Microstructure characteristics and mechanical properties of Al/Mg joints manufactured by magnetic pulse welding

The effective connection of 1050 Al and AZ31 Mg was realized by magnetic pulse welding.The maximum tensile-shear force of the dissimilar Al/Mg metal lap joint reached 97%of that of the 1050 Al alloy base material by optimizing the process parameters.The microstructure of dissimilar Al/Mg welded joints was analysed by Scanning Electron Microscope(SEM),Energy Dispersive Spectrometer(EDS)and Electron Backscattered Diffraction(EBSD).The results show that the key to obtaining high shear strength of Al/Mg dissimilar metal joints is mainly due to the following two reasons.On the one hand,grain refinement and element interdiffusion occur at the interface.On the other hand,no intermetallic compounds are formed at the interface.

Microstructure and mechanical properties of AZ61 magnesium alloy prepared by repetitive upsetting-extrusion

The process of repetitive upsetting-extrusion （RUE） was used to achieve severe plastic deformation （SPD） for an as-cast AZ61 magnesium alloy in temperature range of 285-380 ℃. The microstructure and mechanical properties of the as-cast and RUE processed AZ61 alloys were investigated. The results indicated that homogeneous fine-grained structure with mean grain size of 3.5 μm was obtained as the accumulated true strain in the axial direction increased to 4.28 after three RUE passes at 285 ℃. The dominant reason of grain refinement was considered the dynamic recrystallization induced by strain localization. It was also found that the microstructural evolution was affected by temperature and accumulated deformation. The mechanical properties of RUE processed AZ61 alloys were significantly improved owing to grain refinement. Furthermore, the relationship between deformation parameters and mechanical properties of AZ61 alloy prepared by RUE processing was revealed by tensile tests carried out at room temperature.

Effects of Irradiation on the Structure-activity Relationship of Konjac Glucomannan Molecular Chain Membrane

To know the effects of irradiation on the konjac glucomannan （KGM） molecular chain membrane, KGM membrane solution was treated with the irradiation dose of 0-20 kGy in this study, and the structure and properties of KGM membrane were analyzed with Infrared spectrum, Raman spectrum, X-ray, SEM scanning and so on. The results revealed that the effects of different irradiation doses on the KGM molecular chain structure were different. Higher irradiation dose （20 kGy） resulted in partial damage against KGM membrane crystal structure, and there was no obvious change for the amorphous structure; with membrane property test, the tensile strength of KGM membrane gradually increased with the increase of irradiation dose and its elongation at break reduced, but these changes were not significant, WVP value reduced; with SEM, the membrane surface treated with irradiation was smoother even than the membrane without treatment. In addition, when increasing the irradiation dose, membrane surface became more even, and arrangement was more orderly and compact. KGM membrane nrooerties, and it is an ideal Irradiation modification could effectively improve the modification method.

EFFECTS OF RARE EARTH MIXTURE ON MECHANICAL PROPERTIES OF CuZnAl SHAPE MEMORY ALLOYS

With thehelpofquantitative metallograph ,tensiletest,electron probeandscan electron mi croscope,theinfluencesof mixture rareearth ( RE) on the grain size, dynamics of grain growth and mechanicalpropertiesof CuZnAlshape memoryalloys wereinvestigated . Theex perimentalresultsshowsthat REcanrefinegrainsgreatly,improvethe mechanicalpropertiesremarkably andchangethetensilefracturefrom brittletypebordered grainstoplastictypeinthecondition of maintainingshape memory properties. Moreover microstructuresrevealthatREwhich accumulates on the grain boundariescan restrain grains’growing. In addition, the mechanismsofrefininggrainsizeandimproving mechanicalpropertiesarealsodiscussed.

