Texture Grain Research Articles

Temperature-stable Characteristics of Textured (Bi,Sm)ScO3-PbTiO3 Ceramics for High-temperature Piezoelectric Device Applications

In this study, textured 0.38(Bi<sub>0.97</sub>Sm<sub>0.03</sub>)ScO<sub>3</sub>-0.62PbTiO<sub>3</sub> (0.38BSS-0.62PT) ceramics with high Curie temperature were evaluated to assess temperature stable characteristics for high-temperature piezoelectric device applications. The 4 vol% BaTiO<sub>3</sub> incorporated 0.38BSS-0.62PT ceramic was fabricated by conventional tape casting. Textured 0.38BSS-0.62PT ceramic was successfully produced at sintering temperature of 1150°C by textured grain growth (TGG). Textured 0.38BSS-0.62PT ceramic exhibited a high degree of crystal orientation of 94% in the [001]-direction. It also showed excellent dielectric and piezoelectric properties, (<i>ε</i><sup>T</sup><sub>33</sub>/<i>ε</i><sub>0</sub> of 1746, <i>d</i><sub>33</sub> of 719 pC/N, <i>k</i><sub>p</sub> of 61.8% and <i>g</i><sub>33</sub> of 45×10<sup>-3</sup>Vm/N, respectively). In addition, it also exhibited relaxor-like ferroelectric characteristics with a large relaxation coefficient (γ) of 1.77 along with high Curie temperature of approximately 373℃. Its temperature stability was satisfactory, resulting from in-situ <i>d</i><sub>33</sub> and <i>k</i><sub>p</sub>, which were lower than 10% below Curie temperature. The electro-strain also showed thermally stable characteristics. Therefore, it is considered that the textured 0.38BSS-0.62PT ceramic has potential for high-temperature piezoelectric device applications.

Mineral–Geochemical and Geotectonic Features of the Lotmvara-II Ultrabasic Sill, Serpentinite Belt (Kola Peninsula)

Abstract —In this paper, we present a description of the characteristics of the Lotmvara-II sill, which is a representative of the Serpentinite Belt (SB) composed of a series of shallowly emplaced ultrabasic intrusive bodies. The Paleoproterozoic SB complexes were derived from a large-scale mantle plume of komatiitic melt. The sill consists predominantly of fine-grained (locally nearly micrograined) harzburgites with subordinate zones of dunites and orthopyroxenites, located in the central and marginal parts, respectively. It formed from an Al-undepleted komatiitic magma of extremely high Mg content and may represent a near-surface laccolithic “ridge.” In general, the sill is comparatively homogeneous and does not have distinct zoning in the distribution of Mg# values in rock compositions (Mg# = 84.2–88.9, average 86.7). Detailed studies show that olivine, chromian spinel, and ilmenite are the most strongly magnesian in the central part of the body. The maximum values of Mg# equal to 90.7–91.4 in the compositions of olivine at the center of the sill are interpreted as “centers of initial crystallization”. The low values of Mg# equal to 73.4–76.4 are attributed to manifestations of the recurrent generation of olivine. The values of Mg# of orthopyroxene in the sill are within the range 84.6 to 92.3. Orthopyroxene grains in a porphyritic texture are surrounded by a rim of calcic amphibole (autometasomatic in origin); they do not differ compositionally from normal grains. The Zn content of the chromian spinel generally decreases toward the marginal parts of the sill. There is an insignificant degree of magmatic differentiation in the sill with respect to the principal components, but incompatible elements (REE and HFSE) locally show increased levels of their relative enrichment, which is reflected in the nature of the mineral associations described. Thus, the sill has a cryptic zonal structure, which is consistent with its overall crystallization from the center to the edges. The data gathered suggest the presence and significant development of volatile components, halogens, CO2, and especially magmatic H2O, which are capable of strongly lowering the liquidus and reducing the density and viscosity of the high-magnesium melt, thereby improving its mobility during ascent from the mantle to the near-surface level of the crust. An increase in fO2 is observed during in situ subvolcanic crystallization of the sill, as noted earlier in the related complexes of the belt. The relatively small volume of the komatiitic magma in the sill crystallized fairly quickly, resulting in unusual mineral intergrowths. Thus, the Lotmvara-II sill is a novel member in the Serpentinite Belt–Tulppio Belt (SB–TB) in the Paleoproterozoic SB–TB megastructure of the Fennoscandian Shield.

