Impact Analysis of Microscopic Defect Types on the Macroscopic Crack Propagation in Sintered Silver Nanoparticles

Sintered silver nanoparticles(AgNPs)arewidely used in high-power electronics due to their exceptional properties.However,the material reliability is significantly affected by various microscopic defects.In this work,the three primary micro-defect types at potential stress concentrations in sintered AgNPs are identified,categorized,and quantified.Molecular dynamics(MD)simulations are employed to observe the failure evolution of different microscopic defects.The dominant mechanisms responsible for this evolution are dislocation nucleation and dislocation motion.At the same time,this paper clarifies the quantitative relationship between the tensile strain amount and the failure mechanism transitions of the three defect types by defining key strain points.The impact of defect types on the failure process is also discussed.Furthermore,traction-separation curves extracted from microscopic defect evolutions serve as a bridge to connect the macro-scale model.The validity of the crack propagation model is confirmed through tensile tests.Finally,we thoroughly analyze how micro-defect types influence macro-crack propagation and attempt to find supporting evidence from the MD model.Our findings provide a multi-perspective reference for the reliability analysis of sintered AgNPs.

Cooperative effect of sodium lauryl sulfate collector and sodium pyrophosphate depressant on the flotation separation of lead oxide minerals from hematite

As a cornerstone of the national economy,the iron and steel industry generates a significant amount of sintering dust containing both valuable lead resources and deleterious elements.Flotation is a promising technique for lead recovery from sintering dust,but efficient separation from Fe_(2)O_(3) is still challenging.This study investigated the cooperative effect of sodium lauryl sulfate(SLS,C_(12)H_(25)SO_(4)Na)and sodium pyrophosphate(SPP,Na_(4)P_(2)O_(7))on the selective flotation of lead oxide minerals(PbOHCl and PbSO_(4))from hematite(Fe_(2)O_(3)).Optimal flotation conditions were first identified,resulting in high recovery of lead oxide minerals while inhibiting Fe_(2)O_(3) flotation.Zeta potential measurements,Fourier transform infrared spectroscopy(FT-IR)analysis,adsorption capacity analysis,and X-ray photoelectron spectroscopy(XPS)studies offer insights into the adsorption behaviors of the reagents on mineral surfaces,revealing strong adsorption of SLS on PbOHCl and PbSO_(4) surfaces and remarkable adsorption of SPP on Fe_(2)O_(3).The proposed model of reagent adsorption on mineral surfaces illustrates the selective adsorption behavior,highlighting the pivotal role of reagent adsorption in the separation process.These findings contribute to the efficient and environmentally friendly utilization of iron ore sintering dust for lead recovery,paving the way for sustainable resource management in the iron and steel industry.

Effect of TbF_(3)diffusion on the demagnetization behavior and domain evolution of sintered Nd-Fe-B magnets by electrophoretic deposition

We studied the magnetic properties and domain evolution of annealed and TbF3-diffused sintered Nd-Fe-B magnets using the electrophoretic deposition method.After TbF_(3)diffusion,the coercivity increased significantly by 9.9 kOe and microstructural analysis suggested that Tb favored the formation of the(Nd,Tb)_(2)Fe_(14)B shell phase in the outer region of the matrix grains.The first magnetization reversal and the dynamic successive domain propagation process were detected with a magneto-optical Kerr microscope.For the TbF_(3)-diffused magnet,the magnetization reversal appeared at a larger applied field and the degree of simultaneous magnetization reversal decreased compared with an annealed magnet.During demagnetization after full magnetization,the occurrence of domain wall motion(DWM)in the reproduced multi-domain regions was observed by the step method.The maximum polarization change resulting from the reproduced DWM was inversely related to the coercivity.The increased coercivity for the diffused magnet was mainly attributed to the more difficult nucleation of the magnetic reversed region owing to the improved magneto-crystalline anisotropy field as a result of Tb diffusion.

