Degradation behaviors,thermostability and mechanical properties of poly(ethylene terephthalate)/polylactic acid blends

It is difficult for polyethylene terephthalate(PET)to degrade,which caused severe pollution.In this work,polylactic acid(PLA)was introduced to improve the degradation of PET.PET/PLA was synthesized by extrusion blending.The thermal,crystalline and mechanical properties of blends were investigated with TGA,DSC,WAXD and universal testing machine.The degradation of the blends in soil,acid and alkaline buffer solutions was assessed,respectively.It was found that the introduction of a little PLA promoted crystallization of PET during injection molding process.The starting decomposition temperature lowered from 412.1 °C of pure PET to 330.4 °C at 50% PLA content,tensile and bending strength of blends gradually decreased with the PLA content increasing,while the degradation rate improved.Alkaline environment was most beneficial for blends to degrade.The degradation mechanism was discussed.

Resistance and Reactance of Monopole Fields Induced by a Test Charge Drifting Off-Axis in a Cold and Collisional Cylindrical Plasma

We study the interaction of a uniform, cold and collisional plasma with a test charged particle moving off-axis at a constant speed down a cylindrical tube with a resistive thick metallic wall. Upon matching the electromagnetic field components at all interfaces, the induced monopole electromagnetic fields in the plasma are obtained in the frequency domain. An expression for the plasma electric resistance and reactance is derived and analyzed numerically for some representative parameters. Near the plasma resonant frequency, the plasma resistance evolves with frequency like a parallel RLC resonator with peak resistance at the plasma frequency pe, while the plasma reactance can be capacitive or inductive in nature depending on the frequency under consideration.

Estimation of plasma parameters of X-pinch with time-resolved x-ray spectroscopy

We estimate the parameters of a Cu plasma generated by an X-pinch by comparing experimentally measured x-rays with synthetic data.A filtered absolute extreme ultraviolet diode array is used to measure time-resolved x-ray spectra with a spectral resolution of∼1 keV in the energy range of 1–10 keV.The synthetic spectra of Cu plasmas with different electron temperatures,electron densities,and fast electron fractions are calculated using the FLYCHK code.For quantitative comparison with the measured spectrum,two x-ray power ratios with three different spectral ranges are calculated.We observe three x-ray bursts in X-pinch experiments with two Cu wires conducted on the SNU X-pinch at a current rise rate of∼0.2 kA/ns.Analysis of the spectra reveals that the first burst comprises x-rays emitted by hot spots and electron beams,with characteristics similar to those observed in other X-pinches.The second and third bursts are both generated by longlived electron beams formed after the neck structure has been completely depleted.In the second burst,the formation of the electron beam is accompanied by an increase in the electron density of the background plasma.Therefore,the long-lived electron beams generate the additional strong x-ray bursts while maintaining a plasma channel in the central region of the X-pinch.Moreover,they emit many hard x-rays(HXRs),enabling the SNU X-pinch to be used as an HXR source.This study confirms that the generation of long-lived electron beams is crucial to the dynamics of X-pinches and the generation of strong HXRs.

Effects of TiC on the microstructure refinement and mechanical property enhancement of additive manufactured Inconel 625/TiC metal matrix composites fabricated with novel core-shell composite powder

The flexible product shape of additive manufacturing(AM)is attractive,but the process suffers from a lack of material property diversity due to a limited number of printable alloys and post-processing options.To overcome this problem,the AM of metal matrix composites(MMCs)is a highly suitable solution because the properties of MMC can be tailored using various reinforcements.Therefore,extensive research has been conducted on the AM of MMCs;however,the major huddle for this process has been the difficulties in preparing feedstock powder and operating the AM process.This study introduces an easily synthesizable core-shell composite powder,which was fabricated by a recently developed process called the SMART process.The core-shell powder has a novel morphology,consisting of a metal core and composite shell,distinguishing it from the powders used in conventional AM approaches.Inconel 625/TiCp composites were fabricated using the core-shell composite powder,with various fractions of TiCp up to 10 vol.%.Compared to additive-manufactured Inconel 625,the additive-manufactured MMCs showed enhanced strength with significantly fewer defects.The results of this study may accelerate the application of MMC fabricated by AM,which offers superior properties and reliability compared to casting and powder metallurgy due to the higher degree of dislocation density and reinforcement dispersion.

