Spark Plasma Sintering of Mg-based Alloys:Microstructure,Mechanical Properties,Corrosion Behavior,and Tribological Performance

Within the past ten years,spark plasma sintering(SPS)has become an increasingly popular process for Mg manufacturing.In the SPS process,interparticle diffusion of compressed particles is rapidly achieved due to the concept of Joule heating.Compared to traditional and additive manufacturing(AM)techniques,SPS gives unique control of the structural and microstructural features of Mg components.By doing so,their mechanical,tribological,and corrosion properties can be tailored.Although great advancements in this field have been made,these pieces of knowledge are scattered and have not been contextualized into a single work.The motivation of this work is to address this scientific gap and to provide a groundwork for understanding the basics of SPS manufacturing for Mg.To do so,the existing body of SPS Mg literature was first surveyed,with a focus on their structural formation and degradation mechanisms.It was found that successful Mg SPS fabrication highly depended on the processing temperature,particle size,and particle crystallinity.The addition of metal and ceramic composites also affected their microstructural features due to the Zener pinning effect.In degradative environments,their performance depends on their structural features and whether they have secondary phased composites.In industrial applications,SPS'd Mg was found to have great potential in biomedical,hydrogen storage,battery,automotive,and recycling sectors.The prospects to advance the field include using Mg as a doping agent for crystallite size refinement and using bulk metallic Mg-based glass powders for amorphous SPS components.Despite these findings,the interactions of multi-composites on the processing-structure-property relationships of SPS Mg is not well understood.In total,this work will provide a useful direction in the SPS field and serve as a milestone for future Mg-based SPS manufacturing.

Effects of Cu and Co additions on the crystallization and magnetic properties of FeNbB alloy

The nanocrystalline-forming element Cu and magnetic element Co are commonly used as additive elements to tune the structure and improve the properties of alloys.In this study,four kinds of amorphous alloys,Fe_(72)Nb_(12)B_(16),Fe_(72)Nb_(12)B_(15)Cu_(1),Fe_(36)Co_(36)Nb_(12)B_(16),and Fe_(36)Co_(36)Nb_(12)B_(15)Cu_(1),were prepared by melt-spinning and annealed at various temperatures to investigate the effects of Cu and Co additions,individually and in combination,on the crystallization and magnetic properties of Fe_(72)Nb_(12)B_(16)alloy.The four kinds of alloys exhibited different crystallization behaviors with different primary crystallization phases observed.For the Fe_(72)Nb_(12)B_(16)alloy,only theα-Mn-type metastable phase formed after annealing.The addition of 1 at.%Cu and 36 at.%Co led to the observation of theα-Mn-type andβ-Mn-type metastable phases,respectively,and a reduction in the crystallization volume fraction in the metastable phase.The Fe_(36)Co_(36)Nb_(12)B_(15)Cu_(1)alloy only exhibitedα-Fe(Co)phase as a primary phase,and the addition of both Cu and Co completely inhibited the precipitation of the metastable phase.Cu clusters were found in energy dispersive spectroscopy elemental maps.Compared with other alloys,Fe_(36)Co_(36)Nb_(12)B_(15)Cu_(1)alloy with both Cu and Co exhibited a lower coercivity(Hc)below 973 K.

Formation of nanocrystalline AZ31B Mg alloys via cryogenic rotary swaging

A bulk nanocrystalline AZ31B Mg alloy with extraordinarily high strength was prepared via cryogenic rotary swaging in this study.The obtained alloy shows finer grains,higher strength,and a negligible tension-compression yield asymmetry,compared with that prepared via room-temperature rotary swaging.Transmission electron microscopy investigations showed that at the initial stage,multiple twins,mostly tension twins,were activated and intersected with each other,thereby refining the coarse grains into a fine lamellar structure.Then,two types of nanoscale subgrains were generated with increasing swaging strain.The first type of nanoscale subgrain contained twin boundaries and low-angle grain boundaries.This type of subgrain appeared at the twin-twin intersections and was mainly driven by high local stress.The second type of nanoscale subgrain was formed within the twin lamellae.The boundaries of this type of subgrain did not contain twin boundaries and were transformed from massive dislocation arrays.Finally,randomly oriented nanograins were obtained via dynamic recrystallization,under the combined function of deformation heat and increased stored energy.Compared with room-temperature rotary swaging,cryogenic rotary swaging exhibits a slower grain refinement process but a remarkably enhanced grain refinement effect after the same five-pass swaging.

