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Microstructural evolution and strengthening mechanisms of Mg-3Sn-1Ca based alloys with additions of different amounts of AlN nano-particles were investigated. It was found that with increasing the amount of AlN nano-particles the grain size decreases obviously. The existence of AlN nano-particles could refine the primary crystal phases CaMgSn, which provided more heterogeneous nucleation sites for the formation of magnesium. Moreover, such nano-particles could also restrict the grain growth during solidification. After adding AlN nano-particles, both the tensile properties at room temperature and high temperature 250 °C and the hardness are largely improved. The improvement of strength is attributed to grain refinement and second phase refinement.

In this work, pre-strain annealing strengthening (PSAS) effect was investigated in an extruded Mg-1.0Gd-1.5 Zn (wt.%) alloy with respect to different grain sizes. The evolution of microstructures was provided by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) under the initial state, pre-compression, intermediate annealing and re-compression conditions. The obtained results showed a grain size-dependent PSAS effect in the alloy. The sample with larger grain sizes corresponded to a higher strengthening effect, which mainly resulted from a more remarkable hindrance for the growth of existing twins and a larger proportion of activation for the nucleation of new twins. This was closely associated with the increase of back stress and friction stress for twin boundary motion impeded by the larger restraint of dislocations, the higher stress field surrounding solutes and the more Zn segregation. In addition to twinning behavior, Guinier Preston (G.P.) zones on basal 〈a〉 dislocations were found after intermediate annealing and provided an extra strengthening by inhibiting the motions of gilding pre-existing dislocations and newly formed ones, but it was independent on the grain size.

Multi-direction impact forging (MDIF) was applied to the as-extruded ZK60 Mg alloy, and the microstructure, texture evolution and yield strength symmetry were investigated in the current study. The results showed that the average grain size of forged piece was greatly refined to 5.3 μm after 120 forging passes, which was ascribed to the segmenting effect of {10–12} twins and the subsequent multiple rounds of dynamic recrystallization (DRX). A great deal of {10–12} twins were activated at the beginning of MDIF process, which played an important role in grain refinement. With forging proceeding, continuous and discontinuous DRX were successively activated, resulting in the fully DRXed microstructure. Meanwhile, the forged piece exhibited a unique four-peak texture, and the initial //ED fiber texture component gradually evolved into multiple texture components composed of //FFD (first forging direction) and //FFD texture. The special strain path was the key to the formation of the unique four-peak texture. The {10–12} twinning and basal slip were two dominant factors to the evolution of texture during MDIF process. Grain strengthening and dislocation strengthening were two main strengthening mechanisms of the forged piece. Besides, the symmetry of yield strength was greatly improved by MDIF process.

In this study, the bending formability of an extruded Mg–9Al–1Zn–0.3Mn–0.9Ca–0.6Y–0.5 MM (AZXWMM91100, wt%) alloy at room temperature is significantly improved through application of a combined precompression and subsequent annealing (PCA) treatment. As the amount of precompression applied along the extrusion direction (ED) (i.e., the total strain) increases from 4% to 6%, the area fraction of ED-oriented grains of the PCA-treated alloy increases, which consequently causes an improvement in its bending formability because these grains accommodate larger tensile strain along the ED during bending. As the temperature of the subsequent annealing treatment increases from 350 °C to 450 °C, both the area fraction of the ED-oriented grains and the average grain size increase, and the residual dislocation density decreases owing to the promotion of boundary migration and occurrence of the recovery process at higher temperatures. Consequently, the bending formability of both the 4%-precompressed and the 6%-precompressed samples increases with an increase in the annealing temperature. However, when the precompressed samples are annealed at 300 °C, their bending formability is lower than that of the extruded alloy because the dislocations formed by precompression remain even after the subsequent annealing at this temperature.

Fine grained ZN20 alloy was obtained by combining equal-channel angular pressing (ECAP) with extrusion. Microstructural observation showed an obvious grain refinement with an average grain size of 10 µm after ECAP. The original bimodal-grained structure composed of coarse grains with strong basal texture and fine grains with random texture was substituted by a new kind of bimodal-grained structure with finer grains and more random texture after 4 passes ECAP at 300 °C. The combination of grain refinement and texture weakening caused the ductility can be increased by 40% compared with the as-extruded alloy. Immersion test in simulated intestinal fluid revealed an improvement of corrosion resistance after ECAP. Grain refinement can stable the corrosion product layer and basal texture is more beneficial for the corrosion resistance than the non-basal texture.

Effects of Al addition to a Mg–Bi binary alloy on its microstructural characteristics and tensile properties after extrusion are investigated via extrusion of Mg–3Bi–xAl (x = 0, 1, and 2 wt%) billets and analysis of the extruded materials. The Al addition negligibly affects the second-phase particles of the extruded alloy; however, an increase in the Al content causes significant decreases in the average grain size and maximum texture intensity of the extruded material owing to an increase in the area fraction of dynamically recrystallized (DRXed) grains. The Al addition improves the strength of the extruded alloy; this improvement is attributed to the enhanced grain-boundary hardening and solid-solution hardening effects induced by grain refinement and Al solute atoms, respectively. As the Al content increases from 0 wt% to 1 wt% and 2 wt%, the tensile elongation increases substantially from 2.8% to 9.4% and 16.9%, respectively. The reduction in the number and size of unDRXed grains with increasing Al content suppresses the formation and coalescence of cracks in the unDRXed grains during tension, which results in a significant improvement in the tensile ductility of the extruded material. During tensile deformation, large undesirable twins that act as crack initiation sites are locally formed in the unDRXed grains of the Mg–3Bi alloy, whereas relatively smaller twins are uniformly formed in both the DRXed and the unDRXed grains of the Mg–3Bi–2Al alloy. Consequently, the extruded Mg–3Bi–2Al alloy has a substantially higher tensile yield strength–elongation product (2924 MPa%) than the extruded Al-free B3 alloy (381 MPa%).

Aging prior to twinning deformation was proposed to alter the precipitate orientation of the plate-shaped β-Mg17Al12 from (0002)α basal planes (named basal plates) to {10 1 ¯ 0}α prismatic planes (named prismatic plates) in AZ31 Mg alloy. The experimental results showed that the compressive yield strength (CYS) of the sample containing prismatic plates increased 40 MPa and the compression ratio raised by 22% compared to that containing basal plates. The underlying strengthening mechanism was analyzed via a yield strengthen (YS) model with a function of grain size, precipitate characters (size, oritention, fraction) and Schmid factor (SF). It revealed that the improvement of CYS was mainly attributed to the altered precipitate orientation and refined grain size produced by twinning deformation. Particularly, the prismatic plates always have a stronger hardening effect on basal slip than basal plates under the same varites of precipitate diameter and SF. Besides, the decreased CRSS ratio of prismatic slip to basal slip revealed that the activity of non-basal slip in Mg alloy might be enhanced. More activated slip systems provided more mobile dislocations, contributing to the large compression ratio of the Mg rolled sheet with prismatic plates.

