查看更多>>摘要：? 2022 The AuthorsThe authors present novel insights into the formation of nanoporous, wet-chemically produced sodium titanate films onto microspherical substrates of varying composition. Microspheres of Ti6Al4V (atomised; ca. 20–50 μm), which were utilised due to their ubiquitous industrial usage relative to metallic titanium, were compared with TiO2 microspheres (flame spheroidised anatase and rutile powders; average ca. 30–40 μm). These were then suspended in 5 M NaOH solutions (60 °C, 24 h), and then characterized (SEM, EDS, XRD, XPS) to determine the extent of sodium titanate generation, and the potential inhibition of formation due to oxygen content. It was found that excessive oxygen content (flame-spheroidised rutile and anatase powders) resulted in inhibition of nanoporous titanate formation, apart from the top few nanometres of the surface, since a diffusion barrier of TiO2 prevents further conversion. The characteristic nanoporous titanate structures were formed on the Ti6Al4V microspheres, ca. 1 μm (999 ± 25 nm) in thickness, whereas no visible alteration to the TiO2 microspheres were seen. High surface concentration (ca. 9.5–17.6 at.%) of Na was seen in all samples via XPS, including the TiO2 microspheres (despite no morphological change), however, only the Ti6Al4V microspheres exhibited moderate Na content (ca. 4.7 at.%) via EDS, illustrating a diffusion gradient during formation. The confirmation of these structures onto microspherical substrates opens the possibility for application in biomaterials, water treatment, and energy fields.
查看更多>>摘要：? 2022 Elsevier Inc.Dual heat treatment, the combination of near-β heat treatment and two-phase field heat treatment, provides an effective approach for near-α titanium alloy to obtain a tri-modal microstructure with excellent comprehensive performance. In this paper, the three-dimensional morphology of a tri-modal microstructure in TA15 Ti-alloy and the evolution mechanisms of equiaxed α and lamellar α were revealed by means of interrupted quenching experiments and three-dimensional reconstruction experiments. It is found that the equiaxed α and the lamellar α showed irregular shapes in three-dimensional space, and the α phases were in contact with each other except for some small and fine lamellar α. During the near-β heat treatment, the decomposition of equiaxed α was caused by β phase wedging at grooves. Grooves formed on the surface of the equiaxed α, extending inwards and further the equiaxed α being separated. In addition, a prediction model of equiaxed α decomposition was proposed in this paper. During two-phase field heat treatment, the increase of equiaxed α size was caused by the merging of adjacent α grains or the adhering growth of fine lamellar α. Some lamellar α decomposed through the mechanism of deflection fracture proposed in this paper, i.e., grooves formed at the substructures of the lamellar α and expanded inwards. The lamellar α on both sides of the grooves deflected at small angles to reduce the interface energy and finally the fracture occurred.
查看更多>>摘要：? 2022The integrated forming process of an Al-Mg-Si alloy was designed, which combined solution heat treatment (SHT) and hot forging into one operation followed by artificial aging. The effect of deformation strains on the microstructure and mechanical properties was investigated by electron backscatter diffraction (EBSD), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and tensile tests. The results show that the tensile strength and yield strength of the compressed specimens were increased by at least 12.9% and 13.8%, respectively, when compared to the undeformed T6 specimen. {001}〈110〉 and {011}〈110〉 texture components were produced at low strains and gradually vanished as strain increased, in contrasting to the T6 specimen, which produced strong recrystallized texture components. As a result of the dynamic recovery (DRV) mechanism, intense {112}〈110〉 and {111}〈110〉 texture components were obtained in the integrally processed specimens at high strains along with a high fraction of low angle grain boundaries (LAGBs). The dispersed Al12(Fe,Mn)3Si phases aided in the formation of cellular structures and facilitated in the development of the DRV. The dislocations significantly accelerated the precipitation of β'' phases, which conversely pined the movement of dislocations and improved the mechanical properties of the Al-Mg-Si alloy.