Effect of Al substitution on phase evolution in synthesized Mg_(2)Cu nanoparticles

The effect of Mg replacement with Al on the discharge capacity of Mg_(2)Cu powder mixture was investigated.The mixture of nano-crystalline powder was prepared via mechanical alloying(MA)technique with a high energy planetary ball mill.In addition,different moles of Al(0.05,0.1,0.15,0.2,and 0.3 M)were substituted to Mg_(2)Cu powder.X-ray diffraction(XRD),scanning electron microscopy(SEM),and transmission electron microscopy(TEM)were used to analyze changes in structure,morphology,and grain size.The obtained powder was utilized as an anode in a nickel-metal hydride battery(Ni-MH).In the specimens with 0.05 M Al content,the orthorhombic structure of Mg_(2)Cu is emerged after 5 h milling.The results reveal that more than 0.1 M Al substitution leads to an appearance of MgCu_(2) peaks.Al substi-tution does not affect microstructure uniformity;however,it causes a decrease in crystalline size and lattice parameters.The selected area diffraction(SAD)pattern elucidates that the electrode with the Mg_(1.9)Al_(0.1)Cu chemical composition and 20 h milling has the maximum discharge capacity.

NaH doped TiO_(2)as a high-performance catalyst for Mg/MgH_(2)cycling stability and room temperature absorption

This paper presents the catalytic effect of NaH doped nanocrystalline TiO_(2)(designated as NaTiOxH)in the improvement of MgH_(2)hydrogen storage properties.The catalyst preparation involves ball milling NaH with TiO_(2)for 3 hr.The addition of 5 wt%NaTiOxH powder into MgH_(2)reduces its operating temperature to∼185℃,which is∼110℃lower than the additive-free as-milled MgH_(2).The composite remarkably desorbs∼7.2 wt%H_(2)within 15 min at∼290℃and reabsorbs∼4.5 wt%H_(2)in 45 min at room temperature under 50 bar H_(2).MgH_(2)dehydrogenation is activated at 57 kJ/mol by the catalyst.More importantly,the addition of 2.5 wt%NaTiOxH catalyst aids MgH_(2)to reversibly produce∼6.1 wt%H_(2)upon 100 cycles within 475 hr at 300℃.Microstructural investigation into the catalyzed MgH_(2)composite reveals a firm contact existing between NaTiOxH and MgH_(2)particles.Meanwhile,the NaTiOxH catalyst consists of catalytically active Ti_(3)O_(5),and“rod-like”Na_(2)Ti_(3)O_(7)species liberated in-situ during preparation;these active species could provide multiple hydrogen diffusion pathways for an improved MgH_(2)sorption process.Furthermore,the elemental characterization identifies the reduced valence states of titanium(Ti<4+)which show some sort of reversibility consistent with H_(2)insertion and removal.This phenomenon is believed to enhance the mobility of Mg/MgH_(2)electrons by the creation and elimination of oxygen vacancies in the defective(TiO_(2-x))catalyst.Our findings have therefore moved MgH_(2)closer to practical applications.

Affinity-Engineered Flexible Scaffold toward Energy-Dense, Highly Reversible Na Metal Batteries