Magnesium (Mg) based alloys are promising candidates for many applications, but their untreated surfaces usually have low strength and hardness. In this study, a single point diamond turning (SPDT) technique was applied to refine the grain size and improve the mechanical properties of the surface layers of Mg-Li alloys. By refining grains in the topmost layer to the nanometer scale (∼ 60 nm), the surface hardness was found to be enhanced by approximately 60%. The atomic plastic deformation process during the SPDT was then studied by the real-time atomistic molecular dynamics (MD) simulations. A series of MD simulations with different combinations of parameters, including rake angle, cutting speed and cutting depth, were conducted to understand their influences on the microstructural evolution and associated plastic deformation mechanisms on the surface layer of the workpieces. The MD simulation results suggest that using increased rake angle, cutting speed and cutting depth can help to achieve better grain refinement. These simulation results, which provide atomic-level details of the deformation mechanism, can assist the parameter design for the SPDT techniques to achieve the high-performance heterogeneous nanostructured materials.

Grain refinement to the nanocrystalline regime is the most effective way to strengthen materials but this often deteriorates the grain-size thermal stability and plasticity. Here we manufactured a nanocrystalline face centred cubic CrCoNi medium entropy alloy with columnar grains via magnetron sputtering. Compression of CrCoNi pillars with diameters of ∼ 1 µm revealed a record high yield strength of ∼5 GPa for pillars with face centred cubic structures and engineering plastic strain of > 30%. The alloy possessed an outstanding grain-size thermal stability even at 1073 K. Both nanocrystalline grain size and a high density of nanotwins/stacking faults are critical to the exceptional yield strength. Deformation twinning, grains refinement during deformation, grain boundary sliding and random grain orientation all contribute to the large plasticity. The outstanding thermal stability is attributed to the sluggish diffusion effect and the low energy of twin boundaries.

We investigated the effects of Sn addition on the microstructural characteristics and mechanical properties of an extruded Mg–Bi binary alloy by comparing Mg–5Bi (B5) and Mg–5Bi–4Sn (BT54). Both the extruded alloys exhibit a partially recrystallized grain structure with a strong extrusion fiber texture and numerous Mg3Bi2 precipitates. However, the addition of Sn significantly decreases the average grain size of the extruded alloy from 123.9 to 75.2 μm. The Sn solute atoms inhibit the activity of dislocation slip, which reduces the internal strain energy accumulated in the dynamically recrystallized (DRXed) grains during extrusion. Consequently, this reduced strain energy leads to the decrease in the DRXed grain size owing to weakened grain growth during natural air-cooling. The extruded BT54 alloy exhibits higher tensile strength and ductility than the extruded B5 alloy. The improvement in the strength by the Sn addition is attributed to the combined effects of grain refinement, Sn solute atoms, and increased dislocation density. The formation of {10–11} and {10–11}-{10–12} twins during tension is suppressed by the grain refinement, thereby improving the tensile elongation considerably.

International audience; Yttrium mono- and di-silicates are excellent candidate materials for Environmental Barrier Coatings (EBC), to protect Ceramic-Matrix Composites (CMC). A large distribution of microstructures can be generated by varying the duration of sintering, the particle size distribution of the precursor and/or the deposition method. In the present work, investigations of the corrosion resistance of yttrium silicate coatings with various microstructures in the high temperature range, under different oxidizing environments are reported. An original experimental methodology has allowed quantifying the influence of the microstructure (especially grain size and grain boundary surface area) on properties such as ionic conductivity, resistance to oxygen diffusion, volatilization rate and surface recession, and showing that they directly affect their protection efficiency against oxidation. Based on these results, guidelines for the design of an optimized yttrium silicate EBC featuring microstructural and compositional variations are proposed.

In the present research, the dynamic recrystallization (DRX) behavior of a newly-developed Mg–Al–Zn–RE alloy with abundant second-phase particles during hot extrusion is investigated by coupling finite element (FE) and cellular automaton (CA) models. A two-dimensional CA model is developed to quantitatively and topologically evaluate the DRX process during deformation with constant forming conditions. Considering the fact that second-phase particles with various sizes extensively exist in the studied Mg–Al–Zn–RE magnesium alloy, models of DRX nucleation and grain growth velocity are modified. The coefficients of the modified CA model are calibrated by isothermal compression experiments of the magnesium alloy. Subsequently, the CA model is coupled with FE analysis to investigate the DRX behavior during the hot extrusions of the Mg–Al–Zn–RE alloy. The DRX behavior of the magnesium alloy at different stages and positions of extruded plates is simulated by the established model. Finer grains near the edge than in the inner of the plates result from higher strain and strain rate. The influence of extrusion conditions on microstructural evolution is explored. Under the employed forming conditions, average grain size decreases 28–62 times from as-cast and solution-treated to as-extruded state due to grain refinement by DRX. With increasing initial billet temperature or extrusion speed, average grain size increases. The finest grains are obtained at the initial billet temperature of 623 K and the extrusion speed of 7.83 mm/s. Low initial billet temperature or high extrusion speed benefits homogeneous grain distribution. The simulated results are in good agreement with experimental ones.

Additive manufacturing (AM) is an advanced manufacturing process that provides the opportunity to build geometrically complex and highly individualized lightweight structures. Despite its many advantages, additively manufactured components suffer from poor surface quality. To locally improve the surface quality and homogenize the microstructure, friction stir processing (FSP) technique was applied on Al-Si12 components produced by selective laser melting (SLM) using two different working media. The effect of FSP on the microstructural evolution, mechanical properties, and corrosion resistance of SLM samples was investigated. Microstructural investigation showed a considerable grain refinement in the friction stirred area, which is due to the severe plastic deformation and dynamic recrystallization of the material in the stir zone. Micro-hardness measurements revealed that the micro-hardness values of samples treated using FSP are much lower compared to SLM components in the as-built condition. This reduction of hardness values in samples treated with FSP can be explained by the dissolution of the very fine Si-phase network, being characteristic for SLM samples, during FSP. Surface topography also demonstrated that the FSP results in the reduction of surface roughness and increases the homogeneity of the SLM microstructure. Decreased surface roughness and grain size refinement in combination with the dissolved Si-phase network of the FSP treated material result in considerable changes in corrosion behavior. This work addresses the corrosion properties of surface treated additive manufactured Al-Si12 by establishing adequate microstructure-property relationships. The corrosion behavior of SLM-manufactured Al-Si12 alloys is shown to be improved by FSP-modification of the surfaces.

In general, different extrusion conditions will affect the microstructure of magnesium alloys and further determine the mechanical properties. The effects of extrusion parameters and heat treatment processes such as extrusion speed, pre-forging, annealing time, extrusion ratio and cooling rate on the microstructure, texture evolution and tensile properties of Mg-2Gd-0.3Zr alloys were investigated in this study. Compared with the as-cast alloy, the extrusion process significantly refines the grains and exhibit the rare earth texture. With the increase of extrusion speed and annealing time, the growth of recrystallized grains is accelerated, leading to the increase of elongation. Large pre-forging deformation achieves to refine the grains by promoting recrystallization nucleation, resulting in increased strength of Mg-2Gd-0.3Zr alloy. Decreasing the extrusion ratio or increasing the cooling rate will introduce coarse un-DRXed grains, which transformed the texture into the basal texture. In particular, the effect of rapid cooling on refining the recrystallized grains is also obvious. Different extrusion conditions influence the mechanical properties of the Mg-2Gd-0.3Zr alloy through the grain size, proportion of non-recrystallization region and texture type.

