查看更多>>摘要：The anisotropic elastic properties, topology structure of brittleness and the transformation of edge dislocations in Ti3Al are studied in detail based on Bond matrix model and the tensor theory of elastic media. The results contain remarkably complex three-dimensional variations in the anisotropy and brittleness with angular distribution. The feature of elastic properties and brittleness in Ti3Al is affected by the elastic anisotropy of the lattice. Their topology surfaces give insights into the relationship between elastic anisotropy and brittleness. It is helpful to understand the dislocation field through comparative study of the edge dislocation in the dislocation coordinate system and crystal coordinate system with tensor theory as well as the Bond matrix model.
查看更多>>摘要：Soft magnetic Co-based bulk metallic glasses (BMGs) with large supercooled liquid region (delta T-x) of 47 K and high saturation magnetic flux density (Bs) up to 1.21 T have been developed in a new Co-Fe-B-P-C alloy system without early transition metal and rare earth elements. Substitution of Co by 10-35 at.% Fe in a Co75B10P7.5C7.5 alloy promotes the occurrence of glass transition and enhances the stability of supercooled liquid and glass-forming ability (GFA). The delta T-x of 37-47 K and a critical sample diameter up to 1.2 mm can be achieved for Co40-55Fe20-35B10P7.5C7.5 BMGs. The improved thermal stability and GFA are attributed to complicated primary crystallization phases and stabilized alloy melts, respectively. The addition of Fe enhances the Bs of the Co-based BMGs from 0.79 to 1.21 T, and increases coercivity from 1.1 to 7.2 A/m. The Co-based BMGs also exhibit high yield strength of 3243-3665 MPa with plastic strain up to 2.3% and low viscosity of around 3.0 x 109 Pa.s in the supercooled liquid state.
查看更多>>摘要：In this work, the electrochemical potentiodynamic polarization and impedance spectroscopy analysis were used to investigate the corrosion behaviors related to microstructural evolutions of Al0.3CoCrFeNiSix and Al0.3CoCrFeNiTix HEAs in the NaCl solution. The results presented that addition of Si promoted the formation of BCC phase, which was regarded as a micro-anode to prevent FCC phase as a micro-cathode from being corroded. While the volume fraction of BCC phase increased to enhance the corrosion resistance of Si-x alloys with increasing Si content. Furthermore, the reduction in the grain sizes of Si-x alloys with increasing Si content could also improve corrosion resistance of the alloys. Therefore, the corrosion resistance of Si-x alloys was increased with increasing Si content. Addition of Ti with a high corrosion resistance of Cl- caused the reduction in the grain sizes of Ti-x alloys, which can improve the corrosion resistance of alloys. However, the high Ti content can destroy the corrosion resistance of the alloys due to the formation of a large amount of precipitated phases. Therefore, as Ti with atomic percentage be equal to that of Al can effectively eliminate the negative influence of precipitated phases and microstructure on the corrosion resistance of alloys, meaning the Ti-0.3 alloy had the best corrosion resistance in Ti-x alloys. The analysis of X-ray photo-electron spectroscopy (XPS) identified that the contents of oxidized Cr3+ and Fe3+ in the passive film are the main contribution to improve the corrosion resistance of Si-x alloy. And the contents of oxidized Cr3+ and Ti4+ in the passive film are the main contribution to improve the corrosion resistance of Ti-x alloy.
查看更多>>摘要：The surfaces parallel and perpendicular to c-axis of commercial N52 Nd-Fe-B magnet were coated with Tb by magnetron sputtering, respectively. The effect of Tb diffusion anisotropy on magnetic and mechanical properties was investigated. The coercivity increased from original 13.66 kOe to 21.90 kOe for the magnet diffusing parallel to c-axis and 19.68 kOe for the perpendicular diffusion, mainly resulting from the formation of (Nd, Tb)(2)Fe14B shells. The bending strength sigma(b) of original magnet revealed obvious anisotropy. The sigma(b) of diffused magnets for parallel to c-axis and perpendicular to c-axis showed a decrease by 1.76% and 6.14%, respectively. The deterioration in mechanical properties was related to internal stress resulting in transgranular fracture near surface of diffused magnet. The difference of magnetic and mechanical properties for the magnets with diverse diffusion direction was mainly caused by anisotropy of Tb diffusion in magnet.