Reducing the cyclic tension-compression asymmetry and cyclic hardening of ZK61 magnesium alloy via the compression-extrusion process

In order to reduce the cyclic tension-compression asymmetry and cyclic hardening that exists widely in magnesium alloys, ZK61magnesium alloys with different texture intensities and grain sizes were fabricated by conventional extrusion and compression-extrusion process. It was found that the compression-extrusion process had a remarkable effect on the texture weakening and grain refining, which significantly improved monotonic tension-compression asymmetry and cyclic tension-compression asymmetry. Under their combined effects, the {10–12} twinning-detwinning behavior of ZK61 magnesium alloy during cyclic tension-compression deformation was effectively suppressed, resulting in a remarkable reduction of the difference of peak stresses in tension and compression. In the meantime, shape asymmetry embodied in a concave-up characteristic of the cyclic hysteresis loops was almost eliminated as the weakening of the detwinning-prismatic slip transition. Twinning-promoted dislocation pile-up and twinning-induced grain segmentation were significantly attenuated with texture weakening and grain refining, leading to a substantial weakening of cyclic hardening. Eventually, ZK61 magnesium alloy with low cyclic tension-compression.

Grain size and shape dependent crystal plasticity finite element model and its application to electron beam welded SS316L

Electron beam welding is an autogenous welding process that leads to microstructural heterogeneities; crystallographic texture, elongated and larger grain size relative to the surrounding parent material. The goal of this study is to predict the changes in mechanical response of the weld fusion zone as a function of grain morphology and texture by using the parent material properties to avoid extensive and costly experimental campaigns. For this reason, a crystal plasticity solver, “University of BRIstol cryStal plasTicity sOLver” (BRISTOL), is implemented in a finite element framework with new constitutive laws to account for the length-scale dependence considering the size and shape of the grains. It is found that the crystallographic texture governs the orientation specific elastic stiffness and yield stress having the most dominant effect on the macroscopic response of the weldment at the grain size scales considered. Crucially the length-scale dependent model allows accurate prediction of the yield strength of the weldment over a range of microstructures, also highlighting the presence of other factors such as prior strain hardening during the welding process and residual stresses.

Texture components and magnetic properties of laser powder bed fusion fabricated near grain-oriented and near non-oriented silicon steel

Silicon steel is a widely used soft magnetic material that requires different texture components for different applications, typically classified as grain-oriented or non-oriented. However, the methods of fabricating such types of silicon steel via laser-powder bed fusion (LPBF) have not been fully investigated. In this study, near grain-oriented and near non-oriented Fe-3.5 wt.%Si silicon steel is fabricated using LPBF by controlling processing parameters. Different textures are investigated using electron backscatter diffraction (EBSD), and the morphology of the molten pool is characterized by optical microscopy (OM) and scanning electron microscopy (SEM). Magnetic properties are measured with alternating current (AC) method. The results show that reducing both the linear energy density (LED) and laser power leads to a change in the side morphology of the molten pool from large, flat, and well-overlapped to small, protuberant, and less-overlapped, resulting in an extremely strong θ-fiber texture or a random distribution of grain orientations, respectively. Additionally, reducing both the laser power and scanning speed causes the top morphology of the molten pool to change from teardrop to elliptical shape at the trailing edge, resulting in a shift in the angle between the 〈001〉 of grains in the θ-fiber texture and the scanning direction from 45° to 30°. Samples with fewer defects (i.e., larger grain size and fewer pores) and a larger area fraction of 〈001〉//H exhibit higher permeability, although this superiority is not so significant due to residual stress and high dislocation in the as-built samples. This study provides insight into the relationship between processing parameters, texture evolution, and magnetic properties in LPBFed silicon steel.