查看更多>>摘要：? 2022This study explored the feasibility of friction stir welding (FSW) of dissimilar butt joints of 3 mm thick Inconel 718 Ni-based superalloy and AISI 204Cu stainless steel. The effect of operating parameters on microstructure and mechanical properties of the weldments were investigated with varying traverse speeds of 40, 70, 90 and 140 mm/min while keeping the rotational speed constant, i.e. 300 rpm. The microstructural characterization was performed using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results revealed that the formation of M23C6 carbide particles and fine equiaxed recrystallized austenite and ferrite grains in the nugget zone led to an increase in mechanical properties. The atomic diffusion region at the joint interface of the Inconel 718 and AISI 204Cu was an average thickness of 1.5 μm showed an fcc microstructure with refined MC carbide particles (average size 40 nm) and NbC carbides (average size 50 nm). In addition, a dragged material from Inconel 718 on the advancing side of the stainless steel 204Cu was found, which was directly affected by the traverse speed and related to the strength of the joint. Grain refinement in the nugget zone caused by dynamic recrystallization was observed at all conditions, improving mechanical properties. Based on the obtained results, the medium traversed speeds, i.e. 70 and 90 mm/min at a rotational speed of 300 rpm, were recommended for the sound weld.
查看更多>>摘要：? 2022 Elsevier Inc.Understanding alloy phase transformations during continuous cooling is important for post-processing design and optimization. In this work, continuous-cooling-transformation (CCT) diagrams of Inconel 718 alloys manufactured by laser powder bed fusion (LPBF) and suction casting are developed under different homogenization conditions. Unlike the available CCT diagrams in the reported studies, no γ″ and γ' precipitates can be observed. NbC and δ are determined to be the precipitates after cooling from the γ matrix. Importantly, homogenization time and manufacturing methods are found to affect the Nb homogeneity in the matrix near NbC particles and thus significantly influence the precipitation process of the δ phase, which has a high content in Nb. In the alloys with high Nb homogeneity, the nucleation process mainly contributes to the precipitation, whereas in the alloys with low Nb homogeneity, the precipitation is primarily associated with the growth process. Subgrains are found to form after cooling at 0.1 K/s and can cause the highest hardness in samples. This work provides a new viewpoint on the study of processing-structure-property relationships during cooling in Inconel 718 and is beneficial to the development of alloy post-processing strategies.
查看更多>>摘要：? 2022 Elsevier Inc.How to improve the acquisition efficiency of electron back scatter diffraction (EBSD) and meanwhile avoid the drifting of images caused by the charge effect is still an issue that needs to be solved urgently for three-dimensional (3D) EBSD characterization of non-conductive ceramic materials. The purpose of this study is to solve the problem based on an experimental and theoretical basis using the yttria-stabilized zirconia (YSZ) coating as the research subject. To eliminate the charge effect, the charge equilibrium point of the YSZ coating was determined using the Duane–Hunt limit method. When the incident energy is equal to the E2 value (3.06 keV), the charge effect on the scanning electron microscopy images of the YSZ coating disappears. However, the incident energy of 3.06 keV exhibits lower EBSD collection efficiency for a 3D EBSD result because of the long exposure time; therefore, increasing the incident energy to 7 keV under the large beam current is a practical way to improve EBSD collection efficiency, which inevitably results in the charge problem again. Furthermore, Ga ion implantation caused the charge effect on the YSZ coating at 7 keV under the large beam current to disappear, which can be attributed to the decrease in bandgap widths and the improvement of electrical conductivity of the t-YSZ phase after Ga ion implantation based on first principles. Calculations of the cohesive energies reveal that Ga ions are more likely to occupy the lattice positions of the YSZ coating after Ga ion implantation. Finally, a high-resolution 3D EBSD image of the YSZ coating was obtained.