The practical deployment of metallic anodes in the energy-dense batteries is impeded by the thermodynamically unstable interphase in contact with the aprotic electrolyte,structural collapse of the substrates as well as their insufficient affinity toward the metallic deposits.Herein,the mechanical flexible,lightweight(1.2 mg cm^(−2))carbon nanofiber scaffold with the monodispersed,ultrafine Sn_(4)P_(3) nanoparticles encapsulation(Sn_(4)P_(3)NPs@CNF)is proposed as the deposition substrate toward the high-areal-capacity sodium loadings up to 4 mAh cm^(−2).First-principles calculations manifest that the alloy intermediates,namely the Na_(15)Sn_(4) and Na_(3)P matrix,exhibit the intimate Na affinity as the“sodiophilic”sites.Meanwhile,the porous CNF regulates the heterogeneous alloying process and confines the deposit propagation along the nanofiber orientation.With the precise control of pairing mode with the NaVPO4F cathode(8.7 mg cm^(−2)),the practical feasibility of the Sn_(4)P_(3) NPs@CNF anode(1^(*)Na excess)is demonstrated in 2 mAh single-layer pouch cell prototype,which achieves the 95.7%capacity retention for 150 cycles at various mechanical flexing states as well as balanced energy/power densities.

Light-stimulated adaptive artificial synapse based on nanocrystalline metal-oxide film

Artificial synapses utilizing spike signals are essential elements of new generation brain-inspired computers.In this paper,we realize light-stimulated adaptive artificial synapse based on nanocrystalline zinc oxide film.The artificial synapse photoconductivity shows spike-type signal response,long and short-term memory(LTM and STM),STM-to-LTM transition and paired-pulse facilitation.It is also retaining the memory of previous exposures and demonstrates spike-frequency adaptation properties.A way to implement neurons with synaptic depression,tonic excitation,and delayed accelerating types of response under the influence of repetitive light signals is discussed.The developed artificial synapse is able to become a key element of neuromorphic chips and neuromorphic sensorics systems.

反相胶团软模板法制备氯化银晶体纳米线研究

The nanosystem has received considerable attention because of its peculiar pheno mena,which is different from macroscopy and microscopy. At present,the upsurge o f researching nanomaterials has shifted from nano particles to one dimensional na nosystem,such as nanowires,nanotubes,and so on.Seen from literatures, the repor ts on carbon nanotubes wer e more,on nanowires were less,and on transition metallic salt nanowires were noth ing .In this paper,AgCl nanocrystalline wires were successfully synthesized by Rever s e Micelle soft Templates, which will open a new way for the synthesis and applic ation of one dimensional nanomaterials.

纳米晶软磁合金环形试样有效磁各向异性的研究(英文)

采用趋近饱和定律首次测定了纳米晶合金环形试样有效磁各向异性常数〈K〉。为了对比测量的准确度,同时测试了传统的晶态坡莫合金环形试样的磁晶各向异性。结果表明,用环形试样可以完成对低矫顽力的软磁材料进行磁各向异性的测定。

GaN纳米固体的氨热合成及其特性研究

Wurtzite structure gallium nitride GaN,a direct bandgap semiconductor,is an ideal material for fabrication of blue/green light emitting diodes,laser diodes, and high powder Integrated Circuites.Up to now,small single crystals,powders and nanomaterials of GaN have successfully synthesized as well as applied films gro wn by MOCVD.In this report,another condensed state of GaN,nanocrystal assembled bulk,was synthesized and its spectra are investigated. Metal gallium or gallium alloys are used as starting materials and haloids used as catalyzer in ammonia.Buff transparent GaN bulks were obtained at 350—500℃.P owder X ray diffraction indicated that the bulks are wurtaite GaN single phase. HRTEM confirmed that the bulks are composed of nanoparticles with average size o f 12mm.The well crystallized particle shows clear diffraction spots.PL spectra of the material are similar to that of GaN singe crystals under the ultraviolet excitation,but blue shift is observed near gap band.Red shift occurs in Raman scattering comparing with single crystals.The materials have the broad potential in the future because it not only possesses of mechanical and optical characteri stics owned by single crystals but also holds the nano properties of the nanoma terials.

机械研磨对FeCuNbSiB微晶合金组织结构的影响

机械研磨对ＦｅＣｕＮｂＳｉＢ微晶合金组织结构的影响张建强，吴炳尧朱建军（东南大学机械工程系，南京２１００１８））（电子工业部第十四研究所，南京２１０００３）ＦｅＣｕＮｂＳｉＢ微晶合金是指由该材料制得的非晶带在略高于晶化温度退火而形成的具有纳米晶相和残...

