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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]

Abstract The microstructure and mechanical behavior of Nb-22Ti-16Si- x Zr alloys (x = 0, 1, 5, 10, 15 at.%) were investigated by using laser solid forming (LSF) additive manufacturing from elemental powder mixture of Nb, Ti, Si and Zr. The as-deposited Nb-22Ti-16Si alloy presented a microstructure consisted of primary Nb-base solid solution (Nbss) dendrite and Nbss/(Nb) 3 Si eutectic dendrites. The eutectic Nbss/γ-(Nb) 5 Si 3 appeared with a morphology of lamellar structural feature when 1 at.%Zr was added, and its content increased with Zr content. Nbss/(Nb) 3 Si eutectic dendrites disappeared when Zr content reaches 10 at.%. Further increasing of Zr (15 at.%) result in the appearance of a hypereutectic microstructure, which consisted by primary γ-(Nb) 5 Si 3 and eutectic Nbss/γ-(Nb) 5 Si 3. As the nominal Zr content increased, the fracture toughness of LSFed Nb-22Ti-16Si- x Zr alloy increases first and reaches the maximum value (15.28 MPa m1/2) in LSFed Nb-22Ti-16Si-5Zr alloy, and then decreases. Highlights • Nb-22Ti-16Si- x Zr alloys were prepared by laser additive manufacturing from elemental powder mixture. • Microstructure evolution mechanisms of LSF Nb-22Ti-16Si-xZr are elucidated. • Fracture behaviors of Nb-22Ti-16Si- x Zr are discussed in detail. • The fracture toughness of as-deposited Nb-22Ti-16Si-5Zr is 15.28 MPa m1/2. [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]

Abstract In this study, four straight walls of Ti-6Al-4V titanium alloy were fabricated by wire and arc additive manufacturing (WAAM) to investigate the effect of deposition parameters on grain morphology evolution and texture characterization in the building direction. A certain volume fraction of equiaxed β grain appeared at the bottom of the wall and can be controlled by deposition parameters, while the columnar β grain zone was on the equiaxed β grain zone. It is indicated that the formation of equiaxed β grains at the bottom of the wall initiated from the recrystallization. There were the large residual stress, strain, and high heating rate when depositing the first several layers near the substrate, which can induce the recrystallization of the already-deposited layers. However, the preferred crystallographic orientations along the building direction formed gradually during the deposition process, then the β grains began to grow epitaxially from the already-deposited layers, and changed to columnar β grains, which lead to a strong 〈001〉 fiber texture in the building direction. In addition, there are also some equiaxed β grains at the top surface of the wall due to the occurrence of the columnar to equiaxed grain transition (CET) in the molten pool. Graphical abstract Image 1 Highlights • A large volume fraction of equiaxed β grains can be obtained in WAAMed Ti-6Al-4V. • Alternative growth between equiaxed and columnar grains can be obtained. • Recrystallization is observed during the WAAMed Ti-6Al-4V process. • The formation of equiaxed β grains is due to various factors. • The texture of equiaxed β grains is much weaker than that of columnar β grains. [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 morphology of microstructure affects the quality of Invar alloy mould when it is repaired with laser melting deposition (LMD). However, it is quite hard to observe the evolution of microstructure in real time. The current study adopted a CA-FE model, i.e, cellular automaton coupled with finite element, to simulate the microstructure evolution of Invar alloy in the LMD process. The mechanism of columnar-to-equiaxed transition in the molten pool was investigated based on the simulation results. In addition, an analysis was completed by comparing the simulation with the experimental results, which verified the feasibility of simulating the microstructure evolution with the CA-FE model in the LMD process. The results indicated that the bottom of the molten pool is filled by the epitaxial growth of columnar grains and the orientation of the columnar grains is consistent with the direction of the maximum temperature gradient in the molten pool. The top of the molten pool is occupied by equiaxed grains. This study provides a referenced value on the quality improvement of the mould repaired by LMD. [ABSTRACT FROM AUTHOR]

