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The highly regarded Fe2P-based magnetocaloric materials are usually fabricated by ball milling, and require an additional extended annealing treatment at high temperatures (at temperatures up to 1423 K for several hours to days). In this work, we show that fabricating Mn1.3Fe0.6P0.5Si0.5 into the form of microwires attained 82.1 wt.% of the desired Fe2P phase in the as-cast state. The microwires show a variable solidification structure along the radial direction; close to the copper wheel contact, Fe2P phase is in fine grains, followed by dendritic Fe2P grains and finally secondary (Mn,Fe)5Si3 phase in addition to the dendritic Fe2P grains. The as-cast microwires undergo a ferro- to para-magnetic transition with a Curie temperature of 138 K, showing a maximum isothermal magnetic entropy change of 4.6 J kg−1 K−1 for a magnetic field change of 5 T. With further annealing, a two-fold increase in the maximum isothermal magnetic entropy change is found in the annealed microwires, which reveal 88.1 wt.% of Fe2P phase. [ABSTRACT FROM AUTHOR]

The oxidation behaviors of molten WE43 (Mg-4.32Y-2.83Nd-0.41Zr, wt%) in resin-sand mold atmosphere were systematically investigated. X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy analyses were employed to identify the phase compositions and microstructures of surface oxide scale. The initial oxide scale characterized by a three-layer structure mainly consisted of MgO, Y2O3, and ZrO2 and then transformed to Y2O3 layers covered by porous MgO after holding at high temperatures. CALPHAD method was used to analyze the oxidation process, and the calculated phase diagrams agreed well with the experimental results. A selective oxidation model was established based on thermodynamic and kinetic analysis to describe the structure transformation of oxide scale in detail. The initial oxidation was controlled by inward diffusion of oxygen due to the protection of surface Y2O3. However, the oxide scale was not protective after long-term oxidation or at temperatures higher than 1073 K due to the oxide fracture, which can be attributed to the increase in stress caused by inner Y2O3 layer growth. Based on experimental results, the oxide growth stress parameter C was estimated to be 0.0013 and 0.0026 for 1023 and 973 K, respectively. This work reveals the underlying oxide growth and fracture mechanisms of molten Mg-Y alloy in mold, and provides guidance for preventing the ignition of magnesium alloys during casting processes. [ABSTRACT FROM AUTHOR]

The Al–50Si alloy, as a kind of potential electronic packaging material, is manufactured by different methods, such as casting and spray deposition. The possible influences of the P refiner on the microstructure of the Al–50Si alloy are investigated at different cooling rates. The refinement mechanism of primary Si phase is discussed in view of the P refiner addition, and the variation of the cooling rates. The thermal conductivity (TC), as a key parameter for electronic materials, is measured. The coupled effects of the cooling rate and the addition of the P refiner during the solidification of the Al–50Si alloy on the TC are elucidated based on structural observations. Furthermore, the porosity in the Al–50Si alloy is treated as a second phase influencing the TC. [ABSTRACT FROM AUTHOR]

Developing light structure materials that work stably at elevated temperatures is a long-standing challenge for many application fields, particularly in the development of aerospace equipment. Zn/Cd alloying elements were prospected to improve the stability of the lightest Mg-Li based alloys; however, little is known about the intermediate-temperature mechanical properties of such alloys. The present work investigated the tensile behaviors of a cold-rolled Mg-Li-Al-Cd-Zn alloy in a temperature range of 30–150 °C. The results indicate that the alloy can host a tensile strength σUTS of 108~121 MPa, a yield strength σYP of 97~109 MPa and elongation εB of 14–15 % at 150 °C, dependent on the tensile direction. The mechanical properties intensively are modulated by temperature through the competition between work hardening and softening. Work hardening due to dislocation blocking by the precipitated MgLi2X phase dominated the deformation at low temperatures, while softening that resulted from dynamic recrystallization was the main effect at high temperatures. Correspondingly, a quasi-cleavage mechanism dominated the fracture at temperatures near room temperature, and microvoid coalescence worked at high temperatures above 100 °C. Our results offer a new experimental understanding of the elevated-temperature mechanical behaviors of Mg-Li alloys and will advance the development of new light magnesium alloys with high stability. [ABSTRACT FROM AUTHOR]