Optimization of residual stress in low-pressure casting of ZL205A alloys

ZL205A alloys are prone to generate serious residual stress due to the long solidification intervals and multi-phase composition. In this study, the low-pressure casting process for ZL205A alloy hemisphere shell casting was investigated and continuously optimized. In the initial process, the knockout time, pouring temperature, preheating temperature of the sand mould, dwelling pressure, and filling rate were 3 h, 710 °C, 30 °C, 65 kPa, and 0.33 kPa·s−1, respectively. Macroscopic properties and microstructural features were simulated using a combination of ProCAST and Thermal-Calc software. Additionally, a series of experimental procedures, including EBSD, SEM, EDS, and XRD tests, were conducted to investigate the formation, morphology, and distribution of the microstructure. Current findings demonstrate that during the solidification process, the maximum temperature difference exceeds 220 °C, the maximum undercooling reaches 49.56 °C, and the maximum effective stress peaks at 301.7 MPa. The residual stress ranges from 20 to 200 MPa. Furthermore, there is no significant texture and preferred grain orientation during nucleation and solidification, and the structure field exhibits an equiaxed crystal but inhomogeneous pattern. Moreover, the finer and more homogeneous the grains and the smaller the deviation in grain orientation, the lower the residual stress. Specifically, two analytical models are developed: one between the casting parameters and the residual stress, and another between the shrinkage defects and the casting parameters. The lowest residual stress is achieved when the knockout time, pouring temperature, preheating temperature of the sand mould, dwelling pressure, and filling rate are 6 h, 725 °C, 250 °C, 95 kPa, and 1.67 kPa·s−1 respectively.

Structure and Optical Properties of Transparent Cobalt-Doped ZnO Thin Layers

Transparent thin layers of cobalt-doped ZnO were produced with the pulsed laser deposition method. The cobalt content of the original solid solution was 20% at. The crystallographic structure was examined by X-ray diffraction, which showed that the fabricated layers crystallized in the wurtzite phase and had a dominant orientation along the a-axis. The texture coefficient (increasing from F = 0.08 for the non-annealed layer to F = 0.94 for the annealed layer at 400 °C) and grain size (D = 110 ÷ 140 nm) were calculated. Optical constants, such as the refractive index n (1.62) and the extinction coefficient k (0.1 ÷ 0.4), were determined from the ultraviolet–visible–near-infrared transmission spectrum using the envelope method. The value of the optical band gap was determined, which is lower than for pure ZnO. Increasing the annealing temperature of the ZnO:Co layer increases the Urbach energy from 0.20 to 0.25 eV, which shows the difference in the type of growth defects in the ZnO matrix.

Distinguishing depositional environments in the beach–dune system of Chandipur, India, based on sediment texture and quartz grain surface features

AbstractAn attempt has been made to discern sedimentary environments in a tropical coastal setting in Chandipur, India, using variations in grain size. Samples were collected along one 100 m‐long cross‐shore transect extending from the tide/aqueous‐influenced seaward region to the aeolian‐dominated landward region. Various grain size data analysis approaches, like bivariate data plots and discrimination functions, were used to discriminate the sedimentary environments and establish the process of sediment deposition. The analytical results suggest that diverse granulometric parameters translate different sedimentary environments such as tidal flat, beach and dune. Additionally, the surface morphologies of quartz grains were used to understand the evolution of recent mechanical, chemical and mechanical–chemical processes in this tropical coastal region. Changes in the surficial microtextural properties of quartz grains were documented at various sites of all geomorphic units along this transect, from the tidal flat to the dune. One‐way analysis of variance (ANOVA) was used to understand the significant differences in microtextural features between these units. Subaqueous surface textures such as large conchoidal fractures, sharp edges, arcuate steps and straight and curved grooves were dominant in the grains of the tidal flat. The presence of meandering ridges, upturned plates, bulbous edges and adhering particles on quartz gradually increases as the transect ascends landward. Correlation plots between distance and microtextures, along with ANOVA, suggest that aeolian transportation modulated the surface textures. Such assessment of distinct sedimentary characteristics and transport processes may serve as a modern analogue for ancient deposits on the siliciclastic coast.

