High yield strength bulk Ti based bimodal ultrafine eutectic composites with enhanced plasticity

Ti-based bulk metallic glass (BMGs) and their bimodal composites are linked with the pronounced strain hardening after yielding but with much low value of strength. Therefore, developing Ti-based alloys with high yield strength and high plasticity is the current challenge. Here, we report the synthesis of ultra-fine grained bulk (UFG) (Ti_0.705Fe_0.295)_100−xGa_x (0 ⩽ x ⩽ 2) bimodal eutectic composites with not only high strength and larger plasticity but also with high yield strength which is one of the important mechanical property for structural application. Reasonably high strength, high yield strength, strain to failure ratio, and enhanced plasticity of ∼7 ± 0.8% was observed in (Ti_70.5Fe_29.5)₉₈Ga₂ composite which is superior than Ti-based BMGs and bimodal composites. Modification of degree of eutectic structure refinement and volume fraction of constituent phases with the addition of Ga are the crucial factors in enhancing the mechanical properties of Ti–Fi–(Ga) composites.     

Influence of the impact sintering temperature on the structure and properties of samples from the different iron powders

The studies of the consolidation, structure and mechanical properties of samples from two types of iron powder are carried out. The coarse and less pure PZH3M2 as well as fine and purer DIAFE5000 powders were used. The samples are obtained by means of impact sintering method in the temperatures range of 500–1100 °C. The impact energy was 1200 J/cm³, and the initial deformation velocity - 6.5 m/s. Samples are obtained in the form of disks with a diameter of 25–27 mm and 9–10 mm high. For carrying out different mechanical tests the bars were cut out from disks. The tensile, compression, three-point bend of notched samples tests were carried out, as well as the Brinell hardness was measured after the corresponding processing of the bars. The characteristics of strength and plasticity of samples depending on the impact sintering temperature are determined. The polished surface of different samples and the fracture surface are investigated. It is established that the high density of samples is reached at a temperature of 600 and 700 °C respectively for fine and coarse powders. The samples obtained at these impact sintering temperatures possess rather low electrical resistivity, high strength, hardness, but the lowered plasticity. Namely, the samples from the PZH3M2 and DIAFE5000 powders sintered at the temperature of 700 °C have respectively: ultimate tensile strength - 406 and 336 MPa, yield stress - 353 and 190 MPa, contraction ratio - 26 and 78%, limit stress (at the fracture) - 501 and 933 MPa, the maximum crack tip stress – 738 and 876 MPa, the fracture energy at a bend of the notched samples - 4.8 and 51.2 J/cm³ and also Brinell hardness - 1467 and 847 MPa. The increase of the samples impact sintering temperature leads to grain growth, decrease of the samples strength and increase of their plasticity. At the same time the structure of samples from the DIAFE5000 powder is more fine-grained than at samples from the PZH3M2 powder.     

Simulations of deformation and damage processes of SiCp/Al composites during tension

The deformation, damage and failure behaviors of 17 vol.% SiCp/2009Al composite were studied by microscopic finite element (FE) models based on a representative volume element (RVE) and a unit cell. The RVE having a 3D realistic microstructure was constructed via computational modeling technique, in which an interface phase with an average thickness of 50 nm was generated for assessing the effects of interfacial properties. Modeling results showed that the RVE based FE model was more accurate than the unit cell based one. Based on the RVE, the predicted stress-strain curve and the fracture morphology agreed well with the experimental results. Furthermore, lower interface strength resulted in lower flow stress and ductile damage of interface phase, thereby leading to decreased elongation. It was revealed that the stress concentration factor of SiC was ～2.0: the average stress in SiC particles reached ～1200 MPa, while that of the composite reached ～600 MPa.     

Selective laser sintering of β-TCP/nano-58S composite scaffolds with improved mechanical properties

Nano-sized 58S bioactive glass (nano-58S) as the dispersed phase was added to β-tricalcium phosphate (β-TCP) to reinforce the mechanical properties, and then the β-TCP/nano-58S composite scaffolds were prepared via selective laser sintering (SLS). The effects of nano-58S on microstructure, mechanical properties, bioactivity, and biocompatibility of the composite scaffolds were evaluated. The results showed that nano-58S was homogeneously dispersed in the β-TCP matrix and the mechanical properties were gradually improved when the amount of nano-58S was no more than a certain value (15 wt.%). However, exceeding this value, nano-58S became the continuous phase and exhibited the brittleness of bioactive glass. Accordingly, the mechanical properties gradually decreased. The maximum fracture toughness and compressive strength were 1.347 ± 0.025 MPa · m^1/2 and 18.2 ± 0.62 MPa, respectively. In vitro tests in the simulated body fluid (SBF) demonstrated that the apatite-like layer formed faster on the composite scaffolds than on the scaffold without nano-58S, indicating that the nano-58S glass could enhance the bioactivity of the composite scaffolds. The MG-63 cells culture experiment proved that nano-58S glass could further facilitate the growth of human osteoblastic cells.     