The bonding layer microstructures and their effects on fracture behaviors of sapphire joined using MgO (0.5%)-Al2O3 (94%)-SiO2 (5.5%) interlayer are analyzed. The results indicate that the bonding layer is composed by facetted Al2O3 grains and pores and they are controlled by joining conditions. The fracture mode is mainly intergranular for the pieces with fine grains and changes into cleavage fracture as the grain size increases. Optimal microstructures can be obtained under the condition of 1700°C, holding time of 1.5 h and pressure of 3 Mpa and the flexure strength corresponding plane bonded pieces may be beyond 250 MPa and plane bonded pieces may reach above 300 MPa. [ABSTRACT FROM AUTHOR]

The hot deformation behavior and microstructure evolution of powder metallurgy (PM) Ti43Al9V0.3Y alloy with fine equiaxed γ and B2 grains were investigated using uniaxial hot compression. Its stress exponent and activation energy were 2.78 and 295.86 kJ/mol, respectively. The efficiency of power dissipation and instability parameters were evaluated, and processing maps at 50% and 80% strains were developed. It is demonstrated that the microstructure evolution was dependent on the temperature, strain, and strain rate. Both temperature and strain increases led to a decrease in the γ phase. Moreover, dynamic recrystallization (DRX) and grain boundary slip both played important roles in deformation. Reasonable parameters for secondary hot working included temperatures above 1100 °C but below 1200 °C with a strain rate of less than 1 s−1 at 80% strain. Suitable hot working parameters at 50% strain were 1150–1200 °C/≤1 s−1 and 1000–1200 °C/≤0.05 s−1. [ABSTRACT FROM AUTHOR]

A novel strategy of microstructure design is introduced to improve the mechanical properties of TiAl alloys, fabricated by powder metallurgy. The gas atomization powder and as-HIPed (Hot isostatic pressing) TiAl are investigated by scanning electron microscopy, energy dispersive spectrometry, transmission electron microscopy, and electron backscattered diffraction. The dispersed submicron precipitate in the microstructure is determined to be Y2O3. A microstructure with uniform fine grain is obtained. The room temperature strength and strain reach 793 MPa and 1.5%, respectively. The strength and strain at 700 °C are still as high as 664 MPa and 9.2%, respectively. The fine grain and precipitate lead to a high room-temperature plasticity. [ABSTRACT FROM AUTHOR]

Here, near α titanium alloy TA15 (Ti-6.5Al–2Zr–1Mo–1V) samples were fabricated by electron beam selective melting (EBSM) and their high-temperature tensile deformation behaviors were studied at 773K–1023K. The results show that the tensile strength decreases gradually with the deformation temperature while the yield ratio increases as temperature increases from 773K to 923K, and then decreases gradually with further increasing the temperature. The deformation mechanism of EBSM-built TA15 samples at elevated temperatures can be ascribed to work hardening caused by the increase of dislocation density, and softening caused by the recovery and recrystallization. The studied TA15 alloy exhibits obvious work hardening behaviors at both 773K and 823K, dynamic recovery occurs during tensile deformation at 873K, and dynamic recrystallization plays a dominant role at 923K–1023K. The EBSM-built TA15 samples have excellent mechanical properties at medium temperatures, and the present results are helpful for the industrial applications of EBSM-built titanium alloy components in the aerospace fields. • Near α titanium alloy Ti-6.5Al–2Zr–1Mo–1V samples were fabricated by electron beam selective melting. • The tensile properties and the high temperature deformation behavior of the EBSM-built TA15 samples were studied. • The tensile strength of the EBSM-built TA15 samples decreases gradually with the increase of deformation temperature. • Work hardening was obvious at 500 °C and 550 °C, whereas dynamic recovery and recrystallization dominate at 650 °C–750 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel high-entropy alloy CoCrFeNi microfibers with heterogeneous gradient structures was developed. • The CoCrFeNi microfibers displays an excellent strength–ductility combination both at 293 K and 150 K. • The deformation mechanisms of the microfibers at ambient and cryogenic temperatures are revealed. Exploring metallic microfibers with an excellent combination of high strength and ductility is a challenge for structural applications under extreme conditions. In this work, a heterogeneous gradient structure was introduced into CoCrFeNi high-entropy alloy (HEA) microfibers via thermomechanical processing. The annealed CoCrFeNi microfiber displays an ultrahigh yield strength of ∼ 1 GPa, an ultimate tensile strength of 1.45 GPa, and an outstanding uniform elongation of 75% at 150 K. These excellent properties originate from the ultrafine grains and heterogeneous gradient structure, as well as the activation of multiple deformation mechanisms including deformation twins, dense dislocations, stacking faults, Lomer-Cottrell locks, phase transformation and 9R phase. Our work not only suggests that HEA microfibers have great potential for structural applications in cryogenic environments, but also sheds light on the design of advanced multi-component metallic microfibers with superior mechanical properties. [ABSTRACT FROM AUTHOR]