Microstructure characteristics and mechanical properties of TiB/Ti-1.5Fe-2.25Mo composites synthesized in situ using SPS process

TiB/Ti-1.5Fe-2.25Mo composites were synthesized in situ using the spark plasma sintering （SPS） method at temperatures of 850-1150 °C. The effect of the sintering temperature on microstructure and mechanical properties of the composites was investigated. The results indicate that the aspect ratio of the in situ synthesized TiB whiskers in Ti alloy matrix decreases rapidly with an increase in sintering temperature. However, both the relative density of the sintered specimens and the volume content of TiB whiskers in composites increase with increasing sintering temperature. Thus, the bending strength of the composites synthesized using SPS process increases slowly with increasing the sintering temperature from 850 to 1150 °C. TiB/Ti-1.5Fe-2.25Mo composite synthesized at 1150 °C using SPS method exhibits the highest bending strength of 1596 MPa due to the formation of fine TiB whiskers in Ti alloy matrix and the dense microstructure of the composite.

NOVEL OXIDATION RESISTANT CARBON SILICON ALLOY FIBRES

Anovel silicon containing carbon precursor was synthesised by reacting a petroleum pitchfraction and polydimethylsilane. The precursor containing about 26wt% Si was meltspunintofibresand then oxidativelystabilised in airto renderthefibresinfusiblebefore pyrolysisat1200℃underinertatmospheretoproduceC Sialloy( CSA) fibres. Theextentofstabili sation wasfoundto becriticalto the development of mechanicalstrength of thefibres which varied with heattreatmenttemperature, showing a maximum at 1200 ℃when thestrength was 1 4 1 6 GPa. Thesestrengthsareremarkably goodconsideringthelow modulus whichis duetothe quite high failurestrains. Thefibrescanshow excellentresistanceto oxidation if given an initialshortexposureto oxygen athigh temperature duetotheformation of an im perceptiblelayer of silica. CSAfibreshavethe advantagesof both carbon fibresand SiCfi bres,thusextended application areascan beenvisaged .

Effect of Freeze-Thaw Cycles on Mechanical Properties and Permeability of Red Sandstone under Triaxial Compression

Geological disasters will happen in cold regions because of the effects of freeze-thaw cycles on rocks or soils, so studying the effects of these cycles on the mechanical characteristics and permeability properties of rocks is very important. In this study, red sandstone samples were frozen and thawed with o, 4, 8 and 12 cycles, each cycle including 12 h of freezing and 12 h of thawing. The P-wave velocities of these samples were measured, and the mechanical properties and evolution of the steady-state permeabilities were investigated in a series of uniaxial and triaxial compression tests. Experimental results show that, with the increasing of cyclic freeze-thaw times, the P-wave velocity of the red sandstone decreases. The number of freeze-thaw cycles has a significant influence on the uniaxial compressive strength, elastic modulus, cohesion, and angle of internal friction. The evolution of permeability of the rock samples after cycles of freeze-thaw in a complete stress-strain process under triaxial compression is closely related to the variation of the microstructure in the rock. There is a highly corresponding relationship between volumetric strain and permeability with axial strain in all stages of the stress-strain behaviour.

Preparation and Mechanical Properties of a Novel Textile Pad for Wound Debridement

Various types of wound debridement approaches are currently available in clinical practice such as autolytie, enzymatic. biodebridement, mechanical, and surgical debridemenl techniques. A critical look at these various options can explain their potential but also their limitations. In this study, a novel textile pad, which is composed of polyester filaments on the fleecy side and a bioeompatible coating on the opposite side, was made to provide a safe, inexpensive, easier and especially more efficient debridement process that can be used in all healthcare settings by all healthcare practitioners. Eighteen kinds of samples were prepared with different pile density, ground yarn count and coating amount. Dimensional morphology, stitch density, mass per unit area and mechanical properties were investigated to study the intrinsic relationship of structure and properties of textile pad for wound debridement. Results showed that tensile strength and suturing strength at piped site increased obviously with the increment of ground yarn count, while the amount of coating could also have a slight impact on these two properties. However, compressive load was mainly affected by pile density, with no obvious relation to ground yarn count and coating amount.