Quantitative analysis on friction stress of hot-extruded AZ31 magnesium alloy at room temperature

Mg alloy AZ31 with ～79% (volume fraction of scattering less than 30°) basal-fiber texture through hot extrusion exhibits strong grain-size dependent yield strength. Samples with grain sizes varying from 4.5 to 22.3 μm were obtained by altering annealing time durations. The Hall-Petch relations of tension and compression are σ_0.2 = 86+200d^?1/2 and σ_0.2 = 17 + 327d^?1/2, respectively. Considering the correlation between grain orientation and deformation modes, a novel weighted average method of calculating friction stress σ₀ was proposed, and results of calculation agreed with the experimental ones, which can reasonably understand the yielding behavior in tension and compression.     

Synthesis of hydroxysodalite zeolite by alkali-activation of basalt powder rich in calc-plagioclase

Hydroxysodalite (H-SOD) microcrystalline particles were synthesized from basalt powder rich in calcic-plagioclase (anorthite) by alkali activation at 80 °C/24 h. Sodium hydroxide (NaOH) solution was used as alkaline activator. The reactivity of the natural solid precursor basalt was studied using differential scanning calorimetry (DSC), and a maximum reaction enthalpy of (?ΔH) of 170 J/g was obtained. The chemical, mineralogical, and textural properties were obtained by using X-ray powder diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and N₂-adsorption-desorption measurements. The synthesized material has a specific BET surface area of 20.5 m² g^?1 approximately 200 times higher than raw basalt material (0.1 m² g^?1). The compressive strength of basalt based H-SOD/sand composite samples cured at 80 °C for 24 h upon using different amounts of the activator (NaOH) was evaluated under dry and saturated conditions. The dry samples with NaOH/basalt mass ratio of 0.12 have reached a compressive strength of 57 MPa. Wet samples, on the other hand, showed a compressive strength of 25 MPa after seven days of soaking in water and four episodes of wetting and drying. The present work illustrates that crystalline H-SOD could be synthesized from cheap basalt powder precursor.     

Strengthening mechanisms in magnesium alloys containing ternary I,W and LPSO phases

This study was aimed at identifying underlying strengthening mechanisms and predicting the yield strength of as-extruded Mg-Zn-Y alloys with varying amounts of yttrium (Y) element. The addition of Y resulted in the formation of ternary I (Mg₃YZn₆), W (Mg₃Y₂Zn₃) and LPSO (Mg₁₂YZn) phases which subsequently reinforced alloys ZM31 + 0.3Y, ZM31 + 3.2Y and ZM31 + 6Y, where the value denoted the amount of Y element (in wt%). Yield strength of the alloys was determined via uniaxial compression testing, and grain size and second-phase particles were characterized using OM and SEM. In-situ high-temperature XRD was performed to determine the coefficient of thermal expansion (CTE), which was derived to be 1.38 × 10^?5 K^?1 and 2.35 × 10^?5 K^?1 for W and LPSO phases, respectively. The individual strengthening effects in each material were quantified for the first time, including grain refinement, Orowan looping, thermal mismatch, dislocation density, load-bearing, and particle shearing contributions. Grain refinement was one of the major strengthening mechanisms and it was present in all the alloys studied, irrespective of the second-phase particles. Orowan looping and CTE mismatch were the predominant strengthening mechanisms in the ZM31 + 0.3Y and ZM31 + 3.2Y alloys containing I and W phases, respectively, while load-bearing and second-phase shearing were the salient mechanisms contributing largely to the superior yield strength of the LPSO-reinforced ZM31 + 6Y alloy.     

Fabrication and characterization of novel biodegradable Zn-Mn-Cu alloys

Zn-Mn-Cu alloys with micro-alloying of Mn and Cu in Zn are developed as potential biodegradable metals. Although the as-cast alloys are very brittle, their ductilities are significantly improved through hot rolling. Among the as-cast and the as-hot-rolled alloys, as-hot-rolled Zn-0.35 Mn-0.41 Cu alloy has the best comprehensive property. It has yield strength of 198.4 ± 6.7 MPa, tensile strength of 292.4 ± 3.4 MPa,elongation of 29.6 ± 3.8% and corrosion rate of 0.050-0.062 mm a~(-1). A new ternary phase is characterized and determined to be MnCuZn18, which is embedded in MnZn13, resulting in a coarse cellular/dendritic MnZn13-MnCuZn18 compound structure in Zn-0.75 Mn-0.40 Cu alloy. Such a coarse compound structure is detrimental for wrought alloy properties, which guides future design of Zn-Mn-Cu based alloys.The preliminary research indicates that Zn-Mn-Cu alloy system is a promising candidate for potential cardiovascular stent applications.     