Using electropulsing treatment (EPT), we proposed a method to effectively tune the free volume content and the mechanical performance of a Zr-based bulk metallic glass (BMG). No crystallization takes place but the atomic scale structure changes during EPT. Appropriate EPT parameter can facilitate the increase in the free volume content, thus tailoring the nanomechanical properties of the studied BMG. • Electropulsing treatment is employed to tune the structure and mechanical properties of a Zr-based bulk metallic glass. • Appropriate EPT parameter facilitates the increase in the free volume content. • The applied current density exerts a crucial role on the incipient plasticity. [ABSTRACT FROM AUTHOR]

Abstract Ti-Al-Si-C-N nanocomposite coatings were deposited on cemented carbide (WC-10 wt%, Co) substrates by reactive magnetron sputtering technique. The effect of C 2 H 2 /N 2 partial pressure ratio on element concentration, deposition rate, microstructure, cross-sectional morphology, hardness and tribological properties of the coatings were studied. The coatings were found to have a nanocomposite structure consisting of nanocrystallities (Ti,Al)(C,N) and amorphous phase. The coating's columnar crystals structure was restrained with the increase of C 2 H 2 /N 2 partial pressure ratio. The deposition rates and nanohardness of coatings firstly increased with the increase of C 2 H 2 /N 2 partial pressure ratio and reached their maximum values of 133 nm/min and 35 Gpa, respectively, at C 2 H 2 /N 2 partial pressure ratio of 1:2 before decreasing. The friction coefficient and wear rates of Ti-Al-Si-C-N coatings dramatically decreased with the increase of C 2 H 2 /N 2 partial pressure ratio and reached the lowest value of 0.17 and 1.1 × 10–6 mm3/Nm, respectively, at C 2 H 2 /N 2 partial pressure ratio of 1:1. Highlights • Deposition of Ti-Al-Si-C-N coatings by using reactive magnetron sputtering technology with N 2 and C 2 H 2 • The microstructure evolution of Ti-Al-Si-C-N coatings is studied as a function of C 2 H 2 /N 2 partial pressure ratio. • The Ti-Al-Si-C-N coatings have a super high nanohardness of 35 GPa and low friction coefficient. • The wear resistance is improved with the increase of C 2 H 2 /N 2 partial pressure ratio. [ABSTRACT FROM AUTHOR]

