Rod-like Phase Research Articles

Microstructure characteristics and tensile properties of multilayer Al-6061/Ti-TA1 sheets fabricated by accumulative roll bonding

In present research, Al-6061/Ti-TA1/Al-6061 multilayered sheets were prepared by accumulative roll bonding at 400℃, 450℃ and 500℃, and then the fabricated sheets were heat treated by two different heat treatment processes. As the rolling temperature increased, tensile strength and elongation increased for same cycle specimens. Heat treatment significantly improved the tensile properties. Tensile tests and interface analyses revealed that, after heat treatment (both 535℃ (1.5 h) solution + 180℃ (6 h) aging, and 560℃ (1.5 h) solution + 180℃ (6 h) aging), Al/Ti multilayers showed better strength and thicker Al-Ti bonding interface layers, which were beneficial for mechanical properties improvement. Furthermore, the rod-like β-Mg2Si phases and refined microstructure in the heat treated aluminum matrix also obviously promoted the tensile properties improvement. Compared with the 2nd cycle ARB specimens, the Ti layers were smaller in size, thinner in thickness and more uniform in distribution after the 3rd cycle ARB. Because of these factors, the tensile strength of the heat treated 3rd cycle specimens was better than the 2nd cycle specimens.

Catechins-Modified Selenium-Doped Hydroxyapatite Nanomaterials for Improved Osteosarcoma Therapy Through Generation of Reactive Oxygen Species.

Osteosarcoma is the most common bone cancer with limited therapeutic options. It can be treated by selenium-doped hydroxyapatite owing to its known antitumor potential. However, a high concentration of Se is toxic toward normal and stem cells whereas its low concentration cannot effectively remove cancer cells. Therefore, the current study was aimed to improve the anticancer activity of Se-HAp nanoparticles through catechins (CC) modification owing to their high cancer therapeutic value. The sequentially developed catechins modified Se-HAp nanocomposites (CC/Se-HAp) were characterized for various physico-chemical properties and antitumor activity. Structural analysis showed the synthesis of small rod-like single phase HAp nanoparticles (60 ± 15 nm), which effectively interacted with Se and catechins and formed agglomerated structures. TEM analysis showed the internalization and degradation of CC/Se-HAp nanomaterials within MNNG/HOS cells through a non-specific endocytosis process. Cell toxicity analysis showed that catechins modification improved the antitumor activity of Se-HAp nanocomposites by inducing apoptosis of human osteosarcoma MNNG/HOS cell lines, through generation of reactive oxygen species (ROS) which in turn activated the caspase-3 pathway, without significantly affecting the growth of human normal bone marrow stem cells (hBMSCs). qPCR and western blot analyses revealed that casp3, p53, and bax genes were significantly upregulated while cox-2 and PTK-2 were slightly downregulated as compared to control in CC/Se-HAp-treated MNNG/HOS cell lines. The current study of combining natural biomaterial (i.e., catechins) with Se and HAp, can prove to be an effective therapeutic approach for bone cancer therapy.

Mean-field model of boomerang nematic liquid crystals with diminished coupling of molecular uniaxial and biaxial susceptibilities.

The mean-field theory approach has been applied to the boomerang type particles from P.I.C. Teixeira, A. Masters, and B. Mulder [Mol. Cryst. Liq. Cryst. 323, 167 (1998)MCLCE91058-725X10.1080/10587259808048440] but with diminished strength of the interaction coefficient responsible for the coupling between molecular uniaxial and biaxial susceptibilities. For the rodlike particles, when the apex boomerang angle is larger than 107.35^{∘}, the stable uniaxial rodlike phase occurs. For smaller angles, beyond the point where the transition is of the second order (the Landau point) and for diminished parameter of molecular biaxial-uniaxial coupling, a biaxial phase is observed with the transition undergoing directly from the isotropic phase. According to the order parameters the character of this transition is of the first order. Such behavior is in accordance with the Sonnet-Durand-Virga model of the biaxial phases. The change in the type of the phase transition order is also illustrated by the changes in the equations of state and the changes in second and third derivatives of the free energy. The possibilities to tailor interaction coefficients of real molecules to obtain such a phase transition scenario are discussed.