Microstructure correlated electrical conductivity of Manganese alloyed nanocrystalline cubic zirconia synthesized by mechanical alloying

Fully stabilized cubic (c) ZrO₂ phase has been synthesized by mechanical alloying (MA) the stoichiometric powder mixture of elemental Mn (5–20 mol%) and monoclinic (m) ZrO₂ at room temperature. XPS study reveals that major part of metallic Mn is ionized to Mn²⁺ oxidation state during MA. Mn-alloyed c-ZrO₂ nanoparticles with ～18 nm particle size have been synthesized within 10 h of MA. Microstructures of the compounds have been precisely evaluated by analyzing the X-ray powder diffraction patterns employing Rietveld refinement and transmission electron microscopy images. A decrease in lattice parameter from 5.11 Å to 5.09 Å is correlated with an increase in oxygen vacancy from 14% to 26% with increasing Mn concentrations. Elemental compositions in the compounds are obtained from electron probe microanalysis. The role of Mn alloying in the polymorphic phase transformation (m → c) has been established with changes in structure and microstructure parameters. Electrical conductivities of all c-ZrO₂ compounds are measured in the temperature range 350–550 °C. Grain and grain boundary contributions to total conductivity are calculated from frequency dependent real and imaginary impedance. Conductivity of Mn alloyed c-ZrO₂ increases with increasing temperature and Mn concentrations. Electrical transport mechanism in the compound is studied by impedance and modulus spectroscopy. The relaxation frequency is found to be temperature, microstructure and composition dependent.     

Thermoplastic micro-formability of TiZrHfNiCuBe high entropy metallic glass

High entropy metallic glasses (MGs) have attracted tremendous attentions owing to high entropy that benefits the probing of new MG-forming systems. However, the micro-formability of high entropy MGs is lack of investigation in comparison with these conventional MG counterparts, which is crucial to the development of this kind of metallic alloys. In this work, the thermoplastic mciro-formability of TiZrHfNiCuBe high entropy MG was systemically investigated. Time-Temperature-Transformation (TTT) curve was first constructed based on isothermal crystallization experiments, which provides thermoplastic processing time of the supercooled high entropy MGs. By comparison with the deformation map, Newtonian flow was found beneficial to the thermoplastic formability. While the thermoplastic forming becomes arduous with reducing mould size to tens micrometer, because of the strong supercooled TiZrHfNiCuBe high entropy MG (fragility = 27). Fortunately, the micro-formability of TiZrHfNiCuBe high entropy MG could be improved by vibration loading, as demonstrated by finite-element-method simulation. Our findings not only systemically evaluate the thermoplastic micro-formability of high entropy MG, but also provide fundamental understanding of the phenomenon.     

A novel water permeable geopolymer with high strength and high permeability coefficient derived from fly ash,slag and metakaolin

In this work, a new water permeable geopolymer with high strength and high water permeability coefficient based on fly ash-slag-metakaolin was proposed. The experimental results show that fresh geopolymer composite exhibits dry characteristic and porous structure. The void ratio is 27.6% and the permeability coefficient reaches 1.70 cm/s. The compressive strength and flexural strength reach about 30 MPa and 6.2 MPa, respectively at 1 day and reach as high as 49 MPa and 11.3 MPa at 28 days of curing, respectively. After 100 freeze-thaw cycles, the terminal remaining mass is still larger than 80% along with internal damages and deteriorations on geopolymer paste coating. The dense microstructure of geopolymer matrix and interfacial transition zone indicates the high compressive strength, flexural strength and high freeze-thaw resistance of water permeable geopolymer.     