The cracking mechanism, especially the initiation and propagation process of cracking, in the overlapping zone (OZ) of laser solid forming (LSF) of IN-738LC alloy was investigated. The results showed that both the solidification cracks and liquation cracks can be found in the OZ of the LSFed IN-738LC specimen. The liquation cracking can be ascribe to the local melting of γ-γ′ eutectic at grain boundaries and could further become the initiation site of solidification cracks in the OZ of LSFed IN-738LC. According to the EBSD analysis and the Rappaz's theoretical model, the cracks in OZ always propagated along the high-angle grain boundaries due to their relatively wider solidification temperature range compared with the lower angle grain boundaries. The thermal stress and residual stress (cracking driving force) of the LSFed IN-738LC deposit was estimated by Vickers micro-indentation method combing a series of microhardness and room temperature tensile testing. It was shown that the residual stress in OZ was obviously higher than that in the inner-track zones due to the different thermal history of the two zones, while the microhardness of the two zones were about at the same level. Preheating was found to be effective in suppressing cracking by reducing the residual stress in LSFed IN-738LC deposit and the crack free deposit was obtained with preheating at 700 °C. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of laser solid formed (LSFed) 300M steel with tempering treatment was investigated. The microstructure of laser solid formed 300M steel with tempering treatment mainly consisted of the tempered martensite, bainite and a small amount of retained austenite. When the tempering temperature increased from 250 °C to 350 °C, the size of martensite lath and martensite blocks changed little. There are two kinds of tempered martensite. With increase of the tempering temperature, ε-carbide in the general tempered martensite transformed to cementite. In another kind of tempered martensite, ε-carbide were found to be precipitated along specific growth directions, with at least two variants for carbide precipitation. The hardness presented an incomplete linear correlation with the tensile strength and the yield strength for LSFed 300M steel. The hardness in LSFed 300M steel had not shown a significant change with increase of the tempering temperature. The tensile strength and yield strength increased first till the tempering temperature reaches 290 ° C–310 ° C then decreased with further increasing the tempering temperature. Especially, the strength dramatically decreased when the tempering temperature was above 310 ° C. However, the elongation and percentage reduction of area changed little with increase of the tempering temperature. The tensile fracture of LSFed 300M steel with tempering treatment presented a ductile fracture pattern. [ABSTRACT FROM AUTHOR]

AlCoCrCuFeNi high-entropy alloy (HEA) particles were laser melt injected on AZ91D substrates using a one-step blown powder method to investigate the interaction between the reinforcement and the substrate in laser surface forming of AlCoCrCuFeNi HEA particle reinforced AZ91D metal matrix composites (MMCs). The results show that some Cu was rejected into the substrate melt during the processing. The Cu content in the melt has a great impact on the microstructure evolution of the formed MMC. When the Cu concentration reached a level of about 30 at.%, the CuMg 2 phase was formed instead of the predicted λ 1 phase. As the Cu content decreases, the λ 1 phase as well as different Mg + CuMg 2 , Mg + λ 1 and Mg + Q eutectics will be formed depending on the Cu concentration in the remaining melt. Moreover, decreasing the Cu content in the AlCoCrCuFeNi HEA particles can also affect the wear properties of the formed MMC because it could result in a plastic deformation to the brittle-like transition of the reinforcement. [ABSTRACT FROM AUTHOR]

Microstructure and mechanical properties of laser solid formed 300M steel were investigated. The as-deposited microstructure presented the tempered martensite, the martensite with a small amount of bainite, and the mixture of martensite and bainite from the bottom to the top of the deposits. After heat treatment, the microstructure was refined and uniform, and consisted of the mixture of tempered martensite, bainite and retained austenite. The hardness only showed a little increase from the bottom to the middle–upper of the as-deposited 300M steel, there was a significant increase in the hardness at the top of as-deposited 300M steel. The hardness in the heat treated deposits tended to be uniform and higher than that in the as-deposited 300M steel. Tensile strength and yield strength of the as-deposited 300M steel were much lower than the wrought standard. Through heat treatment, the tensile properties of laser solid formed 300M steel were improved significantly and reached the forgings standard. [ABSTRACT FROM AUTHOR]

Highlights: [•] The anomalous eutectic was obtained in the bottom of the sample with the low laser scanning velocity of 0.1mm/s. [•] The free nucleation and rapid growth of eutectic should be a necessary condition for the formation of anomalous eutectic. [•] The microhardness of anomalous eutectic is lower than that of regular lamellar eutectic. [ABSTRACT FROM AUTHOR]