Ce-containing hot-deformed magnets by grain boundary diffusion of DyF3 were prepared. The samples were characterized by X-ray diffraction, a scanning electron microscope, a transmission electron microscope, a magneto-optical Kerr effect microscope and a magnetic properties measurement system to analyze the mechanism of DyF3 diffusion enhancing the coercivity. The results show that the coercivity of Ce-containing hot-deformed magnets is increased from 1.41 to 1.95 T by grain boundary diffusion of 3 wt% DyF3, and is further enhanced to 2.05 T after annealing treatment. The thermal stability of coercivity and remanence is improved. The annealing condition in this work crucially plays a role in thickening the grain boundary phase. Microstructure analysis reveals that the continuous and thick grain boundary phase formed after DyF3 diffusion can weaken the magnetic coupling between grains, and suppress the platelet shaped grain size and the aspect ratio. The Dy-containing shell structure formed by the partial diffusion of Dy into the main phase can increase the magnetic anisotropy field, which is the main reason for the coercivity improvement. After optimizing the structure by DyF3 diffusion, the “dendritic-like” reverse domain is transformed into the “dot scattered-like” reverse domain.

Aluminum alloys with ultra-strength and high-toughness are fundamental structural materials applied in the aerospace industry. Due to the intrinsic restriction between strength and toughness, optimizing a desirable combination of these conflicting properties is always challenging in material development. In this study, 171 sets of data were curated based on the characteristics of high-strength and high-toughness aluminum alloys in the literature. Then, a machine learning design system (MLDS) with a property-oriented design strategy was established to rapidly discover novel aluminum alloys with ductility and toughness indexes (with elongation δ=8%–10% and fracture toughness KIC=33–35 MPa·m1/2) comparable to those of current state-of-the-art AA7136 aluminum alloys when the ultimate tensile strength (UTS) exceeded approximately 100 MPa, with values reaching 700–750 MPa. With the MLDS for experimental verification, three typical candidate alloys show satisfactory performance with UTS of 707–736 MPa, δ of 7.8%–9.5%, and KIC of 32.2–33.9 MPa·m1/2. The high contents of Mg and Zn alloying elements in the novel alloys form abundant η′ phases, which produce a significant hardening effect, while the reasonable matching of Cr, Mn, Ti and Zr dispersoids refines the grain size. The decreased Cu content compared with that in the AA7136 alloy inhibits the formation of the σ phase and S phase, so that the alloys show high toughness.

From the perspective of high-temperature applications, materials with excellent high-temperature mechanical properties are always desirable. The present work demonstrates that the binder-free nanopolycrystalline WC ceramic with an average grain size of 103 nm obtained by high-pressure and high-temperature sintering exhibits excellent mechanical properties at both room temperature and high temperature up to 1000 °C. Specifically, the binder-free nanopolycrystalline WC ceramic still maintains a considerably high Vicker hardness HV of 23.4 GPa at 1000 °C, which is only 22% lower than the room temperature HV. This outstanding thermo-mechanical stability is superior to that of typical technical ceramics, e.g. SiC, Si3N4, Al2O3, etc. Nanocrystalline grains with many dislocations, numerous low-energy, highly stable Σ2 grain boundaries, and a relatively low thermal expansion coefficient, are responsible for the observed outstanding high-temperature mechanical properties.

The property evaluation of Aluminum alloys a quite a challenging task and is an essential one to achieve improved mechanical and metallurgical properties during casting. This paves the way for the present research, in which the casting of commercial A356 and A319 Al alloys have been performed under stationary and vibratory state. The vibrational recurrence has been varied between 0 Hz and 400 Hz with a constant amplitude of 15 μm during casting. Thereafter, the quality of both casted materials has been evaluated by measuring their yield strength, ultimate tensile strength and % elongation. Experimental results revealed that the higher intensity of oscillation improves mechanical properties with the reduced grain size of α-Al. It has been also observed that the fraction of nucleation sites is increased due to the vibration.

Orthorhombic magnesium niobate is known to exhibit exceptional dielectric and photoluminescence properties. With the intention to evaluate these properties, MgNb2O6 (MN2) was synthesized at 900 °C for 6 h through a two-stage process. The phase examination was done by XRD and Raman spectroscopy. XRD analysis confirmed orthorhombic crystal structure with average crystallite size of 41 nm, approximately. The d-value and (hkl) plane corresponding to highest intensity was examined 2.9486 A and (3 1 1), respectively. Raman spectroscopic analysis clarified various vibration bands of MN2 ceramics. The grain size was assessed close to 87 nm from FESEM analysis considering the grain distribution plot. The microstructure analysis by HRTEM reveal nanoparticles of average size of 41.83 nm. The clear lattice image and prominent spots in SAED confirm crystallinity of prepared ceramics. The PL result of the prepared ceramics at 900 °C indicated blue emission spectrum near 442 nm. The material prepared at 900 °C exhibited band gap of 2.65 eV using diffuse reflectance spectroscopic analysis. The dielectric constant (er) and tanδ were also investigated where er was measured 27.8 and 20.8 for material prepared at 800 and 900 °C, respectively. Low tanδ (dielectric loss) was also noted in present investigation.

The influence of different synthesis routes and the heat treatments on the fundamental physical properties of the potassium bismuth ferrite oxide KBiFe2O5 (KBFO) is investigated. The polycrystalline KBFO is prepared using a solid-state reaction route followed by conventional heating (SSR) and the sol–gel method followed by conventional heating (SGC) and microwave heating (SGM). The monoclinic phase of the prepared sample is confirmed from the Rietveld refined X-ray diffraction analysis. XRD confirms crystallite size decrease from SSR (165 nm) to SGM (91 nm) sample. The surface morphology reveals that grain size varies from 4 µm (SSR) to 100 nm (SGM). The observed variation in Raman intensity and FWHM indicates the effect of different synthesis routes on the particle sizes of KBFO. The optical energy band gap increases from 1.59 eV (SSR) to 1.73 eV (SGM) with changes in the synthesis route and heat treatment. Temperature-dependent dielectric (25 °C to 560 °C) data at 1 MHz frequency shows a significant variation in dielectric value followed by a transition at 510 °C (TC) in all the prepared samples. The dielectric value of the SSR sample almost 50 times larger than the SGC and SGM samples of KBFO.