CeO2-Cu2O composite nanofibers: Synthesis,characterization photocatalytic and electrochemical application

The present study describes fabrication and electrochemical classification of one-dimensional CeO₂-Cu₂O nanofibers for photocatalysis and supercapacitor application. The utilized CeO₂-Cu₂O composite was prepared by sol–gel electrospinning method using Polyvinylpyrrolidone (PVP), Ce(NO₃)₃?6H₂O and Cu(CH₃COO)₂ as precursors. The physicochemical properties of the synthesized samples were characterized using special characterization approaches such as X-ray diffractometer (XRD), energy dispersive X-ray analysis (EDX), electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). As compared to pristine CeO₂, the UV–vis spectrum of CeO₂-Cu₂O composite exhibited the absorption peak which shifted to higher wavelength. The photocatalytic activity results indicated the substantial degradation of MB dye by ～92% over the surface of CeO₂-Cu₂O nanocomposite catalyst under visible light illumination. The CeO₂-Cu₂O composite possessed higher photocatalytic activity and electrochemical capacitance than the pristine samples as supercapacitor electrode materials. The CeO₂-Cu₂O composite exhibits a specific capacitance of 329.64 F g^?1 at 5 mV s^?1, which is higher than that of the pristine CeO₂ (192.5 F g^?1) nanofibers. These results suggest the applicability of fabricated composite nanofibers as visible light active photocatalyst and as electrode material for supercapacitors.     

Design and preparation of gradient graphite/cermets self-lubricating composites

Based on the functionally graded materials (FGMs) design concept, the laminated-graded graphite/cermets self-lubricating composite was prepared to achieve the integration of mechanical properties and lubrication performance of the cermet. The effects of the layer number and thickness of graded structure on residual stresses in the gradient composites were investigated by finite element method (FEM). From the FEM analyses, the optimal gradient structure design was obtained corresponding to the following parameters: the number of graded layers n = 2 and the thickness of graded structure t = 1 mm. According to the optimum design, a graded graphite/cermets self-lubricating material with two layers was fabricated by a typical powder metallurgy technique. Compared with the homogenous graphite/cermets composite, the surface hardness and indentation fracture toughness of graded composite were increased by approximately 15.9% and 6.3%, respectively. The results of X-ray diffraction (XRD) stress measurement identified the existence of residual compressive stress on the surface of graded composite. Additionally, the friction and wear tests revealed that the wear resistance of the graphite/cermets self-lubricating composite was improved significantly via the graded structural design, whereas the coefficient of friction changed slightly.     

Strain rate dependent plastic mutation in a bulk metallic glass under compression

This paper reported a strain rate dependent plasticity in a Zr-based bulk metallic glass (BMG) under axial compression over a strain rate range (1.6 × 10⁻⁵–1.6 × 10⁻¹ s⁻¹). The fracture strain decreased with increasing strain rate up to 1.6 × 10⁻³ s⁻¹. A “brittle-to-malleable” mutation occurred at strain rate of 1.6 × 10⁻² s⁻¹, subsequently, the macro plasticity vanished at 1.6 × 10⁻¹ s⁻¹. It is proposed that the result is strongly related to the combined action of the applied strain rate, the compression speed, and the propagating speed of the shear band. When the three factors coordinated in the optimal condition, multiple mature shear bands were initiated simultaneously to accommodate the applied strain, which propagated through the specimen and distributed homogeneously in space, dominating the overall plastic deformation by consuming the entire specimen effectively.     

Metallic glass–steel composite with improved compressive plasticity

A Zr_52.5Cu₁₈Ni_14.5Al₁₀Ti₅ bulk metallic glass toughened with a commercially available spring-shaped steel wire has been produced by centrifugal casting. The addition of the steel spring significantly affects shear band nucleation and propagation through the blockage, deflection and multiplication of shear bands at the glass–spring interface. As a result of the more homogeneous distribution of the plastic strain, the room temperature plasticity increases from 0.9% for the monolitic glass to about 4% for the glass–spring composite. Given the low volume fraction of the spring used in the composite (4.2 vol.%), these results demonstrate the extreme effectiveness of the steel spring for improving the plasticity of the metallic glass.     

Influence of size and distribution of W phase on strength and ductility of high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca alloy processed by indirect extrusion

A high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca(wt%) alloy containing W phase(Mg_3Y_2Zn_3) prepared by permanent mold direct-chill casting is indirectly extruded at 350?C and 400?C, respectively. The extruded alloys show bimodal grain structure consisting of fine dynamic recrystallized(DRXed) grains and unrecrystallized coarse regions containing fine W phase and β2' precipitates. The fragmented W phase particles induced by extrusion stimulate nucleation of DRXed grains, leading to the formation of fine DRXed grains, which are mainly distributed near the W particle bands along the extrusion direction. The alloy extruded at 350?C exhibits yield strength of 373 MPa, ultimate tensile strength of 403 MPa and elongation to failure of 5.1%. While the alloy extruded at 400?C shows lower yield strength of 332 MPa,ultimate tensile strength of 352 MPa and higher elongation to failure of 12%. The mechanical properties of the as-extruded alloys vary with the distribution and size of W phase. A higher fraction of DRXed grains is obtained due to the homogeneous distribution of micron-scale broken W phase particles in the alloy extruded at 400?C, which can lead to higher ductility. In addition, the nano-scale dynamic W phase precipitates distributed in the un DRXed regions are refined at lower extrusion temperature. The smaller size of nano-scale W phase precipitates leads to a higher fraction of un DRXed regions which contributes to higher strength of the alloy extruded at 350?C.     