Influence of rolling temperature on the interfaces and mechanical performance of graphene-reinforced aluminum-matrix composites

To study the influence of rolling on the interfaces and mechanical performance of graphene-reinforced Al-matrix composites, a rolling method was used to process them. Using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and tensile testing, this study analyzed the micromorphology, interfaces, and mechanical performance of the composites before and after rolling. The experimental results demonstrates that the composites after hot rolling has uniform structures with strong interfacial bonding. With an increase in rolling temperature, the tensile strength and elastic modulus of the composites gradually increase. However, when the rolling temperature is higher than 500°C, granular and rod-like Al4C3 phases are observed at the interfaces and the mechanical performance of the composites is degraded. When the rolling temperature is 480°C, the composites show the optimal comprehensive mechanical performance, with a tensile strength and elastic modulus of 403.3 MPa and 77.6 GPa, respectively, which represent increases of 31.6% and 36.9%, respectively, compared with the corresponding values prior to rolling.

An atomic-resolution investigation of precipitation evolution in Al-Mg-Ag alloys

The compositional and structural evolution of precipitates in Al-Mg-Ag alloy were investigated by atomic resolution high-angle annular dark-field scanning transmission electron microscopy. The study suggests that Ag-addition promoted the formation of elliptical- shaped GP zones at the early-aged stage. Then the GP zones transformed to metastable MgAg phase and the orientation relationship between the precipitate and Al-matrix was (1 0 0)MgAg//(1 0 0)α. The equilibrium phase in Al-Mg-Ag alloy can be speculated as rod-like body-centered cubic T phase (Mg32(Al, Ag)49) with the lattice parameter of a = 1.41 nm. The rod-like MgAg phase and T phase serve as the key strengthening mechanism of Al-Mg-Ag alloys at the peak-age stage. In addition, the role of GBPs in the strengthening effect of Al-Mg-Ag alloys was also discussed in detail.

Microstructure and mechanical properties of in-situ nano γ-Al2O3p/A356 aluminum matrix composite

In this study, the nanometer in-situ γ-Al2O3 particles reinforced aluminum matrix composites was successfully fabricated by the A356 aluminum alloy and Co3O4 powder at 850 °C by means of in-situ reaction in the high temperature melt. The effects of γ-Al2O3 particle and cobalt element on the microstructure and properties of the composites were investigated in detail. The endogenous γ-Al2O3 and cobalt could modify the coarse plate like eutectic Si into fine fibrous like and refine the second dendrite arm spacing (SDAS) of the grains simultaneously. When the content of cobalt was lower than 0.57% and content of γ-Al2O3particles was lower than 0.6 vol%, the particles distributed uniformly in the grain, however, when the particulate amount was up to 0.8 vol%, the particles would distribute at the grains boundaries or form as a rodlike phase. The grain size was sharply refined to 200 μm when the particulate content was 0.8 vol%. It was found that the ultimate tensile strength (UTS), elongation of the 0.6 vol% γ-Al2O3/A356 composites had arrived at the maximum that had enhanced by 43.6% and 85.7% in comparison to the matrix respectively, which were attributed to the homogeneous distribution of the nanoparticles, the refinement of the SDAS of the α-Al grains and the modification of the eutectic Si phases.

Effect of La2O3 on the in-situ reaction products in Al–CuO–Ti–C system

The Aluminum Matrix Composites were manufactured by in situ reactive near liquidus cast of La2O3 powder, aluminum powder, CuO powder, Ti powder, graphite powder with 6063 aluminum alloy as the matrix using the contact reaction method. The x-ray Diffraction, Differential Scanning Calorimeter, Scanning Electron Microscope and Energy Dispersive Spectroscopy were utilized to study the phase evolution and observe the morphology and distribution of the in situ products. The effect of La2O3 on the in situ reaction products in Al–CuO–Ti–C system was investigated. The results manifest that the microstructure of the in situ reaction products in the Al–CuO–Ti–C system is composed of needle-like and lath-like Al3Ti phase, nearly globular-like Al2O3 and granular-like TiC. The microstructure of the in situ reaction products in the Al–CuO–Ti–C-La2O3 system is composed of blocky-like and short rod-like Ti2Al20La phase, globular-like Al2O3 and granular-like TiC. By comparing the two systems, the addition of La2O3 eliminates the needle-like Al3Ti phase of 120 μm and the agglomerated lath-like Al3Ti phase of 50 μm, forms the blocky-like and short rod-like Ti2Al20La of under 20 μm. At the same time, it improves the agglomeration phenomenon of TiC and Al2O3 particles, making them more diffusely distributed in the matrix. The size of TiC and Al2O3 particles reduces from 1 μm to 0.5 μm and 5 μm to 1 μm, respectively.

