mn,Fe) transformed into Al 12 (Mn,Fe) 3 Si, and its morphology gradually evolved from skeleton into particle. Meanwhile, needle-like AlMnSi precipitated and grew up in the α-Al dendrite trunk. The ultimate tensile strength increased from 349 ± 9 MPa in the as-deposited state to 430 ± 3 MPa after aging at 300 °C. However, it dropped to 358 ± 1 MPa when the aging temperature increased to 350 °C. The addition of Sc caused precipitation strengthening of secondary Al 3 Sc after aging treatment, but the grain refinement effect of primary Al 3 Sc was inhibited since Sc tended to segregate at the frontier of the Mn-containing pre-precipitates. [Display omitted] • A dense Sc modified Al-Mn-Fe-Si alloy was designed for SLM process with large processing window. • Microstructure evolution and tensile properties were characterized from multi-scales. • The precipitation strengthening of primary Al 3 Sc was affected by Mn-containing phase. [ABSTRACT FROM AUTHOR]

• Local-heterogeneous laminar structure in WAAMed 2219 leads to the improved stress during deformation. • The θ′ in deposit sample results in high deformation resistance in hot deformation (<380 °C). • DRV acts as the main deformation mechanism and DRX as the auxiliary one. ga1 This study investigates the hot deformation behavior and relative microstructural evolution of a wire + arc additive manufactured (WAAMed) 2219 Al alloy, in which hot compression was conducted in the temperature range of 300–480 °C at the strain rates of 0.01–10 s−1 with a true strain of 60%. The local-heterogeneous microstructure shows an alternated distribution of equiaxed and columnar grains. The θ′ phase precipitates near the grain boundaries owing to heat accumulation. These microstructural characteristics lead to a higher stress resistance during hot deformation as compared to as−cast and wrought 2219 Al alloys. The calculated activation energy for the WAAMed 2219 Al is 161.1 KJ/mol, slightly higher than that of the as−cast sample. The proportion of low-angle grain boundaries is 70–80% in the as−deformed WAAMed 2219 Al alloy, which is mainly attributed to the dynamic recovery behavior with an auxiliary dynamic recrystallization. Additionally, the dynamic recrystallization grains fraction increases with a decrease of the Zener-Hollomon parameter. With a constant strain rate and an increased deformation temperature (300–480 °C), the micro-hardness firstly decreased and then gradually increased. The nanoindentation results show that the influence of hot deformation conditions on the elastic modulus of the hot deformed WAAMed 2219 Al alloy is not obvious. [ABSTRACT FROM AUTHOR]

The relationship between microstructural characteristics and anodic dissolution behaviour plays a crucial role in the process control of the electrochemical machining technology (ECM). An additive-manufactured Ti6Al4V alloy produced by direct energy deposition (DED) exhibited a finer lamellar α+β structure within the considerably coarser columnar prior-β grains as compared to the traditional forged Ti6Al4V alloy consisting of equiaxed α and transformed β phases. The electrochemical anodic behaviour of DED-produced Ti6Al4V alloy was investigated in a 15-wt.% NaCl solution and compared with that of the forged Ti6Al4V alloy. Electrochemical measurements showed that the DED-produced Ti6Al4V exhibited higher resistance to corrosion and lower electrochemical machinability than did the forged Ti6Al4V alloy. The high phase boundary density, originating from the refinement of constituent phases, increased the stability of the passive film formed on the surface of the DED-produced Ti6Al4V, thereby improving the corrosion resistance, while the high fraction of β phase in the Ti6Al4V deposit decreased the rate of anodic dissolution. The lower composition difference of solutes of DED-produced Ti6Al4V was beneficial to its higher resistance to corrosion. The fine and lath-type α phases led to a competitively high level of microscopic flatness of the Ti6Al4V alloy after the electrochemical dissolution. • Microstructural characteristics of LSF-produced and forged Ti6Al4V alloy were compared. • Anodic behaviour of Ti6Al4V alloy was closely related to the forming processes. • Selective dissolution of α phase was affected by solutes partitioning and phase size. • Corrosion resistance of Ti6Al4V alloy was affected by phase boundary density and phase content. [ABSTRACT FROM AUTHOR]