Thermal expansion behavior of sintered Nd–Fe–B magnets with different Co contents and orientations

The thermal expansion behavior of sintered Nd–Fe–B magnets is a crucial parameter for production and application.However, this aspect has not been thoroughly investigated. In this study, three different sintered Nd–Fe–B magnets with varying Co content(Co = 0, 6, 12 wt%) were prepared using the conventional powder metallurgy method, and four magnets oriented under different magnetic fields were prepared to compare. The thermal expansion behavior for the magnets was investigated using a linear thermal dilatometry in the temperature range of 20℃–500℃. It was found that, the coefficient of thermal expansion(CTE) increases with the increase of Co contents, while the anisotropy of thermal expansion decreases.The introduction of Co leads to continuous changes from negative to positive thermal expansion in the vertically oriented direction, which is important for the development of zero thermal expansion magnets. The thermal expansion of nonoriented magnets was found to be isotropic. Additionally, the anisotropy of thermal expansion increases with the increase of orientation degree. These results have important implications for the development of sintered Nd–Fe–B with controllable CTE.

Optimization of the grain boundary diffusion process by doping gallium and zirconium in Nd–Fe–B sintered magnets

As the channel for grain boundary diffusion(GBD)in Nd–Fe–B magnets,grain boundary(GB)phases have a very important effect on GBD.As doping elements that are commonly used to regulate the GB phases in Nd–Fe–B sintered magnets,the influences of Ga and Zr on GBD were investigated in this work.The results show that the Zr-doped magnet has the highest coercivity increment(7.97 kOe)by GBD,which is almost twice that of the Ga-doped magnet(4.32 kOe)and the magnet without Ga and Zr(3.24 kOe).Microstructure analysis shows that ZrB_(2)formed in the Zr-doped magnet plays a key role in increasing the diffusion depth.A continuous diffusion channel in the magnet can form because of the presence of ZrB_(2).ZrB_(2)can also increase the defect concentration in GB phases,which can facilitate GBD.Although Ga can also improve the diffusion depth,its effect is not very obvious.The micromagnetic simulation based on the experimental results also proves that the distribution of Tb in the Zr-doped magnet after GBD is beneficial to coercivity.This study reveals that the doping elements Ga and Zr in Nd–Fe–B play an important role in GBD,and could provide a new perspective for researchers to improve the effects of GBD.

Low temperature solid-phase sintering of sintered metal fibrous media with high specific surface area

A procedure of low temperature solid-phase sintering（LTSS） was carried out to fabricate sintered metal fibrous media（SMFM） with high specific surface area.Stainless steel fibers which were produced by cutting process were first plated with a coarse copper coating layer by electroless plating process.A low-temperature sintering process was then completed at about 800 °C for 1 h under the protection of hydrogen atmosphere.The results show that a novel SMFM with complex surface morphology and high specific surface area（0.2 m2/g） can be obtained in this way.The effect of sintering temperature on the surface morphology and specific surface area of SMFM was studied by means of scanning electron microscopy and Brunauer-Emmett-Teller.The damage of micro-structure during the sintering process mainly contributed to the loss of specific surface area of SMFM and the optimal sintering temperature was 800 °C.

Decarburization and improvement of ultra fine straight WC-8Co sintered via microwave sintering

Cemented tungsten carbide with ultra fine grains was prepared via microwave sintering.η phase（W3Co3C） was formed on the surface of the samples during the preparation process.Extra carbon black was premixed and the influence of carbon content on mechanical properties was studied.The results show that the maximum value of hardness and transverse rupture strength are HRA 93.2 and 3396 MPa respectively when the carbon black content is 0.45%.The microstructure investigated by SEM show that the WC grains growth mainly occurs during the early stage of microwave sintering by the coalescence of grains.

Design and fabrication of sintered wick for miniature cylindrical heat pipe

Miniature cylindrical metal powder sintered wick heat pipe （sintered heat pipe） is an ideal component with super-high thermal efficiency for high heat flux electronics cooling. The sintering process for sintered wick is important for its quality. The sintering process was optimally designed based on the equation of the heat transfer limit of sintered heat pipe. Four-step sintering process was proposed to fabricate sintered wick. The sintering parameters including sintering temperature, sintering time, sintering atmosphere and sintering position were discussed. The experimental results showed that the proper sintering temperature was 950 ℃ for Cu powder of 159μm and 900 ℃ for Cu powders of 81 and 38 μm, respectively, while the wick thickness was 0.45 mm and sintering time was 3 h. The optimized sintering time was 3 h for 0.45 and 0.6 mm wick thickness and 1 h for 0.75 mm wick thickness, respectively, when copper powder diameter was 159μm and sintering temperature was 950 ℃. Redox reduction reaction between H2 and CuO during sintering could produce segmentation cracks in Cu powders as a second structure. Sintering at vertical position can effectively avoid the generation of gap between wick and the inner wall of pipe.