High damping NiTi/Ti3Sn in situ composite with transformation-mediated plasticity

The concept of transformation-induced plasticity effect is introduced in this work to improve the plasticity of brittle intermetallic compound Ti₃Sn, which is a potent high damping material. This concept is achieved in an in situ NiTi/Ti₃Sn composite. The composite is composed of primary Ti₃Sn phase and (NiTi + Ti₃Sn) eutectic structure formed via hypereutectic solidification. The composite exhibits a high damping capacity of 0.075 (indexed by tan δ), a high ultimate compressive strength of 1350 MPa, and a large plasticity of 27.5%. In situ synchrotron high-energy X-ray diffraction measurements revealed clear evidence of the stress-induced martensitic transformation (B2 → B19′) of the NiTi component during deformation. The strength of the composite mainly stems from the Ti₃Sn, whereas the NiTi component is responsible for the excellent plasticity of the composite.     

Properties of sintered glass-ceramics prepared from plasma vitrified air pollution control residues

Air pollution control (APC) residues, obtained from a major UK energy from waste (EfW) plant, processing municipal solid waste, have been blended with silica and alumina and melted using DC plasma arc technology. The glass produced was crushed, milled, uni-axially pressed and sintered at temperatures between 750 and 1150 °C, and the glass-ceramics formed were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mechanical properties assessed included Vickers's hardness, flexural strength, Young's modulus and thermal shock resistance. The optimum sintering temperature was found to be 950 °C. This produced a glass-ceramic with high density (～2.58 g/cm³), minimum water absorption (～2%) and relatively high mechanical strength (～81 ± 4 MPa). Thermal shock testing showed that 950 °C sintered samples could withstand a 700 °C quench in water without micro-cracking. The research demonstrates that glass-ceramics can be readily formed from DC plasma treated APC residues and that these have comparable properties to marble and porcelain. This novel approach represents a technically and commercially viable treatment option for APC residues that allow the beneficial reuse of this problematic waste.     

Deformation behavior of a Ti-based bulk metallic glass composite with excellent cryogenic mechanical properties

Excellent mechanical properties as high as 2760 MPa fracture strength and 18.4% plastic strain are obtained in Ti₄₈Zr₂₀Nb₁₂Cu₅Be₁₅ bulk-metallic-glass (BMG) composite at cryogenic temperature (77 K). The novel cryogenic plasticity of present composite is determined by good cryogenic plasticity of dendrites induced effective interaction between dendrites and shear bands. Improved cryogenic yield strength of dendrites is responsible for the increase of cryogenic yield strength of the present composite. Continuous matrix other than the dendrites is believed to initiate the fracture behavior. This finding demonstrates that in situ dendrite-reinforced BMG composites can be a kind of promising materials for low-temperature applications.     

Tensile,creep behavior and microstructure evolution of an as-cast Ni-based K417G polycrystalline superalloy

The Ni-based K417G superalloy is extensively applied as aeroengine components for its low cost and good mid-temperature (600–900 °C) properties. Since used in as-cast state, the comprehensive understanding on its mechanical properties and microstructure evolution is necessary. In the present research, the tensile, creep behavior and microstructure evolution of the as-cast K417G superalloy under different conditions were investigated. The results exhibit that tensile cracks tend to initiate at MC carbide and γ/γ′ eutectic structure and then propagate along grain boundary. As the temperature for tensile tests increases from 21 °C to 700 °C, the yield strength and ultimate tensile strength of K417G superalloy decreases slightly, while the elongation to failure decreases greatly because of the intermediate temperature embrittlement. When the temperature rises to 900 °C, the yield strength and ultimate tensile strength would decrease significantly. The creep deformation mechanism varies under different testing conditions. At 760 °C/645 MPa, the creep cracks initiate at MC carbides and γ/γ′ eutectic structures, and propagate transgranularly. While at 900 °C/315 MPa and 950 °C/235 MPa, the creep cracks initiate at grain boundary and propagate intergranularly. As the creep condition changes from 760 °C/645 MPa to 900 °C/315 MPa and 950 °C/235 MPa, the γ′ phase starts to raft, which reduces the creep deformation resistance and increases the steady-state deformation rate.