The effect of melting modes on microstructure evolution and tensile properties of selective laser melted (SLM-ed) Sc modified Al–Mn alloy (Al–5Mn-0.6Sc) is investigated in this work. With the transition of melting mode from conduction to keyhole by coinstantaneous increasing the laser power from 200 W to 380 W and the scanning speed from 800 mm/s to 1400 mm/s, the columnar grain width significantly decreases by 88% from 34.9 μm to 4.2 μm. Consequently, the yield strength and the elongation increase simultaneously from 266 MPa and 10% to 308 MPa and 17%, which increase by 16% and 70%, respectively. The refinement and orientation diversification of the grains caused by keyhole mode simultaneously improve the strength and elongation by inducing the Hall-Petch effect and enhancing the crack path tortuosity. This work reveals the feasibility and the mechanism of changing melting mode acts as a method to regulate the SLM-ed microstructure and mechanical properties. • The microstructure of Al–5Mn-0.6Sc alloy is refined by inducing keyhole mode. • The tensile strengths and ductility are enhanced after inducing keyhole mode. • The precipitation of primary Al 3 Sc is inhibited by Mn-containing phase. [ABSTRACT FROM AUTHOR]

Alloying process and processing optimization are most effective methods to modify the microstructure and mechanical properties of Nb-Si based alloys. In this work, Nb-22Ti-16Si- x Mo(x = 5–20 at%) alloys were successfully fabricated by a laser directed energy deposition additive manufacture with elemental powder mixtures. The effect of Mo on the microstructure, micro-hardness, nano-hardness and fracture toughness of Nb-22Ti-16Si- x Mo alloy were investigated. The results indicated that the addition of Mo in Nb-22Ti-16Si alloy is promoting the formation of Ti(Nb) 5 Si 3 and β-Nb 5 Si 3 phases and inhibiting the formation of Nb 3 Si phase. Mo was preferentially enriched in the niobium solid solution (Nbss) phase. The volume fraction of Nbss phase first increases then slightly decrease, while Ti(Nb) 5 Si 3 phase was increased with Mo content, especially Nbss matrix also become more continuous. The solidification path of Nb-22Ti-16Si- x Mo alloys show a certain deviate from the prediction by the Scheil solidification models. Mo alloying in Nb-22Ti-16Si alloy also lead to the increase in the young's modulus and nano-hardness of Nbss and β-Nb 5 Si 3 phases. The fracture toughness of Nb-22Ti-16Si- x Mo(x = 5–20 at%) alloys first increases to 12.2 MPa m1/2 when Mo content increases to 10 at%, then decreases with further increases in Mo content, while their micro-hardness shows the opposite trend. • Nb-22Ti-16Si- x Mo alloys additively manufactured by laser directed energy deposition. • The microstructure evolution of as-deposited Nb-22Ti-16Si- x Mo alloys are studied. • Mo added imposes significant influences on microhardness and nano-hardness. • Fracture behaviors of Nb-22Ti-16Si- x Mo are discussed and the K Q of as-deposited Nb-22Ti-16Si-10Mo is 12.2 MPa m1/2. [ABSTRACT FROM AUTHOR]

Heat treatment processing is commonly applied for additively manufactured metal materials, since the as-fabricated material frequently exhibits high internal stress and self-cracking. In this work, a heat treatment route was applied to an additively manufactured Ti-6Al-4V alloy, and its effect on the dynamic compressive behavior was investigated. The experimental results showed that the heat treatment process not only increased the dynamic compressive strength of the material, but also induced a change of the dynamic compressive strength from isotropic to anisotropic. In addition, the strain rate sensitivity of the material was reduced by heat treatment, even though both the as-deposited and heat-treated samples demonstrated positive sensitivity to the loading rate. Microstructural analysis suggested that the grain size and morphology were the same before and after heat treatment, while the internal stress increased due to heat treatment. [ABSTRACT FROM AUTHOR]

