Sintering Treatment Research Articles

Novel fabrication of low-cost Ti–Cu alloy by electroless copper plating and vacuum sintering

We report a novel fabrication method of low-cost Ti–Cu alloy. Cu coated Ti powders with core-shell structure are prepared by electroless copper plating of spherical Ti powders. The growth mechanism of core-shell Ti@Cu powders is illustrated. The sintered Ti–Cu alloy exhibits excellent mechanical properties due to the homogeneous distribution of the fine Ti2Cu particles in the Ti matrix after sintering treatment.

Iron Species-Supporting Hydrophobic and Nonswellable Polytetrafluoroethylene/Poly(acrylic acid-co-hydroxyethyl methacrylate) Composite Fiber and Its Stable Catalytic Activity for Methylene Blue Oxidative Decolorization.

Polytetrafluoroethylene emulsion was ultrasonically mixed with an extremely spinnable poly(acrylic acid-co-hydroxyethyl methacrylate) solution to get a dispersion with good spinnability, and the obtained dispersion was then wet-spun into water-swellable fiber. Crosslinking agents and iron species were simultaneously introduced into the water-swellable fiber through simple impregnation and water swelling. A composite fiber with Fenton reaction-catalyzing function was then fabricated by sequentially conducting crosslinking and sintering treatment. Due to crosslinking-induced good resistance to water swelling and PTFE component-induced hydrophobicity, the composite fiber showed a highly stable activity to catalyze H2O2 to oxidatively decolorize methylene blue (MB). Within nine cycles, the composite fiber could decolorize more than 90% of MB within one minute in the presence of H2O2 and did not show any attenuation in MB decolorization efficiency. The composite fiber still could reduce the total organic carbon of MB aqueous solution from 18.3 to 10.3 mg/L when used for the ninth time. Therefore, it is believable that the prepared fiber has good and broad application prospects in the field of dye wastewater treatment.

ZnS nanoparticles embedded in N-doped porous carbon xerogel as electrode materials for sodium-ion batteries

zinc sulfide (ZnS) has attracted extensive attention as an electrode material for sodium-ion batteries (SIBs) due to its high capacity and abundant resource. In order to improve the cycling stability, ZnS nanoparticles embedded in N-doped porous carbon xerogel (ZnS/N-CX) were prepared via a facile electrostatic assembly, followed by a high-temperature sintering treatment. In contrast to the retention rate of bare ZnS electrode (6.4%), the ZnS/N-CX electrode shows better capacity retention (51.8%) at a current density of 0.5 A g−1, and delivers a reversible capacity of 312 mAh g−1 at a current density of 0.1 A g−1. This is because the porous N-CX derived from polyelectrolytes can enhance the ZnS nanoparticles' conductivity during long-term cycling. Besides, X-ray diffraction analysis is used to confirm the (de)sodiation mechanism during the 1st cycle of the ZnS/N-CX electrode. In addition, X-ray photoelectron spectroscopy analysis indicates that polymeric components in the solid electrolyte interphase (SEI) prefer to form on the surface of loaded N-CX, resulting in a massive Na+ consumption and rapid decrease of initial Coulombic efficiency (CE). The analysis of electrochemical impedance spectroscopy reveals that the increase of interface resistance is suppressed in long-term cycling, with respect to the bare ZnS electrode. Therefore, these results prove that the synergistic approach of supporting/coating N-CX can be applied in the metal sulfides to achieve improved performance in terms of Na+ storage capacity.