Microstructural characterization of intermetallic phases in a solution-treated Mg–5.0Sm–0.6Zn–0.5Zr (wt%) alloy

Although Zn–Zr intermetallic phases have been frequently reported in solution-treated Mg–RE–Zn–Zr systems (RE presents rare earth), the types, crystal structures and influence on precipitation remain to be systematically investigated. In this work, the intermetallic phases formed during solution treatment in a Mg–Sm–Zn–Zr alloy were studied using transmission electron microscopy. Four types, namely the plate phase, the spindle-like phase, the nano-scale granuliform phase and the rod-like phase were revealed. Except the first one, the other three ones are Zn–Zr phase. In addition, the granuliform phase presents quadrate-shaped or lath-shaped and was identified as Zn2Zr3. However, these two Zn2Zr3 phases with different shapes follow quite different orientation relationships with Mg matrix. Furthermore, three kinds of rod-like phases were observed: one across the grain boundary but only coherent with one grain, one covered by jagged Mg3Sm precipitates and one with no surficial phase. The former twos are Zn2Zr3 while the later one is Zn2Zr. Finally, this work indicates that only the plate MgZn2 phase and the rod-like Zn2Zr3 phase in the grain interior will act as heterogeneous nucleation sites for the Mg3Sm precipitates, thus influencing the precipitation.

Microstructures, Mechanical Properties, and Corrosion Behavior of As-Cast Mg⁻2.0Zn⁻0.5Zr⁻xGd (wt %) Biodegradable Alloys.

The Mg–Zn–Zr–Gd alloys belong to a group of biometallic alloys suitable for bone substitution. While biocompatibility arises from the harmlessness of the metals, the biocorrosion behavior and its origins remain elusive. Here, aiming for the tailored biodegradability, we prepared the Mg–2.0Zn–0.5Zr–xGd (wt %) alloys with different Gd percentages (x = 0, 1, 2, 3, 4, 5), and studied their microstructures and biocorrosion behavior. Results showed that adding a moderate amount of Gd into Mg–2.0Zn–0.5Zr alloys will refine and homogenize α-Mg grains, change the morphology and distribution of (Mg, Zn)3Gd, and lead to enhancement of mechanical properties and anticorrosive performance. At the optimized content of 3.0%, the fishbone-shaped network, ellipsoidal, and rod-like (Mg, Zn)3Gd phase turns up, along with the 14H-type long period stacking ordered (14H-LPSO) structures decorated with nanoscale rod-like (Mg, Zn)3Gd phases. The 14H-LPSO structure only exists when x ≥ 3.0, and its content increases with the Gd content. The Mg–2.0Zn–0.5Zr–3.0Gd alloy possesses a better ultimate tensile strength of 204 ± 3 MPa, yield strength of 155 ± 3 MPa, and elongation of 10.6 ± 0.6%. Corrosion tests verified that the Mg–2.0Zn–0.5Zr–3.0Gd alloy possesses the best corrosion resistance and uniform corrosion mode. The microstructure impacts on the corrosion resistance were also studied.

Concurrence of spinodal decomposition and nano-phase precipitation in a multi-component AlCoCrCuFeNi high-entropy alloy

The concurrence of spinodal decomposition and nano-phase precipitation in an AlCoCrCuFeNi high-entropy alloy produced by arc melting, spray casting and melt spinning was investigated in the present work. It is shown that the present high cooling rate cannot inhibit the concurrence of spinodal decomposition and nano-phase precipitation. In the solidification and annealing process, three typical structures including Cu-rich nano-precipitates of FCC structure, Al-Ni-rich plate of B2 structure, and Fe-Cr-rich plate of A2 structure were observed; meanwhile, the width of modulated plate decreased with the increase of the cooling rate. An interesting phenomenon was observed in the as-annealed microstructure that Al-Ni and Fe-Cr spinodal plates were weakened or vanished rather than strengthened, due to the atom diffusion and composition homogenization. Different from spinodal decomposition plates, the Cu-rich nano-precipitates grew into rod-like phase from point-like or oval phase in the whole process. The intersection angle of newborn rod-like nano-phases tended to 60°, following the K-S crystallographic relationship.