Fabrication of High‐Responsivity Sb2Se3‐Based Photodetectors through Selenization Process

AbstractSb2Se3 has great potential for applications in near‐infrared sensors because of its narrow bandgap, environmental friendliness, and high absorption coefficient. However, the low conductivity of Sb2Se3 is an obstacle to the further development of high‐performance optoelectronic devices. In this study, to address this challenge, the selenization process is adopted. The incorporation of Se atoms into Sb2Se3 facilitates the crystallization of the films and the formation of [hk0]‐textured grains at a lower temperature than unselenized Sb2Se3. The selenized films possess larger grains than the unselenized ones at the same temperature. X‐ray photoelectron spectroscopy (XPS) results show that annealing causes the generation of donor‐like point defects (e.g., Vse and SbSe) and SeO2. The 250 °C‐annealed selenized Sb2Se3‐based photodetectors (PDs) have a high responsivity of 1130 mW A−1 and a specific detectivity of 4.62 × 1011 Jones. The PDs exhibit a fast response time (i.e., rise/fall time of 4.54 ms/8.50 ms), sensitivity of 94.2 at 20 mW cm−2, and external quantum efficiency of 155% at 200 µW cm−2. Further, the selenized PDs have good stability to moisture and air. Based on the XPS, X‐ray diffraction, and transmission electron microscope results, the improved performance of the selenized Sb2Se3‐based PDs is described and discussed.

Bioabsorbable WE43 Mg alloy wires modified by continuous plasma-electrolytic oxidation for implant applications. Part I: Processing, microstructure and mechanical properties

In our work, a novel processing strategy for the continuous fabrication and surface modification of wires from Magnesium alloy WE43 by means of plasma-electrolytic oxidation (PEO) is presented. In the first step, wires with a strong basal texture and small grain size (≈ 1 μm) were manufactured by combined cold drawing and in-line stress-relief heat treatment steps that optimized the mechanical properties (in terms of strength and ductility) by means of annealing. In a second step, and to the best of our knowledge for the first time ever, the wires were continuously surface-modified with a novel plasma electrolytic oxidation process, which was able to create a homogeneous porous oxide layer made of MgO and Mg3(PO4)2 on the wire surface. While the oxide layer slightly diminished the tensile properties, the strength of the surface-modified wires could be maintained close to 300 MPa with a strain-to-failure ≈ 8 %. Furthermore, the thickness of the oxide layer could be controlled by immersion time within the electrolytic bath and was adjusted to realize a thicknesses of ≈ 8 μm, which could be obtained in <20 s. Our experiments showed that the chemical composition, morphology and porosity of the oxide layer could be tailored by changing electrical parameters. The combined cold drawing and heat treatment process with additional continuous plasma electrolytic oxidation processing can be upscaled to produce a novel generation of bioabsorbable Mg wires with optimized mechanical, degradation and biological performance for use in biomedical applications.

Creep anisotropy behavior, deformation mechanism, and its efficient suppression method in Inconel 625 superalloy

Mill products, such as sheets, usually show obvious anisotropy in their mechanical properties, which greatly affects both their applications and workability. In this study, the orientation-dependent tensile and creep behaviors of Inconel 625 alloy sheets with weak local textures were systematically investigated at 650℃. The results showed that Inconel 625 superalloy exhibits nearly isotropic tensile properties; however, obvious creep anisotropy appears when loading along different directions. Creep life in the rolling direction (150 ± 5 h) was approximately 4.5 times longer than in the transverse direction (33 ± 1 h). Severe creep anisotropy was found to be determined by two aspects: (i) the change in deformation mechanisms along the rolling direction (a combination of boundary sliding, dislocation slipping, and twinning) and the transverse direction (dislocation slipping). Stronger impingement of slip bands on grain boundaries accelerated intergranular crack initiation and propagation during loading along the transverse direction, which resulted in a short creep life. (ii) The differences in strain compatibility at grain boundaries (i.e., creep loading along the transverse direction resulted in the initial grains forming strong Brass, Cu, and S textures). Creep cracks preferentially nucleated at the junctions between Cu/Brass texture grains, as these interfaces exhibit the worst strain compatibility (Luster–Morris parameter m′ ≤ 0.22). Furthermore, pre-stress aging (PSA) treatment is proposed as an efficient method to suppress creep anisotropy. The discrepancy rate of creep life was found to be reduced by nearly 50% after PSA treatment.