Thermistors manufactured from nioubium oxide in the ZrO2-Bi2o3 / Termistores manufacturados de óxido de nioúbio no ZrO2-Bi2o3

Thermistors are thermal resistors that allow high changes in the dielectric constant due to the sensible temperature change. The thermistors can be P.T.C.R and N.T.C.R. They are devices applied within the oil exploration industry, automobiles and electronics. The ceramic powders were obtained from stoichiometric quantities by ball milling with subsequent compaction, sintering and heat treatment from 825 ° C for 24 hours and cooled to room temperature. The samples were characterized by X-ray diffraction, scanning electron microscopy, calculation of the apparent density, dielectric constant and qualitative thermistor factors, called temperature coefficient and characteristic ratio. The samples from the mixture between the niobium zirconia-bismuth oxides obtained significant results for commercial and industrial application in the respective temperature ranges, between 30ºC-80ºC and 460ºC-600ºC.

Scalable and environmentally friendly mechanochemical synthesis of nanocrystalline rhodostannite (Cu2FeSn3S8)

This study demonstrates scalable mechanochemical synthesis of rhodostannite Cu2FeSn3S8 nanocrystals. On the contrary to the previous reports focused on the synthesis of stannite Cu2FeSnS4 reporting the rhodostannite impurity, we succeeded in preparing stannite-free product after milling. Pure elements were used for a solvent-free production in a batch of 100 g using an eccentric vibratory mill. The progress of the synthesis was monitored by X-ray diffraction and magnetometry, which both confirmed a successful reaction progress until 6 h of milling. However, further treatment (until 10 h) did not result in an improvement, as quite a high saturation magnetization (7.8 emu/g) and clearly evident diffraction at around 44° in the XRD pattern of the product due to the presence of ferromagnetic un-reacted iron with content slightly above 5% was evidenced. The product is sulfur- and tin-deficient, with crystallite size of around 12 nm. In-depth SEM/EDS analysis has shown the inhomogeneity of Fe distribution due to unfinished reaction. The bandgap of the produced material was 1.29 eV. The spark plasma sintering treatment resulted in complete consumption of non-reacted iron, but partial decomposition to stannite Cu2FeSnS4 was observed. The product is an intrinsic semiconductor with high electrical resistivity, and is therefore unsuitable for thermoelectric application. However, its thermal conductivity is low, thus it could be used as an electrically and thermally insulating material.

Analysis of Concentration Dependent Interdiffusion Coefficient Under the Condition of Pre-Existing Non-uniform Solute Distribution

A numerical inverse method is used to calculate concentration dependency of interdiffusion coefficient under a condition of pre-existing non-uniform solute distribution, which is impossible to do by standard techniques including the Boltzmann–Matano, Sauer–Freise, Hall, and Wagner methods. The results show that in contrast to what has been implicitly assumed in the literature, “calculation-error-free” concentration-dependent interdiffusion coefficient can be significantly influenced by non-uniform solute distribution that pre-exists in a material prior to a diffusion process. In such cases, the use of concentration-dependent interdiffusion coefficient obtained by the standard techniques, such as, the Boltzmann–Matano, Sauer–Freise, Hall, and Wagner methods, to model, predict or analyze diffusion effects during multi-stage materials processing, such as, sintering, brazing, coating and heat treatments, can be considerably unreliable.

Processability of metal-filament through polymer FDM machine

FDM is one of the simplest and cheapest available additive technologies, mostly limited to polymeric materials. Metal-FDM process may overcome this limit using a metal filament bounded with polymer, which is removed through debinding and sintering treatments. Producing metal components using an economic machine would make it possible to produce non-critical components with complex geometry at an industrial level and at low-cost. This work aims to investigate whether a low-cost commercial 3D printer may be able to print a metal filament and what are the achievable density and the shrinkage on the final part. An experimental campaign (24 factorial plan) was performed, considering as variable factors the nozzle temperature, the infill pattern, the print speed and the layer thickness. Statistical tools as the boxplot for determining outliers and the analysis of variance (ANOVA) were used to evaluate the results, identifying which process parameters ad their interactions affect the selected indicators (density and shrinkage). The results show that the conversion of a low-cost FDM machine from polymer to metal filament is possible, generating repeatable and stable results. The process is faster and less expensive than the existing powder-bed-fusion based metal AM technology. The best combination of printing parameters was identified considering as target point the density of the “traditional” AISI 316L steel. Different behaviors in terms of shrinkage were identified: trends are stable and very similar for X and Y directions, independently from the printing parameters, while the interaction between temperature and other parameters causes higher variability along the Z-axis.

