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In this paper,using 304 stainless steel material 1 mm in diameter to fuse electron beam deposition rapid prototyping,by controlling the wire feed speed,electronic beam intensity and molding parameters such as the same,choose different forming path was 180 mm × 40 mm × 20 mm of print samples,after tensile test,Its microstructure and mechanical properties were observed and studied. By electron beam additive manufacturing,dense block material without macroscopic defects can be obtained. The average particle size of 304 stainless steel printed is no more than 10 μm,and contains fine uniform precipitation phase. Sample to print,staggered reciprocating print and improved staggered reciprocating print under the path of tensile strength of about 683 MPa,878 MPa,970 MPa,respectively the three print path molding samples can reach the hardness and tensile strength of 515 MPa or requirements,tensile fracture analysis,staggered print mode fracture to ductile fracture,staggered reciprocating type fracture to brittle fracture. The staggered reciprocating printing and the improved staggered reciprocating printing method have better density,better tensile strength and other mechanical properties.

Wire arc additive manufacturing (WAAM) has been widely used due to its advantages of low cost and high efficiency. However, one of the unsolved problems in WAAM is the heat accumulation. In this study, the compressed argon‐based interlayer active cooling (AC) process is employed to reduce heat accumulation, and the influence mechanism on microstructure and mechanical properties of Ti–6Al–4V samples are revealed. It is shown in the results that the introduction of interlayer AC leads to the interlayer temperature decreases from 468 to 53 °C, and the widths of prior‐β grains and αGB are refined. The increase of cooling rate (380–604 °C s−1) results in the transformation of large‐sized colonies into finer basket weave structure, accompanied by the production of martensite α'. The finer basket weave structure increases the strength of the samples, while the narrower αGB and the high‐angle grain boundaries increase the resistance of crack propagation. The high dislocation density caused by the faster cooling rate increases the plastic deformation to a certain extent. As a result, the interlayer AC improves the strength and plasticity of the samples simultaneously, the samples change from brittle and ductile‐mixed fracture to ductile fracture mode. [ABSTRACT FROM AUTHOR]

WAAM-LDM hybrid additive manufacturing can achieve high efficiency and high precision preparation of Ti-6Al-4V alloy. However, the inhomogeneous microstructure of WAAM-LDMed Ti-6Al-4V samples results in overall poor tensile properties. Therefore, this paper attempts to ameliorate the inhomogeneous microstructure of the hybrid sample by STA, and simultaneously improve the strength and plasticity. The results showed that the WAAM zone and HAZ were composed of α colonies, the RZ and LDM zone were distributed with fine basketweave structure of the AD samples. With the introduction of STA, the microstructure of each zone of the hybrid sample changes and transformed into a 'dual-phase' structure with bi-modal α p and β t. With the increase of aging temperature, the volume fraction of β t increased and the volume fraction of α p phase decreased, accompanied by the formation of bulk α phase and the coarsening of α s phase. It is worth noting that the strength of WAAM zone was obviously improved by STA, and the fracture positions of the STA samples were randomly distributed in the WAAM and LDM zones. Additionally, with the aging temperature increased, the strength of WAAM-LDMed samples was weakened, and the ductility was improved because the coarsened bulk α played a role of coordinating deformation in the tensile process. The excellent strength and ductility (UTS = 976 MPa, YS = 876 MPa, EL = 13.57%) of WAAM-LDMed samples was achieved at aging temperature 750 °C, compared with the AD samples (UTS = 860 MPa, YS = 767 MPa, EL = 12.5%). Finally, by optimizing the STA (940 °C/1 h/WQ + 750 °C/4 h/AC), the amelioration of the microstructure and the improvement of the strength-ductility of the hybrid samples were achieved. • The microstructure of WAAM-LDM sample is homogenized into α p + β t by STA. • STA treatment makes the strength of WAAM zone comparable to that of LDM zone. • The WAAM-LDM sample prepared by STA obtain excellent strength and ductility. [ABSTRACT FROM AUTHOR]

In this article, the Ni-46.1Al-7.8Mo (at.%) alloy was directionally solidified at different growth rates ranging from 15 μm/s to 1000 μm/s under a constant temperature gradient (334 K/cm). The dependence of microstructural length scales on the growth rate was investigated. The results show that, with the growth rate increasing, the primary dendritic arm spacings (PDAS) and secondary dendritic arm spacings (SDAS) decreased. There exists a large distribution range in PDAS under directional solidification conditions at a constant temperature gradient. The average PDAS and SDAS as a function of growth rate can be given as λ = 848.8967 V and λ = 64.2196 V, respectively. In addition, a comparison of our results with the current theoretical models and previous experimental results has also been made. [ABSTRACT FROM AUTHOR]

A simple in-situ method was introduced to prepare hydroxyethyl cellulose/poly(acrylic acid) (HEC/PAA) blend hydrogels by forming an interpenetrating network (IPN). Storage modulus (G′) and loss modulus (G″) were improved dramatically compared to HEC. To prove that hydrogen bonds and chemical crosslinking played major roles in improving the hydrogel strength and toughening, and to optimize the components of HEC/PAA blend hydrogels, a series of blend hydrogels with different ratios of HEC to PAA were designed and the corresponding Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), rheological tests, and swelling properties were compared. Crosslinked HEC/PAA blend hydrogel (mol/mol = 1:1) showed the best properties appropriate for opening up biomedical applications of the hydrogel. [ABSTRACT FROM AUTHOR]