Mechanistic investigation on Ce addition in tuning recrystallization behavior and mechanical property of Mg alloy

Constructing bimodal grain structure is a promising approach to achieve the high strength-ductility synergy in Mg alloy. Formation of bimodal grain is closely related to the dynamic and/or static recrystallization process, which has not been fully understood in the typical Mg-RE based alloy. In this work, it is claimed for the first time that the minor Ce addition (∼0.3 wt%) into Mg matrix significantly promotes the pyramidal <c+a> and non-basal <a> dislocations at the early stage of extrusion, which consequently enhances the formation of sub-grain boundaries via the movement and recovery of pyramidal II-type <c+a> dislocations. At this stage, fine sub-grain lamellae are widely observed predominantly due to the low migration rate of sub-grain boundary caused by the limited mobility of <c+a> dislocations. At the later stage, the sub-grains continuously transform into dynamic recrystallized (DRXed) grains that have 〈101¯0〉 Taylor axis and also strong fiber texture, indicating substantial activation of pyramidal II-type <c+a> dislocation. The low mobility of <c+a> dislocations, accompanied with the solute drag from grain boundary (GB) segregation and pinning from nano-phases, cause a sluggish DRX process and thus a bimodal microstructure with ultra-fined DRXed grains, ∼0.51 µm. The resultant texture hardening and grain refinement hardening effects, originated from bimodal microstructure, result in a yield strength of ∼352 MPa, which is exceptional in Mg-Ce dilute alloy. This work clarifies the critical role of Ce addition in tuning recrystallization behavior and mechanical property of magnesium, and can also shed light on designing the other high-performance Mg alloys.

Part geometry-driven crystallographic texture control in a 3D-printed austenitic steel – a strategy for near-monocrystalline microstructure generation

We propose and employ a novel X-shaped geometry to strengthen the 〈001〉 || z crystallographic texture – distinctive of the electron beam powder-bed fusion technique, for a 3D-printed austenitic stainless steel of type 316 L. The prism angles of the X-shaped parts are varied among 60, 90, and 120 degrees (X-60, X-90, and X-120) to investigate the effect it has on the parts’ properties. Strikingly, the strength of the 〈001〉 || z crystallographic texture and columnar grain width with increasing prism angle is seen to follow a ‘bell-curve’ profile which peaks with the X-90 shape. A distinct mechanical response of X-shaped samples is obtained with X-60 samples showing significantly stronger strain-hardening behavior along with cracking concentrated along the grain boundaries between 〈110〉 || z and 〈001〉 || z grains. Molecular dynamics simulations are utilized to rationalize this phenomenon.

Microstructure-property correlations in as-built and heat-treated compositionally graded stainless steel 316L-Inconel 718 alloy fabricated by laser powder bed fusion

The microstructures and the mechanical properties of a laser powder bed fusion manufactured compositionally graded alloy of the austenitic stainless steel 316L and Inconel 718, in the as-built and heat-treated conditions, were investigated. In all the cross sections of the as-built compositionally graded alloy, along the compositional gradient direction, which is perpendicular to the build direction, the microstructure primarily consists of sub-micron sized cells embedded within <001> textured columnar grains of the γ phase along with Laves phases at their grain boundaries. Heat treatment, which involves solutionizing at 1040 °C for 1 h followed by annealing at 720 °C and 620 °C for 10 h each, leads to coarsening of Laves phases, slight modification in texture and the annihilation of the sub-grain structure of the compositionally graded alloy, but does not alter the columnar grain size. It also leads to precipitation of the γ" and γ' phases in the portions of the compositionally graded alloy with >70 wt% of IN718. The hardness, yield strength and tensile strength of the compositionally graded alloy increase but ductility decreases from the SS316L-rich end to the IN718-rich end along the gradient direction. Heat treatment smoothens the variations in YS and UTS along the gradient direction in cross sections with <82 wt% IN718 but reduces their relative magnitude compared to that of the as-built condition. The heat-treated compositionally graded alloy exhibits significantly higher YS and UTS but lower ductility than that in the as-built condition, in portions with ≥82 wt% IN718. These mechanical property variations are analyzed in detail by considering variations in the composition, microstructural features, and contents of different phases in the as-built and heat-treated compositionally graded alloy. Finally, an appraisal on the appropriate compositional gradient and utility of the heat treatment of the compositionally graded alloy is discussed in the context of specific requirements in structural applications.