Improved strengthening efficiency of nanoreinforcements realized by a novel melt spinning process

Abstract

Effect of the morphology of long-period stacking ordered phase on mechanical properties and corrosion behavior of cast Mg-Zn-Y-Ti alloy

In this study, three different morphologies of long-period stacking ordered (LPSO) phase, i.e. lamellar, block-like, and rod-like, were obtained through various heat treatment processes. The effect of the morphology of LPSO phase on mechanical properties and corrosion behavior of cast Mg-Zn-Y-Ti alloy was investigated accordingly. The results suggested that the block-like LPSO phases in the as-cast alloy transformed into the rod-like LPSO phases during heat treatment at high temperature, while the low temperature was conducive to the precipitation of lamellar phases in the grain interior. The formation of the rod-like LPSO phases resulted in an increase of 42% in elongation while maintaining a high tensile strength. In addition, the alloys with the rod-like LPSO phases exhibited more uniform corrosion mode and better corrosion resistance than the alloys with the block-like LPSO phases, so the former had excellent comprehensive properties. The precipitation of the lamellar LPSO phases not only reduced the mechanical properties, but also accelerated the corrosion rate and produced severe localized corrosion. Therefore, the mechanical properties and corrosion resistance of the alloys could be improved by regulating the morphology of LPSO phases.

Photocatalytic enamel/TiO2 coatings developed by electrophoretic deposition for methyl orange decomposition

The aim of this study was to obtain photocatalytic coatings, capable to decompose organic pollutants, through Electrophoretic Deposition (EPD) of enamels containing respectively 0%, 5%, 10%, 15% (in wt%) of TiO2 onto carbon steel substrates. High quality and homogeneous coatings were obtained by applying 12.5 V during 10 s, as the best EPD conditions. The layers were subsequently heat treated at 740 °C for 10 min, in order to obtain dense glazes.Rietveld refinement of XRD patterns and Raman results show that, after the heat treatment at 740 °C, TiO2 mostly exists as anatase, responsible of the photocatalytic effect. Semi-quantitative chemical analysis indicate segregation of TiO2 on the coatings surface, reaching saturation in the sample with 10 wt% TiO2. FEG-SEM observations reveal rod-like and spherical Ti-rich phases along the cross section of the coatings; some Ti was also dissolved into the enamel. 3D topographical mapping shows that, by adding TiO2, surface roughness increases significantly.Photocatalytic tests were carried out using a 2 × 10−5 M aqueous solution of Methyl Orange (MO) as an organic pollutant. By comparing the decomposition rate of MO achieved with the pure enamel (0% of TiO2) and with the sample with 10% of TiO2, it was shown that the addition of 10% of TiO2 results in 90% photocatalytic efficiency.Moreover, the permeation of organic compounds and their UV degradation were studied by measuring the water contact angle onto the enamel surface directly after dipping into oleic acid and after various UV irradiation times. The longer the UV irradiation time, the lower the contact angle, down to a minimum of 14.54° after 8 h of UV irradiation. This means, the compound was initially adsorbed on the enamel/TiO2 coating surface (10 wt% TiO2) but was efficiently decomposed upon UV irradiation.

Peritectic reaction between two primary Mn-rich phases during solidification of Al-Si-Cu-Mn heat-resistant alloy and the effect of cooling rate on it