Comparative study of β-Si_3N_4 powders prepared by SHS sintered by spark plasma sintering and hot pressing

β-Si3N4 powders prepared by self-propagating high-temperature synthesis （SHS） with additions of Y2O3 and Al2O3 were sintered by spark plasma sintering （SPS）. The densification, microstructure, and mechanical properties of Si3N4 ceramics prepared using this method were compared with those obtained by hot pressing process. Well densified Si3N4 ceramics with finer and homogeneous microstructure and better mechanical properties were obtained in the case of the SPS technique at 200°C lower than that of hot pressing. The microhardness is 15.72 GPa, the bending strength is 716.46 MPa, and the fracture toughness is 7.03 MPa·m1/2.

An Approach for Preparation of Excellent Antiwear PTFE Nanocomposites by Filling As-prepared Carbon Nanotubes/Nanorods(CNT/CNR)Mixed Nano-Carbon Material

The one-dimensional carbon nanotubes/nanorods(CNT/CNR)mixed nano-carbon material was successfully prepared by halloysite nanotubes(HNTs)as the template for the first time,in which CNT was formed through PVA modification in internal surface of HNTs and CNR was obtained by nanocasting PVA in hollow nanostructure of HNTs.The CNT of the mixture with flexible structure has ca.20 nm in pore diameter and ca.500 nm in length,whereas the CNR with hard and solid structure shows ca.30 nm in diameter and ca.2μm in length.For application as fillers,the CNT/CNR mixed nano-material is used to reinforce the properties of polytetrafluoroethylene(PTFE).The mechanical and tribological properties of PTFE nanocomposites were intensively examined by a series of testing.The ring-on-ring counterface was used to evaluate the tribological behavior of the nanocomposites.The results showed that the volume wear rate of the CNT/CNR-reinforced PTFE nanocomposite after being filled with 0.3%of CNT/CNR was only 1/700 of that of the pure PTFE under a load of 200 N and a rotary speed of 200 r/min,while other mechanical and tribological performance was comparable to the performance of pure PTFE,which exhibited a desirable application prospect.

Effects of salinity on the nail-holding power of dimension lumber used in light-frame wood building

We studied the effect of salinity on nail-hold- ing power in wood construction. In saline solution, the holding power of nails was less than in purified water. With the increase of salt concentration, the surface and side nail- holding power of the wood specimens both declined, but the differences between salinity treatments were not sig- nificant. However, compared to the surface and side nail- holding power, the power on the edge was generally less and the difference was not obvious in different salt con- centrations. In the same salt concentration, with the extension of the processing cycle, the performance of holding power of nails showed a downward trend, expect the temporary rise in the middle.

Effect of Mg-Zn-Nd spherical quasi-crystals on microstructure and mechanical properties of ZK60 alloy

To improve the strength, toughness, heat-resistance and deformability of magnesium alloy, the microstructure and mechanical properties of ZK60 alloy strengthened by Mg-Zn-Nd spherical quasi-crystal phase (I-phase) particles were investigated. Mg40Zn55Nd5 (I-phase) particles in addition to α-Mg, MgZn phase and MgZn2 phases can be obtained in ZK60-based composites under normal casting condition by the addition of quasi-crystal containing Mg-Zn-Nd master alloy. The experimental results show that the introduction of Mg-Zn-Nd spherical quasi-crystal phase into ZK60 alloy makes a great contribution to the refinement of the matrix microstructures and the improvement of mechanical properties. While adding Mg-Zn-Nd spherical quasi-crystal master alloy of 4.0wt.%, the ultimate tensile strength and yield strength of ZK60-based composite at ambient temperature reach their peak values of 256.7 MPa and 150.4 MPa, which were about 17.8% and 24.1% higher respectively than those of the ZK60 alloy. The improved mechanical properties are mainly attributed to the pinning effect of the quasi-crystal particles (I-phase) at the grain boundaries. This research results provide a new way for strengthening and toughening of magnesium alloys as well as a new application of Mg-based spherical quasi-crystals.

