查看更多>>摘要：Cu/Mg-composite rods, inside the Cu-shells of which 1 or 400 Mg-filaments are contained, were obtained by hydmextrusion at room temperature. The structure, microhardness and electrical properties of the obtained composites have been studied both in the as-extruded state and after various heat treatments. It is shown, at heating to 450 degrees C, that the solid-state reactions between copper and magnesium lead to the formation of the porous Mg-based solid solution and two sub-layers of CuMg2 and Cu2Mg intermetallic phases (thick and thin, respectively) at the interface. As a result of heating to 530 degrees C, high-strength filaments based on these intermetallic phases are formed in the composites. Annealing at 750 degrees C completely changes the structure of Cu/Mg-composites. Instead of 400 Mg-filaments, one core is formed, which has an eutectic structure and consists of Cu-based fcc-solid solution with islands of Cu2Mg-phase. It was found that, as a result of these reactions, the microhardness of filaments increases by more than an order of magnitude, while the electrical resistivity of the composite remains almost unchanged. The subsequent deformation further increases the strength of Cu/Mg-composites. A conclusion is made that the method for obtaining high-strength Cu/Mg-composite wires tested in this work is new and promising.
Kumar, Ravi RanjanGupta, Rohit KumarSarkar, AdityaPrasad, M. J. N., V...
15页
查看更多>>摘要：In present study dissimilar metal joints between austenitic stainless steel (modified SS321) and alpha-Ti alloy (Ti-5Al-2.5Sn ELI) were produced by solid-state diffusion bonding process performed at different temperatures (750-950 degrees C) in vacuum. The effects of bonding temperature, time and pressure on interface microchemistry and microstructure were analyzed and subsequently the local hardness of interface layer(s) and the bond (shear) strength of the joints were evaluated. The results indicate the formation of four layers comprised of intermetallic phases viz. sigma, chi, lambda + Fe2Ti + FeTi and beta-Ti at the joint interface, and their width increased with increase in the bonding temperature and time. The maximum shear strength of similar to 348 MPa, which is similar to 65% of the shear strength of SS321, was noted for the joint formed at the bonding temperature of 850 degrees C. This was achieved primarily due to complete collapse of surface asperities making intimate contact at the joint surface with formation of optimal width of interface layers having minimum embrittlement effect. The fractography of the specimens failed under shear loading revealed the transition of failure of the joints from featureless brittle fracture to mixed mode of ductile-brittle failure to quasi-cleavage brittle fracture with increasing the bonding temperature. Furthermore, it was noticed that the bonded joint specimens failed either through chi (layer 2) or lambda + Fe2Ti + FeTi (layer 3). Interestingly, the optimized diffusion bonding parameters of the dissimilar metal joints of SS321/Ti-5Al-2.5Sn ELI have yielded different shear strength levels for the similar metal joints of SS321/SS321 (similar to 35% of base alloy) and Ti-5Al-2.5Sn ELI/Ti-5Al-2.5Sn ELI (75% of base alloy).
查看更多>>摘要：Using Tb0.27Dy0.73Fe1.95 as a model alloy, we generate (Tb, Dy)Fe-2 and (Tb, Dy)Fe-3 phases with preferred orientations. We study the mechanism that determines the preferred crystal orientation of a peritectic alloy under high magnetic fields. Adjusting the preparation parameters yields four Tb0.27Dy0.73Fe1.95 alloys with respective < 110 >, < 111 >, < 112 >, and < 113 > directions of the peritectic (Tb, Dy)Fe-2 phase parallel to the high magnetic field. The < 11 (2) over bar0 >, < 0001 >, < 10 (1) over bar0 >, and < 10(13)over-bar > directions of the corresponding primary (Tb, Dy)Fe-3 phase are parallel to the magnetic field. We deduce the orientation relationships ((1) over bar 11)//(0001) and [110]//[11 (2) over bar0] for the (Tb, Dy)Fe-3 and (Tb, Dy)Fe-2 phases. The growth velocity and high magnetic field do not change the orientation relationships of these two phases. The high magnetic field induces the rotation of the primary (Tb, Dy)Fe-3 phase and then affects the orientation of the peritectic (Tb, Dy)Fe-2 phase. Magnetic torque induces stacking of the {0001} plane perpendicular to the magnetic field, meaning the c-axis of the primary (Tb, Dy)Fe-3 phase aligns parallel to the field. At this time, the {111} plane of the (Tb, Dy)Fe-2 phase grows perpendicular to the magnetic field, as reflected in the preferred orientation of the (Tb, Dy)Fe-2 phase along the < 111 > direction.