Cube texture contains two easy magnetization directions 〈001〉 parallel to rolling and transverse direction, respectively, which is the most ideal magnetic texture suitable not only for transformers but also for rotating machines. In this study, a strong cube texture with ODF density of 50.73 mrd was successfully obtained by regulating the recrystallized grain orientation using cross-rolling and pulsed electric current, compared to conventional thermal annealing (the average cube texture intensity is ~10 mrd in lots of latest studies). Cross cold rolling process intentionally “created” metastable deformed cube orientation in oriented silicon steel and the specific recrystallization texture rotation path was identified under pulsed electric current in 5 min: {114} →{114} →{114} →{001} →{001} . The cube-oriented grains were induced by pulsed electric current (800 °C) and rapid heating (51.9 °C/s, 750 °C), while the cube grains were observed in the annealed samples at the high temperature (1060 °C). Recrystallized grain size of pulsed samples is about twice that of the annealed sample. This phenomenon is considered that the concurrent effects of electron wind force and Joule heating affected the nucleation, growth and rotation of cube grains by reducing the nuclear barrier, producing higher grain boundary mobility and structural evolution towards a state with lower electrical resistance. This idea of current-controlled texture is worthy of popularization in more materials and the realization of an electromagnetic field to crystal orientation selection is an interesting topic.

The sand castings of Mg–Y–RE–Zr series alloys are widely utilized in the large scales and complex shapes in the aerospace industry, as a result of which there are always some cast defects in the products. In this study, the feasibility of repair welding of sand-cast Mg–4Y–3RE–0.5Zr alloy by tungsten inert gas (TIG) welding was scrutinized with different welding currents from 150 to 210 A. The results indicated that defect-free repaired joints with good appearance could be acquired at 170 and 190 A. Interestingly, the grain size of the fusion zone (FZ) was refined initially and then increased with the linear increment of welding current. Because at the higher heat inputs, although the cooling rate of the molten pool was reduced, substantial constitutional supercooling for the grain refinement was attained after the Zr particles were transformed into Zr solutes. The tensile strength of the repaired joint at 170 A was 195 MPa with the maximum joint efficiency of 87.8%, and the elongation reached to 124.4% of the sand-cast base material (BM). However, serious grain coarsening and continuous eutectic structures generated in heat-affected zone (HAZ) above 190 A resulted in the weakening of the joint due to the brittle intergranular fracture.

In the present work a new thermal conductivity model is developed for two-phase composite materials, which are consisted of a continuous matrix and dispersed 3D-particles separated from each other by the matrix as a function of grain size and volume ratio of the dispersed particles at different temperatures. The model is applied to reproduce experimental thermal conductivity values of cemented carbide systems WC-Co and WC-Ag. Good agreement was found between measured thermal conductivity data originating from both this work and recent literature and the calculated ones only using semi-empirical parameters for the interfacial thermal resistance (ITR) values at WC/Co, WC/Ag and WC/WC interfaces as a function of temperature. Additionally, the temperature and grain size dependence of the thermal conductivity for WC is established for the first time. The model works well for the case when the matrix (Ag) has a higher thermal conductivity compared to that of the WC particles and also for the case when the matrix (Co) has a lower thermal conductivity compared to that of the WC particles. The new model forms a physically sound basis for further development / materials design of cemented carbides and particle-reinforced composite materials.

The microstructure, texture and mechanical property evolution of the extruded Mg-xY (x = 1, 5 wt.%) alloys during equal channel angular pressing (ECAP) were systematically investigated using an optical microscope, electron backscatter diffraction (EBSD) and uniaxial tensile test. The Mg-Y alloys exhibited a weakened basal texture before the ECAP, and the texture was further weakened with the max basal poles dispersed along ∼45° between the extrusion direction and the transverse direction after the ECAP. The Mg-5Y alloys always exhibited a finer grain size comparing to that of Mg-1Y for the same ECAP process. With a proper ECAP process, both the strength and elongation of Mg-5Y alloy could be improved simultaneously after the ECAP, i.e., the yield strength (273.9 ± 1.2 MPa), ultimate strength (306.4 ± 3.0 MPa), and elongation (23.9 ± 1.0%) were increased by 10%, 6%, and 72%, respectively, comparing to that before the ECAP. This was considered to be arose from the combined effects of grain refinement, significant improved microstructure homogeneity and solid solution hardening. In addition, it was found that Mg-Y alloy with better comprehensive properties could be obtained by the decreasing-temperature ECAP processes. The yield strength-grain size relationship could be well described by the Hall-Petch relation for all the ECAPed Mg-Y alloys, which was consistent with that the texture changes did not significantly affect the average Schmid factors of basal, prismatic and pyramidal slips for both Mg-Y alloys.

The latest research shows the construction of a biodegradable composite based on magnesium (Mg-Zn-Mn) by means of friction mixing. The Zn and Mn micro powder parts were enhanced to increase corrosion resistance and mechanical properties on a surface dependent on Mg-alloy. The microstructure and mechanical properties have been studied for their influence on various forms of FSP process parameters: tool-geometry (Tg), movement speed (TS) and rotations speed (Rs). The analysis of the Mg-based composite as formed has been investigated with microstructure, elemental and phase composition. The Vickers' micro-hardness tester and universal testing machine calculated the micro-hardness and tensile strength of the as formed Mg-based composite (UTM, BIS). The microstructural test showed that a Mg-base composite with a coarse grain size range of approximately 25 μm was also distributed with the reinformed material in the matrix. The mechanical properties are tensile resistance (UTS) of 125 MPa with an elongation percentage of 13.47 percent and are smaller than the young 35 MPa modulus near the cortical bone of the cortical bone.

Ytterbium (Yb) containing magnesium alloys have aroused extensive interest due to their excellent mechanical properties after thermomechanical processing and heat treatment. Unfortunately, the sole effect of Yb addition on the microstructure and mechanical properties of pure Mg matrix remains uncertain to date. In this work, the effects of Yb concentration on the texture development and tensile properties of pure Mg matrix during hot extrusion and the subsequent annealing were systematically investigated. The results revealed that the constitutional supercooling induced by Yb addition refined the as-cast microstructure but exerted a negligible effect on the original columnar grain morphology. When extruded at 300 °C, the dynamic recrystallization (DRX) process was considerably retarded. The in-grain misorientation axes (IGMA) analysis combined with TEM observation indicated that non-basal slips operated with increasing Yb concentration. Specifically, the prismatic 〈a〉 slip should be robustly activated in Mg–1.0 Yb extrudate, promoting the formation of the texture with {10–10} plane normal to the extrusion direction (ED), while for the Mg–2.0 Yb counterpart, the increased activity of pyramidal 〈c + a〉 slip and the relaxation of basal/ dislocations generated an ED-tilted texture component. The preferential grain growth dominated the subsequent annealing texture development at 400 °C when a comparable grain size was achieved. An obvious ED-tilted texture intensity with the peak around 〈–12–13〉 was observed in Mg–2.0 Yb alloy, which was primarily caused by grains with the basal orientation vanished and with the non-basal orientations intensified due to a higher concentration of Yb solute. Favored by the grain refinement, the Mg–2.0 Yb extrudate exhibited a high tensile yield strength of 304 ± 3.5 MPa, while the subsequently annealed counterpart presented a favorable elongation to failure of 14.8 ± 1.2%, which mainly due to the homogeneous grain structure, weak ED-tilted texture, and dissolution of coarse phases after high-temperature annealing.