Al-Mg-Sc-Zr is a high-performance Al alloy developed for laser additive manufacturing (LAM). The addition of Sc/Zr can stimulate both grain-boundary and precipitation strengthening, which are closely related to the precipitation behavior of the primary and secondary Al 3 (Sc,Zr) phases, respectively. For LAM, laser direct energy deposition (L-DED) and laser powder bed fusion (L-PBF) are two typical processes. However, little is known about the disparities in the microstructural evolution and strengthening behavior of Al-Mg-Sc-Zr alloys under the L-PBF and L-DED processes. In this study, a comparative analysis of the microstructure and strengthening behavior of L-DED- and L-PBF-processed Al-Mg-Sc-Zr alloys was conducted. Owing to the higher cooling rate during L-PBF, fewer primary Al 3 (Sc,Zr) phases precipitated during solidification, and more secondary Al 3 (Sc,Zr) phases formed during aging, resulting in higher precipitation strengthening. More importantly, the ultrafine grains at the submicron scale in the L-PBF sample not only enhanced grain-boundary strengthening but also provided additional strengthening owing to the lack of mobile dislocations in the microstructure. This work is helpful for further optimizing the mechanical properties of LAM-processed Al-Mg-Sc-Zr alloys. • L-DED-processed Al-Mg-Sc-Zr alloy exhibited a continuous yield behavior. • L-PBF-processed Al-Mg-Sc-Zr alloys exhibited a discontinuous yield behavior. • The lack of mobile dislocations under L-PBF endowed an additional strengthening. [ABSTRACT FROM AUTHOR]

Abstract: Two kinds of laser scanning paths, i.e. single direction raster scanning (SDRS) and cross direction raster scanning (CDRS), were used to prepare Inconel 718 alloy parts by laser solid form (LSF) technology. The microstructures and mechanical properties of LSF Inconel 718 samples were investigated. It is shown that the as-deposited microstructure of SDRS sample is composed of columnar dendrites which grow epitaxially along the deposition direction; but in the CDRS sample, the continuous directional growth of columnar grains is inhibited and the orientation deviation of dendrites in two adjacent layers increases. The as-deposited grains of the CDRS sample are finer than those of the SDRS sample. After heat treatment, recrystallization occurs and grains of both samples are refined. However, the recrystallized grains in SDRS sample are not as uniform as that of the CDRS sample. Tensile testing at room temperature indicates that the ultimate tensile strength of these two samples is similar; however, the ductility of the CDRS sample is much better than that of the SDRS sample. Fracture surface examination presents a transgranular mode of crack propagation for the SDRS sample and a mixture of transgranular and intergranular modes of crack propagation for the CDRS sample. The inhomogeneity of grain size is considered to be the prime reason for the worse ductility of the SDRS sample. [Copyright &y& Elsevier]

Abstract: Ti–50wt% Ni alloys were fabricated by laser solid forming (LSF) using pure Ti and Ni powders. Effects of laser process parameters (laser power and scanning speed) on the deposited microstructures were investigated. With increasing scanning velocity and decreasing laser power, as-deposited microstructure exhibited an evolution from primary TiNi dendrite to two-phase TiNi+B2 dendrite and finally to TiNi+Ti2Ni anomalous eutectic, meantime, the characteristic size of the dendritic arms also decreased. The experimental results were further compared with the model of Trivedi, Magnin, Kurz (TMK model) of eutectic growth and Kurz, Giovanola, Trivedi (KGT model) of dendrite growth. The experimental results are in a reasonable agreement with KGT model. [Copyright &y& Elsevier]

• Combined with thermodynamic calculation, the formation mechanisms of grain morphology and Laves phase are discussed in detail. • The contribution of different strengthening mechanisms to yield strength is quantitatively calculated. • The cause of anisotropy of fatigue crack growth rate in vertical and horizontal specimens is clarified. The microstructure and the anisotropy of mechanical properties for Inconel 625 superalloy prepared by directed energy deposition (DED) were investigated in this study. The microstructure of as-deposited sample was mainly composed of epitaxial columnar grains, which showed a z-shaped distribution along the deposition direction. Combined with thermodynamic calculation, the formation mechanism of Laves phase in as-deposited Inconel 625 superalloy was discussed in detail. Owing to the anisotropic microstructure of as-deposited sample, tensile properties and fatigue crack growth (FCG) behavior showed significant anisotropy. Compared to vertical sample, the grain boundary volume fraction in horizontal sample was larger, which caused that the ability of grain boundary strengthening and the resistance of fatigue crack growth were higher in horizontal sample during tensile and fatigue crack growth process. As a result, the yield strength and the ultimate tensile strength of horizontal sample were higher, while the fatigue crack growth rate was lower. However, the elongation of horizontal sample was smaller than that of vertical sample caused by the Laves phase distribution. [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]

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]