We have recently reported that the quaternary Ni 49.0 Mn 38.4 Sb 11.7 Si 0.9 alloy showed enhanced refrigeration capacity due to the wide working temperature interval and narrow magnetic hysteresis loss via Si-doping. Here we systematically investigate the microstructure, martensite transformation and magnetic transition behaviors of Ni 50 Mn 38 Sb 12-x Si x (x = 0, 1, 2, 3) alloys. Ni 50 Mn 38 Sb 12-x Si x (x = 0, 1, 2) alloys exhibited a full solid-solution state with a four-layer modulated orthorhombic (4O) martensite structure. However, three phases formed in Ni 50 Mn 38 Sb 9 Si 3 alloy, and lath-like martensite twins existed only in α phase at room temperature. The martensite transformation temperature decreased with the increasing Si content when the Si atomic content increased from 0% to 2%, but significantly increased when Si content reached to 3% because of the increase of the valence electron concentration ( e / a ) of matrix phase (α phase). The martensitic transformation also occurred in the β phase below room temperature in Ni 50 Mn 38 Sb 9 Si 3 alloy. Furthermore, the martensite transformation temperature range enlarged and the thermal hysteresis narrowed with the addition of Si atomic content from 0% to 2%, of which Ni 50 Mn 38 Sb 10 Si 2 alloy had the widest martensite transformation temperature range and narrowest thermal hysteresis, which was supposed to have great magnetocaloric effect (MCE). However, when x = 3, the thermal hysteresis increased significantly and the transition character changed to a second-order phase transition above room temperature; a magneto-structural coupling of the first-order martensitic transformation and second-order magnetic transition also existed below room temperature, which all would result in low MCE. [ABSTRACT FROM AUTHOR]

Wire-arc additive manufacturing can fabricate components with complex geometries efficiently compared with other manufacturing methods. However, the uncontrolled grain size and tensile residual stress in as-fabricated components have limited their applications. In this study, laser shock peening, an innovative surface treatment technique, was specially-combined with wire-arc additive manufacturing to refine microstructure, modify stress state and enhance tensile properties of as-printed 2319 aluminum alloy. After peening, the average grain size decreased from 59.7 μm to 46.7 μm, and the percentage of grains with low angle boundaries increased from 34% to 70%. High density of dislocations and mechanical twins were generated and resulted in the increase of micro-hardness. Residual stresses were modified from tensile to compressive state with a maximum value around 100 MPa. Yield strength was remarkably increased by 72%. This combined printing and peening manufacturing strategy provides microstructure and quality control of manufactured components for practical applications. [ABSTRACT FROM AUTHOR]

As important aeronautics and astronautics materials, the Al-Zn-Mg-Cu alloys have been fabricated by spray deposition. The effects of Mg and Cu on the microstructures and mechanical properties were systematically investigated. The S (Al 2 MgCu) and θ (Al 2 Cu) phases exist in equilibrium solidification conditions, but they were not found in the rapid solidification conditions due to the change of solidification paths and phase components during the spray deposition process. The volume fraction of the secondary phases/precipitates increases with increasing Mg content, which leads to the improvement of yield strength as well as to raise tendency of intergranular fracture. Undissolved phases can be promoted by increasing Cu content in the Mg-rich (∼2.65 wt% Mg) alloys. Furthermore, Cu has weak effects on yield strength but plays a positive role in maintaining the peak strength value of the alloys in overaged condition. The alloy with a medium (Mg+Cu) content shows superior overall properties: the ultimate tensile strength (UTS), yield strength (YS) and elongation can reach values of 812 ± 3 MPa, 780 ± 3 MPa and 7.0 ± 0.7%, respectively. [ABSTRACT FROM AUTHOR]

In this work, the effect of Sc content on the microstructures and mechanical properties of Al-Zn-Mg-Cu-Zr alloys prepared using spray deposition was studied. Microstructure observations reveal that not only the grain size, but also the coarse secondary phase can be refined by Sc addition through the formation of a hybrid structure coupled by η-MgZn 2 and Al 3 (Sc, Zr) phases near and at the grain boundaries. It is inferred that the primary Al 3 (Sc, Zr) particles can act as nucleation sites for the η-MgZn 2 phase during the deposition process. With the increase of Sc content, the continuous secondary phase at the grain boundaries converts gradually into small discontinuous particles, which contributes to the considerable improvement in tensile strength and elongation. The alloy with 0.2 wt% Sc exhibits excellent combinations of ultimate tensile strength of 831±3 MPa and elongation of 10.2 ± 0.4% after T6 heat treatment, and the elongation increases by almost 50% compared to the Sc-free base alloy. [ABSTRACT FROM AUTHOR]