Al-V-B master alloy is promising for refining Al-Si alloys, yet its optimal composition with superior efficacy remains to be explored. In this work, the evolution of refining phases in the Al-10Si/Al-V-B system with different V:B ratios was evaluated by thermodynamic calculations, based on which the Al-V-B refiners with V:B = 1:1 and 5:1 were designed. Refining trails demonstrated that they could significantly reduce the grain size of Al-10Si (wt.%) alloy from 1736 to 184–245 μm with industrial addition amount. Detailed examinations results clarify that when V:B ratio is 1:1 the nucleation particle is (V,Al)B2, which has a VB2-AlB2 core-shell structure and therefore presents the nucleation capability as AlB2 particle. When V:B ratio is as high as 5:1, the nucleation particle is pure VB2. Density functional theory (DFT) calculation indicates that (0 0 0 1) VB2/(1 1 1) α-Al interface has the lowest interfacial energy such that highest nucleation potency among other types of diboride/α-Al interfaces under consideration. The outcomes of this work provide fundamental guidance to develop superior V-B based refiners for Al-Si alloys.

In the present study, a fully lamellar Ti6Al4V alloy was severely deformed by high pressure torsion (HPT) process under a pressure of 7.5 GPa up to 10 revolutions. Experimental results revealed that the microhardness of Ti6Al4V was increased remarkably by about ∼ 41% and saturated at about 432 Hv after the HPT process. A relatively uniform bulk nanostructured Ti6Al4V alloy with an average grain size of about 52.7 nm was obtained eventually, and no obvious formation of metastable ω phase was detected by XRD analysis. For the first time, the tribological properties of the HPT processed Ti6Al4V alloy were investigated by a ball-on-disc test at room temperature under a dry condition. It was found that HPT process had a great influence on the friction and wear behaviors of Ti6Al4V alloy. With increasing the number of HPT revolutions, both friction coefficient and specific wear rate were obviously decreased due to the reduction of abrasion and adhesion wears. After being deformed by 10 HPT revolutions, the friction coefficient was reduced from about 0.49 to 0.37, and the specific wear rate was reduced by about 48%. The observations in this study indicated that HPT processed Ti6Al4V alloys had good potential in structural applications owing to their greatly improved mechanical and tribological properties.

Lean alloy (low alloyed) is beneficial for long-term sustainable development of metal materials. Creating a nanocrystalline microstructure is a desirable approach to improve biodegradability and mechanical properties of lean biomedical Mg alloy, but it is nearly impossible to realize. In the present study, the bulk nanocrystalline Mg alloy (average grain size: ~70 nm) was successfully obtained by hot rolling process of a lean Mg-2wt.%Zn (Z2) alloy and both high strength ((223 MPa (YS) and 260 MPa (UTS)) and good corrosion resistance (corrosion rate in vivo: 0.2 mm/year) could be achieved. The microstructure evolution during the rolling process was analyzed and discussed. Several factors including large strain, fine grains, strong basal texture, high temperature and Zn segregation conjointly provided the possibility for the activation of pyramidal slip to produce nanocrystals. This finding could provide a new development direction and field of application for lean biomedical Mg alloys., Graphical abstract Image 1, Highlights • The nanograins rounded by Zn atoms segregation are achieved in a lean biodegradable Mg-2wt.%Zn alloy by hot rolling process. • The nanocrystalline Mg–2Zn alloy demonstrates a high strength and good degradation properties. • Microstructures and rolling condition conjointly provided the activation of pyramidal slip to produce nanocrystals in Mg–2Zn alloy.

Based on composition of Finemet alloy, structures and soft magnetic properties of Fe73.5Cu1Nb3–xSi13.5B9Yx (x = 0, 0.5, 1.0, 1.5) alloys formed by replacing Nb (niobium) by Y (yttrium) were studied in this paper. The research results show that when x = 0 or 0.5, rapidly solidified as-cast alloy is Fe amorphous single-phase structure, and Y atoms are dispersed in matrix; when x = 1.0 or 1.5, crystalline phase precipitates. Fe73.5Cu1Nb3–xSi13.5B9Yx (x = 0, 0.5, 1.0, 1.5) alloys begin to precipitate α-Fe(Si) solid solution phase after crystallization annealing above 480 °C, when x = 0.5, grain size is 12.6 nm, which shows that Y can replace Nb in small amount and refine grain size. Fe73.5Cu1Nb2.5Si13.5B9Y0.5 alloy has excellent soft magnetic properties: μm value is 813.1 × 103, which is 36% higher than that of Finemet alloy; μi value is 154.6 × 103, close to that of Finemet alloy, and Bs and Hc values are 1.24 T and 0.56 A/m, respectively, better than those of Finemet alloy. In addition, Fe73.5Cu1Nb2.5Si13.5B9Y0.5 alloy has excellent soft magnetic properties at high temperature, μe value only reduces by 8.8% at 1 kHz with ambient temperature increased from 30 to 150 °C, and μe value is 128.02 × 103 in 150 °C, which is 15.74% higher than that of Finemet alloy.

Super-high strength NbTaTiZr high-entropy alloys (NbTaTiZr HEAs) have been successfully fabricated by the mechanical alloying (MA) with spark plasma sintering (SPS) technology, which is 2-fold compared with that of NbTaTiZr HEAs prepared by vacuum arc melting (VAM). After the SPS process, the bulk NbTaTiZr alloy samples are provided with dual-phase body-centered cubic (BCC) structure and nanoscale grain size about 500 nm that is obviously smaller than that of NbTaTiZr HEA fabricated by VAM. When the sintering temperature is 800 °C, the compressive fracture strength is the highest reaching at 2511 ± 78 MPa. When the sintering temperature is 1000 °C, the fracture strain is the highest reaching at 12.8%, and compressive fracture strength and yield strength also reach at 2274 ± 91 MPa and 2172 ± 47 MPa, respectively. The excellent mechanical properties of bulk NbTaTiZr alloy samples are attributed to the merits of MA and SPS, and the collaboration effect of ultra-fine grains strengthening, solid solution strengthening and interstitial solid solution strengthening.

With the increasing demand for light weight design in industries such as aerospace and automotive, sheet metallic materials with high strength and low density have been intensively manufactured and widely applied. However, plastic deformation induced surface roughening is an undesirable and a practically unavoidable phenomenon for sheet metallic materials and becomes the subject of great attention in recent years. The evolution of surface roughening plays important roles in the strain limit of the deformation and also significantly influences the product quality and application. This paper provides a comprehensive overview of both experimental and numerical modelling contributions to understand the surface roughening behaviour of sheet metallic materials during various plastic deformation and manufacturing processes. It has been found that roughening of the free surface or necking of the interface is induced by grain scale strain heterogeneity and strongly dependent on the strain the material experienced, strain state and direction, grain size and texture, lubrication, mechanical properties of materials, rolling parameters, etc. By controlling and optimising these parameters, the surface roughening can be optimised for different materials and processing techniques to suit different applications.