In order to demonstrate the transformation relation of two primary Al13Mn4Si8 and Al15Mn3Si2 phases during solidification of Al-12Si-4Cu-2Mn (in wt%) alloy, verification experiments through controlling cooling rate of solidification and quenching at different stages during solidification were designed and the microstructure was characterized by optical microscope, scanning electron microscope and transmission electron microscope. The cooling rate during solidification plays a decisive role in the formation of primary Mn-rich phases. Fast cooling rate favors the slender rod-like Al13Mn4Si8 phase and slow cooling rate leads to the formation of dendritic Al15Mn3Si2 phase.A great number of symbiotic complexes, constituted with inner Al13Mn4Si8 and outer Al15Mn3Si2 phases, are found in the transition area of the surface and center of the casting with a middle cooling rate. Microstructure observation of the liquid quenching samples demonstrates that the first phase formed during solidification must be 2D lath-like Al13Mn4Si8 phase whether with high cooling rate or with slow cooling rate. And 3D dendritic Al15Mn3Si2 phase is transformed from 2D Al13Mn4Si8 by a peritectic reaction: L+ Al13Mn4Si8→All5Mn3Si2, which is dependent of the cooling rate during solidification. A schematic model with double nose curves was established to exhibit the influence of cooling rate on the peritectic reaction. With sufficient high cooling rate, this peritectic reaction will be suppressed completely. When the cooling rate is slow enough, the peritectic reaction will proceed completely. However, in case of middle rate, the peritectic reaction will happen but incompletely.

The reaction mechanism analysis and mechanical properties of large-size Al2O3/ZrO2 eutectic ceramics prepared by a novel combustion synthesis

Large-size Al2O3/ZrO2 eutectic ceramics (Φ53 × 75 mm) were successfully fabricated based on the exothermic reaction between Al and Zr(NO3)4 via a novel combustion synthesis under low pressure. The reaction mechanism was analyzed using the thermodynamics method. In the reaction process, the intermediate products of AlN were partially converted into ZrN phase, and the remaining AlN phase decomposed into nitrogen. The Al2O3/ZrO2 composite materials with 85.74 vol% eutectic were obtained with the mole ratio of ZrO2:Al2O3 reached 0.9:1. The rod-like ZrO2 phase with a diameter ~ 268 nm was in-situ embedded in Al2O3 phase; the average eutectic interspacing is ~ 183 nm, and the average width of grain boundary is 520 nm. The hardness and fracture toughness of Al2O3/ZrO2 eutectic ceramics are 17.8 GPa and 10.6 MPa m1/2, respectively. The excellent mechanical properties are ascribed to the fine microstructure and special phase composition.

PH-sensitive release of insulin-loaded mesoporous silica particles and its coordination mechanism

In this work, we investigated the feasibility of employing metal ion that coordinated with amino group grafted mesoporous silica as a pH-sensitive release carrier of insulin. Mesoporous silica particles were firstly grafted with amino groups. After coordination of metal ions onto the surface of mesoporous pore, insulin was loaded onto mesoporous silica particles through coordination bonds with metal ions. Insulin-loaded mesoporous silica particle with an acid sensitivity between the pH range of physiological environment (pH 7.4) and diabetic acidosis (pH 7.0) and with an insulin encapsulation rate of 74.50% was identified by investigating the influence factors of pH response value. The morphology of particles was confirmed by different analytical methods, indicating that insulin-loaded mesoporous silica particles maintained the rod-like and orderly hexagonal phase mesoporous structure. The coordination mechanism results showed that half of the amino groups on the carrier were coordinated with Cu2+, and insulin was successfully coordinated with Cu2+ without any damage on the secondary structure. The amount of insulin coordination with Cu2+ was positively correlated with the pH of the reaction solution. The cytotoxicity result shows that SBA15-NH2-Cu2+-Ins was biocompatible with cells in the concentration ranging from 25 to 100 μg·mL−1. In vivo study preformed on rats showed that the insulin-loaded particles elicited a period hypoglycemic response. Furthermore, fluorescence and UV methods revealed that insulin-loaded mesoporous silica particles had no significant effect on the secondary structure of serum albumin.

Interfacial evolution in Sn–58Bi solder joints during liquid electromigration

For Sn–58Bi low temperature solder alloy, local molten induced from electromigration Joule heating might change the atomic diffusion and interfacial behavior. In this paper, the diffusion behavior and interfacial evolution of Cu/Sn–58Bi/Cu joints were studied under liquid–solid (L–S) electromigration in molten solder and were compared with the interfacial behaviors in solid–solid (S–S) electromigration in solid solder. L–S or S–S electromigration was realized by applying a current density of 1.0 × 104 A/cm2 to molten solder at 150 °C or solid solder at 25 °C, respectively. During S–S electromigration, Bi atoms were driven towards anode side under electromigration induced flux and then accumulated to form Bi-rich layer near anode interface with current stressing time increasing. During L–S electromigration, Bi atoms were reversely migrated from anode to cathode to produce Bi segregation at cathode interface, while Cu atoms were rapidly dissolved into molten solder from cathode and migrated to form large amounts of Cu6Sn5 rod-like phases near anode interface. The reversal in the direction of Bi atoms may be attributed to the reversal in the direction of electromigration induced flux and correspondingly the change on effective charge number of Bi atoms from negative to positive.