The influence of annealing temperature on microstructure evolution and mechanical properties of CoCrFeNiMn 0.75 Cu 0.25 high-entropy alloy (HEA) was systematically investigated. As the annealing temperature increases, the grain becomes coarser, Cr-rich phase precipitates, and annealing twins appear in the matrix. The low angle grain boundary (LAGB) changes to high angle grain boundary (HAGB), which reduces the strength and increases the ductility of the studied HEA. The deformation bands, grain boundaries, and triple junctions of the grains are the preferred recrystallized nucleation sites. Based on the microstructural evolution, the contribution of the Cr-rich phase, LAGBs, HAGBs, and twin boundaries to the yield strength was analyzed by the modified Hall-Petch equation. These results may provide some guidance on tailoring the microstructures and mechanical properties for superior HEAs design. • The influence of annealing temperature on the microstructure and mechanical properties of a rolled HEA was discussed. • The deformation bands, grain boundaries, and triple junctions are the preferred recrystallized nucleation sites. • The microstructural evolution, and the contribution of LAGBs, HAGBs, and TBs to the yield strength was analyzed. [ABSTRACT FROM AUTHOR]

Tailoring microstructure and mechanical properties of structural materials to meet application requirements is a long-standing challenge in materials science. Here we have studied the effects of laser energy density (LED) on the microstructure and mechanical properties of single-track CoCrFeMnNi high entropy alloy (HEA) samples fabricated by laser directed energy deposition (LDED). The results indicate that the molten pool size of the single-track HEA samples gradually increases with increasing LED. All of the samples possess a single face-centered cubic (FCC) solid solution structure. The microstructures of the single-track HEA samples are mainly composed of columnar and equiaxed grains, and as the LED increases, their grain size increases while the micro-hardness decreases. Additionally, the relationship among the processing parameters, cooling rate and grain size was investigated via combining the numerical simulation and experimental observations. This work provides mechanistic insights into establishing the processing-structure-property relationships in the additively manufactured HEAs and contributes to achieve LDED of tunable HEA parts with desired microstructure and mechanical performance. [Display omitted] • LDED was utilized to manufacture the CoCrFeMnNi HEA with different laser energy densities. • The effects of laser energy density on microstructure and mechanical properties were studied. • The processing-structure-property relation for LDED of HEA was established. [ABSTRACT FROM AUTHOR]

Impedance output stability of Co-rich amorphous wires depends largely on the wire-terminal-connection, which can be accomplished by composite electroplating towards a robust sensor application. The present experimental results indicated that Ni/Cu composite layer composed of Ni, Cu plating and passivating treatment show a homogeneous microstructure, and excellent surface wettability, weldability and thermal expansion coefficient matching under variable temperature of wire-terminal-connecting. The properties of composite electroplated layer are mainly influenced by cathode current density, electroplating time and electrolyte temperature. The inhomogeneous distributed clustering-regions, disproportionated reaction, tendency of hydrogen brittleness and crack have been reduced by optimized coactions of intermolecular Van der Waals force, inner diffusion and mechanical bonding of electroplated layer. Therefore, the wire-terminal-connection is able to effectively improve impedance output stability by minimizing the disturbance of stray capacity, decreasing radio-frequency wave emission and electromagnetic signal attenuation, and suppressing the destabilization or concussion. [ABSTRACT FROM AUTHOR]