Rapid production of AZ91 Mg alloy by extrusion based additive manufacturing process

ABSTRACT AZ91 magnesium alloy parts were successfully produced using a novel extrusion-based additive manufacturing process. The green parts were built in two different orientations and subjected to debinding and sintering treatments. The as-built alloy showed a heterogeneous microstructure made up of α – Mg matrix, Al8Mn5 second phase particles, MgO layers and Mg17Al12continuous precipitates. After solution treatment followed by aging, Mg17Al12 discontinuous precipitates were observed. The sintered samples showed a yield strength and ultimate tensile strength of 79 and 207 MPa, respectively, in the horizontal configuration. Analysis of the fracture surfaces revealed that a continuous network of magnesium oxide layer around the powder particles act as preferential path for crack propagation.

Towards high performance GNFs/Ti composite through simultaneously manipulating laminated microstructure and interface reaction

Bulk graphene nano-flakes (GNFs)-reinforced Ti matrix composite (GNFs/Ti) was obtained by laminated microstructure design. By means of a novel flake powder assembly approach, the GNFs possessed high compatibility with Ti flakes and achieved uniform dispersion in matrix. Powder mixtures were consolidated through low-temperature sintering and short-time heat treatment strategy to simultaneously manipulate the interface reaction and microstructure. Compared with the unreinforced Ti matrix, GNFs/Ti composites were shown to obtain significantly improved strength. Specially, the 0.46 vol% GNFs/Ti composite heat-treated at 1023 K for 450s exhibited the exceptional well ductility with a superior high compressive yield strength of ~2 GPa, which was interpreted by the strong GNFs-Ti interface, and the extrinsic toughening effect as a result of the laminated microstructure and improvement of matrix grain bonding. This work provided a feasible way to construct the high performance nano-carbon reinforced Ti-based composites, and underscore the importance of interface reaction and microstructure design for achieving the well strength-ductility combination.

­Effect of sintering treatment time on the sintering behaviour and thermal shock resistance of Li2O-Al2O3-SiO2 glass-ceramics

ABSTRACT In order to determine the correlation of flexural strength and thermal shock resistance properties, the sintering behavior of Li2O-Al2O3-SiO2 (LAS) glass-ceramics at different sintering treatment times and the effect of thermal shock cycles on LAS glass-ceramics were investigated. The LAS glass-ceramics were isothermally treated at 1100°C from 1.5 to 4.5 h. Phase transformation of major crystalline of β-spodumene and minor crystalline of ZrTiO4 revealed unchanged as sintering treatment time increased. The physical properties of LAS glass-ceramics that were sintered for 3.5 h demonstrated an increased density (2.45 g/cm3) and less porosity percentage (0.62%). The prolonged sintering treatment affected the microstructure whereby the mean grain size increased from 0.55 to 0.67 µm which also demonstrated the increase of microhardness in the range between 3.90 and 5.47 GPa. The flexural strength of LAS glass-ceramics revealed an enhancement of 158 MPa when sintered for 3.5 h. The thermal shock resistance properties were assessed at 500°C from one to seven cycles via thermal shock tests. After four thermal shock cycles, LAS glass-ceramics showed an improvement of 82% of residual strength from its original strength, due to a decrease in the formation of pores and an increase in the crystallinity and percentage of β-spodumene.

