Na partitioning during thermomechanical processing of an Mg-Sn-Zn-Na alloy

Microstructural characterization was used to examine the changes that occur in an Mg-6Sn-5Zn-0.3Na alloy from casting to extrusion at either 623 K or 723 K (350 _C or 450 _C) followed by artificial aging at 473 K (200 _C). In particular, the partitioning of Na was examined at each step using STEM-EDS mapping. Na atoms were found to preferentially partition to the Mg-Zn phase when present. After extrusion, when no Mg-Zn was observed, the spherical Mg2Sn particles were found to be enriched in Na, particularly at the higher extrusion temperature. Artificial aging following extrusion resulted in a change in Na partitioning, and a coarse distribution of Mg-Zn precipitate rods. Na microadditions led to a high as-extruded hardness, but a significant tension–compression yield asymmetry was still observed at room temperature. The compressive yield strength was found to decrease significantly after 1000 hours of aging.

Recrystallization kinetic behavior of copper-bearing strip cast steel

In the present study, copper-bearing low carbon steels were produced by direct strip casting (DSC) method on a pilot scale. The effects of copper on mechanical, microstructural, and recrystallization behavior were investigated. As-cast microstructure mainly consists of polygonal ferrite and Widmanstatten ferrite. The increase in Cu increases the amount of Widmanstatten ferrite and induces the formation of bainite in the as-cast condition. It was found that copper increases strength and hardness by solid solution strengthening, grain refinement, and precipitation hardening and the increment is significant above 1% Cu in as-cast condition. Six different compositions were selected for recrystallization study. All the samples were cold rolled to 70% reduction and annealed at three different temperatures, 600, 650, and 700°C for various times. Recrystallization responses were strongly dependent on initial microstructure and Cu content and the effect is dramatic between 1 and 2% Cu. Recrystallization time and temperature were found to be increased with increase in copper content.

A concrete certificateless signature scheme without pairings

Certificateless public key cryptography was introduced to avoid the inherent key escrow problem in identity-based cryptography, and eliminate the use of certificates in traditional PKI. Most cryptographic schemes in certificateless cryptography are built from bilinear mappings on elliptic curves which need costly operations. Despite the investigation of certificateless public key encryption without pairings, certificateless signature without pairings received much less attention than what it deserves. In this paper, we present a concrete pairing-free certificateless signature scheme for the first time. Our scheme is more computationally efficient than others built from pairings. The new scheme is provably secure in the random oracle model assuming the hardness of discrete logarithm problem.

Effect of sorghum flour addition on in vitro starch digestibility, cooking quality and consumer acceptability of durum wheat pasta

Whole grain sorghum is a valuable source of resistant starch and polyphenolic antioxidants and its addition into staple food like pasta may reduce the starch digestibility. However, incorporating nondurum wheat materials into pasta provides a challenge in terms of maintaining cooking quality and consumer acceptability. Pasta was prepared from 100% durum wheat semolina (DWS) as control or by replacing DWS with either wholegrain red sorghum flour (RSF) or white sorghum flour (WSF) each at 20%, 30%, and 40% incorporation levels, following a laboratory-scale procedure. Pasta samples were evaluated for proximate composition, in vitro starch digestibility, cooking quality, and consumer acceptability. The addition of both RSF and WSF lowered the extent of in vitro starch digestion at all substitution levels compared to the control pasta. The rapidly digestible starch was lowered in all the sorghum-containing pastas compared to the control pasta. Neither RSF or WSF addition affected the pasta quality attributes (water absorption, swelling index, dry matter, adhesiveness, cohesiveness, and springiness), except color and hardness which were negatively affected. Consumer sensory results indicated that pasta samples containing 20% and 30% RSF or WSF had acceptable palatability based on meeting one or both of the preset acceptability criteria. It is concluded that the addition of wholegrain sorghum flour to pasta at 30% incorporation level is possible to reduce starch digestibility, while maintaining adequate cooking quality and consumer acceptability.

Microstructure and mechanical properties of silk from different components of the Antheraea pernyi cocoon

Silk fibres from different components of the Antheraea pernyi silkworm cocoon, namely peduncle, outer floss, and cocoon shells (outermost layer and pelade layer) were studied in detail to gain insights into the structure-property-function relationship. Among the fibres from different components, peduncle fibres are the softest with the largest viscoelastic lag, which may reduce the oscillation amplitude when a cocoon hangs on a twig. Fibres from the outermost layer are the toughest and have the largest breaking energy. Outer floss fibres have the highest content of sericin (about 11.98%) but their hardness and elasticity are intermediate. Pelade fibres are shape - preservable and stable with superior hardness and elasticity. The understanding of the properties of different silk fibres is essential for understanding their respective roles in the function of a silk cocoon and will also inspire new designs of protective materials under stringent environmental conditions.

