查看更多>>摘要：In-situ laser deposition of Ni powder as an interlayer has been exploited to join dissimilar metals, titanium and stainless steel. Direct fusion joining of these materials often suffers from longitudinal cracks due to the formation of hard and brittle intermetallics of Ti and Fe, and also transverse cracks because of large difference in their thermal expansion coefficients. The Ni-interlayer mitigated the longitudinal cracks by acting as an effective barrier to elemental diffusion, thus restricting the growth of brittle intermetallics. As the thermal expansion coefficient of Ni lies between that of SS and Ti, this acted as a functionally graded layer to reduce the thermal residual stresses, thus preventing the formation of transverse cracks across the joint. Maximum ultimate tensile strength of the weld joints obtained was 375 MPa. Results were analyzed by performing various microstructural characterizations using scanning electron microscopy, x-ray diffraction, and energy-dispersive X-ray spectroscopy. The novelty of this method is its easy adaptability in three dimensions contour welding any dissimilar metals using an interlayer of a compatible material.
查看更多>>摘要：In the grinding process, the magnitude of the grinding force has a serious impact on the surface quality of the workpiece and the tool life. In order to explore the influence of different grinding parameters on the grinding force in the ultrasonic-assisted grinding process, this paper carried out an ultrasonic-assisted single-grain high-speed grinding experiment. First, the forms of abrasive wear were analyzed, and the reasons for the formation of different abrasive wears were discussed. The results showed that the grinding force of a single abrasive in-creases with the increase of abrasive wear volume. In addition, based on the condition that the abrasive particles are constantly worn over time during the machining process, a new type of dynamic grinding force model for ultrasonic-assisted high-speed grinding of single abrasive particles was established based on the relationship of abrasive wear volume changes with time. The model was verified experimentally by ultrasonic-assisted single-grain grinding of QT500-7 ductile cast iron, and the change law of single-grain grinding force with time under different parameters was explored. It was found that under the same parameters, the axial force of a single abrasive particle is always greater than the tangential force, and the grinding force increases with the increase of workpiece linear speed. The maximum error between the experimental value and the simulated value of the grinding tangential force is about 34 %, and the maximum error of the normal force is about 23 %, but the variation trend of the two with time is basically the same.
查看更多>>摘要：Additive manufacturing (AM) technology has drawn tremendous attention in producing lightweight and complex metallic components. In this work, a thin wall of AZ31 Mg alloy with fine equiaxed grains was fabricated via gas tungsten arc-based wire arc additive manufacturing (WAAM-GTA) technology. The grain structure, dislocation, and texture of the hot-rolled and WAAM-GTA AZ31 samples were analyzed by EBSD, while the matrix and dispersed phases were characterized by EDS and X-ray diffraction. The 3D porosity of samples was examined quantitatively by an X-ray computed tomography (XCT). The results show that dominated equiaxed alpha-Mg grain structure was obtained together with negligible precipitated phase. The mechanical properties of WAAM-GTA AZ31 were superior to their cast counterparts and close to those of wrought AZ31, and their correlation to microstructure and defects were explored. Moreover, the WAAM-GTA AZ31 showed excellent electromechanical corrosion performance in 3.5 % NaCl solution as compared to the hot-rolled AZ31 plate. The WAAM-GTA technology therefore offers new routes to fabricate AZ31 Mg components with equiaxed grain structure, as well as favorable mechanical properties and electromechanical corrosion performance.
Dubinin, O. N.Chernodubov, D. A.Kuzminova, Y. O.Shaysultanov, D. G....
8页
查看更多>>摘要：Additive manufacturing (AM) allows printing parts of complex geometries that cannot be produced by standard technologies. Besides, AM provides the possibility to create gradient materials with different structural and physical properties. We, for the first time, printed gradient soft magnetic materials from paramagnetic powders (316L steel and Cu-12Al-2Fe (in wt.%) aluminium bronze)). The magnetic properties can be adjusted during the in-situ printing process. The saturated magnetization value of alloys reaches 49 emu g(-1). The changes in the magnetic properties have been attributed to the formation of the BCC phase after mixing two FCC-dominated powders. Moreover, the phase composition of the obtained gradient materials can be predicted with reason-able accuracy by the CALPHAD approach, thus providing efficient optimization of the performance. The obtained results provide new prospects for printing gradient magnetic alloys.