Microstructural characterization and mechanical properties of self-reinforced Si_3N_4 ceramics containing high oxynitride glass

Self-reinforced Si_3N_4 ceramics containing high oxynitride glass have beenfabricated by the control of microstructure evolution and p-Si_3N_4 grain growth. The effects of thesize distribution of the elongated p-Si_3N_44 grains, and the p-Si_3N_4 grain growth as well as theoxynitride glass chemical characteristic on the microstructure and mechanical properties wereinvestigated. The experimental results show that the p-Si_3N_4 grains in high oxynitride glass growto elongated rod-like crystals and form the stereo-network structure. Under the sintering conditionsof 1800 deg C and 60 min, a quite uniform microstructure with an average aspect ratio of 6.5 and anaverage of 1 mu m can be obtained. A large amount of oxynitride glass phase with high nitrogencontent enhances the elevated temperature fracture toughness because of its high softeningtemperature and high viscosity. In the present material, the crack deflection and pullout of theelongated rod-like P-Si_3N_44 grains are the primary toughening mechanisms.

High-frequency induction heated sintering of ball milled Fe-WC nanocomposites

Fe-WC nanocomposites were successfully fabricated by high-frequency induction heated sintering of ball milled nanostructure powders. The ball milled powders were characterized by X-ray diffraction. Density measurements by the Archimedes method show that all sintered samples have the relative density higher than 95%. Studies on the effects of WC content, milling speed, and milling time indicate that a higher milling speed and a more WC content lead to the improvement of mechanical properties. There is a very good distribution of WC particles in the Fe matrix at the milling speed of 650 r/rain. For the sintered sample 20-5-650 （20wt% WC, milling time of 5 h, and milled speed of 650 r/min）, the maximum Brinell hardness and yield stress are obtained to be 3.25 GPa and 858 MPa, respectively. All sintered samples have brittle fracture during compression test except the sample 20-5-650.

Effect of magnesium on dispersoid strengthening of Al-Mn-Mg-Si(3xxx) alloys

The effects of magnesium addition on the dispersoid precipitation as well as mechanical properties of 3xxx alloys wereinvestigated. The microstructures in as-cast and heat-treated conditions were evaluated by optical microscopy and transmissionelectron microscopy. The results reveal that Mg has a strong influence on the distribution and volume fraction of dispersoids duringprecipitation heat treatment. The microhardness and yield strength at ambient temperature increase with increasing Mg content. Thesolid solution and dispersoid strengthening mechanisms of materials after heat treatment are quantitatively analyzed. Dispersoidstrengthening for the alloys is the predominant strengthening mechanism after precipitation heat treatment. An analytical model isintroduced to predict the evolution of ambient-temperature yield strength.

EFFECT OF Fe_2O_3 ON WELDING TECHNOLOGY AND MECHANICAL PROPERTIES OF WELD METAL DEPOSITED BY SELF-SHIELDED FLUX CORED WIRE

Five experimental self-shielded flux cored wires are fabricated withdifferent amount of Fe_2O_3 in the flux. The effect of Fe_2O_3 on welding technology and mechanicalproperties of weld metals deposited by these wires are studied. The results show that with theincrease of Fe_2O_3 in the mix, the melting point of the pretreated mix is increased. LiBaF_3 andBaFe_(12)O_(19), which are very low in inherent moisture, are formed after the pretreatment. Themechanical properties are evaluated to the weld metals. The low temperature notch toughness of theweld metals is increased linearly with the Fe_2O_3 content in the flux due to the balance betweenFe_2O_3 and residual Al in the weld metal. The optimum Fe_2O_3 content in flux is 2.5 percent approx3.5 percent.