Ti-SrO metal matrix composites for bone implant materials

Titanium-strontia (Ti-SrO) metal matrix composites (MMCs) with 0, 1, 3 and 5% (weight ratio) of SrO have been fabricated through the powder metallurgy method. Increasing the weight ratio of SrO from 0 to 5%, the compressive strength of Ti-SrO MMCs increased from 982 MPa to 1753 MPa, while the ultimate strain decreased from 0.28 to 0.05. The elastic moduli of Ti-3SrO and Ti-5SrO MMCs were higher than those of Ti and Ti-1SrO MMC samples. Additionally, the micro hardness of Ti-SrO MMCs was enhanced from 59% to 190% with the addition of SrO. The enhanced compression strength and micro hardness of Ti-SrO MMCs were attributed to the Hall-Petch effect and the SrO dispersion strengthening in the Ti matrix. MTS assay results demonstrated that Ti-SrO MMCs with 3% SrO exhibited enhanced proliferation of osteoblast-like cells. Alkaline phosphatase activity of cells was not influenced significantly on the surface of Ti-SrO MMCs compared with pure Ti in a term longer than 10 days. The cell morphology on the Ti-SrO MMCs was observed using confocal microscopy and scanning electron microscopy, which confirmed that the Ti-3%SrO MMCs showed optimal in vitro biocompatibility. This journal is © the Partner Organisations 2014.

Water-soluble acrylamide sulfonate copolymer for inhibiting shale hydration

Here we report a water-soluble acrylamide sulfonate copolymer for inhibiting shale hydrate formation. The copolymer, denoted as PANAA, was synthesized via copolymerization of acrylamide (AM), N,N-diallylbenzylamine (NAPA), acrylic acid (AA), and 2-(acrylamide)-2-methylpropane-1-sulfonic acid (AMPS). The performance of this new water-soluble copolymer for inhibiting shale hydration was investigated for the first time. The retention ratio of apparent viscosity of 2 wt % PANAA solution can reach 61.6% at 130 C and further up to 72.2% with 12 000 mg/L NaCl brine. The X-ray diffraction studies show that the addition of copolymer PANAA (5000 mg/L), in combination with a low loading of KCl (3 wt %), remarkably reduces the interlayer spacing of sodium montmorillonite (Na-MMT) in water from 19.04 to 15.65 Å. It has also found that these copolymer solutions, blending with KCl, can improve the retention of indentation hardness from 22% to 74% and increase the antiswelling ratio up to 84%. All results have demonstrated that the PANAA copolymer not only has excellent temperature-resistance and salt-tolerance but also exhibits a significant effect on inhibiting the hydration of clays and shale. © 2014 American Chemical Society.

Refinement of retained austenite in super-bainitic steel by a deep cryogenic treatment

The effect of a deep cryogenic treatment on the microstructure of a super-bainitic steel was investigated. It was shown that quenching the super-bainitc steel in -196°C liquid nitrogen resulted in the transformation of retained austenite to two phases: ~20 nm thick martensite films and some nano carbides with a ~25 nm diameter. Some refinement of the retained austenite occurred, due to formation of fine martensite laths within the retained austenite. The evolution of these new phases resulted in an increase in the average hardness of the super-bainitic steel from 641 to ~670 HV1. © 2014 ISIJ.

The microstructure and properties of energetically deposited carbon nitride films

The intrinsic stress, film density and nitrogen content of carbon nitride (CNx) films deposited from a filtered cathodic vacuum arc were determined as a function of substrate bias, substrate temperature and nitrogen process pressure. Contour plots of the measurements show the deposition conditions required to produce the main structural forms of CNx including N-doped tetrahedral amorphous carbon (ta-C:N) and a variety of nitrogen containing graphitic carbons. The film with maximum nitrogen content (~ 30%) was deposited at room temperature with 1.0 mTorr N2 pressure and using an intermediate bias of - 400 V. Higher nitrogen pressure, higher bias and/or higher temperature promoted layering with substitutional nitrogen bonded into graphite-like sheets. As the deposition temperature exceeded 500 °C, the nitrogen content diminished regardless of nitrogen pressure, showing the meta-stability of the carbon-nitrogen bonding in the films. Hardness and ductility measurements revealed a diverse range of mechanical properties in the films, varying from hard ta-C:N (~ 50 GPa) to softer and highly ductile CN x which contained tangled graphite-like sheets. Through-film current-voltage characteristics showed that the conductance of the carbon nitride films increased with nitrogen content and substrate bias, consistent with the transition to more graphite-like films. © 2014 Elsevier B.V.

Machinability assessment of titanium alloy Ti-6Al-4V for biomedical applications

Titanium alloy (Ti-6Al-4V) has a wide range of application in various fields of engineering. Titanium is mainly used to manufacture aerospace components like landing gear, fuselage, wings, engines etc. and biomedical components like hip joint, knee joint, dental implants etc. Titanium has outstanding material properties such as corrosion resistance, fatigue strength, tensile strength and a very good biocompatibility which makes this material very alluring for biomedical applications. Contrary, the machinability of the material is problematic because of the phase transformations and thus, titanium alloy is a challenge for machining operation. This research is a comparative analysis between the implants manufactured by traditional method of casting and machining. The femoral stem of the hip joint replacement is designed and the component is machined using a five-axis CNC machine.The machined component was subjected to surface roughness testing, tensile testing and bulk hardness testing. The values were compared with the values of titanium implants manufactured by casting. © (2014) Trans Tech Publications, Switzerland.