Selective laser melting (SLM) of Zr 55 Cu 30 Al 10 Ni 5 (Zr55) bulk metallic glasses (BMGs) with Zr55 original unannealed powders and annealed powders has been investigated, which is an effort to reveal the influence of crystallization state of powders on the crystallization behavior of remelted zone (RZ) and heat affected zone (HAZ). The as-prepared Zr55 powders consist of amorphous matrix and Al 5 Ni 3 Zr 2 -type phase. When the Zr55 origin powders are annealed at 600 K, 800 K and 1000 K, the microstructure of amorphous matrix is transformed into amorphous, metastable + stable phases and entirely stable phases, respectively. After SLM of these different powders, the gradient microstructure with three crystalline zones (nanocrystal, dendritic eutectic, spherulite) is found from RZ to HAZ for all the deposits. However, the size and density of dendritic eutectic in the top of HAZ is much smaller for the deposits prepared by annealed powders than that by the unannealed powders. In contrast to top of HAZ, abundant multiphase spherulites are formed at the bottom of HAZ for the deposits prepared by the powders with or without annealed. The detailed microstructural and numerical model results reveal that the crystallization at the top of HAZ is mainly dominated by the rapid growth of quench-in clusters or nuclei in RZ, but the crystallization at the bottom of HAZ is controlled by both the nucleation and growth of these clusters or nuclei. It is precisely because the average size of quench-in clusters or nuclei increases but total quantity decreases during annealing, resulting in the increase of thermal stability in RZ and the suppression of crystallization in the top of HAZ for the deposits with annealed powders. • The Zr55 BMGs are prepared by SLM with the original powder and annealed powders. • The crystallization behavior during SLM of powders with various state is analyzed. • The crystallization in the top of HAZ is lower for the deposit with annealed powders. • The crystallized volume fraction in the deposit is calculated by the numerical model. [ABSTRACT FROM AUTHOR]

Abstract In this work, the dense Ti-7.5Mo sample (over 99.5%) was prepared by using laser powder bed fusion (L-PBF) from powder mixture of pure Ti and pure Mo. Through the use of mechanical mixture process, Mo particles present an uniform distribution. As the laser scanning speed decreases from 1700 mm/s to 1000 mm/s, the sample's relative density increases from 85.5% to 99.5%. The microstructural analysis indicates that Mo particle was mostly fully melted during laser melting. But, some large sized Mo particles were partial melted, which possesses gradient interface structure. Then, the tensile properties of as-fabricated samples under several laser scanning speed were determined. The results shows that the as-fabricated dense sample presents Young's modulus, ultimate tensile strength and strain at failure about of 70 GPa, 740 MPa and 9.2% respectively. Given to this low Young's modulus, which is approximate to bone of 30 GPa, the L-PBF processed Ti-7.5Mo shows great application potential in implant component. Graphical abstract Image 1 Highlights • Dense Ti-7.5Mo (over 99.5%) was prepared by selective laser melting from powder mixture. • Special conchoidal structure, which consists by α and β Ti, appears at as fabricated sample. • The modulus and UTS of as-fabricated dense sample are about of 70 GPa and 700 MPa. [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]

• The Cl- ions in the solution promote the passive dissolution reaction process. • The dissolved surface in the chloride-containing solution is significantly flatter. • The transpassive dissolution rate and current efficiency are enhanced by Cl- ions. The electrolyte solution significantly affects electrochemical machining. This study investigates the electrochemical dissolution behavior of a laser solid formed Hastelloy X nickel-based superalloy in 15 wt% NaNO 3 , 7.5 wt% NaNO 3 + 7.5 wt% NaCl, and 15 wt% NaCl solutions. The Cl- ions in the electrolyte solution accelerates the passive dissolution rate because the electrochemical reactions at the metal/film and film/solution interfaces are promoted. During the transpassive dissolution process, the Cl- ions in the electrolyte solution weaken the hindering effect of the transpassive film on the dissolution process, resulting in a faster transpassive dissolution rate and a higher current efficiency. Furthermore, the flatness of the dissolved surface in the chloride-containing solution is significantly higher than that in the chloride-free solution. Two models are proposed to illustrate the passive and transpassive dissolution behaviors. This study provides theoretical guidance for the selection of electrolyte solutions for the electrochemical machining of laser solid formed nickel-based superalloys. [ABSTRACT FROM AUTHOR]

