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Showing papers on "Grain size published in 2021"


Journal ArticleDOI
TL;DR: In this paper, the authors report that refinement of magnesium grains can not only improve its strength, but also its ductility, due to the activation of more slip systems, and they find that fine-grained Mg exhibits enhanced work hardening and ductility as well as uniform elongation.

119 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of grain size on the strength and ductility of Mg alloys are summarized and fine-grained Mg-alloys with high strength and high ductility developed by various severe plastic deformation technologies and improved traditional deformation methods are introduced.
Abstract: Magnesium (Mg) alloys, as the lightest metal engineering materials, have broad application prospects. However, the strength and ductility of traditional Mg alloys are still relativity low and difficult to improve simultaneously. Refining grain size via the deformation process based on the grain boundary strengthening and the transition of deformation mechanisms is one of the feasible strategies to prepare Mg alloys with high strength and high ductility. In this review, the effects of grain size on the strength and ductility of Mg alloys are summarized, and fine-grained Mg alloys with high strength and high ductility developed by various severe plastic deformation technologies and improved traditional deformation technologies are introduced. Although some achievements have been made, the effects of grain size on various Mg alloys are rarely discussed systematically and some key mechanisms are unclear or lack direct microscopic evidence. This review can be used as a reference for further development of high-performance fine-grained Mg alloys.

111 citations


Journal ArticleDOI
TL;DR: In this paper, a few-layer graphene nanoplatelets reinforced aluminum matrix composites via deformation-driven metallurgy under coupled thermo-mechanical effect were obtained.

83 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed understanding of how the processing conditions control the micro- and mesostructures and, in turn, the mechanical performance, especially regarding fracture resistance, is presented.

74 citations


Journal ArticleDOI
TL;DR: In this article, the corrosion behavior at open circuit potential (OCP) and discharge properties under applied anodic currents of two α-Mg based Mg-Li alloys, i.e., LAZ131 and LAZ531, with different microstructural features for primary Mg air batteries are investigated.

74 citations


Journal ArticleDOI
10 Feb 2021-Nature
TL;DR: In this paper, the authors report the facile mass production of UFG structures in a typical Fe-22Mn-0.6C twinning-induced plasticity steel by minor Cu alloying and manipulation of the recrystallization process through the intragranular nanoprecipitation of a coherent disordered Cu-rich phase.
Abstract: Steels with sub-micrometre grain sizes usually possess high toughness and strength, which makes them promising for lightweighting technologies and energy-saving strategies. So far, the industrial fabrication of ultrafine-grained (UFG) alloys, which generally relies on the manipulation of diffusional phase transformation, has been limited to steels with austenite-to-ferrite transformation1–3. Moreover, the limited work hardening and uniform elongation of these UFG steels1,4,5 hinder their widespread application. Here we report the facile mass production of UFG structures in a typical Fe–22Mn–0.6C twinning-induced plasticity steel by minor Cu alloying and manipulation of the recrystallization process through the intragranular nanoprecipitation (within 30 seconds) of a coherent disordered Cu-rich phase. The rapid and copious nanoprecipitation not only prevents the growth of the freshly recrystallized sub-micrometre grains but also enhances the thermal stability of the obtained UFG structure through the Zener pinning mechanism6. Moreover, owing to their full coherency and disordered nature, the precipitates exhibit weak interactions with dislocations under loading. This approach enables the preparation of a fully recrystallized UFG structure with a grain size of 800 ± 400 nanometres without the introduction of detrimental lattice defects such as brittle particles and segregated boundaries. Compared with the steel to which no Cu was added, the yield strength of the UFG structure was doubled to around 710 megapascals, with a uniform ductility of 45 per cent and a tensile strength of around 2,000 megapascals. This grain-refinement concept should be extendable to other alloy systems, and the manufacturing processes can be readily applied to existing industrial production lines. Bulk ultrafine-grained steel is prepared by an approach that involves the rapid production of coherent, disordered nanoprecipitates, which restrict grain growth but do not interfere with twinning or dislocation motion, resulting in high strength and ductility.