Recently, laser additive manufacturing (LAM) of Al–Mg–Sc–Zr alloys has been considered an important method for developing a new generation of high-performance Al alloys. However, one of the key differences between LAM and conventional casting/wrought processes is that it has a unique combination of rapid solidification and in-situ solid-state transformation induced by repeated thermal cycling during deposition. In addition, owing to its near-net shape characteristics, subsequent plastic deformation processing is typically not an option to improve the as-built microstructure. To gain insight into the effect of the complex thermal history during LAM on the microstructural evolution and mechanical properties of the novel alloy systems, an Al–Mg–Sc–Zr alloy was processed via laser-directed energy deposition (L-DED) using a substrate with air cooling (AC) or water cooling (WC). The results show that the solidification microstructure was closely related to the dynamic solidification conditions in the molten pool, which promoted the transition from an equiaxed grain structure at low cooling rate (AC) to a heterogeneous grain structure at high cooling rate (WC). Furthermore, in-situ precipitation occurred during the repeated high-temperature thermal cycling in the AC sample, while it was effectively suppressed in the WC sample by lowering the peak temperature during thermal cycling. After aging, the yield strength of the WC sample was enhanced to ~2 times that of the AC sample, while the uniform elongation was still comparable to that of the AC sample. To achieve good mechanical properties for L-DED-processed Al–Mg–Sc–Zr alloys, it is crucial to conduct integrated control of the thermal history during both rapid solidification and in-situ precipitation. [ABSTRACT FROM AUTHOR]

• The Nb-Ti-Si-based alloy additively manufactured by powder-feeding laser directed energy deposition. • The microstructure evolution of as-deposited and HIP-processed Nb-Ti-Si based alloy are studied. • HIP treatment weakened the oxidation resistance of Nb-Si-Ti-based alloy deposit at 1250 °C and the reason is elucidated 4 No pest-oxidation is observed on the as-deposited alloy at 800 °Cfor 100h. A powder-feeding laser directed energy deposition process has been used for preparing Nb-Ti-Si-based alloys from elemental powder mixtures. The effects of hot isostatic pressing (HIP) on the microstructure evolution and isothermal oxidation at 800 °C and 1250 °C are studied. The as-deposited alloy shows a eutectic microstructure with β-Nb 5 Si 3 dendrites existing in the solid-solution niobium (Nbss) matrix and β-Nb 5 Si 3 +Nbss anomalous eutectic in the interdendritic zones. A eutectoid reaction of β-Nb 5 Si 3 →Nbss+α-Nb 5 Si 3 occurs after HIP. The oxidation rate for the HIP-processed alloy was 1.33 times that of the as-deposited alloy at 1250 °C. No pest-oxidation is observed on the as-deposited alloy at 800 °C. [ABSTRACT FROM AUTHOR]

• A novel low modulus, high strength Ti-7.5Mo was prepared by SLM from mixed powder. • An heterogeneous conchoidal structure consists by α and β phase appears. • The α/β synergism effect offers low modulus, high strength and ductility. The powder mixture, which used as feedstock materials in selective laser melting (SLM), always brings the undesirable problem in microstructure and then mechanical properties, due to its inhomogeneous chemical composition and stability. In this work, the in-situ SLMed Ti-7.5Mo alloy presents an heterogeneous conchoidal structure (hcp α-Ti and bcc β-Ti) from elemental powder mixture. During the SLM, the Mo, which possesses high melting temperature and density, was partial melted and then driven by Marangoni flow in molten pool. Thus, elemental micro-segregation appears with a result of special conchoidal structure. The SLMed sample shows low Young's modulus (70 GPa) with high tensile strength (>700 MPa) and ductility (9%), given to the synergism effect of β channel and α island. [ABSTRACT FROM AUTHOR]