Superior mechanical properties and strengthening mechanisms of lightweight AlxCrNbVMo refractory high-entropy alloys(x=0,0.5,1.0)fabricated by the powder metallurgy process

Light and strong AlxCrNbVMo(x=0,0.5,and 1.0)refractory high-entropy alloys(RHEAs)were designed and fabricated via a the powder metallurgical process.The microstructure of the AlxCrNbVMo alloys consisted of a single BCC crystalline structure with a sub-micron grain size of 2-3μm,and small amounts(<4 vol.%)of fine oxide dispersoids.This homogeneous microstructure,without chemical segregation or micropores was achieved via high-energy ball milling and spark-plasma sintering.The alloys exhibited superior mechanical properties at 25 and 1000℃compared to those of other RHEAs.Here,CrNbVMo alloy showed a yield strength of 2743 MPa at room temperature.Surprisingly,the yield strength of the CrNbVMo alloy at 1000℃was 1513 MPa.The specific yield strength of the CrNbVMo alloy was increased by 27%and 87%at 25 and 1000℃,respectively,compared to the AlMo_(0.5) NbTa_(0.5)TiZr RHEA,which exhibited so far the highest specific yield strength among the cast RHEAs.The addition of Al to CrNbVMo alloy was advantageous in reducing its reduce density to below 8.0 g/cm^(3),while the elastic modulus decreased due to the much lower elastic modulus of Al compared to that of the CrNbVMo alloy.Quantitative analysis of the strengthening contributions,showed that the solid solution strengthening,arising from a large misfit effect due to the size and modulus,and the high shear modulus of matrix,was revealed to predominant strengthening mechanism,accounting for over 50%of the yield strength of the AlxCrNbVMo RHEAs.

In-situ synthesis of TiC/Fe alloy composites with high strength and hardness by reactive sintering

Fe alloy composites reinforced with in-situ titanium carbide （TIC） particles were fabricated by reactive sintering using different reactant C/Ti ratios of 0.8, 0.9, 1 and 1.1 to investigate the microstructure and mechanical properties ofin-situ TiC/Fe alloy composites. The microstructure showed that the in-situ syn- thesized TiC particles were spherical with a size of 1-3 }~m, irrespective of C/Ti ratio. The stoichiometry of in-situ TiC increased from 0.85 to 0.88 with increasing C/Ti ratio from 0.8 to 0.9, but remained almost unchanged for C/Ti ratios between 0.9 and 1.1 due to the same driving force for carbon diffusion in TiCx at the common sintering temperature. The in-situ TiC/Fe alloy composite with C[Ti ~ 0.9 showed improved mechanical properties compared with other C/Ti ratios because the presence of excess carbon （C/Ti = 1 and 1.1） resulted in unreacted carbon within the Fe alloy matrix, while insufficient carbon （C/Ti = 0.8） caused the depletion of carbon from the Fe alloy matrix, leading to a significant decrease in hardness. This study presents that the maximized hardness and superior strength of in-situ TiC/Fe alloy composites can be achieved by microstructure control and stoichiometric analysis of the in-situ synthesized TiC par- ticles, while maintaining the ductility of the composites, compared to those of the unreinforced Fe alloy. Therefore, we anticipate that the in-situ synthesized TiC/Fe alloy composites with enhanced mechanical properties have great potential in cutting tool, mold and roller material applications.

蒙特卡罗计算中颗粒型燃料的随机分布模型比较

高温气冷堆是新一代反应堆系统的热门候选堆型,已经受到国际上越来越多的关注。为设计和分析这种堆型,因其特有的包覆颗粒燃料引入了双重非均匀性,需要应用随机分布模型。对粗网格模型、细网格随机(FLS)模型、随机顺序添加(RSA)模型、子网格随机(Sub-FLS)模型和Metropolis模型等进行了研究,通过计算分析比较给出了各种模型的优缺点。结果表明:子网格随机模型和连续的RSA模型非常接近参考值,但是连续RSA模型的建模时间随着燃料体积份额的增加连续快速上升。

Effect of tellurium on the microstructure and mechanical properties of Fe-14Cr oxide-dispersion-strengthened steels produced by additive manufacturing

