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For additive-manufactured nickel-based superalloy, heat treatment is an effective method to modify the microstructure and mechanical properties. The strength and ductility of as-deposited GH4099 have been improved via heat treatment. The results indicate that the microstructure of as-deposited sample was mainly composed of epitaxial growth columnar grains. And the ( γ + γ ' ) eutectic phase formed at the terminal solidification stage because of the segregation of Al and Ti elements. After solution treatment at 1120 °C for 2 h, the columnar dendrites were replaced by smaller equiaxed grains with twin boundaries due to the occurrence of recrystallization. The γ ' phase precipitated in the matrix after the aging treatment at 800 °C for 8 h. By comparing the tensile properties at room temperature of three states samples, it could be found that the solution treated samples had the lowest strength with the highest plasticity, while the solution-aging treated samples had the best performance with high strength and ductility. After aging treatment, though the dislocation density decreased after solution treatment, the precipitated γ ' phase could block dislocation movement to improve the strength of GH4099. Additionally, the formation of refine equiaxed grains and twin boundaries promoted ductility to some degree during the tensile process.

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 Widmanstatten (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.

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.

The microstructure and mechanical behavior of Nb-22Ti-16Si-xZr 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)3Si eutectic dendrites. The eutectic Nbss/γ-(Nb)5Si3 appeared with a morphology of lamellar structural feature when 1 at.%Zr was added, and its content increased with Zr content. Nbss/(Nb)3Si 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)5Si3 and eutectic Nbss/γ-(Nb)5Si3. As the nominal Zr content increased, the fracture toughness of LSFed Nb-22Ti-16Si-xZr alloy increases first and reaches the maximum value (15.28 MPa m1/2) in LSFed Nb-22Ti-16Si-5Zr alloy, and then decreases.

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.

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.

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.

In this study, the effect of solution heat treatments on the microstructure and mechanical properties of Inconel 625 superalloy fabricated by laser solid forming was investigated. The microstructure of deposit was mainly composed of columnar grains, which didn't change until the solution temperature reached 1200 °C after solution heat treatment. Due to the large size Laves phase which can pin grain boundary and obstruct grain boundary migration, the recrystallization fully occurred when the solution temperature exceeded 1200 °C. With the increment of the solution temperature, the average diffusion coefficient of solute elements and the dissolution velocity increased obviously. Besides, the volume fraction and size of Laves phase decreased, and the dislocation density decreased apparently. As a result, the microhardness and yield strength decreased with the increment of the solution temperature, but the tensile strength didn't change much after solution heat treatment, and the elongation increased significantly with the solution temperature improving. The room-temperature tensile properties in different states of Inconel 625 fabricated by laser solid forming were higher than those of Inconel 625 fabricated by casting.

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.

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.

In this work, the alloying effect of similar atom substitution of Co for Fe on the glass-forming ability as well as mechanical and magnetic properties of Fe71.7-xCoxB16.7Si8.3Zr3.3 and Fe72.5-yCoyB16.7Si8.3Hf2.5 (x, y = 0, 5, 10, 15, 20 and 25) glassy alloys has been studied. Our experiments show that the substitution of Co for Fe causes a decrease in the glass-forming ability. By increasing the content of Co, the critical glass formation size gradually decreases from 2.5 mm to 1 mm. Nano-indentation results indicate that both the Young's modulus and hardness increase with increasing Co content in the bulk glassy alloys. The Fe51.7Co20B16.7Si8.3Zr3.3 bulk glassy alloy exhibits a microhardness, Hv = 13.5 GPa, and a Young's modulus, E = 230 GPa, the microhardness being the highest among all the Fe-based metallic bulk materials reported to date. All of the glassy alloys exhibit good soft magnetic properties with high saturation magnetization (1.12–1.33 T) and low coercive force (0.6–5.2 A/m).

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.

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% NaNO3, 7.5 wt% NaNO3 + 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.

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.

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.

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.

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.

The effect of Ti addition on the cracking and microhardness of Ni-based superalloy Inconel 625 during the laser solid forming was investigated. With the increase of Ti content, the crack rate decreased till nil because of shrunken solidification temperature range and sufficient liquid phase healing the solidification cracks by back-filling in the terminal solidification stage. The addition of Ti promoted the formation of (γ+Laves) eutectic phase and led to the transformation of morphology of the Laves phase from the dotted or short rod to the lamellar and massive network. When the content of Ti exceeded 5 wt %, the microhardness of the alloys improved by 100 HV compared with the alloys containing below 5 wt % Ti addition. The increase in microhardness can be mainly ascribed to a network distribution of the (γ+Laves) eutectic phase.

The method of selective laser melting (SLM) is a new manufacturing technology which has been regarded as a potential candidate to prepare bulk metallic glasses (BMGs) without limit of critical dimensions. However, obstacles still remain since the crystallization is rather hard to be sustained in the heat affected zone (HAZ) during the preparation of BMGs, due to the existence of cyclic heating process. In order to find the possibility of inhibiting the crystallization behavior in the HAZ, the micro-structural evolution of Ni 75 Al 25 metallic glass during the cyclic heating process at different temperature variation rates was studied with Molecular Dynamics (MD) simulation. The results reveal that at low temperature variation rates relatively, the crystallization begins during the heating or cooling process depends on the relaxation time between the glass transition temperature T G and the maximum heating temperature T MAX . The relaxation time also affects the transformation mode of crystal structure after the completion of crystallization behavior. When the temperature variation rate rises to 5 × 10 13 K/s, the decline of nucleation occurred: during the heating process, the heating rate is so high that the nuclei at the low temperature could come into the embryo at the high temperature which lead to the fusion of crystal embryos. And the decline of nucleation provides a new possibility for the research on the inhibition of crystallization behavior in the HAZ during the preparation of BMGs with SLM.

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 + Mg7Zn3 homogeneously distributed along the boundaries of solid solution structure α-Mg. Meanwhile, at a laser energy density of 600 J/mm3, 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.

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, e-carbide in the general tempered martensite transformed to cementite. In another kind of tempered martensite, e-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.

Ba, Mn single and co-doped BiFeO3 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/cm2) for Bi0.9Ba0.1FeO3 and large remanent magnetization (Mr∼0.834 emμ/g) and coercive field (Hc∼938 Oe) for Bi0.95Ba0.05Fe0.9Mn0.1O3 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 BiFeO3 (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 Fe2+ and Mn4+ 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.