Steel matrix composites (SMCs), reinforced by ceramic particles, have received a consistent attention in recent years. Using conventional methods to prepare SMCs is generally challenging, and the mechanical properties of conventionally fabricated SMCs are limited. In this study, we successfully fabricated high-performance SMCs by laser powder bed fusion (LPBF) of a composite powder consisting of Fe-based alloy powder and submicron-sized WC particles. The effect of laser energy density on the phase formation, microstructural evolution, overall density and resulting mechanical properties of LPBF-fabricated composites was investigated. The present results show that a novel Fe2W4C carbidic network precipitates in the solidified microstructure entailing segregations along the boundaries of cellular sub-grains. The presence of this carbidic network hampers the growth of sub-grains even at elevated temperatures, and hence, stabilizes the grain size though prepared at a broad range of different energy densities. The exact distribution of the Fe2W4C carbides depends on the employed laser energy densities, as for instance they are more uniformly distributed at higher energy input. The density of LPBF samples reaches the maximum value of 99.4 % at 150 J/mm3. In this parameter set, high microhardness of ∼753 HV, compression strength of ∼3350 MPa and fracture strain of ∼24.4 % are obtained. The enhanced mechanical properties are ascribed to less metallurgical defects, higher volume fraction of the martensitic phase and increasing pile-up dislocations resulting from the pinning effect by Fe2W4C carbide.

The high-manganese steels are important structural materials, owing to their excellent toughness at low temperatures. However, the microstructural causes for their unusual properties have not adequately been understood thus far. Here, we report a reversal relationship between impact toughness and grain size in a high-manganese steel and its unrevealed microscopic mechanisms, which result in an excellent low-temperature toughness of the steel. Our investigations show that with increasing grain size the impact toughness of the steel can be improved drastically, especially at low-temperatures. Advanced electron microscopy characterization reveals that the enhanced impact toughness of the coarse-grained steel is attributed to the twinning induced plasticity and transformation induced plasticity effects, which produce large quantities of deformation twins, ehcp-martensite and α′bcc-martensite. Inversely, in the fine-grained steels, the formation of deformation twins and martensite is significantly inhibited, leading to the decrease of impact toughness. Microstructural characterizations also indicate that ehcp-martensite becomes more stable than α′bcc-martensite with decreasing temperature, resulting in characteristic microstructures in the coarse-grained samples after impact deformation at liquid nitrogen temperature. In the coarse-grained samples under impact deformation at -80 °C, ehcp-martensite transformation, α′bcc-martensite transformation and deformation twinning all occur simultaneously, which greatly improves the toughness of the steel.

The ultrafine Mo-Y2O3 composite powders were successfully synthesized by innovative freeze-drying method. Consequently, the freeze-dried Mo-Y2O3 composite powders with high sintering activities possess an average grain size of 54 nm. After low temperature sintering at 1600 °C, the Mo-Y2O3 alloys maintaining a high density (99.6 %) have the finest grain size (620 nm) comparing with available literature about oxide dispersion strengthened molybdenum alloy (ODS-Mo). The oxide particles remain their small size (mainly

The electrochemical properties of a friction stir processed (FSPed) equiatomic CrMnFeCoNi high-entropy alloy (HEA) was investigated in an aerated 0.5 M Na2SO4 electrolyte solution at room temperature. The microstructural analysis reveals a highly refined stir zone (SZ) with an average grain size that decreases from the top region of the SZ to the bottom region of the SZ (also known as shear-processed zone; SPZ). However, the region below the SPZ, (i.e. below the plunge depth) experienced an increase in average grain size and dislocation densities compared to the other regions. There is no secondary phase observed in the FSPed region, however, the microstructural evolution in the FSPed region affects the electrochemical behavior of the HEA. Cr2O3 passive layer was observed to form on the FSPed HEA, leading to excellent corrosion properties from the polarization corrosion tests. Grain refinement in the SZ enhances the rapid formation of the passive layer, thus, leading to better corrosion properties in the front surface of the FSPed HEA. The localized corrosion behavior of the FSPed HEA was predicted to be caused by the micro-galvanic nature of the HEA, which leads to an increase in polarization at the anodic sites (pits). A numerical model was established using the corrosion parameters from the experiment to simulate the localized corrosion behavior on the surface of the FSPed HEA in a neutral environment. The predicted initial pitting potential and corresponding current density agree well with the experimental results. The model is also capable of tracking the dissolution of the pits over longer periods.

The top-down method was used to fabricate the TiNi1+xSn half-Heusler alloy. Several knotty problems have been solved using the top-down method, including the generation of impurity phases, the visible discrepancy in the grain size of the TiNi2Sn second phase, and irregular variations in the Seebeck coefficient (S), electrical conductivity (σ), and thermal conductivity (κ) with increasing Ni content. The generation of a large number of incoherent interfaces between the half-Heusler (HH) and full-Heusler (FH) phases fabricated by the top-down method drastically improved σ and retained κ and S, thereby leading to an enhancement in the dimensionless figure of merit (ZT) by ∼19 % for the TiNi1.05Sn sample as compared to the ZT of the samples prepared by the conventional method.

[EN] The sinterability of 3Y-TZP/TiO2 materials using micrometre-sized ZrO2 and nanometre-sized TiO (16 wt%) by one-step fast microwave sintering at low temperature (1200¿1300C) was investigated. Firstly, in situ detailed analysis of the dielectric properties of the material with temperature was carried out in order to measure the capacity of the material to transform microwave energy into heat. Another related parameter associated to microwave sintering is the penetration depth of the microwave radiation into the material, which showed great homogeneity from 400¿C. Secondly, the effect of sintering conditions on microstructure, density, hardness and coefficient of thermal expansion was evaluated. The X-ray diffraction study and microstructural characterization demonstrate that it is possible to obtain fully dense pieces (>99%) by microwave sintering, a condition yielding to a coarse-grained (~1¿2 ¿m), quite hard (~13.7 GPa) 3Y-TZP/TiO material. However, the most important feature is the significant reduction of the thermal expansion coefficient as compared to that of 3Y- TZP. In addition, the results from conventional sintering at 1400¿1500 C with 2 and 6 h of dwell time are examined and compared. The materials obtained at 1500¿C showed high density with grain size and hardness similar to those obtained by microwave but with a dramatic difference in the power consumption of the sintering cycle, since the materials obtained by microwave used a maximum absorbed power of 120 W and a heating cycle of only 40 min., The authors are grateful to the Generalitat Valenciana for the fund-ing support for the Santiago Grisolia program (GRISOLIAP/2018/168) and to the Ministry of Science, Innovation and Universities (Spain) through the projects RTI2018-099033-B-C32 and C33 (MCIU/AEI/FEDER, UE) and RYC-2016-20915.

Ultrafast High-temperature Sintering (UHS) allows consolidation of ceramics in just a few tens of seconds. The green body is placed within a carbon felt heated by the Joule effect at temperatures up to 3000 °C. Here, we propose a combined experimental and numerical analysis to enable the fabrication of fully dense and fine-grain α-Al2O3 samples using a multistep computer-controlled current profile. Reference samples processed using a single step current formed cracks at the onset of shrinkage due to their uneven temperature distribution. Fully coupled simulations accounting for electric current, voltage, power, temperature and shrinkage allowed us to improve the experimental setup and to define the current profiles required to UHS highly dense (i.e., relative density > 99 %) 3 mm thick samples with an average grain size of 0.77 μm.