A series of stoichiometric NiAl alloys contain four different concentrations of Mo (7.8, 9, 13, 16 at.%) were directionally solidified in the Bridgman-type directional solidification furnace for four different growth rates ( V = 1.5-6 μm/s) in a constant temperature gradient ( G = 334 K/cm). the microstructures of the alloys produced with the different growth rates at a constant temperature gradient tended to form fully fibrous structures. The fiber spacings λ were measured from transverse section of the specimen. The variation of λ with respect to growth rate ( V) and composition ( C) were determined by linear regression analysis. It has been found that λ decreases with the increasing values of V and C. The results are compared with theoretical models and previous experimental published data. [ABSTRACT FROM AUTHOR]

Abstract: Cellular eutectic microstructures with fully lamellar morphology were observed in the directionally solidified Ni–31Al–32Cr–6Mo (at%) hypereutectic alloy at withdrawal rates of 15, 25 and 50μm/s, but the morphologies of cellular microstructures did not change consecutively with increasing withdrawal rate. The growth interfaces were deep cellular at withdrawal rates of 15 and 50μm/s, but it changed to be shallow cellular at rate of 25μm/s. The reason is that the interface undercooling comes to minimum at the middle rate of 25μm/s. If the interface undercooling decreases, the tendency of constitutional undercooling will be weaken. The small constitutional undercooling will increase the interface stability, so that the interface morphology changes from deep cellular to shallow cellular. The shallow cellular growth interface led to a perfect cellular eutectic microstructure, which was analogous to the planar eutectic microstructure. In this case, the widths of the intercellular regions were narrowest, no coarse or irregular plates existed at the cell boundaries, and the thicknesses of the lamellae were almost uniform. The properties of the alloy may be markedly improved. [Copyright &y& Elsevier]

Abstract: Solidification microstructure and growth interface morphology of directionally solidified Ni–31Al–32Cr–6Mo(at.%) hypereutectic alloy were studied. The experiments were carried out at higher temperature gradient of about 250 K cm−1 with different withdrawal rates of 4–500 μm s−1. When the withdrawal rate was less than 50 μm s−1, the primary Cr(Mo) dendrites were gradually eliminated through competitive growth between the primary phase and the eutectic phase. When the withdrawal rate exceeded 100 μm s−1, no primary phase formed, eutectic phase grew directly. Fully eutectic microstructures with lamellar morphology were observed at all withdrawal rates. With increasing withdrawal rate V, the growth interface changed from planar to cellular and then dendritic, the solidification microstructure also transformed from planar eutectic to two-phase cellular eutectic and dendritic eutectic. The microstructure was refined and the eutectic interlamellar spacing λ decreased according to the relationship of λ = 4.82V −0.42. Compared to the alloy at eutectic composition, the volume fraction of Cr(Mo) strengthening phase was increased obviously. [Copyright &y& Elsevier]

Abstract: The microstructure and mechanical property of directionally solidified Ni–30.95Al–32Cr–6Mo–0.05Hf (at%)–0.1Dy (wt%) alloy were investigated by means of OM, SEM, TEM, EPMA, three-point bending tests and high-temperature tensile tests. With the withdrawal rate increasing from 6 to 120μm/s, the microstructure changes from planar eutectic to cellular or dendritic eutectic, and both the interlamellar spacing and eutectic cell size decrease gradually. The relation between interlamellar spacing and withdrawal rate can be obtained as . The corresponding room temperature fracture toughness first increases and then decreases, which should be attributed to the microstructural evolution at different withdrawal rates. Moreover, some toughness mechanisms are responsible for the improvement of fracture toughness, such as crack bridging, interface debonding and microcrack linkage. The high-temperature tensile strength is low at the planar growth rate (10μm/s), and it increases gradually with the increase of withdrawal rate. The strengthening mechanism is also discussed. [Copyright &y& Elsevier]

Abstract: The effect of various Dy content on the microstructure of Ni–31Al–32Cr–6Mo hypereutectic alloy was studied at the withdrawal rates of 6, 30 and 90 μm/s. The results show that the solid–liquid interface morphology has an evolutionary process of planar → cellular → dendritic interface with the increasing withdrawal rate. The primary Cr(Mo) dendrites are gradually weeded out through competitive growth between the primary phase and the eutectic phase. The volume fraction of primary Cr(Mo) dendrites decreases with the modest addition of Dy (0.05 wt.%) at 6 μm/s. When the withdrawal rate increases to 30 μm/s, the appropriate addition of Dy (0.1 wt.%) refines the microstructure, such as the width of intercellular zone and the lamellar thickness in the intercellular zone. With the increase of withdrawal rate to 90 μm/s, the addition of Dy has no significant effect on the microstructure. In addition, the white Dy-containing phase can occur in the boundary of eutectic cells when the Dy content is no less than 0.1 wt.%. [Copyright &y& Elsevier]