Sliding wear behaviour of Fe/316L/430-Ti(C,N) composites prepared via spark plasma sintering and subsequent heat treatment

A series of novel steel—Ti(C,N) composites was fabricated by spark plasma sintering (SPS) and subsequent heat treatment. The hardness, indentation fracture resistance, and wear behaviour of the steel—Ti(C,N) composites were compared with those of the unreinforced samples, and their potentials were assessed by comparison with traditional cermet/hardmetal systems. The results showed that with the addition of 20wt% Ti(C,N), the wear rates of the newly examined composites reduced by a factor of about 2 to 4 and were comparable to those of cermets and hardmetals. The martensitic transformation of the steel matrix and the formation of in situ carbides induced by heat treatment enhanced the wear resistance. Although the presence of excessive in situ carbides improved the hardness, the low indentation fracture resistance (IFR) value resulted in brittle fracture, which in turn resulted in poor wear property. Moreover, the operative wear mechanisms were investigated. This study provides a practical and cost-effective approach to prepare steel—Ti(C,N) composites as potential wear-resistant materials.

Study on forming accuracy of ZrO2 ceramic materials prepared by DLP technology

DLP technology is one of the 3D printing methods for ceramic materials, and its forming accuracy is affected by the preparation of ceramic slurry, debinding and sintering process. In view of three different slurry preparation methods and solid content, the flow characteristics of slurry were studied. The reasonable debinding and sintering process was formulated, and the debinding and sintering treatment were carried out. The influence of slurry preparation methods on the forming accuracy of green parts and sintered parts was found out. The results show that with the increase of solid content, the viscosity of slurry also increases and the fluidity becomes worse. Increasing milling time and rotating speed can improve the flow characteristics of the slurry with 70% zirconia solid content. The C method can not only increase the solid content of the slurry, but also reduce the shrinkage of the sintered parts and improve the dimensional accuracy of the sintered parts.

Effects of Heat-Treatment on Microstructures and Mechanical Properties of Hot Deformed Ti-6Al-4V Alloy

In this paper, Ti-6Al-4V alloy were successfully fabricated using a Spark Plasma Sintering (SPS), thermal deformation and heat treatment process. SPS sintering is divided into two steps: The first step is low-temperature molding at 600°C and 300 MPa, and the second step is thermal deformation at 800°C, with a deformation of 70%. The effects of solution treatment and aging process at temperatures above and below the β transformation point on the microstructure and mechanical properties of Ti-6Al-4V are investigated. The study found that the mechanical properties were better after treatment (900°C, 30 min+ water quenching +550°C, 4 h).

Factors affecting the tribotechnical properties of sintered materials

The article considers the issues of production of powder antifriction materials based on iron by methods of pressing and rolling powder mixtures. The analysis of influence of composition of materials, technological conditions of their production and other factors on the structure, mechanical and tribotechnical properties of powder sliding bearings was carried out. During the operation of the machine, its elements, subjected to various influences, change in state, size and properties. The effectiveness of developments in the field of tribotechnical materials is determined by the properties of these materials, as well as the speed and breadth of their industrial use. The effect of porosity of samples on their tribotechnical properties and hardness after sintering and additional heat treatment is studied. The results of tribotechnical tests of iron-copper-graphite sintered sulfided compositions, not alloyed and doped with phosphorus, as well as materials including additional lubricant components: graphite, molybdenum disulfide or calcium fluoride, are presented. On the basis of tests, it was found that in conditions of liquid friction, alloying with phosphorus has a decisive effect on increasing wear resistance, and without supplying lubricant to sintered samples with impregnated oil, wear is more than an order of magnitude higher compared to the conditions of liquid friction.

Degreasing cotton used as pore-creating agent to prepare hydrophobic and porous carbon cathode for the electro-Fenton system: enhanced H2O2 generation and RhB degradation.