查看更多>>摘要：To avoid substrate softness, AA7075 were rapidly soldered using a Sn-9Zn solder at 200 degrees C under ultrasonication. The effect of acoustic intensity on the microstructure and mechanical properties of the soldered joint was studied. The acoustic intensity inside the solder was improved by decreasing the lap width without increasing the input ultrasonic power. Results showed that the softness of the substrate was almost avoided with minimal hardness decrease. The acoustic intensity increased by four times when the width of the lap clearance was reduced from 0.8 mm to 0.2 mm. Pronounced erosion of the substrate occurred under high acoustic intensity. Thus, the content of Al in the joint seam increased from 3.35% to 10.84% after reducing the lap width from 0.8 mm to 0.2 mm. The joint seam was characterized by interlaced fine/coarse Sn-Zn eutectic. The Sn and Zn grains had average sizes of 2.31 and 0.31 mu m in the fine eutectic and 3.03 and 0.41 mu m in the coarse eutectic. Increasing the acoustic intensity during soldering can effectively increase joint strength. The maximum shear strength of 65.4 MPa and hardness of 29.5 HV were obtained in the joint soldered at 0.2 mm. The cavitation bubble with a nucleation diameter of 10 mu m had a large liquid velocity of 7653 m/s, a temperature over 1800 K, and a pressure of 4 x 10(12) Pa during its collapse.
查看更多>>摘要：In this study, wear and corrosion behavior of a novel borided high manganese steel (HMS) produced by the researchers was investigated. After the sheets were cold-rolled, they were annealed. HMS was borided at 850, 900, and 950 degrees C for 2, 4, and 6 h through the pack-boriding process. Borided HMS uncommonly exhibited a sawtooth morphology like low alloy steels due to similar crystal structures of MnB and FeB. XRD analysis showed the existence of SiC, FeB, MnB and Fe2B phases. The present study indicated a silicon-rich zone by EDX mapping. The formation mechanism of silicon-rich zones was explained and expressed with the term "compact transfer of silicones". The boriding time and temperature increased the thickness of the boride layer from 26.13 mu m to 109.04 mu m. The highest hardness value was observed in sample 5 (1757 HV0.05). The activation energy of borided HMS was quite low compared to several high alloy steels in the literature. Daimler-Benz Rockwell-C adhesion test showed that adhesions of borided HMS surfaces were sufficient. The "egg-shell effect" that emerge due to the high silicon rate did not occur. In the wear tests applied under 5, 10, and 15 N loads, the borided HMSs exhibited a better wear resistance compared to the base metal (BM). However, the wear test was applied under 5 N load and BM had a better performance than several borided HMSs because of the phase transformations. In general, the borided samples had lower corrosion rates compared to the unborided ones.
查看更多>>摘要：Ultrasonic vibration was proposed to enhance interface bonding of Mg/Al bimetal prepared by a novel lost foam compound casting (LFCC) to obtain high strength Mg/Al bimetal. The results showed that the interface of the Mg/Al bimetal without ultrasonic vibration was mainly composed of layer I (Al3Mg2 + Mg2Si), layer II (Al12Mg17 + Mg2Si), and layer III (Al12Mg17 + delta-Mg eutectic). Under the ultrasonic vibration, the Mg2Si and Al12Mg17 phases and the Al12Mg17 + delta-Mg eutectic at the interface were remarkably refined. After the ultrasonic vibration was applied, the Mg2Si phase was uniformly dispersed in the whole interface, and the continuous oxidation inclusion defect was eliminated. As a result, the microhardness of the entire interface became more uniform, and the shear strength of the Mg/Al bimetal significantly increased by 86.5 %, reaching 69 MPa, compared to the bimetal without ultrasonic vibration. The fracture surface of the Mg/Al bimetal without ultrasonic vibration exhibited an apparent brittle fracture morphology. Under the assist of the ultrasonic vibration, the shear strength of the bimetal was improved mainly due to the refinement of the interfacial microstructure, and the fracture surface of the Mg/Al bimetal generated a partial plastic deformation in the interface layer.