IN718Plus superalloy with hierarchical microstructure has been successfully manufactured by laser directed energy deposition (LDED). Along building direction, microstructure varies from composing of epitaxial columnar grains oriented along <001> γ direction to equiaxed grains in flower like configuration. Striped Laves phase and fine γ'/γ'' precipitates form in the columnar grains, and would transform into fine Laves phase particles and nanoscale γ' precipitates at equiaxed layer. To improve the compositional homogeneity and microstructural stability, high temperature solution treatment has been explored on the superalloy. The treatment would not affect the morphology and orientation of columnar grains, but would redissolve Laves phase precipitates. Double aging treatment has also been performed to obtain homogeneous distributed γ' precipitates, and the synergistic regulation of microstructure enhances the mechanical property significantly, as causing the room temperature yield strength and tensile strength increased from 0.88 GPa and 1.14 – 1.04 GPa and 1.28 GPa, respectively. Moreover, the excellent mechanical property would be maintained upon 704 ℃, with yield strength of 0.93 GPa, tensile strength of 1.04 GPa and high elongation of 27.3%. [Display omitted] • IN718Plus superalloy with hierarchical microstructure has been successfully manufactured by LDED. • As-deposited microstructure is composed of columnar to equiaxed grains with hierarchical Laves phase and γ'/γ'' precipitates. • Appropriate heat treatment process has been explored as 1100 ℃/1.5 h + 788 ℃/8 h + 704 ℃/8 h to ameliorate the performance. • Excellent 704 ℃ tensile properties have been obtained with tensile strength of 1.04 GPa and elongation of 27.3%. [ABSTRACT FROM AUTHOR]

Fabricating gas sensors with a facile, environmentally benign method to detect chemical vapor with high sensitivity and selectivity is of great importance for environmental monitoring. A biomorphic NiO/ZnO nanocomposite has been facilely synthesized in one step using a poplar tree leaf template (PTLT). A PTLT NiO/ZnO nanocomposite was constructed with the generic form of a PTLT and the morphology resembled the spongy structure of mesophyll tissue. Compared to routine ZnO-based materials, the PTLT NiO/ZnO nanocompite, generated with the biomorphic template, had a smaller average size and exhibited a p-n heterojunction at the n-type ZnO interface. PTLT NiO/ZnO detected n-butanol with great sensitivity (Rair/Rgas = 106-100 ppm) and selectivity (5–10 times greater response than the other vapors) at 240 °C as a gas sensor on a gas sensing platform. Compared to PTLT ZnO, PTLT NiO/ZnO demonstrated enhanced gas sensing properties, which were attributed to high concentration of oxygen vacancies and the formation of p-n heterojunctions. PTLT NiO/ZnO p-n heterojunction nanocomposite employed as gas sensor to detect n-butanol showed great gas sensing properties on the sensing platform. Image 1 • A method was used for synthesis of biomorphic NiO/ZnO nanocomposite for gas sensor. • NiO/ZnO maintained the biomorphic structure of mesophyll tissue of poplar leave. • The optimal sensor performed great n-butanol gas sensing properties and selectivity. [ABSTRACT FROM AUTHOR]

The α variant selection of integral as-deposited Ti-6Al-4V prepared by laser solid forming (LSF) has been investigated by Electron Backscattered Diffraction (EBSD). Six types of α variants exist all areas in the deposited cuboid although its microstructure varies from basket-weave to Widmanstätten (and undeveloped basket-weave) to ultrafine basket-weave along building direction. Clusters of three α variants always dominate in medium steady zone until the columnar to equiaxed transition (CET transition) occurs. α variant selection causes strong alteration of high angle grain boundaries (HAGBs), which might be correlated with self-accommodation of shape strains. Super variant selection in medium steady zone. Image 1 • The α variant selection of LSF Ti-6Al-4V has been investigated by EBSD. • Six types of α variants exist all areas in varying macro- and microstructures. • Clusters of three variants with 60° α/α GB always dominate in columnar grains. • The variant selection might be related with self-accommodation of shape strains. [ABSTRACT FROM AUTHOR]

Abstract Long-striped Laves phases are considered to be crack sources in laser repaired Inconel 718 during stress rupture test. In order to obtain fine Laves phases, Nd:YAG pulse laser is used to fabricate Inconel 718 superalloy on a wrought Inconel 718 substrate in this study. The microstructures and stress rupture properties of pulse laser repaired Inconel 718 superalloy after DA treatment (720 °C × 8 h/furnace cooling at 50 °C/h to 620 °C × 8 h/air cooling) and 900STA treatment (900 °C × 20 min/air cooling+720 °C × 8 h/furnace cooling at 50 °C/h to 620 °C × 8 h/air cooling) are investigated by using SEM and TEM. The results shows that granular Laves phases can be obtained when pulse laser is used. The formation of granular Laves phase is related to high cooling rate (G·R) and low ratio of temperature gradient to growth rate (G/R). The critical values of G·R and G/R are 104 and 107, respectively. After 900STA treatment, δ phase precipitates around the granular Laves phases. But there is no δ phases existing in the DA samples. The surrounding δ phases can induce stress concentration, resulting in that the elongation of the 900STA samples is worse than that of the DA samples. However, the regions denuded in Nb element around the δ phases can delay the formation of the vacancies, which leads to that the stress rupture life of the 900STA samples is better than that of the DA samples. Graphical abstract Image 1 Highlights • The deformation behaviors of Laves phase under different loads have been analyzed. • The selection map of Laves phase morphology has been established. • The effects of granular Laves and the surrounding δ phase have been investigated. [ABSTRACT FROM AUTHOR]