查看更多>>摘要：Observation regarding the SEM and TEM images of the precipitation and growth morphology of topologically close-packed (TCP) phase indicates that the orientation relationships between the TCP phase with different morphologies and the matrix are not that similar. Concerning with this phenomenon, via DFT calculations, the possible interface structures between the sigma phase and the matrix gamma as well as the mu phase and the matrix gamma have been established and discussed under different orientation relationships. The experimental characterizations and simulated calculations reveal that the orientation relationships between TCP phase and the matrix determine interplanar spacing mismatches and the interface energy of the low index dense arrangement interfaces of the two phases, while the two parameters exert influence on the growth and morphology of TCP phase. The interface energy of the sigma/gamma interface with (111)(gamma)/(001)(sigma) orientation is small while its interplanar spacing mismatch is large, so the TCP phase under this orientation relationship tend to take planar expansion along interface instead of growing layer by layer parallel to the plane, giving rise to plate-like morphology. However, those of the sigma/gamma with (110)(gamma)//(1-10)sigma and the mu/gamma with (110)(gamma)//(111)(mu) are just the opposite, so the TCP phases under these orientations tend to grow layer by layer instead of expand along plane, forming needle-like or rod-like morphology eventually.
查看更多>>摘要：Strain path transition is a common phenomenon during continuous stamping operations of sheet metal and can potentially alter the forming limit of the material. Enabling strain path change in a single experiment is a key challenge faced by several researchers. To understand the effect of continuous strain path change on material forming limits, detailed material characterisation is needed where the material is deformed while the strain path of the material is changed continuously. In this work, a test method was developed, which consisted of a novel mechanical rig and specimen design. The mechanism allowed DP600 steel and AA5182-O aluminium samples to change strain paths continuously without unloading the specimen. Digital image correlation measurements of the strain evolution of the samples during tests showed that the technique was able to alter the strain path of the sample from uniaxial to biaxial strain path. In particular, the measurements showed that the transition from uniaxial to biaxial strain paths was sharper in DP600 than AA5182-O. The test was repeated in a scanning electron microscope (SEM) chamber to observe the behaviour of the microstructure during the strain path transition. The microstructural strain evolution showed rotation of strain bands while the evolution of electron back scattered diffraction (EBSD) maps conveyed grain rotation during continuous strain path change in both the materials. The strain path transition controlled the rotation of grains with preferred crystallographic orientations.
查看更多>>摘要：The in-suit precipitation evolution of micro-sized NbC in Fe-25 wt.% Cr-3.5 wt.% C-2.0 wt.% Nb alloy was studied by the HTCSLM, SEM and TEM observations in this paper. The morphology and size of NbC changed in four stages: pyramidal and triangular about 20 mu m-* multi-pyramidal about 20 mu m-* octahedral about 3 mu m-* worm-like about 300 nm. The three-dimensional morphology of initially precipitated NbC is determined as a pyramid. And the morphology of other micro-sized NbC was formed by the aggregation of pyramidal sub nucleus. The final worm-like NbC comes from the influence of surrounding austenite during eutectic reaction. The precipitation mechanism was clarified by the modified thermodynamic calculations, considering the crystal morphology. This study is a further understanding of the precipitation evolution and mechanism of the micro sized NbC in the melt of HHCCI.
查看更多>>摘要：In this study, Alloy 247LC samples were built with different laser powder bed fusion (L-PBF) process parameters. The samples were then subjected to solution heat treatment at 1260 degrees C for 2 h. The grain size of all the samples increased significantly after the heat treatment. The relationship between the process parameters and grain size of the samples was investigated by performing a design of experiment analysis. The results indicated that the laser power was the most significant process parameter that influenced the grain height and aspect ratio. The laser power also significantly influenced the grain width. The as-built and as-built + heat-treated samples with high, medium, and low energy densities were characterized using a field emission gun scanning electron microscope equipped with an electron backscatter diffraction detector. The micrographs revealed that the cells present in the as-built samples disappeared after the heat treatment. Isolated cases of twinning were observed in the grains of the as-built + heat-treated samples. The disappearance of cells, increase in the grain size, and appearance of twins suggested that recrystallization occurred in the alloy after the heat treatment. The occurrence of recrystallization was confirmed by analyzing the grain orientation spread of the alloy, which was lower and more predominantly <1 degrees in the as-built + heat-treated conditions than in the as-built conditions. The microhardness of the as-built + heat-treated samples were high which was plausible because gamma' precipitates were observed in the samples. However, the L-PBF process parameters had a very low correlation with the microhardness of the as-built + heat-treated samples.