Herein, we reported the influences of accumulated direct current annealing (ADA) on the GMI properties and microstructures of Zr-doped melt-extracted (Co 68.15 Fe 4.35 Si 12.25 B 12.25 Zr 3 ) amorphous microwires. There indicated that ADA-ed wires enhanced GMI properties and improved the microstructures remarkably in comparison with as-fabricated wires. The maximum GMI ratio [Δ Z / Z 0 ] max and equivalent magnetic circumferential anisotropy field (EMCAF) of ADA-ed microwires were increased to 256.01% and 4 Oe at 20 MHz, respectively, which are more than nearly 8 and 2 times of 33.62% and 1.6 Oe for as-fabricated wires, respectively. Moreover, the maximum magnetic field response sensitivity ( ξ max ) increased to 372.57%/Oe, which is much higher than the as-fabricated wires of 44.71%/Oe. The remarkable enhancement of GMI performance was considered as the microstructural evolution including structural relaxation, appearance of nano-crystallization, and circumferential arrangement of surface magnetic domains. Nano-crystallization degree and circumferential magnetic domains arrangement were effectively improved by actions of Joule thermal energy and circular magnetic field generated ADA as shown in HRTEM and magnetic force microscope (MFM) analysis. Based on above, both the excellent GMI performances and relatively large ξ max values indicate the ADA is an effective annealing technique for thermal treating the melt-extracted amorphous wires which applied for potentially magnetic sensor in detecting low-intensity magnetic fields. [ABSTRACT FROM AUTHOR]

The effects of superheat temperature, content of modifier (P) and T6 heat treatment on the microstructure and mechanical properties of the Al–50Si alloy have been investigated systematically by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results indicate that the primary Si exhibits a plate-like morphology, with average size decreasing with increasing of the superheat temperature for the unmodified alloy. The morphology of primary Si changes to small blocky shape at an optimal P content of 0.5 wt.%, and the nucleation temperature increases for the alloy with 1.3 wt.% P because of the ease of formation of the AlP phase. The nucleation temperature is lower for 0.5 wt.% P due to lack of P atoms at relatively higher temperature. The ultimate tensile strength was enhanced by the addition of P followed by the T6 heat treatment, and the maximum ultimate tensile strength (∼160 MPa) was observed for the sample containing 0.5 wt.% P. [ABSTRACT FROM AUTHOR]

Bulk metallic glass (BMG), Zr 46 Cu 37.6 Ag 8.4 Al 8 (ZrCuAlAg), has been systematically evaluated in terms of microstructure, compressive properties, and wear resistance, aimed at exploring its use as a novel biomedical material. For comparison, the above-mentioned tests were also performed on Zr 51.9 Cu 23.3 Ni 10.5 Al 14.3 , Zr 51 Ti 5 Ni 10 Cu 25 Al 9 , and Ti 40 Zr 25 Ni 12 Cu 3 Be 20 BMGs, pure Ti and Ti–6Al–4V alloy. ZrCuAlAg BMG exhibits higher strength, higher hardness, and better wear resistance than other materials. All the results imply that the Ag-bearing ZrCuAlAg BMG with excellent mechanocompatibility will open up a new path for biomedical applications. [ABSTRACT FROM AUTHOR]

• The formation mechanism of bifilm defect in Mg-Gd-Y-Zr alloy is revealed as surface Y 2 O 3 oxide film shrinkage. • The bifilm in Mg-Gd-Y-Zr alloy contains Zr-cores. • Microcracks resulted by the shrinkage of bifilm is elucidated responsible for the generation of Zr-core. Mg-Gd-Y-Zr alloy has excellent mechanical properties at room and high temperatures, but its high oxidation properties can also result in a significant number of bifilm defects. However, its formation mechanism was not revealed so far, which was explored in the present work. The results showed that the surface oxide film folds into a grid-like double layer structure defect during solidification, due to the difference of thermal expansion coefficient between surface oxide film and matrix. In addition, the oxide film produces microcracks. As the magnesium alloy melt fills the crack, Zr precipitates into crystal nucleus with peritectic reaction and Y 2 O 3 accumulates. These results would shed new lights on the understanding of shrinkage formation of bifilm defects and improving the defects control of magnesium alloy castings. [ABSTRACT FROM AUTHOR]