Microstructural characterization of Ni-based self-fluxing alloy after selective surface-engineering using diode laser

The microstructural characterization of thermal-sprayed Ni-based self-fluxing alloy (Metco-16C®) after laser-assisted homogenization treatment was performed. To this end, a high-power diode laser system was used. This supported the real-time control of the target homogenization temperature at the substrate surface. Non-homogeneities of the macrosegregation of certain elements (C and Cu) and the local concentration of Cr-based carbides and borides in certain regions in the as-sprayed state could be enhanced with the application of homogenization. After homogenization at 1423 K, the hardness of the thermal-sprayed layer was found to have increased by 1280 HV from the as-sprayed state (750 HV). At this homogenization temperature, the microstructure of the thermal-sprayed layer consisted of a lamellar structuring of the matrix phase (austenite and Ni3Si) with fine (<5 μm) carbides and borides (the rod-like phase of Cr5B3, the lumpy phase of M23C6, and the extra-fine phase of M7C3). Despite the formation of several kinds of carbides and borides during homogenization at 1473 K, the lowest hardness level was found to be less than that of the as-sprayed state, because of the liquid-state homogenization treatment without formation of lamellar structuring between austenite and Ni3Si.

Determination of Three-Dimensional Morphology and Inner Structure of Second-Phase Inclusions in Metals by Non-Aqueous Solution Electrolytic and Room Temperature Organic Methods

The secondary-phase particles in metals, particularly those composed of non-metallic materials, are often detrimental to the mechanical properties of metals; thus, it is crucial to control inclusion formation and growth. One of the challenges is determining the three-dimensional morphology and inner structures of such inclusions. In this study, a non-aqueous solution electrolytic method and a room-temperature organic technique were developed based on the principle of electrochemistry to determine the three-dimensional morphologies and inner structures of non-metallic inclusions in Al-killed steel, Si-killed steel, and ductile cast iron. The inclusions were first extracted without any damage to the inclusions, and then the collected inclusions were wrapped and cut through Cu ion deposition. The results revealed that the inclusions in Al-killed steel had an irregular morphology, that those in the Si-killed steel were mainly spherical, and that almost all the spheroidal graphite in the ductile cast iron featured a uniform globular morphology. In addition, nucleation was not observed in the inner structures of the inclusions in the Al-killed steel, while some dendritic or rod-like MnS phase precipitates appeared on the silicate inclusion surfaces, and some silicate-rich phases were detected in their inner matrix. For spheroidal graphite, rare-earth oxides (one particle or more) were observed as nuclei in the center of almost every graphite particle. The formation and evolution of inclusions in these types of metals can be better understood by means of the two developed methods.

Deformation and heat treatment ability of three-layer 6009/7050/6009 Al alloy clad slab prepared by direct-chill casting

Abstract Three-layer 6009/7050/6009 aluminum alloy clad slab was fabricated by an innovative direct-chill casting process. To study the response of the clad slab to plastic deformation and heat treatments, homogenization annealing, hot rolling, solution and aging were successively performed on the as-cast 6009/7050/6009 clad samples. The results revealed that excellent metallurgical bonding between 7050 alloy layer and 6009 alloy layer was achieved under optimal parameters. The clad ratio obviously decreased when the annealed sample was rolled to 55% hot reduction level, and then changed slightly with further rolling. Furthermore, the content of rodlike Zn-rich phases increased significantly in 7050 alloy layer in the homogenized clad samples after rolling at 55%, 65% and 75% hot reduction levels, and the higher level of hot reduction resulted in narrower diffusion layer. Subsequent solution and aging significantly improved the hardness in 7050 alloy layer, interfaces and 6009 alloy layers of the rolled samples except for the thin side for the 75% hot reduction sample.