Spark plasma sintering of ZrB2 powders synthesized by citrate gel method

The densification behavior of nanocrystalline zirconium diboride (ZrB₂) powders with nickel (5 vol%) is reported by spark plasma sintering (SPS) technique. SPS experiments were performed at 1600 and 1900 °C with 65 MPa pressure and 1 min holding time. A maximum relative density around 95% was obtained after SPS processing of ZrB₂ at 1900 °C while the density of ZrB₂ sample sintered at 1600 °C reached 88% of the theoretical density. Hardness and fracture toughness values are 11 GPa and 4.11 MPa m^1/2 for the sample sintered at 1600 °C and 13.7 GPa and 2.65 MPa m^1/2 for the sample sintered at 1900 °C, respectively.     

Sintering Behavior of Al/B4C-AlB12-Al2O3 Nanostructure Composite Synthesized by In Situ Processing Method

The aim of this article is to study the effect of time and temperature of sintering on the properties and microstructure of Al/B₄C-AlB₁₂-Al₂O₃ nanocomposite synthesized via in situ processing method. In this method, a mixture of Al-B₂O₃-C, as starting materials, was activated and reacted in a planetary ball mill under Argon atmosphere. The phase analysis, morphology, and particles size were studied by x-ray diffraction and scanning electron microscopy methods. The composite powders were compressed with uniaxial cold press and then were sintered at different temperatures (470-600 °C) for various times (30-90 min). The density, hardness, and compressive strength of sintered samples were investigated. The results revealed that by increasing the sintering temperature and sintering time, both hardness and compaction strength of nanocomposite reach to maximum at 560 °C. The results showed that the sample sintered at 560 °C for 90 min had highest sintered density (≈2590 kg/m³) and highest hardness value of ~88 BHN with compaction strength of ~313 MPa. Nanosize and homogeneous distribution of in situ formed ceramic particles were observed in the synthesized composite.     

Wear and thermal stability of nano-TiB2 modified TiCN-WC-Co-Cr3C2 cermet

This work discusses the friction, wear and thermal response of TiCN-WC-Co-Cr₃C₂ cermet modified by the addition of TiB₂ nanoparticles. The specimens were prepared by spark plasma sintering by adding different weight percentages (5, 10 and 15) of TiB₂ nanoparticles in TiCN-WC-Co-Cr₃C₂ cermets. The sintered pieces were subjected to sliding wear under an unlubricated condition and a constant load of 20 N at sliding velocities of 0.23 m/s, 0.35 m/s and 0.47 m/s against a steel disc of 48 mm diameter. Friction was the maximum at a sliding velocity of 0.23 m/s. The wear loss decreased with increasing speed of sliding and was between 10⁻⁵ to 10⁻⁶ mm³. The wear rates and coefficient of friction were highly dependent on microstructure and mechanical properties of the cermets. Abrasion and adhesion were the active modes of wear. Heating of the samples was carried out at 600 °C, 800 °C and 1000 °C for 4 h. A substantial mass gain and decrease in hardness were observed in the specimen annealed at 1000 °C, for which Scanning Electron Microscopy revealed considerable grain growth and XRD showed oxide phases. A cermet containing 15% TiB₂ nanoparticles displayed the lowest volumetric wear at room temperature, but had rather low thermal stability. Response surface methodology was used to develop models and regression equations for wear and thermal stability.     

Self-compacting high density tungsten–bronze composites

Green compacts of W–bronze were encapsulated in shells of bronze powder, placed in a ceramic mold and sintered in alumina tube furnace at 1150 °C. Throughout the sintering cooling stage the differential coefficient of thermal expansion ΔCTE of W–bronze was employed to induce an external compressive densification action. The process included simultaneous sintering, hot isostatic pressing (HIP) and infiltration act to enhance densification. By this technique, pilot sintered compacts of different W50–80 wt.%–pre-mix bronze of 97–99% theoretical density were produced. This process resulted in compacts of higher hardness, higher sintered density and better structure homogeneity as opposed to similar compacts densified by the conventional sintering process. The results showed a gain in hardness by 10–20% and in density by 5–15%. The impact of different cooling rates of 3, 4, 8 and 30 °C min^?1 on sintered density, microstructure and densification mechanisms was examined and evaluated. Low cooling rates of 3 and 4 °C min^?1 gave the best results.     

