查看更多>>摘要：? 2022 Elsevier Inc.To obtain aluminum titanate (AT, Al2TiO5) ceramics with excellent mechanical properties, the ZrO2 was introduced into AT flexible ceramic to modify the microstructure of it. Results show that ZrO2 can significantly improve the mechanical properties of AT flexible ceramics. When the addition of ZrO2 is 8 wt% and 12 wt%, the optimal strain and strength increase by ~52% and ~ 46%, respectively. The statistical results show that ZrO2 can not only refine the AT grains but also improve the aspect ratio, which leads to more events of grain pull-out and transgranular fracture. Since the generated ZrTiO4 is pinned in the AT grain boundary microcracks, the phenomenon of branching and deflection of main crack will increase, rising the resistance of main crack propagation. It is expectable that the discovery of this work is benefitted to solve the brittle limitation of ceramics.
查看更多>>摘要：? 2022The strain-control low cycle fatigue behaviour of a γ'-strengthened Co-based single-crystal superalloy was investigated at 900 °C. The fatigue life of the alloy was longer than conventional Co-based superalloys due to strengthening provided by the γ'. Additionally, it is found that slip bands consisting of many tangled dislocations and stacking faults continuously cut through the γ' phase with the strain amplitude above elastic limit, which is the main deformation mechanism. The planar slip deformation mode has resulted in crystallographic fracture. In contrast, few dislocations were observed in the sample cycled below elastic limit and severe oxidation at surface introduced Co3W/γ layer and recrystallization leading to mode I crack.
查看更多>>摘要：? 2022 Elsevier Inc.Ion bombardment is one of the powerful methods to modify the surface characteristics of materials. In this study, SiC ceramic is bombarded under different fluences by 60 keV Ar-ion beam. The effects of Ar ion bombardment on the surface microstructure and subsequent wetting of SiC ceramic using AgCu-Ti filler metal are investigated. Ar ion bombardment can break the Si[sbnd]C bond of SiC cell, thus, SiCx(x < 1), SiCx(x < 1) twins and the amorphous layer are generated in the SiC surface with the increase of fluence from 1×1014/cm2 to 1×1017/cm2. With the increase of fluences, the contact angle decreases by the acceleration of interfacial reaction rate as a result of the break of Si[sbnd]C bond in SiC surface in the rapid spreading stage. The amorphous layer is gradually formed in the SiC surface, requiring more time to reach the equilibrium stage for droplets, while the bonding quality of the SiC/AgCu-Ti wetting interface is obviously improved. Significant modification in the microstructural and excellent wetting behavior are obtained by leveraging the ion bombardment technique.
查看更多>>摘要：? 2022 Elsevier Inc.Biodegradable Zn-based alloys exhibit promising application prospects due to their suitable degradation rates and acceptable biocompatibility. However, unstable mechanical properties during room-temperature storage limit their application potential. In this study, Zn-2Cu-0.8Li (wt%) alloy wires with excellent and stable mechanical properties were prepared by hot extrusion followed by multi-pass cold drawing. For the as-extruded Zn-2Cu-0.8Li alloy of a [1ˉ21ˉ0]//ED texture, (Li, Cu)Zn4 phase (volume fraction: 84.4 ± 2.4%) is found to be the matrix, and the remaining phase is Zn-based solid solution (η-Zn phase). During cold drawing, the (Li, Cu)Zn4 phase was continuously elongated, and its original texture gradually evolved into intensive [011ˉ0]//DD fiber texture. In contrast, the η-Zn phase exhibits an evidently refined grain structure and weakened texture due to dynamic recrystallization (DRX). Accordingly, the ultimate tensile strength was significantly improved from348.1 ± 3.1 MPa (as-extruded rod: ? 6 mm) to 450.3 ± 8.7 MPa (as-drawn wire: ? 3 mm), with the elongation decreasing from 37.1 ± 2.1% to 29.5 ± 1.3%. After 6-month natural aging, the as-drawn wire showed desirable mechanical stability, with basically unchanged mechanical properties. The corrosion rate of as-drawn wire with a diameter of 3 mm in c-SBF solution exhibits a 46% increase (from 212.07 ± 10.73 μm/year to 309.81 ± 16.53 μm/year) after cold drawing. Given the excellent mechanical properties and suitable corrosion rate, the Zn-2Cu-0.8Li wires are proposed as a promising material for biodegradable implants.