查看更多>>摘要：The improvement of comprehensive properties including hardness, toughness, adhesion strength, and wear resistance of the hard coating is highly desirable for various applications. Herein, a new strategy involving in situ solid-phase diffusion (ISSD) is utilized to fabricate a novel molybdenum carbide composite coating (MCCC) with double-layer structure on cast iron (CI). MCCC is composed of two layers, the outermost layer (Layer I) is a completely dense Mo2C layer, and just beneath it is a Fe3Mo(3)C(Si) composite transitional layer (Layer II) which connects the outer layer and the CI substrate. The squares of the thickness of the Layer I, Layer II, and MCCC are found to be proportional to the ISSD time, thus following the classic parabolic law. The hardness, elastic modulus, and fracture toughness of the coating surface reach 24.6 +/- 0.5 GPa, 483.5 +/- 3.1 GPa, and 3.0 +/- 0.1 MPa.m(1/)(2) . With the evolution of the microstructure in the coating along the thickness direction, the hardness and elastic modulus gradually decrease, while the fracture toughness gradually increases. Furthermore, the result of scratch test shows that the adhesion strength between Layer I and Layer II is approximately 93.4 N, while the adhesion strength between the coating and the substrate is greater than 93.4 N. Therefore, this work provides a new route for the fabrication of MCCC with double-layer structure capable of combining superhardness, excellent toughness, and superior adhesion strength.
查看更多>>摘要：ABSTR A C T 7075 aluminum alloy has high strength but its formability is poor at room temperature. To improve its plastic deformation capability, a new forming method, electrically assisted electromagnetic forming (EAEMF), is introduced and investigated. Our results indicate that the major and minor strain (i.e. the forming limits) of the material following EAEMF increases by 42.3% and 40.0%, respectively, compared to (conventional) electro-magnetic forming (EMF). The respective increase thanks to the new method is even higher (by 76.4% and 83.9%) compared to quasi-static (QS) deformation. Furthermore, the yield strength and tensile strength of the material are reduced by 3.6% and 2.6%, compared with conventional EMF, while the elongation can be increased by 21.6% using EAEMF. The texture and microstructure of the alloy were investigated by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that both grain size and texture strength decrease after EAEMF, while the brass and S textures become more dominant. The dislocation density of the material used for EAEMF is low, and directional alignment of dislocations occurs. This is related to the impulse current promoting the dislocation motion. In addition, Joule heating (by the electric current) enables a dynamic recovery during the deformation process, which reduces both the flow stress and the effect of work hardening. However, it also increases elongation.
查看更多>>摘要：The microstructure, mechanical properties, and corrosion resistance of a Zr + Er modified Al-Zn-Mg-Cu alloy after different retrogression and re-aging (RRA) treatments were investigated. Results show that the main precipitates after different heat treatment change from GP zones + eta' + Al3(Er, Zr) phase (T6) to eta' + Al3(Er, Zr) phase (RRA180-30) and then to eta + T phase (RRA200-30). The component, size, and distribution of precipitated phases would be affected by the regression time and temperature during RRA treatment. It is concluded that the uniformly dispersed precipitate phase in matrix and narrow precipitate-free zones (PFZs) could significantly improve the strength of Al-Zn-Mg-Cu alloy, and the grain boundary precipitated phase (GBPs) with moderate size and large interparticle distance could improve the alloy's corrosion resistance. Besides, a wider PFZ within a certain range is beneficial to improve the intergranular corrosion (IGC) performance. Therefore, it is important to accurately control the heating temperature and retrogression time during the retrogression stage to regulate the characteristics of precipitated phases and achieve the best balance of mechanical properties and corrosion resistance.
NSTL
Elsevier