• TA15 titanium alloy was fabricated by EBSM with different parameters. • Basketweave structure and Widmanstatten structure were co-existed in EBSM-built samples. • Process window of martensite phase α′ in EBSM-built TA15 samples was obtained. • Samples with a mixture of (α′ + α + β) phases process a higher strength and lower plasticity than that with fully lamellar (α + β) phases. Ti6.5Al2Zr1Mo1V was fabricated via electron beam selective melting (EBSM) with different process parameters to study the diversity of microstructure. Results demonstrate that samples with a flat surface can be obtained when the ratio of beam current to scanning speed fluctuated between 5.0 and 7.5 as other parameters were fixed. Basketweave structure and Widmanstatten structure were observed to co-exist in EBSM-built samples under different parameters, while martensite phase α′ was more likely to form under low beam current and high scanning speed. Samples with a mixture of (α′ + α + β) phases possess a higher strength and lower plasticity than that with fully lamellar (α + β) phases due to the stress concentration at the α′/β interface in inhomogeneous microstructure. [ABSTRACT FROM AUTHOR]

Abstract: The isothermal deformation of a V-shaped component was simulated by the DEFORMTM process simulation software. The material flow, internal stress and temperature of the billet’s interior were investigated during the process of deforming, and the simulation results showed that bar billet is more suitable than sheet billet for producing the V-shaped component. The real isothermal deformation process was carried out with bar billet, and the microstructure of the shaped component was greatly refined. After heat treatment, the ultimate tensile strength (UTS) of the component can reach 817MPa. The results show that isothermal deformation is a low cost and high efficient compaction technique for produce components from the spray formed Al–Zn–Mg–Cu alloy. [Copyright &y& Elsevier]

Melt-extracted amorphous Co68.15Fe4.35Si12.25B15.25 microwires were drawn at ambient temperature into different diameters and the dependence of tensile properties and microstructural evolution on the degree of deformation was investigated. The cold-drawn wire with 51% area cross-section reduction exhibits a tensile ductility of 1.64%, with a tensile strength exceeding 4000MPa. Deformation-induced Co-rich nanocrystals were observed in the cold-drawn wires and proved to be capable of arresting the quick extension of shear bands and leading to the enhanced global plasticity of the microwires. [ABSTRACT FROM AUTHOR]

Abstract: Mg–5Y–3Nd–0.6Zr–xGd (x =0, 2 and 4wt.%) alloys were prepared by metal mould casting technique, the structures and mechanical properties were investigated. The alloys were mainly composed of α-Mg solid solution and β-phase. With increasing Gd content, Mg5RE phase increased and the grain was refined. The Mg–5Y–3Nd–2Gd–0.6Zr alloy exhibited highest ultimate tensile strength and Mg–5Y–3Nd–0.6Zr alloy showed highest yield strength at room temperature. With increasing amount of Gd, the thermal resistance was improved. The Mg–5Y–3Nd–4Gd–0.6Zr alloy exhibited highest UTS and YS at 250°C, they were about 1.27 times higher than those of Gd-free alloy, which was mainly attributed to the increase of the β-phase and Mg5RE strengthening phase. [Copyright &y& Elsevier]

Abstract: Mg–4Al–4Nd–0.5Zn–0.3Mn alloy was prepared by metal mould casting method. Microstructure, aging behavior, mechanical properties and fracture morphology of the alloy were investigated. The results showed that α-Mg, Al11Nd3, Al2Nd and Mg32(Al,Zn)49 phases were the main phases of the as-cast alloy. And the long rod-like Al11Nd3 phase was decomposed to granular Al2Nd through T6 heat treatment. The tensile strength was also enhanced by T6 treatment. The yield strength was increased by 17% and 21% at RT and 150°C, respectively. It was mainly because that the precipitates were refined through T6 treatment and this became more benefit to hinder dislocations slipping. [Copyright &y& Elsevier]