A porous carbon cathode was prepared using graphite, polytetrafluoroethylene (PTFE), and degreasing cotton (DC) through sintering treatment. The carbonization of DC by heat treatment played an ideal role in pore-creating, which weakened the mass transfer resistance of O2, and as a result, the adoption of degreasing cotton significantly improved the performance of H2O2 electro-generation. The optimized cathode was able to generate 567 mg L-1 H2O2 with a current efficiency (CE) of 86.7% by the electrochemical reaction of 60 min in a divided reactor. Furthermore, the degradation of rhodamine B (RhB) was carried out by an electro-Fenton system using the optimal cathode selected. The developed electro-Fenton system exhibited an excellent RhB degradation performance. The RhB solution of 50 mg L-1 was decolorized completely by the treatment of 10 min. Moreover, the degradation of 50~90 mg L-1 RhB solution presented over 90% TOC removal by the treatment of 120 min, indicating the ideal mineralization of organic pollutants. In addition, it was found that •OH was the major oxidizing specie responsible for the organics degradation. Finally, the possible pathway of RhB degradation in the electro-Fenton system was proposed by GC-MS analysis. The adoption of natural fibers for pore-creating provides an innovative and low-cost method to prepare porous cathode, which may promote the application of electro-Fenton oxidation in wastewater treatment.

Low-temperature sintering behavior of fly ash from hazardous waste incinerator: Effect of temperature and oxygen on ash properties

Hazardous waste incineration fly ash (HFA) is high risk for the environment due to heavy metals leaching and other pollutants. Sintering treatment potentially reduces the mass and volume of HFA and immobilizes heavy metals in ceramic-like bodies. However, HFA contains a large amount of heavy metals, thus sintering at too high a temperature will lead to the volatilization of heavy metals. The low-temperature sintering behavior of HFA at different temperature (450 °C, 670 °C and 900 °C) and different atmospheres (21% O2, 47.3% O2, 60.5% O2 and 100% O2) was investigated in this study. The mass loss, morphology, bulk density, elemental composition, heavy metal leaching rate, and mineral phase transformation of sintered ash were experimentally tested. With increasing sintering temperature, more mass of HFA was lost and the leaching rate of heavy metals decreased. For instance, sintered at 450 °C, 670 °C and 900 °C under air, the mass losses were 4.30%, 6.58%, and 17.96%, the leaching rate of Pb were 19.37%, 2.74%, and 0.65%, respectively. Sintered ash became denser and formed ceramic-like particle due to thermal agglomeration and chemical reactions. The bulk density significantly increased, which was favorable to reduce space occupancy for fly ash landfill. Oxygen-rich atmosphere could make the fly ash denser and inhibit the volatilization and leaching of Pb. The obtained findings are beneficial for deep understanding of the sintering behavior of HFA at low-temperature.

Distribution and chemical species transition behavior of chlorides in municipal solid waste incineration fly ash during the pressure-assisted sintering treatment

High chloride content in municipal solid waste incineration (MSWI) fly ash is a critical restriction for the recycling and re-utilization due to the acceleration of the corrosion process in construction material. Therefore, the investigation of chloride distribution and transition behavior in fly ash is of great significance. In this study, the distribution and chemical species of chloride in fly ash were first analyzed through varying mechanical pressures (10, 30, 50, 70, and 100 MPa) and sintering temperatures (300 °C, 400 °C and 500 °C) during the pressure-assisted sintering process. Instrumental analyses of SEM-EDX, element mapping, XPS, XRD and chloride leaching concentration were conducted to explore the chloride transition behavior. The results suggested that chlorides were homogeneously distributed on the surface of fly ash particles, which was significantly influenced by the microstructure change during the pressure-assisted sintering process. In addition, the chloride migration was enhanced by the pore shrinkage under different mechanical pressures and the increased atomic mobility at various temperatures. The mineral results showed that the main crystals in raw fly ash were NaCl, KCl and CaClOH, and the minerals were transformed into more complex and stable crystal phases, such as Ca10(Si2O7)2SiO4Cl2(OH)2 and Ca10(SiO4)3(SO4)3Cl. The transformation of chloride from soluble salts to stable Cl-containing minerals is beneficial to the immobilization of chloride, which suggested that pressure-assisted sintering could effectively decrease the chloride leaching concentration. This study provides a further understanding of chloride transition and distribution behavior during pressure-assisted sintering treatment.