BaZrO3-based materials doped with a trivalent cation have excellent chemical stability and relatively high proton conductivity which makes them potential proton conducting oxide materials for various electrochemical device applications such as hydrogen processing, high-temperature electrolysis, and solid electrolyte in fuel cells. However, BaZrO3 showed poor sinterability, requiring high sintering temperatures (1700–2100 °C) with longtime sintering (20–100 h) to achieve the desired microstructure and grain growth. This sintering problem can be solved by slightly doping BaZrO3 with a sintering aid element. Therefore, in this study, two different zirconate proton conductors: BaZr0·9Y0·1O3-α (BZY) and BaZr0·955Y0·03Co0·015O3-α (BZYC) were sintered in an air atmosphere and an oxygen atmosphere for 20 h in the temperature range of 1500–1640 °C. The sinterability was evaluated by analyzing the XRD diffraction patterns, lattice constant, lattice strain, crystallite size, relative density, open porosity, closed porosity, surface morphology, grain size, and grain boundary distribution, using the XRD, SEM, EDX, and Archimedes density measurement methods. It is concluded that in an oxygen atmosphere, sintering aid Co not only improves the relative density but also produces highly dense fine particles with clear grain boundaries which are promising for electrochemical hydrogen device applications.

The applicability of CaCu3Ti4O12 (CCTO) ceramics in modern microelectronics has been widely investigated; however, CaCu3Ti4O12 suffers large loss tangents, which limits its applicability. We employed a solid-state reaction method to prepare a new cation–anion codoping system incorporating Sn and F ions that can reduce the loss tangent and improve the electrical properties of CaCu3Ti4O12 ceramics. The microstructure, dielectric response, nonlinear current–voltage characteristics, and electrical properties of the grains and grain boundaries of the (Sn–F) codoped CCTO ceramics (SF-CCTO) were investigated. Sn strongly suppressed the grain growth by reducing the grain boundary mobility, while F enhanced the densification of the sintered ceramics. Both the dielectric permittivity and loss tangent of the SF-CCTO ceramics tended to decrease with decreasing mean grain size owing to the increased codopant concentration. Notably, a large dielectric permittivity of ~3 × 104 with a low loss tangent of ~0.5 was achieved. Moreover, the breakdown electric field of the SF-CCTO ceramic was increased from ~200 V/cm (for the undoped CCTO ceramic) to ~200 V/cm. The Schottky barrier height at the grain boundary was enhanced by doping CaCu3Ti4O12 with Sn and F ions. The reduced loss tangent and enhanced nonlinear electrical properties were attributed to the significant increase in the total grain boundary resistance resulting from the reduced mean grain size and the increased potential barrier height. The nonlinear electrical properties and dielectric behavior is well described in terms of the internal barrier layer capacitor structure using the Maxwell–Wagner relaxation model. This method may be applied to other polycrystalline ceramics to improve their dielectric and nonlinear electrical properties.

The effects of large thermal gradient annealing on the microstructure of 10 mol% gadolinium doped ceria (GDC) were investigated. GDC powder was prepared by solvent deficient method and sintered at 1650 °C for 10 h to achieve dense ceramics with ~8 μm grain size. The densified GDC samples were subsequently annealed using a 60 W infrared laser at over 2100 °C for 1 h under a thermal gradient equivalent to ~0.3–0.5 °C/μm. The post-annealed samples at 2150 °C for 1 h exhibit grains with average length and width of 37 and 28 μm, respectively. Electron backscattered diffraction (EBSD) analysis revealed that the post-annealed sample at 2150 °C consists of grains oriented close to five principal directions ( , and on [0 0 1], and and on [0 1 0]) within a tolerance angle of ±10°, whereas the grains of the pre-annealed sample are randomly oriented. Gadolinium diffuses 20–30 μm away from the irradiated surface, with the measured composition of regions deeper than 30 μm, Ce0.86Gd0.14O1.93, is close to that of the pre-annealed sample, Ce0.87Gd0.13O1.94. Enhancement of total conductivity of the post-annealed GDC (1.1 × 10-3 S cm-1 at 500 °C, and 2.1 × 10-2 S cm-1 at 700 °C) is observed when compared to the pre-annealed GDC (3.1 × 10-5 S cm-1 at 500 °C, and 1.7 × 10-3 S cm-1 at 700 °C), and points to the decrease in the grain boundary (GB) resistivity. This could be attributed to both the change in GB area and grain alignment.

B2O3 and CuO were codoped into 6Nd[(Zn0.7Co0.3)0.5Ti0.5]O3–4(Na0.5Nd0.5)TiO3 (abbreviated as 6NZCT–4NNT) ceramics as sintering aids. The influences of the sintering aids on the sintering characteristics, microstructure and microwave dielectric properties of the 6NZCT–4NNT ceramics were systematically investigated as a function of the proportion of B2O3 and CuO. Codoping could greatly reduce the sintering temperature from 1410 °C to 1150 °C, indicating that B2O3/CuO are good sintering aids for 6NZCT–4NNT ceramics. The B2O3/CuO sintering aids had no significant impact on the phase purity of the investigated ceramics, even though a solid solution was formed due to Cu2+ ion substitution. However, they had evident influences on the surface morphology and grain size. The average grain size was enlarged with increasing amounts of CuO in the B2O3/CuO sintering aids. Remarkable deterioration of the microwave dielectric properties for 6NZCT-4NNT ceramics was not observed when codoping an appropriate amount of B2O3 and CuO. The 6NZCT–4NNT ceramics codoped with 2.0 mol% B2O3 and 2.0 mol% CuO sintered at 1150 °C for 3 h exhibited a homogeneous microstructure and promising microwave dielectric properties: an appropriate dielectric constant (er = 49.37), a high quality factor (QF = 47,295 GHz), and a near-zero temperature coefficient of resonant frequency (TCF = +0.9 ppm/°C).

In order to improve mechanical properties of 6082 aluminum alloy, the SiCp/Al 6082 composites were prepared by the addition of the micron-sized SiC particles combined with the squeeze casting. The effects of the SiCp content and squeeze casting on the microstructure and mechanical properties of the 6082 aluminum alloy were investigated by SEM, EDS, TEM, tensile testing and hardness testing analysis methods. Research results exhibited that the SiCp content and squeeze casting had a significant impact on the microstructure and mechanical properties of the 6082 aluminum alloy. The addition of the SiCp refined the grain size of the 6082 aluminum alloy while caused the increase of the porosity with increasing the SiCp content, especially in the permanent mold casting condition. Compared to the permanent mold casting, the squeeze casting obviously reduced pore defects, refined grain size and made the SiCp distribute evenly as well as bond tightly with the Al matrix. The tensile strength, yield strength, elongation, elastic modulus and hardness of the 6082 aluminum alloy obtained with the SiCp and squeeze casting were remarkably improved, and the optimal mechanical properties were obtained with a 2 wt.% SiCp, and they increased 10.73 %, 72.7 %, 193.9 %, 23.5 % and 25.2 %, respectively, compared to those of the 6082 aluminum alloy obtained without SiCp and squeeze casting. The fracture surface of the SiCp/Al 6082 composites obtained with the squeeze casting was dense and exhibited a ductile fracture mode.