Study on Nanocrystalline Rare Earth Mg-Based System Hydrogen Storage Alloys with AB_3-Type

A sort of rare earth Mg-based system hydrogen storage alloys with AB3-type was prepared by double-roller rapid quenching method. The alloys were nanocrystalline multi-phase structures composed of LaNi3 phase and LaNi5 phase by X-ray diffraction and scanning electron microscopy analyses, and the suitable absorption/desorption plateau was revealed by the measurement of P-C-I curve. Electrochemical studies indicate that the alloys exhibit good electrochemical properties such as high capacity and stable cycle life, and the discharge capacity is 369 mAh·g-1 at 0.2 C (72 mA·g-1), after 460 cycles, the capacity decay was only 19.4% at 2 C (720 mA·g-1).

A Dye-sensitized Nanocrystalline Solid State Photovoltaic Cell

A new type of dye-sensitized nanocrystalline solid state photovoltaic cell based on the wide band gap n-TiO2/p-Cul heterojunction was fabricated. Tetra-carboxyphenyl porphyrine （TPP（COOH）.）, squarylium cyanine derivative （So-（CH2）,SO3,-Py+） and ruthenium bipyridyl complex （RuL2,（NCS）3,） were used as photosensitizers. Larger photocurrents and photovoltages were shown in the cell sensitized by ruthenium bipyridyl complex and can be fijrther increased by intercalation of a TiO2, thin

High Oxygen Nanocomposite Barrier Films Based on Xylan and Nanocrystalline Cellulose

The goal of this work is to produce nanocomposite film with low oxygen permeability by casting an aqueous solution containing xylan,sorbitol and nanocrystalline cellulose.The morphology of the resulting nanocomposite films was examined by scanning electron microscopy and atomic force microscopy which showed that control films containing xylan and sorbitol had a more open structure as compared to xylan-sorbitol films containing sulfonated nanocrystalline cellulose.The average pore diameter,bulk density,porosity and tortuosity factor measurements of control xylan films and nanocomposite xylan films were examined by mercury intrusion porosimetry techniques.Xylan films reinforced with nanocrystalline cellulose were denser and exhibited higher tortuosity factor than the control xylan films.Control xylan films had average pore diameter,bulk density,porosity and tortuosity factor of 0.1730 μm,0.6165 g/ml,53.0161% and 1.258,respectively as compared to xylan films reinforced with 50% nanocrystalline cellulose with average pore diameter of 0.0581 μm,bulk density of 1.1513 g/ml,porosity of 22.8906% and tortuosity factor of 2.005.Oxygen transmission rate tests demonstrated that films prepared with xylan,sorbitol and 5%,10%,25% and 50% sulfonated nanocrystalline cellulose exhibited a significantly reduced oxygen permeability of 1.1387,1.0933,0.8986 and 0.1799 cm^3×μm/m^2×d×k Pa respectively with respect to films prepared solely from xylan and sorbitol with a oxygen permeability of 189.1665 cm^3×μm/m^2×d×k Pa.These properties suggested these nanocomposite films have promising barrier properties.

Is the Crystalline Lattice Structure in Nanocrystalline Materials Different from the Perfect Crystal Lattice?

A thermodynamic analysis of the ultrafine crystallites in nanocrystalline materials was presented inthis work.It was deduced that the structure of the nm-sized crystalline grains is different from theperfect crystal lattice,characterized by two possible structure changes;supersaturation of alloy ele-ments and crystal lattice distortion resulted from supersaturation of vacancies.Some experimental ev-idences in the literature,which are in agreement of the thermodynamic consideration,indicate thatthe structure changes in the nm-sized crystallite seems to be a consequential feature of thenanocrystalline materials.

Microwave Permeability Change of FeCo Nanocrystalline During High Energy Ball Milling

The microwave magnetic properties of the ball milled FeCo particles were investigated as functions of ball milling time (t) using microwave electromagnetic parameters analysis techniques. The results show that the imaginary part of intrinsic dynamic permeability (μ_i) of the ball-milled particles is much bigger than that of raw powders. μ_i strongly depends on t and exhibits several slightly damped ferromagnetic resonances. These phenomena are in qualitative agreement with the formation of the corresponding microstructure or the Aharoni’s model of non-uniform exchange resonance modes. The present microwave permeability behavior indicates that nanocrystalline materials with the same grain size may exhibit different properties that depend upon the microstructure, which provides a possibility for manufacturing high performance microwave absorber.