3D printing is a fast-emerging technology, and a shape is fabricated using layer-by-layer deposition of a material in a bottom-up manufacturing operation. Here a porous nickel/polyaniline nanocages multiscale supercapacitor synthesized using 3D printing technology is fabricated. The porous structure of iron-nickel and polyaniline nanocages can increase the specific surface area which lead to enhance the specific capacitance. 3D printing technology is presented in energy devices to accurately fabricate the delicate structure. [ABSTRACT FROM AUTHOR]

The mechanical properties of many metallic materials have been optimized by magnetic field-assisted additive manufacturing, however, there is still a gap in high-entropy alloys (HEAs) in this field, which is not conducive to the control and optimization of the microstructure and properties of HEAs. This work studied the tensile properties of laser powder bed fusion (LPBF) CoCrFeMnNi HEA. After applying a magnetic field, the relative density increased, and the grain size became larger and more uniform. Because of amperage force, crystallographic textures gradually change from< 100 > to< 110 > and< 111 > , which contributes to the improvement of tensile properties. Additionally, low-angle grain boundaries and geometrically necessary dislocations decrease, while the Schmidt factor increases. In the results of these changes, most factors contribute to improving the mechanical property, eventually optimizing the strength and ductility simultaneously. This indicates that magnetic field-assisted LPBF is promising to be an important means to optimize the mechanical properties of HEAs. • The HEA prepared by magnetic field-assisted additive manufacturing was studied for the first time. • The existence of a magnetic field changes the microstructure of CoCrFeMnNi obviously. • Magnetic field-assisted additive manufacturing can improve both strength and ductility of CoCrFeMnNi. • <101>and<111>crystallographic textures of CoCrFeMnNi have better tensile property than<001>. [ABSTRACT FROM AUTHOR]

AlSi7Mg alloy manufactured by selective laser melting (SLM) was subjected to different heat treatments to satisfy the need for excellent mechanical and thermal properties. Effect of direct aging (DA), annealing (AN) and solution + aging (SA) treatment on microstructure, mechanical and thermal properties of SLMed AlSi7Mg alloy was investigated. The results showed that the molten pool boundaries which can be clearly observed in the as-built sample fade away with the increasing heat treatment temperature. The heat treatments have slight effects on the morphology and size of α-Al grains. However, significant differences can be observed in the characteristics of substructure. For the DA treatment, the Al-Si network becomes discontinuous and simultaneously promotes the precipitation of nano-sized Si particles from the supersaturated Al matrix. The original Al-Si network becomes discontinuous and coarsening in the AN sample. For the SA sample, the original cellular structure and eutectic Al-Si network completely disappeared. Coarsened and irregularly shaped Si particles, fine equiaxed Si particles as well as the needle shaped Fe-rich precipitations were observed. The room temperature tensile test showed that the strength of DA sample is the highest, followed by as-built, AN, and SA samples in a descending order. The thermal diffusivity of SA sample is the highest, followed by AN, DA and as-built sample in a descending order. • Heat treatment was used to modify the mechanical and thermal properties of AlSi7Mg. • There is a trade-off relationship between the mechanical and thermal properties. • Effects of microstructure on mechanical and thermal properties was discussed. [ABSTRACT FROM AUTHOR]