The present study aims to reveal the mechanism of element vaporization of Ti-6Al-4V alloy during selective laser melting (SLM). The equations of Redlich–Kister and the thermodynamics principles were employed to calculate the vaporization thermodynamics, which contributes to the obtaining the vaporization kinetic based on the Chapman-Enskog theory and the diffusion model. According to the achieved vaporization model, the elements with the most prominent tendency and flux to vaporize were distinguished. Moreover, the effect of the process parameters on the vaporization of Al and Ti is experimentally investigated using inductively coupled plasma optical emission spectrometer (ICP) technology. The analyzed results of the chemical composition of the powders and builds show a great agreement with the kinetic results calculated by the vaporization model. Notably, the element vaporization can be curbed by regulating the laser energy input. [ABSTRACT FROM AUTHOR]

A Ti–6Al–4V alloy wall with 80 vol.% equiaxed prior-β grains was fabricated via wire and arc additive manufacturing. However, the equiaxed prior-β grains were characterized by strong texture. Formation mechanisms of the equiaxed prior-β grains were discussed. The tensile results presented a much lower anisotropy than that in other studies. [ABSTRACT FROM AUTHOR]

In order to understand the formation mechanism of a special nanostructure of γ' and γ" co-precipitated phase which present an important potential in the improvement of high thermal stability, strength and ductility in the superalloy, the influence of the atomic ratio of (Al+Ti)/Nb on the microstructures of the Ni-Cr-Al-Ti-Nb alloys has been investigated using laser directed energy deposition (DED). As the ratio of (Al+Ti)/Nb increases in the as-deposited and heat-treated alloy, the precipitation ability of γ' phase in the alloy is improved, accompanied with a reduction in the precipitation of γ" phase. When this ratio reaches 1.5 with the alloy composition of Ni-13.5Cr-5.26Al-1.95Ti-4.8Nb (at.%), the γ' and γ" co-precipitated nanostructure with the pattern of γ" phase attaching to six surfaces of the cubic γ' phase is generally produced in the as-deposited and heat-treated alloy. Furthermore, it was revealed that Ti element has the critical effect on the formation of this compact co-precipitated nanostructure. • Influence of (Al + Ti)/Nb ratio on precipitation of γ' and γ" phase were investigated. • The γ' and γ" compact co-precipitated nanostructure formed in DED-ed Ni-based alloy. • The compact co-precipitated nanostructure has excellent thermal stability at 750 °C. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) of AlMgScZr alloy has garnered significant attention as a high-strength aluminum alloy. However, its low modulus, Portevin-Le Chatelier (PLC) behavior, and weak strain hardening capability restrict its application in the aerospace sector. In this study, SiC/AlMgScZr composites with different SiC content have been successfully fabricated using LPBF. The inherent bimodal grain structure of AlMgScZr alloy was not completely altered by the addition of SiC particles. However, with increasing SiC content, heat accumulation increased, and the solidification cooling rate decreased. This led to an increase in the size of α-Al grains in the 5 wt% SiC/AlMgScZr composites. Meanwhile, movable dislocations can be efficiently preserved inside the grains, where they effectively accumulate and become entangled. Consequently, the strain hardening capability of the 5 wt% SiC/AlMgScZr composites improved by approximately 58 % compared to AlMgScZr alloy, with a strain hardening index (n) reaching 0.29. Additionally, the addition of SiC particles led to an increase in the elastic modulus (81.0 GPa). Furthermore, the reaction between Mg atoms and SiC particles resulted in the formation of Mg 2 Si, which altered the distribution of Mg elements and initiated the reactive precipitation of a Mg-rich phase. There is no competition between the diffusive migration of solute atoms and the motion of movable dislocations within the composites. The additional SiC particles effectively eliminated the PLC effect in the LPBF of AlMgScZr alloy. This work provides essential guidance for developing high-strength and high-stiffness aluminum matrix composites with excellent processing properties in LPBF technology. [ABSTRACT FROM AUTHOR]