Dense alumina ceramics were additively manufactured efficiently through a 3D gel printing process. Hydroxyethyl cellulose (HEC) was applied to ensure the printability and rigid of the gel made from boehmite. A multi-step liquid desiccant drying method was implemented to improve the drying efficiency. The results showed that the solid loading and HEC addition were two useful parameters for adjusting the rheology properties of the gel to make it suitable for 3D printing. With polyethylene glycol(PEG) added as liquid desiccants, the printed bodies with section size of 10 mm could be dried within 26 h during which the deformation and crack formation was avoided despite a high linear shrinkage of 45 % was encountered. The successful preparation of dense monolithic alumna ceramics parts with an average grain size of 1 μm, 99 % of the theoretical density and a flexural strength of 380 ± 45 MPa indicated the potential of this process.

The effects of SiC (20, 25, 30 vol %) and TiC (5, 10, 15 vol %) addition on microstructure, phase evolution, densification, and mechanical characteristics of microwave sintered ZrB2 based composites were investigated. The lattice parameters of secondary phases [(Zr, Ti)B2 and (Zr, Ti)C)] decreased with SiC and TiC addition. The analytically calculated residual stresses in the matrix and reinforcement phase were found to be tensile and compressive. The densification, microhardness, compression and flexural strength enhanced with SiC addition from 20 to 30 vol % in the ZrB2-5vol. % TiC composites. However, the fracture toughness decreased with SiC addition from 20 to 30 vol % due to larger SiC grain size and a higher degree of SiC interconnectivity in the composites. The mechanical characteristics further enhanced by the TiC addition from 5 to 15 vol % in the ZrB2 -25 SiC (vol. %) composites. The highest densification, microhardness, compression and flexural strength were observed for the ZrB2-25 SiC-10 TiC (vol. %) composite. Whereas the ZrB2-25 SiC-15 TiC (vol%) composite observed the highest fracture toughness due to higher compressive residual stress and prominent toughening mechanisms such as crack deflection, particles pull out and crack bridging.

The combination of multiple loss characteristics is an effective approach to achieve broadband microwave wave absorption performance. The Fe-doped SiOC ceramics were synthesized by polymer derived ceramics (PDCs) method at 1500 °C, and their dielectric and magnetic properties were investigated at 2–18 GHz. The results showed that adding Fe content effectively controlled the composition and content of multiphase products (such as Fe3Si, SiC, SiO2 and turbostratic carbon). Meanwhile, the Fe promoted the change of the grain size. The Fe3Si enhanced the magnetic loss, and the SiC and turbostratic carbon generated by PDCs process significantly increased the polarization and conductance loss. Besides, the magnetic particles Fe3Si and dielectric particles SiO2 improved the impedance matching, which was beneficial to EM wave absorption properties. Impressively, the Fe-doped SiOC ceramics (with Fe addition of 3 wt %) presented the minimum reflection coefficient (RCmin) of −20.5 dB at 10.8 GHz with 2.8 mm. The effective absorption bandwidth (EAB, RC

It is a challenge to reduce the dielectric loss and increase the tunability of pure barium strontium titanate (BST) films for microwave tunable application because these two properties change simultaneously. Herein, a novel composite of strontium titanate (ST) and potassium-doped BST (KBST) has been designed as ST/KBST/ST sandwich-type film with various ST and KBST layers. X-ray diffraction patterns show that the film exhibits cubic perovskite polycrystalline structure composed of BST and ST phase, mainly grow along (110) crystal plane with average grain size of less than 20 nm and decreasing BST phase/ST phase ratio with increasing film thickness. Scanning electron microscope shows that no interfacial layer can be observed, indicating that ST and KBST are fully compounded. Low dielectric loss and high tunability at -10 – 10 V and stable and excellent dielectric properties at 1 GHz are achieved, meeting the needs of microwave tunable application at high frequency. The surface structures are also studied by other analysis methods, and ST/MgBST/ST sandwich-type film is compared.

Mg–0.5Bi–0.5Sn alloys with and without microalloying with 0.5 wt% Mn were subjected to extrusion, and the effect of Mn microalloying on the microstructural characteristic and corrosion behavior of the extruded alloys was investigated. The results indicated that the average grain size and the density of dislocations decreased, and a new Mg26.67Mn65.47Fe7.86 second phase as well as grain boundary segregation of Sn atoms could be observed in certain micro-regions of the extruded dilute Mg–0.5Bi–0.5Sn–0.5Mn alloy. The tailoring of microstructure resulted in the significant enhancement in corrosion resistance (Rp increased from 1095.91 Ω cm2 to 5008.79 Ω cm2). In addition, grain boundary segregation resulted in intergranular corrosion and led to the dissolution of Sn atoms. Hence, the dissolution rate of the matrix in Mg–0.5Bi–0.5Sn–0.5Mn alloy could be inhibited by the corrosion product film containing an intermediate product (SnO2).

This work is devoted to investigate the structural and electrical properties of the Ce, Gd-doped YBCO superconductors bulk ceramics. YBa2-xRExCu3O7−δ (x = 0, 0.01, 0.05, 0.1) (RE = Gd, Ce) samples were prepared by means of conventional solid-state reaction. X-ray diffraction analysis was carried out to identify the present phases in the as-prepared samples followed by the determination of their lattice parameters. Fourier Transform Infrared Spectroscopy (FTIR) was used to identify the functional groups. Furthermore, the morphology and the surface roughness of the studied samples were characterized using Scanning Electronic Microscopy (SEM) and Atomic Force Microscopy (AFM). Vickers Micro-hardness of the as-prepared samples was examined. Besides, the electrical resistivity measurements were achieved to determine the critical transition temperature TC and the critical current density JC. The effect of Ce and Gd additions is clearly noticed in the obtained results, where all the prepared samples are superconductors with the presence of Y123 as a major polycrystalline phase. From the XRD patterns, the intensities of the Y123 corresponding peaks decrease with further increasing the Ce and Gd contents. In addition, the variation of the cell parameters was significant after additions of both Ce and Gd, which affect the grain size and the oxygen content of the YBa2-xRExCu3O7−δ system. An improvement of the structure and surface roughness is observed on SEM and AFM images. Likewise, Vickers micro-hardness has increased after the Ce and Gd additions. Although, the critical transition temperature TC was not further increased upon Ce or Gd additions compared to the undoped YBCO samples. Nevertheless, an exception has been recorded with an increase of TC for YBa2-xRExCu3O7−δ with (RE = Gd, x=0.01) to reach 88 K. In contrary, an improvement of the deduced critical current density JC was achieved for all Ce-doped YBCO samples unlike those of Gd-doped samples.