Role of dynamic recrystallization and grain growth on the formation of abnormal basal texture in a high-alloyed Mg-Al-Zn extruded alloy

A commercial Mg-8.1Al-0.58Zn-0.27Mn alloy (mass%, AZ80) was extruded using different temperature and extrusion ratio. The microstructural development was thoroughly investigated by electron backscatter diffraction. A typical basal texture with the vertical alignment of the (0001) poles to the extrusion direction became main texture component regardless of the extrusion conditions. Notably, dynamically recrystallized grains, which had the parallel alignment of the (0001) poles to the extrusion direction, were formed at the initial stage of extrusion. However, such abnormally textured grains were consumed by basal-textured grains when the extrusion was performed at a relatively low temperature or using a high extrusion ratio of 50. In contrast, apparent intensity corresponding to the abnormal texture component was preserved during the extrusion at 400 °C using a relatively low extrusion ratio of 10. The low extrusion ratio facilitated the growth of the abnormally textured grains, which maintained a certain amount of the texture component having the parallel alignment of the (0001) poles to the extrusion direction.

Investigation of the influence of misorientation-dependent anisotropy on the microstructure evolution under magnetic field: A multi-phase-field study

The influence of magnetic field-driven grain growth in a polycrystalline microstructure is studied via the multi-phase-field approach with the assumptions of isotropic and anisotropic grain boundary (GB) energy. Simulations are carried out using a two-dimensional representative volume element of titanium polycrystalline with the hexagonal crystal structure. The GB energy is a function of the misorientation angle by Read-Shockley equation and is independent of the GB inclination. The simulation results illustrate that the grain growth kinetics and final texture influentially depend on the initial texture when considering the misorientation-dependent anisotropy of GB energy. If the Euler angle φ 2 is randomly distributed for all of the grains, the simulation results are similar for isotropic and anisotropic GB energies. Whereas the simulation results for anisotropic GB energy are significantly different from the isotropic case by considering φ 2 = 0 for all grains. The elongation of grains, the aggregation of grains with analogous orientations, and deceleration of texture evolution and grain growth kinetics are its most important features. Also, the impact of magnetic field intensity is examined and, it is illustrated that the difference in simulation results for isotropic and anisotropic GB energies decreases with increasing the magnetic field intensity.

Non-monotonic evolution of microstructure and fatigue properties of round bar–plate rotary friction welding joints in 304 austenitic stainless steel

In this study, the structure and fatigue properties of a new type asymmetric round bar–plate rotary friction welding (RFW) joints with three kinds of welding time, 0.8 s, 1.2 s and 3.6 s, were investigated. The results show that the RFW processing evolves from the heat stage to the quasi-steady stage with a trade-off of dynamic recrystallization (DRX) and grain boundary sliding (GBS). From 0 s for the base metal (BM) to 3.6 s, the DRX intensity changes from strong to weak relative to the GBS intensity, resulting in the non-monotonic evolution of the microstructure, e.g., the texture, the average grain size and the geometrically necessary dislocation, with welding time. The evolution results in non-monotonic evolution of the fatigue properties: specimens with welding time of 0.8 s, 1.2 s and 3.6 s, have fatigue lives of approximately 150,000, 200,000, and 100,000 cycles, respectively. The microstructure evolves with the welding time through the texture strength, grain size, and dislocation density, affecting the dislocation and slip mobility. This evolution not only directly affects the rates of crack initiation and extension, but also makes the initiation point of fatigue crack change on the fillet, which affects the fatigue life.