查看更多>>摘要：? 2022 The AuthorsOxide Dispersion Strengthened (ODS) steels are potential candidate materials for application as structural components of fission and fusion reactors, known for their high thermal stability, high resistance to creep and to radiation-induced damage. These attractive properties result from the presence of the fine and highly thermally stable yttrium?oxygen (Y-O) based nanoparticles, which exert a strong Zener pinning force to hinder the grain boundary movement, and are able to pin dislocations and trap radiation induced defects. In the present work, the effect of annealing at 1400 K on the microstructure and oxide nanoparticles in a 0.3% Y2O3 ODS Eurofer steel was assessed. The material was characterized with Scanning Electron Microscopy, Transmission Electron Microscopy and Atom Probe Tomography in a reference condition and after annealing at 1400 K, followed by cooling at different rates. The results showed that the average diameter of the oxide nanoparticles increases from 3.7 ± 0.01 nm to 5.3 ± 0.04 nm, after annealing at 1400 K for 1 h. The particles present a well-known core/shell structure, with a core rich in Y, O and V and a shell rich in Cr. The effect of the increase in oxide nanoparticle size on the microstructure is discussed in terms of the Zener pinning force.
查看更多>>摘要：? 2022 Elsevier Inc.Strain distributions around the fatigue crack during the low cycle fatigue of high-strength ferrite + martensite dual-phase (DP) and tempered martensite (Mt) steels were visualized during cycles from the initial state to the crack initiation and crack propagation using a digital image correlation analysis applied to replica films. The replica film successfully transcribed the microstructure on the specimen surface. Although both the DP and Mt. steels exhibited a high tensile strength, the work-hardening rate of the DP steel was higher than that of Mt. steel. Although the numbers of cycles to failure (Nf) in the DP and Mt. steels were almost the same at the total strain amplitudes (εt) of 0.005–0.008 and 0.02–0.03, the Nf in the DP steel was higher than that in the Mt. steel at the εt of 0.008–0.02. The cracks were generated and propagated along the high-tensile-strain regions in both steels and were initiated when the accumulated strain along the loading direction exceeded a critical value regardless of the value of εt or the steel applied. The increment of the accumulated strain in the Mt. steel was higher than that of the DP steel at the εt of 0.01, whereas it was almost the same between those at the εt of 0.03. The inhomogeneity of the strain distribution, which was quantitatively evaluated from the histogram of the strain distribution, increased as the number of fatigue cycles increased. The strain was rather inhomogeneously introduced in the Mt. steel in comparison to the DP steel at the εt of 0.01, whereas almost no difference in the inhomogeneity of the strain distribution was detected between the steels at the εt of 0.03. Thus, the inhomogeneous strain distribution may promote crack initiation and propagation, resulting in a low Nf at the εt of 0.008–0.02 in Mt. steel.
查看更多>>摘要：? 2022 Elsevier Inc.The mechanism of deformation banding in cold rolling Al[sbnd]Mg alloy is investigated in detail with regards to local lattice rotation and related dislocation slip. The formation of deformation bands (DBs) has a strong orientation dependency where they populate in grains with 〈111〉 and 〈001〉 directions close to the normal direction and 〈101〉 directions close to the rolling direction. On the contrary, DBs are hardly observed in grains close to the {101}〈111〉 orientations. Experimental and numerical analysis indicates that activated secondary slips and their related lattice rotation account for this orientation dependency. The activation of secondary single slip or secondary coplanar slip plays a vital role in the formation of DBs. DBs are formed when the primary and secondary slips lead to sustainable opposite lattice rotations, which gradually split the grain and develop into DBs. Meanwhile, the tendency of the development of Goss texture during the early rolling stage is observed to arise from the generation of DBs.