Nanocrystalline La2Mo2O9 and Its Characterization

In this work, both the thermal expansion and electrical conductivity of nanocrystalline La2Mo2O9 were studied.The nanocrystalline powder of La2Mo2O9 was obtained by sol-gel method, and with the help of SHP (superhigh pressure)up to 4.5 × 104 atm at 700 ℃ for a short time, and the nanocrystalline powder was densified without obvious particle size growth. The electrical conductivity of nanocrystalline La2Mo2O9 was one orderof magnitude lower than that of the microcrystalline sample at the same temperature. Owing to the phase transition, the microcrystalline La2Mo2O9 has an abrupt increase of thermal expansion with a peak value of 48 × 10-6 K-1 at 556 ℃. For the nanocrystalline material, the peak value increases to 112 × 10-6 K-1 at 520 ℃. On the other hand, above 600 ℃ the significant growth of particle size of the nanocrystalline La2Mo2O9 was observed, accompanying by a tremendous increase of thermal expansion with a peak value of third higher than that of La2Mo2O9.

Structure and Luminescent Properties of Co-doped Nanocrystalline Y_2O_3∶Eu

Nanocrystalline Y2O3∶Eu powders doped with different metal ions M （M: Li +,Na +,K +,Mg （2+）,Sr （2+）,Ba （2+）,B （3+） and Al （3+）） were synthesized by glycine combustion. Their structure and luminescent properties were studied and compared with each other. The nanocrystalline Y2O3 were cubic in symmetry by XRD pattern. It can be concluded that co-doping can modify the size and crystallinity of nanoparticles. As a consequence,the luminescent properties such as the fluorescent intensity,lifetime of （（） 5D0）-（（） 7F2） and the location of charge transfer band （CT band） vary with co-dopants. The variation depends more strongly on the crystallinity of nanoparticles than the size. Especially,in Li +-doped Y2O3∶Eu nanoparticles,the emission intensity improves as large as three times than that of undoped ones.

Effects of Magnetic Annealing on Magnetic Properties in Nd_4Fe_(76)Co_3(Hf_(1-x)Ga_x)B_(16) Alloy

The best linear fit of H_c(T)/M,(T) vs 2k_1(T)/μ_0M s^2(T) infers that H_c is determined by a nucleation process in nanocrystalline two-phase magnet.The condition of the grain shapes is improved after adding Hf and Ga,but the surfaces are deteriorated by some precipitates on the boundary.Taking into account the values of α,N_(eff),the results of TEM,and Moessbauer spectroscopy,the magnetic field heat-treatment not only induces grain refinement but also causes a uniform distribution of the soft and hard phases.It is one recommendable method to improve the condition of the microstructure.Both the remanence and energy product values are increased by 20%— 30%for all ribbons after annealing with magnetic field.The magnetic interaction in Nd_2Fe_(14)B/Fe_3B + αFe based nanocrystalline two-phase magnets is studied using δM plots in this paper.It is found that the exchange coupled interaction is greatly enhanced in the sample annealed with magnetic heat-treatment,specially,Nd_4Fe_(76)Co_3Hf_(0.5)Ga_(0.5)B_(16) which achieves the highest energy product(BH)_(max)=126.4kJ/m^3.

Investigation of Nanostructured WC-Co Alloy Prepared by Mechanical Alloying

ＩｎｖｅｓｔｉｇａｔｉｏｎｏｆＮａｎｏｓｔｒｕｃｔｕｒｅｄＷＣＣｏＡｌｏｙＰｒｅｐａｒｅｄｂｙＭｅｃｈａｎｉｃａｌＡｌｏｙｉｎｇＭａＸｕｅｍｉｎｇ，ＪｉＧａｎｇ，ＺｈａｏＬｉｎｇａｎｄＤｏｎｇＹｕａｎｄａ（马学鸣）（嵇罡）（赵凌）（董远达）Ｉｎｓ...