Effect of Y Alloying on Microstructure and Mechanical Properties of AZ61 Magnesium Alloy Sheets Applied as 3C Electronic Product Shells

AZ61 magnesium alloy sheets can be applied as 3C (computer, communication, and consumer) electronic product shells. However, due to their poor plasticity and relatively low strength, the application of AZ61 alloy sheets is limited. The composition modification of AZ61, especially rare earth element alloying, is a good choice to improve the strength and plasticity of AZ61 alloy sheets. In this paper, the strength and plasticity of AZ61 sheets with different contents of Y were studied in detail. We found that the addition of 0.9 wt.% of Y not only improved the strength, but also significantly enhanced the plasticity. As a result, the yield strength of AZ61 increased from 167 MPa to 186 MPa, and the elongation increased from 9.5% to 18%. The reasons can be explained as follows: the Al2Y phase formed by adding Y consumed a large amount of the Al element, thus avoiding the formation of the brittle phases Al8Mn5 and resulting in the improved mechanical properties of the sheets. At the same time, the weakened texture and dispersed grain orientation also effectively improved the plasticity of the sheets. This study will provide a good solution to improve the strength and plasticity of AZ61 sheets without significantly increasing the production cost.

Texture development and grain boundary phase formation in Ce- and Ce-La-substituted Nd-Fe-B magnets during hot-deformation process

In this study, the influence of Ce- and Ce-La-substitution for Nd in Nd-Fe-B magnets on their magnetic and microstructural changes in the course of the hot-deformation process was investigated to gain insight into further reducing the Nd content in fine-grained Nd-Fe-B hot-deformed magnets. We found that the [001] texture and microstructure of the RE-rich grain boundary phases, which are the factors that determine the remanence and coercivity of hot-deformed magnets, were deteriorated by the Ce- and Ce-La-substitution. This is because the volume fraction of the RE-rich liquid formed in the grain boundaries during the hot-press and hot-deformation decreased due to the Ce- and Ce-La-substitution, thereby increasing the friction between the 2:14:1 grains while the c-axes of grains were aligned by grain rotation and decreasing the RE concentration of grain boundary phases. In particular, the Ce-La-co-substitution further prevented the liquid formation within the grain boundaries of the magnets during hot-press and hot-deformation because the wettability of the RE-rich liquid on the 2:14:1 grains became poor when La was substituted for Nd in the 2:14:1 grains. These results indicate that there is room for further improvement in both the remanence and coercivity of the Ce- and Ce-La-substituted magnets by introducing additional liquid into the grain boundaries prior to hot-press and hot-deformation. By applying the Nd-Cu infiltration process to the melt-spun ribbons (intermediate infiltration, I-infiltration), both the remanence and coercivity of the Nd-saving (Nd0.7Ce0.3)-Fe-B and (Nd0.7Ce0.225La0.075)-Fe-B hot-deformed magnets were successfully improved.

Exceptional reversed yield strength asymmetry in a rare-earth free Mg alloy containing quasicrystal precipitates

This work reports an exceptional reversed yield strength asymmetry at room temperature for a rare-earth free magnesium alloy containing a mass of fine dispersed quasicrystal (I-phase) precipitates. Although exhibiting traditional basal texture, it owns an exceptional CYS/TYS as high as ∼1.17. Electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) examinations indicate pyramidal <c + a> and prismatic <c> dislocations plus tensile twinning being activated after immediate yielding in compression while basal and non-basal <a> dislocations in tension. I-phase particles transferred the concentrated stress by self-twinning to provide the driving force for tensile twin initiating in neighboring grains, thereby significantly increasing the critical resolved shear stress of tensile twinning to possibly the level of pyramidal <c + a> slip, finally leading to the dominance of pyramidal <c + a> slip plus tensile twinning in texture grains. This results in a higher contribution on yield strength by ∼55 MPa in compression than in tension, which reasonably agrees with the experimental yield strength difference (∼38 MPa). It can be concluded that I-phase particles influence deformation modes in tension and in compression, finally result in reversed yield strength asymmetry.