71 citations


Journal ArticleDOI
TL;DR: In this paper, the microstructures and mechanical properties of Inconel 718 (IN718) alloy fabricated by selective laser melting (SLM) are evaluated in as-built, direct aging (DA), and homogenization+aging (HA) conditions on considering the effect of applied loading direction.
Abstract: The microstructures and mechanical properties of Inconel 718 (IN718) alloy fabricated by selective laser melting (SLM) are evaluated in as-built, direct aging (DA), and homogenization + aging (HA) conditions on considering the effect of applied loading direction. The results show that the microstructure of as-built and DA specimens consist of the intracrystalline fine degenerated dendritic structures (0.6–1 μm in spacing) with a high density of dislocations (1013–1014 m−2). Fine dendritic structures disappear after HA treatment, and the average geometrically necessary dislocation (GND) density decreases to 1012 m−2. A quantitative analysis of strengthening mechanisms is established by taking into consideration the grain boundary, solid solution, precipitation and dislocation strengthening. For the as-built and DA specimens, the contribution to the yield strength by dislocation strengthening is ~85 MPa in vertical deposition and ~170 MPa in horizontal deposition, respectively, and the Laves phases provide approximately 100–110 MPa. The contribution of precipitation strengthening to the strength increment in the DA and HA specimens is 590–600 and 830–850 MPa, respectively. The precipitation strengthening is mainly contributed by shearing mechanisms among which coherency strengthening plays dominant effect rather than order strengthening. For as-built, DA, and HA regimes, the specimens always exhibit higher strength along the horizontal direction than that along the vertical direction. The anisotropy of yield strength in the as-built and DA specimens is mainly attributed to the difference in dislocation density and effective grain size, and the anisotropy of yield strength in the HA specimens is mainly caused by the difference in effective grain size and Taylor factor.

68 citations


Journal ArticleDOI
TL;DR: In this paper, a strategy of designing small grain sizes and abundant amorphous grain boundaries is proposed to improve the energy storage properties under the guidance of phase field theory, and the results show that the grain size and grain boundaries are carefully controlled by the high-energy ball milling method and two-step sintering strategy.

65 citations


Journal ArticleDOI
TL;DR: In this paper, an equiatomic AlCoCrFeNi high-entropy alloy (HEA)-particle-toughened, Zr-based metallic glass composites by spark plasma sintering is presented.

65 citations


Journal ArticleDOI
TL;DR: In this article, the influence of the vibration parameter on the degree of undercooling and nucleation rate of the molten metals was investigated, and the experimental results showed that the grain size obtained under the application of ultrasonic vibration was finer than that obtained under condition of conventional laser cladding.
Abstract: Laser cladding has shown advantages in metal component forming. However, the accompanying issues, such as inner microstructural defects and poor mechanical properties, require further investigation. In this study, laser cladding technology was combined with ultrasound to improve the performance of the formed parts. Based on the cooperative effect of acoustic streaming and acoustic cavitation during the metal solidification process, the influence of the vibration parameter on the degree of undercooling and nucleation rate of the molten metals was investigated. The experimental results show that the grain size obtained under the application of ultrasonic vibration was finer than that obtained under condition of conventional laser cladding. When the amplitude was 25 μm, the average grain size was 0.522 times of that of non-vibration. The phase structure of the precipitates and the chemical composition changed markedly. In addition, the effects of high-frequency vibration on the mechanical properties of the cladding layer were also analysed through contrast experiments. The results indicate that applying high-frequency vibration can effectively reduce porosity, while improving the microhardness and wear resistance. Quantitatively, the friction coefficient was 0.628 times that without ultrasound and 0.709 times that of conventional processing when the amplitude was 25 μm.

64 citations


Journal ArticleDOI
TL;DR: In this article, the synthesis, characterization, and electrical properties of tungsten oxide thin films deposited using the hot filament chemical vapor deposition (HFCVD) system on stainless steel 316L substrate were studied.