A series of Ti-2Al- y Mo ( y = 2,5,7,9,12) alloy samples were produced from blended elemental Ti, Al and Mo powders using the laser solid forming technology. The influence of the β stabilizer Mo on the morphology of the grains, the size and the distribution of the α laths, the Vickers hardness and the tensile properties of Ti-2Al- y Mo alloys were explored under designated laser processing parameters. It was found that the microstructure in Ti-2Al-5Mo, Ti-2Al-7Mo, Ti-2Al-9Mo, and Ti-2Al-12Mo deposited layers were composed of irregular columnar grains that grow epitaxially, with some small equiaxed grains in the upper region, while that of the Ti-2Al-2Mo alloy was composed of large columnar grains. The grain size decreased, while the thickness of equiaxed grains layer increased with increasing Mo content. This indicates a tendency towards columnar-to-equiaxed transition with increasing Mo. The dominant β grains form a basketweave microstructure composed of primary α laths, secondary α laths and retained β phase. It was also observed that with increasing Mo content, both the size of primary α laths and secondary α laths decreased significantly, while the number of secondary α laths increased sharply, and the Ti-2Al-12Mo is also constituted of α phase and β phase. The Young's modulus of Ti-2Al-7Mo, Ti-2Al-9Mo, and Ti-2Al-12Mo were basically the same within experimental error. Tensile testing of the specimens showed that Ti-2Al-7Mo exhibits a good combination of strength and elongation to failure. As a result, this material can be considered suitable as a viable feedstock for laser additive manufacturing. [ABSTRACT FROM AUTHOR]

In this work, the microstructural evolution of a directed energy deposited near β titanium alloy, Ti5Al2Sn2Zr4Mo4Cr, during post-heat treatment was investigated, and its effect on the mechanical properties was evaluated. The results showed that the equilibrium volume fraction of the α phase was reached in the first 30 min over a temperature range of 720–840 °C. Fine basketweave α laths (α BW) were homogenously distributed within the prior β grains at 840 °C. Both fine α BW and α colonies developed from the grain boundary α layers (α GBW) were obtained in the sample solutions treated at 720, 760, and 800 °C. Water-quenching and air-cooling were employed to retain the β phase at room temperature. The α phase volume fraction increased significantly and reached the equilibrium volume fraction during the furnace-cooling process. In addition, the manner in which the samples were subjected to isothermal temperatures can strongly affect the evolution of the α phase. The homogenized specimen containing a single β phase exhibited the lowest strength and the highest plasticity. The strength increased and the ductility decreased after subtransus solution treatment. The difference in the mechanical properties can be attributed to the differences in the α and β phases caused by the various heat treatments. The modified rule of mixtures appropriately described the relationship between the yield strength and microstructure characteristics. • The transformation kinetics of directed energy deposited near β Ti alloy was studied. • The manner in which the sample was subjected to isothermal temperature strongly affect the α phase evolution. • The relationship between the yield strength and microstructure was described. [ABSTRACT FROM AUTHOR]

Rapid solidification process is an effective method to improve the corrosion behavior of Mg alloys. In the present study, laser melting, as a typical rapid solidification process, was used to fabricate Mg–5.6Zn–0.5Zr (ZK60). With the increase of laser energy density, the crystalline structures experienced successive changes: clustered finer dendrites→uniform equiaxed grains→coarsened equiaxed grains. Moreover, the fully divorced eutectic α-Mg + Mg 7 Zn 3 homogeneously distributed along the boundaries of solid solution structure α-Mg. Meanwhile, at a laser energy density of 600 J/mm 3 , ZK60 was dense with an optimal hardness of 89.2 Hv and hydrogen evolution rate of 0.006 ml cm −2 h −1 . The enhanced corrosion resistance was attributed to the refined grain, homogenized microstructure and extended solid solution caused by laser rapid solidification. [ABSTRACT FROM AUTHOR]

Ba, Mn single and co-doped BiFeO 3 ceramics were prepared by combination of solid-state reaction and rapid sintering method. Enhanced ferroelectric and ferromagnetic properties were observed in Ba, Mn co-doped ceramics. Large remnant polarization ( Pr ∼40.87 μC/cm 2 ) for Bi 0.9 Ba 0.1 FeO 3 and large remanent magnetization ( Mr ∼0.834 emμ/g) and coercive field ( Hc ∼938 Oe) for Bi 0.95 Ba 0.05 Fe 0.9 Mn 0.1 O 3 were acquired, respectively. The analysis of structure and valence measured by X-ray diffraction (XRD), Raman spectrum and X-ray photoelectron spectroscopy (XPS) show that an appropriate doping ratio of Ba and Mn ions in BiFeO 3 (BFO) plays an important role in facilitating microstructure distortion and transition, which are favorable for enhancing ferroelectric properties of BFO ceramics. Furthermore, the existence of Fe 2+ and Mn 4+ ions in Ba Mn co-doped BFO contributes to the ferromagnetic property. These results demonstrate that ions co-doping is an effective way to modulate the room-temperature ferroelectric and ferromagnetic properties for multiferroic applicability of BFO. [ABSTRACT FROM AUTHOR]