查看更多>>摘要：? 2022M50 bearing steel, as the important material used in aeroengine bearing, exhibits low cold working capacity with high susceptibility to produce voids. This would lead to the deterioration of mechanical property, which critically limits the industrial application of cold ring rolling (CRR) in M50 bearing rings. In this work, the mechanism of void healing in cold rolled aeroengine M50 bearing steel subjected to electroshocking treatment (EST) was investigated by combining experimental and simulation studies. The experimental results obtained using the three-dimensional X-ray microscopy (3D-XRM) technique show that the porosity of the CRR samples decreases from 0.26% to 0.09% after EST. The healing effect of larger voids is not obvious, while small voids are likely to be healed under EST. The simulation results indicate that due to the inhomogeneous distribution of the physical field, the local thermal compressive stress of as high as 2565.9 MPa is generated around the ellipsoidal void and thus drives void healing process. The healing process of ellipsoidal voids under EST can be divided into elastic and plastic deformation stages considering von Mises yield criterion. In the initial stage, only a small elastic deformation of 53.53 nm occurs in the minor axis direction of the void. In the plastic deformation stage, the material flows along the normal direction of the void with a reduction in the aspect ratio, thereby compressing the void surfaces and promoting their healing. Additionally, the degree of void healing depends on the shape characteristics (curvature and aspect ratio) of the void rather than the current direction. This research elucidates a new elastoplastic mechanism of void healing under EST, which also provides a promising prospect for the application of CRR in M50 bearing steel.
查看更多>>摘要：? 2022 Elsevier Inc.After 70% cold-rolling at 25 °C and annealing at 1100 °C for 1 h, an Fe27Co24Ni23Cr26 high-entropy alloy had a bimodal-grained structure with two peak size distributions of 43.3 and 105.2 μm. Both annealing microtwins and annealing nanotwins can be found in the small and large grains. The thickness of the annealing microtwins was in the range of 10–30 μm, while that of annealing nanotwins was 5–150 nm. The samples were separately deformed under a Hopkinson bar compression system at strain rates of 2500 and 7000 s?1 at 25 °C. The higher strain-rate caused an increase in the flow stress of up to 48%, from 992 to 1470 MPa, when the strain was 0.4. In 7000 s?1 deformed-samples, original strip-like annealing-nanotwins of 10–30 nm thickness were refined by profuse single-variant deformation-nanotwins of 1–2 nm thickness. Moreover, the ultra-fine annealing-nanotwin of 5.2 nm thickness was revealed to be further partitioned by two variants of deformation-nanotwins of 0.6 nm thickness. The hierarchical structures, composed of micrometer, nanometer and sub-nanometer twins, are herewith reported.
查看更多>>摘要：? 2022 Elsevier Inc.W-based alloys prepared via oxide dispersion strengthening have shown enhanced mechanical performance in previous studies. In this paper, multi-doped W alloys with composition of W-xAl-0.5Y2O3 (x = 0, 0.1, 0.5, 0.9 wt.%) were fabricated via ball milling and spark plasma sintering (SPS), and effects of Al addition on microstructure and mechanical properties were investigated. Types of particles in W-xAl-0.5Y2O3 alloys were identified using the electron probe microanalysis (EPMA) and transmission electron microscopy (TEM), which was closely related with the ratio of Y:Al. Complex Y3Al5O12 particles were observed in all the multi-doped W alloys with addition of Al due to the reaction of 3Y2O3 + 5Al2O3 → 2Y3Al5O12 at the sintering temperature of 1600 °C during SPS process. The atomic ratio of Y:Al in W-0.1Al-0.5Y2O3 was larger than the stoichiometric ratio of Y:Al in Y3Al5O12, leading to remaining Y2O3. However, the ratio of Y:Al was less than the stoichiometric ratio of 3:5 in both W-0.5Al-0.5Y2O3 and W-0.9Al-0.5Y2O3, where the particles of Al2O3 were identified consequently. Among these alloys, W-0.5Al-0.5Y2O3 exhibited the most refined microstructure with a uniform distribution of smaller dispersion particles, leading to the superior mechanical strength and ductility.
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