Bio-inspired hydrogen-bond cross-link strategy toward strong and tough polymeric materials

It remains a huge challenge to create advanced polymeric materials combining high strength, great toughness, and biodegradability so far. Despite enhanced strength and stiffness, biomimetic materials and polymer nanocomposites suffer notably reduced extensibility and toughness when compared to polymer bulk. Silk displays superior strength and toughness via hydrogen bonds (H-bonds) assembly, while cuticles of mussels gain high hardness and toughness via metal complexation cross-linking. Here, we propose a H-bonds cross-linking strategy that can simultaneously strikingly enhance strength, modulus, toughness, and hardness relative to polymer bulk. The H-bond cross-linked poly(vinyl alcohol) exhibits high yield strength (140 MPa), reduced modulus (22.5 GPa) in nanoindention tests, hardness (0.5 GPa), and great extensibility (40%). More importantly, there exist semiquantitive linear relationships between the number of effective H-bond and macroscale properties. This work suggests a promising methodology of designing advanced materials with exceptional mechanical by adding low amounts (1.0 wt %) of small molecules multiamines serving as H-bond cross-linkers.

Impact of grain microstructure on the heterogeneity of precipitation strengthening in an Al-Li-Cu alloy

The effect of grain microstructure on the age-hardening behavior is investigated on recrystallized and un-recrystallized Al-Cu-Li alloys by combining electron-backscatter-diffraction and micro-hardness mapping. The spatial heterogeneity of micro-hardness is found to be strongly dependent on the grain microstructure. Controlled experiments are carried out to change the pre-strain before artificial ageing. These experiments lead to an evaluation of the range of local strain induced by pre-stretching as a function of the grain microstructure and results in heterogeneous formation of the hardening T1 precipitates.

Water-soluble complexes of an acrylamide copolymer and ionic liquids for inhibiting shale hydration

Here, we report water-soluble complexes of an acrylamide copolymer and ionic liquids for inhibiting shale hydration. The copolymer, denoted as PAAT, was synthesised via copolymerisation of acrylamide (AM), acrylic acid (AA) and N,N-diallyl-4-methylbenzenesulfonamide (TCDAP), and the ionic liquids used were 3-methyl imidazoliumcation-based tetrafluoroborates. X-ray diffraction showed that compared with commonly used KCl, the water-soluble complex of PAAT with 2 wt% ionic liquid 1-methyl-3-H-imidazolium tetrafluoroborate (HmimBF4) could remarkably reduce the d-spacing of sodium montmorillonite in water from 19.24 to 13.16 Å and effectively inhibit clay swelling. It was also found that the PAAT-HmimBF4 complex with 2 wt% HmimBF4 could retain 75% of the shale indentation hardness and increase the anti-swelling ratio to 85%. 13C NMR revealed that there existed interactions between PAAT and HmimBF4. Moreover, the thermal stability of the PAAT-HmimBF4 complex is superior to PAAT, suggesting that this water-soluble complex can be used to inhibit clay and shale hydration in high-temperature oil and gas wells.

On the Bauschinger effect in dual phase steel at high levels of strain

The effect of volume fraction and hardness of martensite on the Bauschinger effect in Dual Phase (DP) steel was investigated for strain levels close to those observed in automotive stamping. Five different grades of DP steel were produced by controlled heat treatment allowing the examination of the Bauschinger effect for three different volume fractions of martensite and three levels of martensite hardness. Compression-tension and shear reversal tests were performed to examine the Bauschinger effect at high levels of forming strain. Good correlation between the shear reversal and the compression-tension test was observed suggesting that for DP steel, shear stress strain data, converted to equivalent stress-strain, may be applied directly to characterize kinematic hardening behavior for numerical simulations. Permanent softening was observed following strain reversal and increased with martensite volume fraction and pre-strain level. While the Bauschinger ratio saturates at 3% pre-strain, the Bauschinger strain increases linearly with forming strain without showing saturation. This suggests that to model material behavior accurately in forming processes involving complex loading paths and high levels of strain, test data generated at high strain is required.

Chip formation mechanism and machinability of wrought duplex stainless steel alloys

This paper investigates the chip formation mechanism and machinability of two-phase materials, such as, wrought duplex stainless steel alloys SAF 2205 and SAF 2507. SEM and optical microscopic details of the frozen cutting zone and chips revealed that the harder austenite phase dissipates in the advancement of the cutting tool, being effectively squeezed out of the softer ferrite phase. Microhardness profiles reveal correlation in hardness from the workpiece material transitioning to the chip. The tool wear (TiAIN + TiN coated solid carbide twist drill) and machining forces were investigated. Tool wear, was dominantly due to the adhesion process which developed from built-up edge formation, is highly detrimental to the flank face. Flute damage was also observed as a major issue in the drilling of duplex alloys leading to premature tool failure. Duplex 2507 shows higher sensitivity to cutting speed during machining and strain hardening at higher velocity and less machinability due to presence of higher percentage of Ni, Mo and Cr.