Experimental Study on the Influence Mechanism of Carbon Fiber/Epoxy Composite Reinforcement and Matrix on Its Fire Performance

The effects of the number of layers,the arrangement of carbon fiber(CF)tow and the epoxy resin(ER)matrix on the fire performance of carbon fiber/epoxy composites(CFEC)were studied by a variety of experimental methods.The results show that the number of layers of CF tow has influence on the combustion characteristics and fire propagation of the composites.The arrangement of CF tow has influence on flame propagation rate and high temperature mechanicalproperties.The mechanism of the influence of the number of layers of CF tow on the composite is mainly due to the different thermal capacity of ER matrix.The effect of the arrangement of CF tow on the fire performance of the composite is mainly due to the inhibition and obstruction of the tow on the combustion of ER matrix.The influence on the high temperature mechanicalproperties is mainly due to the different arrangement direction of CF tow.The fitting equation of the mechanicalproperties of the samples was obtained.This equation could be used to predict the samples’tensile strength from 25°C to 150℃by comparing with the experimental results.Taking the carbon fiber woven cloth(C)applied in the fuselage material as an example,combining the influencing factors of various parameters in the fire field,some suggestions are put forward combined with the research conclusion.

Thermo-Mechanical Processing of Iron-Phosphorous-Carbon Alloys

Phosphorous is widely considered as an impurity in steels. Consequently, its role as an important alloying element in iron could never be established. The present paper deals with the exploitation of phosphorous as a useful alloying element in iron in conjunction with carbon by way of improved thermo-mechanical processing leading to a tough steel equivalent to high strength low alloy steels. It was observed that phosphorous is pushed towards ferrite grains by carbon which in turn forms pearlite along ferrite grains. Suitable adjustment in the amounts of carbon and phosphorous yields an attractive set of mechanical properties after appropriate processing. Typical chemistry and processing combinations yields UTS: 700 MPa and % El: 25% Area under the stress-strain curve: 60 Joules.

Investigation of Mechanical Behavior of Defective Carbon Nanotubes Using Molecular Dynamics Simulation

Carbon nanotubes （CNTs） having pristine structure （i.e., structure without any defect） hold very high mechanical properties. However, CNTs suffer from defects ＇which can appear at production stage, purification stage or be deliberately introduced by irradiation with energetic particles or by chemical treatment. In this article, mechanical properties of single-walled nanotubes with defects are studied under both compressive and tensile loads using molecular dynamics （MD） simulations. Two types of defectStone-Wales and vacancy defects with different defect densities are considered for present investigation. Molecular simulations are carried out using the classical MD method. The Brenner potential is used for carbon-carbon interaction in the CNT. Temperature of the system is controlled by velocity scaling. Simulation results show that the defects have negligible effect on the modulus of elasticity of nanotubes. However, they have significant effect on the failure stress and strain of the nanotubes.

Research and development of nanocrystalline W/W-based materials: novel preparation approaches, formation mechanisms, and unprecedented excellent properties

Tungsten(W)has become the most promising plasma-facing material(PFM)in fusion reactor,and W still faces performance degradation caused by low-temperature brittleness,low recrystallization temperature,neutron irradiation effects,and plasma irradiation effects.The modification of wW-based materials in terms of microstructure manipulation is needed,and such techniques to improve the performance of materials are the topics of hot research.Researchers have found that refining the grain can significantly improve the strength and the irradiation resistance of Ww-based materials.In this paper,novel approaches and technique routes,including the"bottom-up"powder metallurgy method and"top-down"severe plastic deformation method,are introduced to the fabrication of nanocrystalline WW-based materials.The formation mechanisms of nanocrystalline WW-based materials were revealed,and the nanostructure stabilization mechanisms were introduced.The mechanical properties of nanocrystalline WW-based materials were tested,and the irradiation behaviors and performances were studied.The mechanisms of their high mechanical properties and excellent irradiation-damage resistance were illustrated.This article may provide an experimental and theoretical basis for the design and development of high-performance novel nanocrystallineW/W-based materials.