Study on the sintering behavior and microstructure development of the powder injection molded T42 high-speed steel

HSS has high strength, wear resistance, and hardness together with an appreciable toughness and fatigue resistance. PIM has received attention owing to its ability to shape without additional processes. The experimental specimens were manufactured using PIM with T42 powders (59 vol.%) and polymer (41 vol.%). The green parts were solvent debound in n-Hexane at 60 °C for 24 hours and further thermally debound in a N₂-H₂ mixed gas atmosphere for 18 hours. The specimens were then sintered in a vacuum (10⁻⁵ mtorr), hydrogen and nitrogen gas atmosphere. In the vacuum, the specimen sintered at 1240 °C had the highest hardness at 520 Hv. In this condition, the carbides were well-distributed and located in the grain. The grain size was 10 μm, and the carbide size was 1 μm. When sintering in a vacuum at over 1260 °C, the carbides converted to eutectic carbide and were located at the grain boundary. Grain growth was observed. The specimens sintered in a nitrogen atmosphere had a lower density and hardness than that produced in the vacuum.     

Sintering behavior of molybdenum‑copper and tungsten‑copper alloys by using ultrafine molybdenum and tungsten powders as raw materials

In this paper, high quality Mo-(10–40) wt% Cu and W-(10–40) wt% Cu alloys were prepared by powder metallurgy using the ultrafine molybdenum and tungsten powders as raw materials. The molybdenum powder with the size of 100–200 nm and tungsten powder with the size of 50–100 nm were prepared by a two-step reduction-process composed of an insufficient carbothermal reduction reaction and the following deep reduction reaction by hydrogen. From the experimental results, it was concluded that at the sintering temperature of 1200 °C to 1300 °C, relative densities of the Mo-(10–40) wt% Cu and W-(10–40) wt% Cu sintered blocks can reach >98%, and at the same time, excellent physical and mechanical properties were achieved. Meanwhile, the larger the content of copper in the alloy, the lower the temperature required for densification. At 1300 °C, the relative density, microhardness and thermal conductivity of the Mo-10 wt% Cu and W-10 wt% Cu sintered blocks are 98.83% and 99.36%, 167 HV and 283 HV, 138.38 W·m⁻¹·k⁻¹ and 154.15 W·m⁻¹·k⁻¹, respectively. Whereas, at 1200 °C, the relative density, microhardness and thermal conductivity of the Mo-40 wt% Cu and W-40 wt% Cu sintered block are 99.68% and 98.87%, 150 HV and 207 HV, 138.38 W·m⁻¹·k⁻¹ and 154.15 W·m⁻¹·k⁻¹, respectively. The present method was much more convenient relative to the traditional infiltration method.     

升温速率对烧结ITO靶材密度和组织的影响

采用化学共沉淀法制备ITO粉体前驱物,在600℃煅烧粉体前驱物4h,得到粒径为20~30nm的ITO粉体。添加1%的聚乙烯醇(PVA)造粒,模压成型制备ITO靶材素坯,设置不同的升温速率,在1550℃氧气氛下烧结素坯,得到ITO靶材。研究了烧结过程升温速率对ITO靶材密度和微观组织的影响。结果表明,在低温阶段(0~500℃)升温速率为3℃/min,高温阶段(500~1550℃)升温速率为8℃/min时,ITO靶材相对密度为99.58%,孔洞极少,近乎完全致密,且靶材宏观上无裂纹。     

直流电弧等离子体法制备In(Sn)-O及Sn(In)(Sb)-O系纳米颗粒

采用一种新的直流电弧等离子体法,通过对熔融的金属进行爆破(或气化),制备出了单相SnO₂、In₂O₃纳米颗粒以及In₂O₃:Sn (ITO)、SnO₂:Sb (ATO)和SnO₂:In:Sb (IATO)多元复合纳米颗粒。XRD结果表明,所制备的SnO₂和In₂O₃基多元复合纳米颗粒均为单相结构,没有其它杂相;TEM结果表明,直流电弧等离子体所制备的单相纳米颗粒分散性好,尺寸约20-50nm。该法合成的纳米ITO和ATO颗粒所制备的ITO靶材和SnO₂电极密度高、电阻率低,表明所制备的ITO和ATO纳米颗粒可以应用于平板显示和导电电极领域。     

Preparation of indium tin oxide targets with a high density and single phase structure by normal pressure sintering process

The present work mainly describes the technology for preparing indium-tin oxide (ITO) targets by cold isostatic pressing (CIP) and normal pressure sintering process.ITO powders were produced by chemical co-precipitation and shaped into an ITO green compact with a relative density of 60% by CIP under 300 MPa.Then,an ITO target with a relative density larger than 99.6% was obtained by sintering this green compact at 1550 ℃ for 8 h.The effects of forming pressure,sintering temperature and sintering time on the...     