Conventionally,Te has primarily been used to improve the machinability of steel and its alloys.In this work,Te was used to refine the grains of an oxide-dispersion-strengthened(ODS)steel produced by additive manufacturing(AM)with fixed processing parameters.Addition of Te to the raw powder produced an ODS steel with a fine-grained microstructure,in contrast to the ODS steel manufactured without Te.Moreover,the addition of Te resulted in superior yield strength and ultimate tensile strength,which was attributed to the combined effects of grain refinement and the finer nanoparticles(NPs)composed of Terich composite NPs and Cr-rich NPs.For the first time,the AM technique was used to obtain grain and nanoparticle sizes of~3.4μm and 6 nm,respectively,from the Te-added ODS steel.

Systematic study of(MoTa)_(x)NbTiZr medium-and high-entropy alloys for biomedical implants-In vivo biocompatibility examination

In this study,the application of medium-and high-entropy(Mo Ta)_(x)Nb Ti Zr alloys in biomedical implants was systematically analyzed.The alloy with the best combination of mechanical properties was selected and characterized for in vitro and in vivo response for the first time to examine its biomedical properties.A logarithmic increase in the hardness and the yield strength was observed as a function of the Mo and Ta content.Alloys with up to 0.4 mol fraction of Mo and Ta showed a plastic strain of more than 30%under compression.The nanoindentation results showed that the addition of Mo and Ta increased the elastic modulus of the system linearly.It was surmised that the addition of Ta and Mo above a critical concentration(mole fraction=0.4)was unfavorable from a biomedical perspective as it increased the brittleness and elastic modulus and decreased the ductility of the system.Therefore,the(Mo Ta)_(0.2)Nb Ti Zr alloy is a potential structural material for biomedical implants because of its excellent strength and ductility.The developed alloy was investigated for its corrosion properties and compared with commercial biomedical alloys.Furthermore,the biocompatibility of the alloy was examined using an in vivo examination.The alloy was implanted in the skeletal muscles of mice for four weeks and the histology of the surrounding tissue was studied.The alloy exhibited strong passive behavior in a phosphate buffer solution and non-toxic soft tissue response.

Mo and Ta addition in NbTiZr medium entropy alloy to overcome tensile yield strength-ductility trade-off

In this study,single-phase NbTiZr and NbTiZr(MoTa)_(0.1) medium-entropy alloys(MEAs)were investigated for their use in biomedical implants.The alloys were prepared by arc melting,and were then cold-rolled,annealed,and characterized in terms of phase analysis,mechanical properties,fractography,and wear resistance.Both alloys showed a single body-centered cubic phase with superior mechanical,and tribological properties compared to commercially available biomedical alloys.Mo and Ta-containing MEAs showed higher tensile yield strength(1060±18 MPa)and higher tensile ductility(~20%),thus overcoming the strength-ductility trade-off with no signs of transformation-induced plasticity,twinning,or precipitation.The generalized stacking fault energy(GSFE)calculations on the{112}<111>slip system by the first-principles calculations based on density functional theory showed that the addition of less than0.2 molar fraction of Mo and Ta lowers the GSFE curves.This behavior posits the increase in ductility of the alloy by facilitating slips although strength is also increased by solid solution strengthening.The wear resistance of both alloys against hardened steel surfaces was superior to that of commercial biomedical alloys.Thus,we concluded that NbTiZr(MoTa)_(0.1)MEA with good tensile ductility is a potential candidate for biomedical implants.

Effects of dispersoid preforming via multistep sintering of oxide dispersion-strengthened CoCrFeMnNi high-entropy alloy

Dispersoid formation and microstructural evolution in an oxide dispersion-strengthened CoCrFeMnNi high-entropy alloy(HEA)using a newly designed multistep sintering process are investigated.The proposed multistep sintering consists of a dispersoid preforming heat treatment of as-milled 0.1 wt%Y_(2)O_(3)-CoCrFeMnNi high-entropy alloy powders at 800℃,followed by sintering at 800–1000℃ under uniaxial pressure.In the conventional single-step sintered bulk,the coarsened BCC Y_(2)O_(3)dispersoids mainly form with an incoherent interface with the HEA matrix.In contrast,finer FCC Y_(2)O_(3)dispersoids,an atypical form of Y_(2)O_(3),are formed in the matrix region after multistep sintering.Nucleation of FCC Y_(2)O_(3)disper-soids is initiated on the favorable facet,the{111}plane of the austenitic matrix,with the formation of a semi-coherent interface with the matrix during the dispersoid preforming heat treatment and it maintains its refined size even after sintering.It is found that dispersoid preforming prior to sintering appears promising to control the finer dispersoid formation and refined grain structure.