Abstract: X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and differential scanning calorimetry (DSC) were performed to investigate the critical cooling rate and thermal stability of Ti40Zr25Ni3Cu12Be20 metallic glass. The critical cooling rate for glass formation of the studied metallic glass is determined to be as low as 3.2K/s, revealing a high glass-forming ability. The activation energies of the alloy are strongly dependent on the cooling rate during rapid solidification. Compared with the ribbon sample, the bulk sample that experiences slower cooling rate during solidification contains a greater degree of medium range orders (MRO), which favors nucleation, therefore leading to its smaller activation energies. [Copyright &y& Elsevier]

• Investigating crack-like defect from the viewpoint of oxide bifilm. • Visualizing the oxide bifilm defects by computed tomography. • Simulating and validating the formation of bifilm. The high oxidation of aluminum alloy would result in abundant oxidation defects. In recent years, bifilm has been increasingly recognized as a source of the metallurgical defects. The crack defects in aluminum alloy casting was investigated in the present work from the viewpoint of bifilm. Computed tomography has been used to image the defects in three dimensions which demonstrated the complexity of the bifilm defect. Detailed energy spectrum analysis showed that the bifilm has different compositions at different thickness. Simulations suggested that the defect is affected by flow field, thus could be eliminated by process optimization. These results would shed new lights on the understanding of the formation of bifilm defects and improve the defects control engineering of castings. [ABSTRACT FROM AUTHOR]

This study deals with the densification of a pre-alloyed TiAl powder with excessive yttrium addition by spark plasma sintering (SPS) technique. The gas-atomized Ti–43Al–5Nb–2V–1Y (at. %) powders were sintered at various temperatures between 1100 and 1250 °C, applying a uniaxial pressure of 40 MPa. The microstructures of pre-alloyed powders and SPSed TiAl alloy samples were analyzed by scanning and transmission electron microscopies. In addition, the compression tests of SPSed alloys was carried out at room temperature (RT). Attention is focused on the existing form and distribution of excess yttrium in the initial powders and the SPSed samples. The initial powder exhibits a dendrite structure, and yttrium-rich phases (YAl 2) are segregated along the interdendritic zone. After sintering, duplex, nearly lamellar (NL) and fully lamellar (FL) microstructures were obtained as a function of the sintering temperature. For duplex and NL microstructures, the YAl 2 phases are fine granular precipitates in homogeneous dispersion state. Conversely, stripe-like YAl 2 precipitates, which surround the α 2 /γ lamellar colonies, emerged in the FL microstructures. Excessive sintering temperature leads to grain growth and serious segregation of the YAl 2 phases, and it deteriorates the mechanical properties of this alloy eventually. Image 1 • TiAl alloy with excessive yttrium addition was prepared by spark plasma sintering. • Fine YAl 2 particles are dispersed in samples sintered at relatively low temperature. • Strip-like YAl 2 phases with network structure formed in FL microstructure. • The SPSed alloys with fine YAl 2 particles own better compression properties. [ABSTRACT FROM AUTHOR]

Ti–48Al–2Cr–2Nb alloy reinforced with ceramic particle Y 2 O 3 was fabricated by induction skull melting (ISM) technique in a vacuum environment. The thermodynamic feasibility of the reactions between nano Y 2 O 3 and molten alloy has been considered. The as-cast microstructure of Ti–48Al–2Cr–2Nb adding nanoY 2 O 3 during melting was analyzed by OM, SEM, EDS and TEM. It is concluded that multiple reinforcements are synthesized and they show different shapes. Y 2 O 3 grows in regular geometry shapes when the content of Y 2 O 3 is about 0.1 at. % and grows in dendritic shapes when the content of Y 2 O 3 is below 0.05 at.%. The work shows that adding nano Y 2 O 3 could refine microstructure of TiAl and improve strength and elongation of TiAl alloy effectively within a certain range. • The evolution of nanoY 2 O 3 in molten TiAl has been studied. • Diffused micron regular geometry particle was formed in the TiAl microstructure. • The TiAl has excellent room temperature strength(752 MPa) and elongation (0.75%). [ABSTRACT FROM AUTHOR]