Journal ArticleDOI
TL;DR: In this paper, electron backscatter diffraction was used to investigate the microstructure evolutions of a newly developed magnesium-rare earth alloy (Mg-9.80Gd)-3.78Y-1.12Sm−0.48Zr) during instantaneous hot indirect extrusion.

Journal ArticleDOI
TL;DR: In this article, an extraordinarily high yield strength, far beyond the predicted values from the Hall-Petch relation and the ROM, is achieved in a specially designed layered titanium that is characterized by alternating coarse-and fine-grain layers (C/F-Ti) where the grain sizes match the layer thicknesses in both the coarse and fine-grained layers.

Journal ArticleDOI
TL;DR: Grain refinement can strengthen the mechanical properties of materials according to the classical Hall-Petch relationship but does not always result in better corrosion resistance as mentioned in this paper. But the fundamental consensus on how grain size influences corrosion behavior has not been reached.
Abstract: Grain refinement can strengthen the mechanical properties of materials according to the classical Hall-Petch relationship but does not always result in better corrosion resistance. During the past few decades, various techniques have been dedicated to refining grain, along with relevant studies on corrosion behavior, including general corrosion, pitting corrosion, and stress corrosion cracking. However, the fundamental consensus on how grain size influences corrosion behavior has not been reached. This paper reviews existing literature on the beneficial and detrimental effects of grain refinement on corrosion behavior. Moreover, the effects of microstructural changes (i.e., grain boundary, dislocation, texture, residual stress, impurities, and second phase) resulting from grain refinement on corrosion behavior are discussed. The grain refinement not only has an impact on the corrosion performance, but also results in microstructural changes that have a non-negligible effect on corrosion behavior or even outweigh that of grain refinement. Grain size is not the only factor affecting the corrosion behavior of metallic materials; thus, the overall influence of microstructures on corrosion behavior should be understood.

Journal ArticleDOI
TL;DR: In this article, a columnar-to-equiaxed transition (CET) was achieved by adding 2.5% CaB6 nanoparticles to the 2024 aluminum alloy, resulting in a highly coherent Al/CaB6 interface.

Journal ArticleDOI
TL;DR: In this article, a high recoverable energy density of 4.77 J/cm3 with prominent efficiency of 85.7% at 570kV/cm is achieved in Sr0.7Bi0.2TiO3 ceramic.

Journal ArticleDOI
TL;DR: In this article, the structural refinement induced by a newly developed Al-5Ti-2B master alloy and subsequent hot working through the extrusion process was studied, and the enhancement of mechanical properties was successfully rationalized based on the grain size, and as a result, Hall-Petch relationships were developed for the yield stress, tensile strength, and hardness.
Abstract: Enhancement of mechanical properties of AZ91 magnesium alloy based on the structural refinement induced by a newly developed Al–5Ti–2B master alloy and subsequent hot working through the extrusion process was studied. The addition of Al–5Ti–2B master alloy resulted in the grain refinement of α-Mg grains mainly due to the inoculating effect of TiB2 particles, where the optimal amount of the grain refiner was found to be ~0.3 wt%. The hot extrusion process led to a remarkable grain refinement and the fracturing and distribution of intermetallics along the extrusion direction. The enhancement of mechanical properties was successfully rationalized based on the grain size, and as a result, Hall-Petch relationships were developed for the yield stress, tensile strength, and hardness. However, the ductility of the extruded alloys was larger than those predicted by the grain size effects alone, which resulted in a superior strength-ductility trade-off compared to the as-cast counterparts. This was related to the disappearance of the grain boundary β-Mg17Al12 phase, closure of casting defects, and formation of a recrystallized and homogeneous microstructure in the extruded alloys.

Journal ArticleDOI
TL;DR: In this paper, a comprehensive study was performed on the laser energy density (Led) and CeO2 content on the structure distribution, microhardness and tribological properties of the coatings.

Journal ArticleDOI
TL;DR: In this article, the effect of volumetric energy density (VED) on the keyhole formation, microstructural evolution and associated mechanical properties of AlSi10Mg fabricated by selective laser melting (SLM) was systematically investigated.