Manufacture, characterization and application of porous metal-fiber sintered felt used as mass-transfer-controlling medium for direct methanol fuel cells

Fabrication, characterization and performance of a porous metal-fiber sintered felt （PMFSF） based on multi-tooth cutting and solid-phase sintering were studied. The PMFSF was used as the anodic methanol barrier in a passive air-breathing direct methanol fuel cell to mitigate the effects of methanol crossover. Compared with the commercial SUS316L felt made of bundle-drawn fibers, this self-made PMFSF has larger pore diameter, polarized pore distribution, irregular fiber shape, rougher surface, lower mass flow resistance and evident hydrophobicity. The results reveal that the use of a PMFSF significantly enhances the cell performance since it helps to maintain a balance between the reactant and product management while depressing methanol crossover. The PMFSF with a porosity of 70% yields the highest cell performance at a methanol concentration of 4 mol/L.

Microstructure and mechanical properties of Ti-45Al-5.5(Cr,Nb,B,Ta) alloy sintered at different SPS temperatures

TiAl alloy bulk samples with the composition of Ti-45Al-5.5(Cr,Nb,B,Ta) (mole fraction, %) were prepared by high energy mechanical milling and spark plasma sintering (SPS) and then heat treatment. The microstructure and mechanical properties after heat treatment of TiAl alloy prepared by SPS at different temperatures were studied. The results showed that the morphology of high energy mechanically milled powder was irregular and the average grain size was about decades micrometers. X-ray diffraction analysis showed that the mechanically milled powder was composed of two phases of TiAl and Ti3Al. The main phase of TiAl and few phases of Ti3Al and TiB2 were observed in the SPS bulk samples of Ti-45Al-5.5(Cr,Nb,B,Ta) alloy. For samples sintered at 900 °C and 1000 °C, the microstructure was duplex structure with some fine equiaxed gamma grains and thin needly TiB2 phases. With the SPS temperature increasing from 900 °C to 1000 °C, the micro-hardness was changed little, the compression strength increased from 1812 MPa to 2275 MPa and the compression ratio increased from 22.66% to 25.59%. The fractography results showed that the compression fracture transform of the SPS Ti-45Al-5.5(Cr,Nb,B,Ta) alloy was rgranular rupture.

Recent developments in selective laser processes for wearable devices

Recently,the increasing interest in wearable technology for personal healthcare and smart virtual/augmented reality applications has led to the development of facile fabrication methods.Lasers have long been used to develop original solutions to such challenging technological problems due to their remote,sterile,rapid,and site-selective processing of materials.In this review,recent developments in relevant laser processes are summarized under two separate categories.First,transformative approaches,such as for laser-induced graphene,are introduced.In addition to design optimization and the alteration of a native substrate,the latest advances under a transformative approach now enable more complex material compositions and multilayer device configurations through the simultaneous transformation of heterogeneous precursors,or the sequential addition of functional layers coupled with other electronic elements.In addition,the more conventional laser techniques,such as ablation,sintering,and synthesis,can still be used to enhance the functionality of an entire system through the expansion of applicable materials and the adoption of new mechanisms.Later,various wearable device components developed through the corresponding laser processes are discussed,with an emphasis on chemical/physical sensors and energy devices.In addition,special attention is given to applications that use multiple laser sources or processes,which lay the foundation for the all-laser fabrication of wearable devices.