查看更多>>摘要：? 2022 Elsevier Inc.Polycrystalline, chemical vapor deposited (CVD) ZnS deposited on a hot isostatically pressed ZnS substrate is studied using scanning electron microscopy (SEM) including electron backscatter diffraction (EBSD) to gain new insights into the growth mechanism during production. The orientations of polar Zn-S-double layers in the zincblende structure of cubic ZnS are analyzed using a recently developed method to determine the polar 〈111〉 axes by EBSD. Here the Hough transform is utilized to find a preferred polar axis in twinned lamellae of industrial CVD-ZnS. The results verify an epitaxial stacking of {111}-layers at the growth front. They furthermore show that the Zn-layer of the analyzed {111}- double layers always points away from the substrate, independent of the polarity of the substrate crystals. If a substrate grain contains a S-layer positioned towards the surface, the polarity in the adjacent CVD grain is inverted, meaning the epitaxial relationship is not perfect.
查看更多>>摘要：? 2022In order to study the effect of magnetic field on the spraying process, a thermal spraying technique of ferromagnetic metal powder assisted by pulsed magnetic field is presented. The Ni60 coating with different Fe content was prepared by pulsed magnetic field assisted supersonic plasma spraying. This process can improve the microstructure, porosity, mechanical properties and tribological properties of the coating. In this paper, a diagram depicting the mechanism for coating formation by pulsed magnetic field assisted spraying was prepared according to the test results for the coatings. We found that the pulsed magnetic field formed at the edge of the poles, and, compared with the Ni base material, the Fe phase material was easily attracted by the magnetic poles, which accelerated its downward movement. During this downward movement, a mixing effect developed within the coating that decreased the coating porosity, made the Cr strengthening phase more uniform, and, as the matrix provided many nucleation sites, further promoted the production of amorphous nanocrystalline phases. Finally, the service performance of the coatings was continuously improved. This process provides a new approach to the design and development of advanced coatings, and it shows great promise for applications in next-generation ferromagnetic metal-based coatings.
查看更多>>摘要：? 2022 Elsevier Inc.In this study, LAZ532 alloy reinforced with Al3La phase in-situ precipitated by adding La2O3 particle was fabricated by melting casting. The hot tensile deformation behaviour of the composite was investigated at deformation temperatures of 423 K ~ 573 K and strain rates of 8.3 × 10?5 s?1–1.7 × 10?3 s?1. The results indicated that the peak stress and elongation at fracture of the composite gradually decreased and increased respectively, with the deformation temperature increased or the strain rate decreased. In particular, the composite exhibited outstanding quasi-superplasticity with elongation to fracture up to 213% at 573 K and 8.3 × 10?5 s?1. Based on the results of theoretical calculation, the activation energy Q of the composite was 97.8 kJ/mol. In addition, by the observation and analysis of microstructure at different strains, the strain induced the precipitation of pearlite-like Al3La phase in the grains during hot tensile deformation. The deformation behaviour of the composite was a synergetic deformation mechanism dominated by GBS, supplemented by DDRX and intragranular slip, and the intragranular slip was dominated by prismatic and pyramidal I <c+a> slips.
查看更多>>摘要：? 2022 The Author(s)The effect of Si addition on the evolution of bainitic transformation, carbon diffusion, carbide formation, and dislocation density in steel was investigated using in-situ high-energy X-ray diffraction (HEXRD). Alloys Fe-0.4C-1.7Mn (in wt%) with 1–4 wt% Si were austenitized at 1273 K and then isothermally heat treated at 573, 623, and 673 K. According to the HEXRD results, increasing Si content reduces the bainitic transformation kinetics and causes the incompleteness of the bainitic transformation to occur at lower bainite volume fraction. This is because i) Si retards carbide formation, impeding the eutectoid bainitic transformation, and leads to the accumulation of carbon at the migrating interface; ii) Si leads to higher strain energy and more dislocations in the austenite that also hinders the migration of the interface. Carbide formation was observed to occur prior to the incomplete transformation stage. During further isothermal holding, the decrease in dislocation density due to dislocation annihilation had little effect on carbide formation or carbon diffusion. Finally, the Si content has a minor effect on the calculated T0, T0’, and WBs lines. The measured carbon content in carbon enriched austenite agrees well with WBs and T0 but not with T0’.
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