Journal ArticleDOI
Yunlong Fu1, Ning Guo1, Cheng Zhou1, Guanghui Wang1, Jicai Feng1 
TL;DR: The 304 stainless steel coating was prepared successfully in water environment directly through an in-situ underwater laser cladding technique utilizing an underwater gas-shielding laser cladded nozzle, and the interaction mechanism of water on cladding coating formation, grain morphology and size, microstructure and corrosion performance was investigated as discussed by the authors.

Journal ArticleDOI
TL;DR: In this article, the effect of initial grain boundaries on the DRX nucleation, the role of primary particles on the particle-stimulated nucleation (PSN) effect, and the influence of two types second-phase particles on DRX behavior were investigated according to four typical ingot conditions (as-homogenized, as-cast, cast-aged, and homogenization-aged).

Journal ArticleDOI
TL;DR: In this paper, the volume fraction of fine grains (FGs, ∼2.5‵m) in the bimodal grain structure can be tailored from ∼30 vol.% in Mg-9Al-1 Zn (AZ91) to ∼52

Journal ArticleDOI
TL;DR: In this article, low-alloy steels with different grain size and crystallographic orientations were prepared by advanced thermo-mechanical processes, and the microstructure and electrochemical corrosion behaviors were characterized by electron backscatter diffraction (EBSD), X-ray photoelectron spectroscopy (XPS), and Electrochemical measurements.

Journal ArticleDOI
TL;DR: In this article, the use of high-intensity ultrasound that controls the process of solidification during AM of 316L stainless steel was investigated, and it was found that the ultrasound favored the columnar-to-equiaxed transition, promoting the formation of fine equiax-ed grains with random crystallographic texture.
Abstract: Metals and alloys fabricated by fusion-based additive manufacturing (AM), or 3D printing, undergo complex dynamics of melting and solidification, presenting challenges to the effective control of grain structure. Herein, we report on the use of high-intensity ultrasound that controls the process of solidification during AM of 316L stainless steel. We find that the use of ultrasound favours the columnar-to-equiaxed transition, promoting the formation of fine equiaxed grains with random crystallographic texture. Moreover, the use of ultrasound increases the number density of grains from 305 mm−2 to 2748 mm−2 despite an associated decrease in cooling rate and temperature gradient in the melt pool during AM. Our assessment of the relationship between grain size and cooling rate indicates that the formation of crystallites during AM is enhanced by ultrasound. Furthermore, the use of ultrasound increases the amount of constitutional supercooling during solidification by lowering the temperature gradient in the bulk of the melt pool, thus creating an environment that favours nucleation, growth, and survival of grains. This new understanding provides opportunities to better exploit ultrasound to control grain structure in AM-fabricated metal products.

Journal ArticleDOI
TL;DR: In this paper, the individual implication of sensitization, grain size, residual strain, and grain boundary character distribution on the semiconducting response of passive film in 304 stainless steel was investigated.

Journal ArticleDOI
TL;DR: The beneficial nature of grain engineering for reduction of ion migration in perovskite solar cells is suggested by the effect of grain size to mitigate ion migration.
Abstract: Ion migration in perovskite layers can significantly reduce the long-term stability of the devices. While perovskite composition engineering has proven an interesting tool to mitigate ion migration, many optoelectronic devices require a specific bandgap and thus require a specific perovskite composition. Here, we look at the effect of grain size to mitigate ion migration. We find that in MAPbBr3 solar cells prepared with grain sizes varying from 2 to 11 μm the activation energy for bromide ion migration increases from 0.17 to 0.28 eV. Moreover, we observe the appearance of a second bromide ion migration pathway for the devices with largest grain size, which we attribute to ion migration mediated by the bulk of the perovskite, as opposed to ion migration mediated by the grain boundaries. Together, these results suggest the beneficial nature of grain engineering for reduction of ion migration in perovskite solar cells.