GROWTH OF MnS IN Fe-CU-C-MnS SINTERED STEELS WITH ADMIXED MnS

MnS growth in sintered steels with admixed Fe, Cu, C and MnS has been investigated by SEM and X-ray diffraction, MnS in Fe-Cu-C-MnS sintered steels in which MnS has been admixed is not stable and MnS growth may be ascribed to sintering between MnS particles or reaction between MnS and Fe, Cu, C elements.

Towards the insights into the deactivation behavior of acetylene hydrogenation catalyst

A series of model catalysts were obtained by treating commercial fresh and spent catalysts unloaded from the factory with different methods, including green oil dipping, extraction and high-temperature regeneration;finally, the deactivation behavior of the commercial catalyst for acetylene hydrogenation were studied. The influence of various possible deactivation factors on the catalytic performance was elucidated via detailed structural characterization, surface composition analysis, and activity evaluation.The results showed that green oil, carbon deposit and sintering of active metal were the main reasons for deactivation, among which green oil and carbon deposit led to rapid deactivation, while the activity could be recovered after regeneration by high-temperature calcination. The sintering of active metal components was attributed to the high-temperature regeneration in hydrothermal conditions, which was slow but irreversible and accounted for permanent deactivation. Thus, optimizing the regeneration is expected to extend the service life of the commercial catalyst.

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.

Integrated high-performance and accurate shaping technology of low-cost powder metallurgy titanium alloys: A comprehensive review

The practical engineering applications of powder metallurgy (PM) Ti alloys produced through cold compaction and pressure-less sintering are impeded by poor sintering densification, embrittlement caused by excessive O impurities, and severe sintering deforma-tion resulting from the use of heterogeneous powder mixtures. This review presents a summary of our previous work on addressing the above challenges. Initially, we proposed a novel strategy using reaction-induced liquid phases to enhance sintering densification. Near- complete density (relative density exceeding 99%) was achieved by applying the above strategy and newly developed sintering aids. By focusing on the O-induced embrittlement issue, we determined the onset dissolution temperature of oxide films in the Ti matrix. On the basis of this finding, we established a design criterion for effective O scavengers that require reaction with oxide films before their dissol-ution. Consequently, a ductile PM Ti alloy was successfully obtained by introducing 0.3wt% NdB6 as the O scavenger. Lastly, a powder- coating strategy was adopted to address the sintering deformation issue. The ultrafine size and shell-like distribution characteristics of coating particles ensured rapid dissolution and homogeneity in the Ti matrix, thereby facilitating linear shrinkage during sintering. As a result, geometrically complex Ti alloy parts with high dimensional accuracy were fabricated by using the coated powder. Our fundament-al findings and related technical achievements enabled the development of an integrated production technology for the high-performance and accurate shaping of low-cost PM Ti alloys. Additionally, the primary engineering applications and progress in the industrialization practice of our developed technology are introduced in this review.

Spark Plasma Sintering of Boron Carbide Using Ti_(3)SiC_(2) as a Sintering Additive

Boron carbide has unique properties for wide application possibilities;however,poor sinterability limits its applications.One approach to overcome this limitation is the addition of secondary phases into boron carbide.Boron carbide based composite ceramics are produced by the direct addition of secondary phases into the structure or via reactive sintering using a sintering additive.The present study investigated the effect of Ti_(3)SiC_(2) addition to boron carbide by reactive spark plasma sintering in the range of 1700-1900℃.Ti_(3)SiC_(2) phase decomposed at high temperatures and reacted with B4C to form secondary phases of TiB2 and SiC.The results demonstrated that the increase of Ti_(3)SiC_(2) addition(up to 15 vol%)effectively promoted the densification of B4C and yielded higher hardness.However,as the amount of Ti_(3)SiC_(2) increased further,the formation of microstructural inhomogeneity and agglomeration of secondary phases caused a decrease in hardness.