查看更多>>摘要：To improve structural performance, bendability and potential functionality of metal-based sandwich sheets, the 3D lattice cores were sandwiched between thin metallic face sheets. The bending properties of sandwich sheets with 3D printed carbon fiber reinforced plastic (CFRP) lattice cores originating from basic topologies of spherical shell, tetrahedral truss and tetrahedral plate were systematically investigated. The effects of core topologies, core relative densities, core heights, face sheet thicknesses on structural properties were clarified. The common failure modes during bending of sandwich sheets, such as face buckling and shear failure of core, were deeply investigated by theoretical models and experimental tests. At a prescribed radius of 60 mm, the sandwich sheets with the bilayered dome, octet truss and plate lattice cores of relative density of 50 %, height of 6 mm and face sheet thickness of 0.5 mm are bendable. This study demonstrates the feasibility of design and production of bendable sandwich sheets with 3D lattice cores based on the theoretical and experimental validations. The designed bendable sandwich sheets can be adopted to replace conventional heavy monolithic metal sheets in various engineering applications, which is anticipated to fulfill the high demand for lightweight functional materials.
Sun, DongZhu, Yan SongLu, Wen ZhuangZuo, Dun Wen...
16页
查看更多>>摘要：In grinding of the boron-diffusion-hardened titanium alloy, with the grinding speed increasing, the strain gradient-dependent strengthening (SGS) effect of TiB whiskers would become obvious, resulting in an improvement of the surface quality. To explore such SGS effect of TiB whiskers, a novel model of the strain gradient-dependent strengthening effect in the primary deformation zone was developed, and then a novel specific grinding energy model was further proposed to quantitatively estimate such SGS effect of TiB whiskers. It indicates that the above two models can adequately demonstrate the SGS effect of TiB whiskers in grinding the borided titanium alloy. The results demonstrate that the grinding performance of the borided titanium alloy was dominated not only by the grinding speed but also by the TiB whiskers. Due to high grinding speed (about 120 m/s) inclining to cause the maximum undeformed chip thickness reduced, when it was closed to the size of TiB whiskers, the SGS effect of TiB whiskers would become obvious, leading to an improvement of surface quality. Furthermore, when the size of TiB whiskers was closed to the sub-micron-scale, the enhanced SGS effect of the sub-micro-sized TiB whiskers tends to generate, causing the surface quality further improved.
查看更多>>摘要：In the present research, a hybrid laser polishing technology combining pulsed laser and continuous wave laser was applied to polish the surface of laser directed energy deposition (LDED) Inconel 718 superalloy components. The surface morphology, microstructure evolution and microhardness of the as-fabricated, the single pulsed laser polishing (SPLP) and the hybrid laser polishing (HLP) processed samples were investigated. The results revealed that the as-fabricated sample has a rough surface with sintered powders. In the matrix, the NbC carbide and Cr2Nb based Laves phase array parallel to the build direction and the small gamma"-Ni3Nb particles precipitate in matrix uniformly. The surface roughness of the as-fabricated sample is 15.75 mu m which is decreased to 6.14 mu m and 0.23 mu m by SPLP and HLP processing, respectively. The SPLP processing refines the grains and secondary phase significantly in the remelted layer which is reconstructured with the cellular structure and plenty of substructures. The HLP processing also refines the grain and secondary phase but the secondary phases still exhibit array distribution. In addition, the tangled dislocations pile up along the interface of secondary phases. Compared with the as-fabricated sample, the SPLP processing decreases the surface microhardness but the HLP processing increases the surface microhardness, and the Young's elasticity modulus of surface layer is improved by SPLP and HLP processing to 282 +/- 5.21 GPa and 304 +/- 5.57 GPa, respectively.
NSTL
Elsevier