Journal ArticleDOI
TL;DR: In this article, the effect of FSP up to 6 passes on the grain structure, second-phase particle distribution, mechanical properties and corrosion resistance of the WE43 magnesium alloy was investigated.
Abstract: Magnesium alloys have many unique properties, mostly benefitting from the low density of magnesium. However, they are not competitive, when compared with other lightweight materials, such as aluminum alloys, particularly in ductility and corrosion resistance. There is a strong need to improve the mechanical properties and corrosion resistance of magnesium alloys. In the present research, friction stir processing (FSP) as a severe plastic deformation process was applied to the WE43 magnesium alloy. The effect of FSP up to 6 passes on the grain structure, second-phase particle distribution, mechanical properties and corrosion resistance of the alloy was investigated. It was found that a continuous network of second-phase particles was present at the grain boundaries, which was considered to be one of the main causes for the poor ductility of the alloy in the as-annealed state. By applying two passes of FSP, the grain structure was significantly refined, changing from an average grain size of 12.4 to 2.5 μm. By further FSP, the grain structure continued to refine to an average grain size of 1.4 μm after 4 passes and remained unchanged after 6 passes. However, the fragmentation and redistribution of second-phase particles continued to occur during the 4th and 6th passes of FSP. Because of these microstructural changes, the uniform strain to maximum stress and the strength of specimens gradually improved with increasing number of FSP passes. The corrosion resistance of the alloy was found to be improved by applying 6 passes of FSP, compared to that of the alloy in the initial as-annealed state, which was attributed to the fragmentation and redistribution of second-phase particles. By applying FSP, the uniformity of the protective passive layer was improved and, in the meantime, the intensity of micro-galvanic coupling leading to pitting corrosion was decreased.

Journal ArticleDOI
TL;DR: In this article, the evolution of microstructure, texture, mechanical properties, and bio-corrosion behavior of ZK60 Mg alloy after applying 3 and 5 passes of repeated upsetting (RU) process were analyzed in detail.

Journal ArticleDOI
TL;DR: In this article, a Ni-rich NiTi alloy was in-situ deposited with different substrate heating temperatures and the evolution of crystallographic orientation, precipitation, phase transformation, and mechanical responses were evaluated.
Abstract: In this investigation, a Ni-rich NiTi alloy was in-situ deposited with different substrate heating temperatures and the evolution of crystallographic orientation, precipitation, phase transformation, and mechanical responses were evaluated. The experimental results indicated that with the increment of substrate heating temperature from 150 °C to 350 °C, the average B2 grain size and the high angle grain boundaries (HAGBs) gradually increased from 53.44 μm to 85.38 μm and 53.6%–62.4%, respectively. The crystallographic texture exhibited a dominant, strong (001) orientation with comparatively weak (111) and (101) orientations in all conditions and the intensity of {100} increased slightly as the substrate heating temperature increased. Moreover, Ni4Ti3 precipitates with an inhomogeneous size distribution were identified within the B2 NiTi matrix. Increasing the substrate heating temperature coarsened the Ni4Ti3 precipitates. All the phase transformation temperatures increased when the substrate heating temperature increased, indicating that the martensitic transformation is more likely to occur. As the substrate heating temperature increased from 150 °C to 350 °C, the yield stress and ultimate tensile stress decreased from 683.9 to 513.1 MPa and 855.2 to 743.8 MPa, respectively, and the ductility decreased from 6.90% to 6.13%. In addition, a remarkable eir, poor recovery ratio and a broad stress hysteresis were obtained during the initial deformation of the cyclic loading-unloading tension. The highest recoverable strain (ere), recovery ratio and elastic energy storage efficiency (ƞ) were obtained in samples processed with the lowest substrate heating temperature. These findings provide useful references concerning process optimization in fabricating Ni-rich NiTi components by WAAM with acceptable microstructure and mechanical properties.

Journal ArticleDOI
TL;DR: In this article, an ultra-fine grained structure with average grain size of 0.9μm was prepared after 6 passes of forging progress, which was ascribed to the occurrence of dynamic recrystallization (DRX).