Enhanced thermoelectric properties of NbCoSn half-Heuslers through in-situ nanocrystallization of amorphous precursors during the consolidation process

Tailoring nanostructures is a general approach used to obtain enhanced thermoelectric properties for halfHeusler compounds because the wide areas of grain and phase boundaries could be scattering centers that lower lattice thermal conductivity.However,a common fabrication method based on the sintering of crystalline precursors crushed from as-cast alloy ingots has limitations in obtaining a homogeneous microstructure without microsized impurity phases,owing to residual elemental segregation from casting.In this study,we used amorphous NbCoSn alloys as a precursor for the sintered specimen to obtain a homogeneous NbCoSn bulk specimen without microsized impurity phases and segregation,which led to the enhanced Seebeck coefficient due to the high purity of the half-Heusler phase after crystallization.Moreover,superplasticity originating from amorphous features enabled the powders to be largely deformed during the sintering process,even at a low sintering temperature(953 K).This resulted in less oxidation at both,the grain boundary and the interior,as the O diffusion pathway was blocked during the sintering process.As a result,the NbCoSn0.95Sb0.05 specimen using an amorphous precursor exhibited an enhanced zT of 0.7,due to the increase in the power factor and a decrease in lattice thermal conductivity compared to the specimen using a crystalline precursor.

The effects of Y pre-alloying on the in-situ dispersoids of ODS Co Cr Fe Mn Ni high-entropy alloy

Oxide dispersion strengthened CoCrFeMnNi high-entropy alloys(ODS-HEAs)were prepared using two different powder preparation methods classified by yttrium addition strategy to investigate the effects of in-situ and ex-situ oxide dispersoid formation on the microstructure and mechanical properties.Systematic micro structural analysis was carried out by X-ray diffraction(XRD),electron backscattered diffraction(EBSD),high-resolution transmission electron microscopy(HRTEM),atom probe tomography(APT),and small-angle neutron scattering(SANS).Cryo-milled powder analysis,grain structure evolution after spark plasma sintering,dispersoid characteristics,and matrix/dispersoid interface structure analysis of the insitu and ex-situ dispersoids within the high-entropy alloy(HEA)matrix were performed.The in-situ dispersoid formation was dominantly observed in the Y-alloyed ODS-HEA through the construction of a coherent interface relationship with complex chemical composition,leading to an increase in the Zener pinning forces on the grain boundary movement.ODS-HEA with in-situ oxide dispersoids enhanced the formation of ultrafine-grained structures with an average diameter of 330 nm at a sintering temperature of 1173 K.This study shows that the Y pre-alloying method is efficient in achieving fine coherent dispersoids with an ultra fine-grained structure,resulting in an enhancement of the tensile strength of the CoCrFeMnNi HEA.

An in-situ Raman spectroscopic study on potential-pO^(2-) phase diagram of lanthanum in LiCl-KCl eutectic melt

The oxidative reaction between lanthanum trichloride and oxide ion was studied in the molten LiCl-KCl eutectic at 773 K by in-situ Raman spectroscopy using an yttria-stabilized zirconia electrode in conjunction with electrochemical methods.The formation of lanthanum oxychloride,LaOCl(s),was confirmed by studying the vibrational properties of crystalline LaOCl and X-ray diffraction analysis.The solubility product of LaOCl in the LiCl-KCl molten eutectic at 773 K is found to be pKsp(LaOCl)=7.569±0.100,by combining the results of Raman spectroscopy and potentiometric titration with the addition of barium oxide.The use of Raman spectroscopic quantitation of dissolved lanthanum ions in the system allows faster and more accurate determination of the stable phase of lanthanum as well as the solubility product of LaOCl compared with that measured by potentiometric titration only.Based on experimentally obtained pKsp and standard equilibrium potentials,the potentialpO2- phase diagram of lanthanum in the molten LiCl-KCl eutectic was reported.