Evaluation of the strengthening mechanism and mechanical properties of high alloyed PM 23−NbC–TaC composite materials through vacuum sintering, sub-zero and heat treatments

This study added different ratios of niobium carbide (NbC) and tantalum carbide (TaC) powders to PM 23 high speed steel (PM 23) powders. The composite powders (PM 23−NbC–TaC) utilized vacuum sintering at 1250, 1270, 1290, and 1310 °C for 1 h, respectively, and the experimental results show that good mechanical properties were obtained by the addition of 6.3 mass% NbC-2.7 mass% TaC (N6.3T2.7) sintered at 1290 °C for 1 h. Meanwhile, the apparent porosity was decreased to 0.23%, and the transverse rupture strength (TRS) and hardness reached 1648.1 MPa and 79.4 HRA, respectively. When optimally sintered PM 23 composites (N6.3T2.7) underwent a series of heat treatments, the TRS and hardness values were obviously enhanced to 1703.3 MPa and 83.5 HRA after quenching, sub-zero, and tempering treatments. Notably, the sub-zero and heat treatments obviously reduced the retained austenite content (0.6 vol%), which effectively enhanced hardness and strength. Consequently, sub-zero plus heat treatment are effective in improving the microstructure and strengthening the sintered PM 23 composites.

Preparation of β"-Al2O3 electrolytes by freeze-drying and SPS

Na-ionic conductivity and mechanical strength are two important parameters for β"-Al2O3 ceramics used as electrolyte materials. In this study, the ice-templating and freeze-drying processes were used to prepare uniformly porous Al2O3 powder with a certain degree of crystallographic orientation. With the help of spark plasma sintering (SPS) process, solid samples were fabricated from the porous power at a low temperature (1100 °C). Finally, highly conductive and highly strong β"-Al2O3 electrolytes were prepared after the solid samples were subject to further treatment at a high temperature (1600 °C). The scanning electron microscopy (SEM) results indicate that integration of the initial SPS process and further high-temperature sintering treatment have turned the freeze-dried Al2O3 powder to β"-Al2O3 samples whose grain structure is similar to the “brick-bridge-mortar” structure. Regarding such β"-Al2O3 samples, the bending strength parallel to the pressure direction is up to 273 MPa; the degree of crystallographic orientation, 0.25, and the ionic conductivity perpendicular to the pressure direction, 0.239 S cm−1 at 350 °C. Therefore, it can be concluded that the combination of freeze-drying, SPS and an additional high-temperature sintering process has helped generate a structure that improves the ion mobility and bending strength of the β"-Al2O3 ceramic, and thereby improving its strength and ionic conductivity.

New insight into fabrication of shaped Mg–X alloy foams with cellular structure via a gas release reaction powder metallurgy route

Shaped Mg alloy foams with closed-cell structure are highly interested for a great potential to be utilized in the fields where weight reduction is urgently required. A powder metallurgical method, namely gas release reaction powder metallurgy route to fabricate Mg–X (X=Al, Zn or Cu) alloy foams, was summarized. The principles on shaped Mg–X foams fabrication via the route were proposed. In addition, the effects of alloying elements, sintering treatment and foaming temperatures on fabrication of shaped Mg–X alloy foams were investigated experimentally. The results show that the key to ensure a successful foaming of Mg–X alloy foams is to add alloying metals alloyed with Mg to form lower melting (< 600 °C) intermetallic compounds by the initial sintering treatment. The foaming mechanism of Mg–X alloy foams also has been clarified, that is, the low-melting-point Mg-based intermetallic compounds melt first, and then reactions between the melt and CaCO3, a foaming agent, release CO gas to make the precursor foamed and finally shaped Mg–X alloy foam with a promising cellular structure is prepared. This route has been verified by successful fabrication on shaped Mg–Al, Mg–Zn and Mg–Cu foams with cellular structure.