The microstructure and properties of nickel-based superalloys under thermal exposure are the key basis for evaluating the high-temperature stability and proposing process optimization strategies. This study investigated the microstructural evolution and the corresponding tensile properties of IN738 alloy with different post-processing states under thermal exposure at 700 °C. The results show that the microstructures of IN738 alloys with different post-processing states (i.e., hot isostatic pressing (HIP) and standard heat treatment (SHT)) are significantly different. For the HIPed sample, large cuboidal γ′ and a small number of ultra-fine spheroidal γ′ precipitates are present in the γ matrix. Under thermal exposure, the size and volume fraction of ultra-fine spheroidal γ′ increase with prolonged thermal exposure time. In comparison, the SHTed sample is characterized as a bimodal distribution of γ′, with large primary cuboidal γ′ and small secondary spherical γ′. The size and volume fraction of primary γ′ increase first and then remain steady under thermal exposure. In particular, the tensile properties under exposure depend highly on the post-processing states. The increase of tensile strength after the thermal exposure in the HIPed sample is attributed to the rising fine spherical γ′ volume fraction. The rising size and volume fraction of primary γ′ in the SHTed sample improve the tensile strength during thermal exposure. • Microstructure and mechanical properties of IN738 highly depend on post-processing states. • Increase of strength in HIPed sample is attributed to rising fine spherical γ′ fraction after thermal exposure. • Rising size and fraction of primary γ′ in SHTed sample improve strength during thermal exposure. [ABSTRACT FROM AUTHOR]

• A high density of multi-scale annealing twins was achieved in LPBF Ni 35 Co 35 Cr 25 Ti 3 Al 2 MEA. • The multi-scale annealing twins, together with nanoprecipitates and dislocations, resulted in gigapascal strength (∼1.4 GPa) and substantial tensile ductility (∼25 %). • The positive effects of the multi-scale annealing twins on plastic deformation were discussed. • The critical relevance of cellular structures in influencing the nucleation behavior of annealing twins was elucidated for the first time. Coherent twin boundaries (CTBs) are internal planar defects that offer a promising pathway for designing advanced metallic materials with superior strength-ductility synergy. However, incorporating nanoscale CTBs into additive manufacturing (AM) microstructures is highly challenging without severe plastic deformation. Here, by utilizing the intrinsic cellular structures in AM alloys, we for the first time achieved a high density of multi-scale annealing twins in a laser powder bed fusion (LPBF) Ni 35 Co 35 Cr 25 Ti 3 Al 2 medium-entropy alloy. These multi-scale annealing twins, together with nanoprecipitates and dislocations, resulted in gigapascal strength (∼1.4 GPa) and substantial tensile ductility (∼25 %). We reveal that the AM-induced cellular structures, decorated with entangled dislocations and Ti segregation at the cellular boundaries, facilitate the abundant nucleation of multi-scale annealing twins through interactions with migrating recrystallization boundaries. Additionally, the cellular precipitation networks enhance the thermal stability of nanoscale annealing twins. Frequent dislocation-TB interactions during deformation contribute to superior strain hardenability and thus good ductility. Synergized multiple strengthening mechanisms, i.e., boundary strengthening, precipitation strengthening, and dislocation strengthening, are responsible for the excellent strength. Our present findings advance the design of AM microstructures by harnessing the beneficial effects of cellular structures and provide valuable guidance for developing alloys with exceptional mechanical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: A novel method of crystal nucleation and detachment from a vibrating chilling solid surface has been proposed to further increase the proportion of equiaxed grains in the solidification microstructure. Using a transparent NH4Cl–H2O alloy, the surface nucleation and evolution behaviors of dendrites were in situ observed. The effects of vibration frequency as well as amplitude on the equiaxed crystallographic morphology were experimentally studied, and the effects of the roughness of solid surface were also considered. The results show that exerting vibration to a chilling metal surface is an effective way to produce a lot of nuclei for forming equiaxed grains microstructure, and with higher vibration frequency and amplitude, much finer equiaxed grains are obtained. Moreover, nucleation on the chilling surface is a much localized behavior, some fixed positions on the chilling surface act as active nucleation sites, of which the number increases with a lowering chilling temperature. [Copyright &y& Elsevier]