Recently, an innovative process chain has been investigated and proposed, using laser-based directed energy deposition technology to produce pre-forms for forging. The advantage of this technology is to get high-performance near-formed parts at a low cost, compared traditional processing. Clarifying the hot workability and the microstructural evolution of as-deposited samples is the key to obtaining high performance parts. In present work, the plastic behaviors and dynamic recrystallization mechanisms of as-deposited nickel-based superalloy are studied. The compression curves are corrected by eliminating adiabatic heating and friction effect. And then the hot deformation activation energy and the constitutive equation of as-deposited sample are obtained. Compared to the wrought Inconel 625, as-deposited Inconel 625 has lower hot deformation activation energy (466.511 kJ/mol). The peak stress gradually decreases, while the recrystallized grain volume fraction gradually increases when deformation temperature increases and strain rate decreases. The characterization results of TEM and EBSD show that the discontinuous dynamic recrystallization mechanism nucleating by the bowing of grain boundaries occupies an absolute dominant position. In addition, combined with the microstructural evolution and hot processing map, the best hot working conditions of as-deposited Inconel 625 are obtained (deformation temperature: 1050–1150 ℃, strain rate: 0.001–0.01 s−1). • Hot compression stress-strain curves of Inconel 625 fabricated by L -DED were corrected by eliminating the influences of adiabatic heating. • The constitutive equation and hot processing map of as-deposited Inconel 625 were established. • The dynamic recrystallization mechanism of Inconel 625 fabricated by L -DED during hot deformation process was discussed. [ABSTRACT FROM AUTHOR]

NiTi alloys with superelasticity and shape memory effects are currently widely used because of its excellent deformation recovery ability, mechanical strength, and biocompatibility. The Ni 50.8 Ti 49.2 alloy was manufactured by using laser solid forming (LSF) technology with pre-alloyed powder in this work. The microstructure, phase transformation and shape recovery of the deposited alloy were influenced by the parameters used in depositing process. The as-deposited Ni 50.8 Ti 49.2 alloy formed by LSF is columnar crystals epitaxially grown along the deposition direction, with a small amount of equiaxed crystals appear between the deposition layers. Two-step/multi-step martensitic transformation occurs in the deposited Ni 50.8 Ti 49.2 alloy. The martensitic transformation temperature slightly changes with the deposition height, whereas the R transformation temperature basically does not change with the deposition height. In the test of the mechanical properties, sample with a laser power of 1700 W and a scanning rate of 680 mm/min has a compression superelastic recovery as high as 9.5%. Moreover, Ti 2 Ni precipitated phase and R phase appeared in all samples, but only the precipitated Ti 2 Ni and R phase in this sample had a certain orientation relationship with the matrix. Shape memory characteristics was also tested by compression deformation, and the maximum recovery strain of shape memory effect is 6.1%, which is obtained in the sample deposited with 1500 W laser power and 480 mm/min scanning rate. [Display omitted] • Columnar crystals grow along the deposition direction in LSF Ni 50.8 Ti 49.2 alloy. • Superelastic recovery as high as 9.5% was obtained in LSF Ni 50.8 Ti 49.2 alloy. • Orientation relationship of precipitation with matrix leads to high recovery rate. [ABSTRACT FROM AUTHOR]

• α phase evolution of DEDed titanium alloy was analyzed based on the thermal history and isothermal transformation kinetics. • The in-situ SEM tensile test was performed in the horizontal and vertical directions to elucidate the deformation behaviors. • The difference in crack initiation and propagation between the fine and coarse α laths were discussed. [Display omitted] α phase evolution and tensile fracture behavior of Ti5Al2Sn2Zr4Mo4Cr alloy fabricated by directed energy deposition (DED) were studied. Samples with a different number of layers were fabricated by the same processing parameters. Microstructure evolution was analyzed based on the thermal history calculated through finite element analysis and isothermal transformation kinetics. The results suggested that the samples exhibit various α phase characteristics. Two kinds of starting microstructures at different layers, single β phase and mixed α/β phases can be obtained depending on the deposited layer's temperature and cooling rate. Further evolution of α phase is closely related to the consecutive thermal cycles with different durations and different temperature amplitudes. The in-situ scanning electron microscopy tensile tests were performed in the horizontal (perpendicular to the build direction) and vertical (parallel to the build direction) directions under the as-deposited and heat treatment conditions. The results showed that the cracks and micro-voids usually initiate on the grain boundaries or α/β interface. α phase characteristic plays an important role in deformation behavior. The sample containing fine α laths usually fractured quickly after the first surface crack was observed. The coarse α laths resulted in a larger crack tip plastic zone and delayed the crack propagation. [ABSTRACT FROM AUTHOR]