查看更多>>摘要：The dealloying performances of the free side and roller side of the Al50Au50 ribbons are investigated under different dealloying conditions. The free side consisting of Al2Au, AlAu, and AlAu2 phases undergoes more severe corrosion than the monophasic AlAu roller side. The Al2Au phase not only acts as an anodic electrode in galvanic corrosion of free side but also leaves nanoporous Au behind and induces further dealloying of AlAu by the capillary action. The oxide film is confirmed as Al-O film with solubilized Au atoms. During corrosion, the Au atoms in oxide film tend to segregate into Au-rich and Au-lacked regions. The Au-rich region remained can enhance the Au-content on surface and impede the further corrosion.
Arab, AliGuo, YansongSktani, Zhwan Dilshad IbrahimChen, Pengwan...
10页
查看更多>>摘要：The mechanical properties and microstructure evolution of AlCoCrFeNi High-Entropy Alloys (HEAs) at different strain rates and temperatures were investigated. High strain rate experiments are performed by the split Hopkinson pressure bar (SHPB) at strain rates of 500,1500 and 2500 s(-1) at three different temperatures (27, 250 and 500 C). And Gleeble machine was used to carry out the experiment at high temperatures (500, 750 and 900 C) under quasi-static compression condition. Stress-strain curves indicated flow stress is increased by raising the strain rate at all temperatures. Microstructure observation of the deformed samples show no any dynamically recrystallized (DRX) occurred at tested condition. However, it is several transgranular cracks are observed in tested samples, the number of the cracks are decreased by rising the temperatures. At temperature higher than the 500 C under quasi-static condition DRX microstructure with unrecrystallized coarse structure with necklace morphology is observed in deformed sample. The average grain size in the DRX region is around 0.5 mu m. It is worth to mention, DRX grains do not show preferred orientations at formed necklace structure.
查看更多>>摘要：Sintered Tb-Dy-Fe materials prepared by the compression molding method have higher relative density and energy density than powder-bonded composites. However, due to the low magnetocrystalline anisotropy and the cubic symmetry of the Laves structure, the orientation degree of sintered materials is relatively low and not beneficial for obtaining large magnetostriction. We prepared the sintered Tb-Dy-Fe/DyCu compacts with preferred < 111 > orientation by applying magnetically oriented powder metallurgy. The dependence of orientation degree and magnetostriction of oriented Tb-Dy-Fe/DyCu sintered compacts on different particle morphology and Tb/Dy ratios were studied. The oriented Tb-Dy-Fe/DyCu sintered compacts prepared from the milled single crystal Tb-Dy-Fe powders gained a higher < 111 > orientation due to the small rotational resistance when magnetic particles move in a magnetic field, achieving improved magnetostriction. Magnetocrystalline anisotropy which determines the rotational torque caused by the magnetic field is one of the important factors affecting the rotation behavior of magnetic particles in a magnetic field. We designed Tb-Dy-Fe alloys with different Tb/Dy ratios which have different magnetocrystalline anisotropy, and prepared the sintered Tb-Dy-Fe/ DyCu compacts under the same process parameters. The magnetocrystalline anisotropy constant K1 of TbxDy1-xFe1.95 (x = 0.27, 0.30, 0.33, 0.50) alloys increased from 0.66 x 10(6) J/m3 to 3.85 x 106 J/m(3) by raising the Tb/ Dy ratios, and the < 111 > orientation degree of sintered Tb-Dy-Fe/DyCu compacts was promoted simultaneously. The oriented Tb0.33Dy0.67Fe1.95/DyCu sintered compact achieved the highest < 111 > orientation degree of 56.6%, resulting in the largest magnetostriction of 1326 ppm and the d33 peak value of 6.81 nm/A.