Phase-Field Simulation of Sintering Process:A Review

Sintering,a well-established technique in powder metallurgy,plays a critical role in the processing of high melting point materials.A comprehensive understanding of structural changes during the sintering process is essential for effective product assessment.The phase-field method stands out for its unique ability to simulate these structural transformations.Despite its widespread application,there is a notable absence of literature reviews focused on its usage in sintering simulations.Therefore,this paper addresses this gap by reviewing the latest advancements in phase-field sintering models,covering approaches based on energy,grand potential,and entropy increase.The characteristics of various models are extensively discussed,with a specific emphasis on energy-based models incorporating considerations such as interface energy anisotropy,tensor-form diffusion mechanisms,and various forms of rigid particle motion during sintering.Furthermore,the paper offers a concise summary of phase-field sintering models that integrate with other physical fields,including stress/strain fields,viscous flow,temperature field,and external electric fields.In conclusion,the paper provides a succinct overview of the entire content and delineates potential avenues for future research.

Oxygen vacancy boosting Fenton reaction in bone scaffold towards fighting bacterial infection

Bacterial infection is a major issue after artificial bone transplantation due to the absence of antibacterial function of bone scaffold,which seriously causes the transplant failure and even amputation in severe cases.In this study,oxygen vacancy(OV)defects Fe-doped Ti O2(OV-FeTiO2)nanoparticles were synthesized by nano TiO2and Fe3O4via high-energy ball milling,which was then incorporated into polycaprolactone/polyglycolic acid(PCLGA)biodegradable polymer matrix to construct composite bone scaffold with good antibacterial activities by selective laser sintering.The results indicated that OV defects were introduced into the core/shell-structured OV-FeTiO2nanoparticles through multiple welding and breaking during the high-energy ball milling,which facilitated the adsorption of hydrogen peroxide(H2O2)in the bacterial infection microenvironment at the bone transplant site.The accumulated H2O2could amplify the Fenton reaction efficiency to induce more hydroxyl radicals(·OH),thereby resulting in more bacterial deaths through·OH-mediated oxidative damage.This antibacterial strategy had more effective broad-spectrum antibacterial properties against Gram-negative Escherichia coli(E.coli)and Gram-positive Staphylococcus aureus(S.aureus).In addition,the PCLGA/OV-FeTiO2scaffold possessed mechanical properties that match those of human cancellous bone and good biocompatibility including cell attachment,proliferation and osteogenic differentiation.

High mechanical strength Si anode synthesis with interlayer bonded expanded graphite structure for lithium-ion batteries

Despite advancements in silicon-based anodes for high-capacity lithium-ion batteries,their widespread commercial adoption is still hindered by significant volume expansion during cycling,especially at high active mass loadings crucial for practical use.The root of these challenges lies in the mechanical instability of the material,which subsequently leads to the structural failure of the electrode.Here,we present a novel synthesis of a composite combining expanded graphite and silicon nanoparticles.This composite features a unique interlayer-bonded graphite structure,achieved through the application of a modified spark plasma sintering method.Notably,this innovative structure not only facilitates efficient ion and electron transport but also provides exceptional mechanical strength(Vickers hardness:up to658 MPa,Young's modulus:11.6 GPa).This strength effectively accommodates silicon expansion,resulting in an impressive areal capacity of 2.9 mA h cm^(-2)(736 mA h g^(-1)) and a steady cycle life(93% after 100cycles).Such outsta nding performance is paired with features appropriate for large-scale industrial production of silicon batteries,such as active mass loading of at least 3.9 mg cm^(-2),a high-tap density electrode material of 1.68 g cm^(-3)(secondary clusters:1.12 g cm^(-3)),and a production yield of up to 1 kg per day.

Effect of Sintering Temperature on the Microstructure and Mechanical Properties of Nanocrystalline Cemented Carbide

WC-Co nanocrystalline nitrogen-containing cemented carbides were prepared by vacuum sintering and low pressure sintering.The sintering processes of Cr_(2)(C,N)doped nano WC-Co powders were studied by using thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC).The effect of sintering temperature on the microstructure and mechanical properties of nanocrystalline cemented carbide was studied by scanning electron microscope(SEM),high resolution transmission electron microscope(HRTEM)and mechanical property test.The results showed that the nano WC grains began to grow in the solid phase sintering stage.A high-performance nano-nitrogen-containing cemented carbide with uniform microstructure and good interfacial bonding can be obtained by increasing the sintering temperature to 1380℃.It has a transverse rupture strength(TRS)of 5057 MPa and a hardness of 1956 HV30.