查看更多>>摘要：To adjust the formation and proportion of the strengthening phase in high entropy alloys (HEAs), the non-metallic Si element was added in non-equiatomic CoCrFeNi HEA. Co30Cr30(FeNi)(40-x)Si-x HEAs (x = 2, 4, 6, and 8 at.%, hereinafter, simplified as HSi2, HSi4, HSi6, and HSi8, respectively) were prepared. The phase evolution, tensile properties, and strengthening mechanisms were investigated. The results show that the phase structures are FCC, rich Cr-Si, and rich Ni-Si phases in HSi2 and HSi4. The rich Cr-Si phase disappears and the rich Ni-Si phase grows gradually with the increase of Si content. HSi6 presents an appropriate proportion of FCC and discontinuous rod-like rich Ni-Si phases. The mixing enthalpy (delta H-mix) is more suitable for the phase prediction in Co30Cr30(FeNi)(40-x)Si-x HEAs. With the increase of Si content, Ni atoms diffuse into the primary rich Cr-Si phase and replace Cr atoms to form a rich Ni-Si phase. The rich Ni-Si phase has a stronger binding force due to the Ni and Si atoms with more negative delta H-mix. The yield strength gradually increases from 215 MPa to 330 MPa with the increase of Si content. HSi6 has excellent tensile strength-ductility synergy with a tensile strength of 694 MPa and a fracture strain of 67.8%, which is attributed to high strain hardening ability. The discontinuous and rich Ni-Si phase plays an important role as a strengthening phase in the deformation process, reducing the free path of dislocation movement and delaying the occurrence of necking. The FCC phase with large plastic deformation ability leads to crack passivation and maintains a certain ductility. More rich Ni-Si phases will deteriorate the ductility of HSi8.
查看更多>>摘要：In the present work, solid-liquid compound casting process was used to fabricate TC4/AZ91D bimetals using thermal diffused Ni-coated TC4 alloy. The effects of thermal diffusion time of Ni-coated TC4 alloy on interface microstructure evolution and mechanical features of TC4/AZ91D bimetals were investigated. The interface microstructure has undergone the evolution of NiTi2, NiTi and Ni3Ti to NiTi2, NiTi and Ni2Ti4O (Mg) at Ni-Ti interface and (Mg2Ni + alpha-Mg) eutectic structure + Ni2Mg3Al ternary phase to eutectic-free (only Al3Ni, Al3Ti and Ni2Mg3Al) at Ni-Mg interface as the thermal diffusion time of Ni-coated TC4 alloy increased from 0.5 h to 5 h and 9 h. The maximum shear strength of 105.2 MPa was obtained for the eutectic-free interface of TC4/AZ91D bimetals when Ni-coated TC4 alloy were thermal diffused by 5 h. The rupture of TC4/AZ91D bimetals mainly takes place at (Mg2Ni + alpha-Mg) eutectic structure or between the interface of Ni3Ti layer/(Mg2Ni + alpha-Mg) eutectic structure when the thermal diffusion time of Ni-coated TC4 alloy is 0.5 h. Besides, with the thermal diffusion time increases to 5 and 9 h, the rupture occurs at the NiTi2 and Ni2Ti4O (Mg) reaction layers, respectively.
查看更多>>摘要：This paper describes the preparation of novel FeCoNiMoW high-entropy alloy coatings using the pulse current electrodeposition method and the effect of pulse current densities of 2, 6, and 10 A/dm(2) on the coatings' characteristics. XRD, TEM, EDS, and FESEM were used to perform phase, elemental, and morphological evaluations, respectively. The coatings' microhardness, magnetic, wear, and corrosion properties were also investigated. The results confirmed the formation of FeCoNiMoW alloy coatings with high entropy. When the current density increased, the morphology changed from a dome to a cauliflower structure. The coexistence of amorphous and nanocrystalline phases was demonstrated by XRD and TEM. Small coercivity (11 Oe-18 Oe) was achieved due to the unique microstructure. The lowest coercivity (11Oe), highest hardness (682 HV), highest wear resistance (COF= 0.5), and highest corrosion resistance (i(corr) = 3.2 mu m/cm(2)) were obtained at a current density of 6 A/cm(2).
NSTL
Elsevier