Synthesis and characterization of Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>Co<Subscript>0.8</Subscript>Fe<Subscript>0.2</Subscript>O<Subscript>3−σ</Subscript>

Perovskite-type Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO) powders were synthesized using two methods, solid-state reaction (SSR) method and citrate-EDTA complexing method (CC-EDTA). Then the powders were pressed to green disks of 19 mm in diameter and sintered at 1140°C for 5 h. The shrinkage rate and relative density of the membranes prepared from the perovskite-type powders were determined and calculated, and the powders and derived membranes were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the shrinkage rates of the two kinds of disks are nearly the same (about 10%). The disks prepared by the SSR method had a bigger grain size and lower relative density than those prepared by the CC-EDTA method. The conductivity of the membranes prepared by the SSR method was about 38 S/cm, higher than that of the membranes prepared by the CC-EDTA method, which was about 30 S/cm, at the same temperature of 600°C.     

Influence of La precursors on structure and properties of CeO2-ZrO2-Al2O3 composite oxides

Three La-doped CeO₂-ZrO₂-Al₂O₃ (CZA) composite oxide samples, namely, CZA-I, CZA-II and CZA-III, were prepared following a co-precipitation method in the presence of La₂O₃, La(NO₃)₃·6H₂O and H[La(EDTA)]·16H₂O precursors, respectively. When the precursor samples are sintered at 1000 °C, the as-prepared composite oxides mainly exhibit the CeO₂-ZrO₂ cubic fluorite phase, while the γ-Al₂O₃ and δ-Al₂O₃ phases appear when the precursor samples are subjected to sintering at 1100 and 1200 °C. CZA-III exhibits improved redox properties after high-temperature treatment compared with CZA-I and CZA-II. CZA-III presents the largest surface area of 97.46 m²/g among the three CZAs when the CZA-III precursor sample is sintered at 1000 °C. Furthermore, the corresponding oxygen storage capacity (OSC) is the largest with value of 400.27 μmol/g when CZA-III precursor sample is sintered at 1000 °C. Additionally, CZA-III exhibits the best thermal stability and the highest reduction temperature. However, by increasing the sintering temperature to 1200 °C, there is a dramatic decline in the properties of surface area and OSC. And a decrease for CZA-III in surface area by 58.94% and a decrease of the OSC value by 74.56% are observed.     

The sintering behavior of quasi-spherical tungsten nanopowders

In this work, the sintering behavior of quasi-spherical tungsten nanoparticles was investigated by analysis the sintered compacts obtained at different sintering temperatures and dwell time, and the influence of microstructures on the density and Vickers microhardness of sintered products was also studied. Experimental results show that particle shape and size distribution are critical to the sintering activity and mechanical properties of obtained compacts. 91.3% of theoretical density (TD) of the compact could be obtained at low sintering temperature of 1500 °C, and the highest hardness of 606 VHN could be achieved when sintered at 1100 °C due to formation of uniform, densely packed sintered compacts with grain size of 235.7 nm. Importantly, unusual linear correlation between grain size and relative density was observed in our experiment, and a cut-off point exists at 85.6% of TD. The kinetic analysis revealed that surface diffusion is responsible for the mass transport during the initial sintering stage.     

Extrusion and selected engineering properties of Mo–Si–B intermetallics

In this study, an extrusion process has been developed to produce defect free, high-density rods of Mo–Si–B material. An initial powder composition (53.5 vol.%, 91 wt.%) of 66 vol.% Mo₅Si₃B_x (T1)–16 vol.% MoB–18 vol.% MoSi₂ was mixed with a paraffin-wax based binder (46.5 vol.%, 9 wt.%) and extruded using a twin-screw extruder. Following binder removal by a combination process of wicking and thermal degradation, the material was sintered at 1800°C. The bulk density of the sintered material was 90–92% of theoretical. Thorough binder removal was evidenced by low impurity levels: 258±6 ppm carbon and 772±10 ppm oxygen. The material demonstrated excellent high temperature oxidation resistance. The calculated parabolic rate constant is 1.1×10⁻² mg²/cm⁴/h at 1600°C. The extruded material was also successfully tested as a resistance heating element. These materials show promise for the development of heating elements with enhanced performance compared to current MoSi₂-based heating elements.     

Influence of Fe and Ti addition on properties of Na<Superscript>+</Superscript>-β/β″-alumina solid electrolytes

Transition metal (Fe, Ti)-doped Na⁺–β/β″-alumina samples were synthesized via a solid-state reaction, and the sintered specimens were characterized using X-ray diffraction, scanning electron microscopy, densitometry, and impedance analysis. The results indicated that both the sintered density and β"-alumina fraction were effectively improved by doping with Fe and Ti because of the increased concentration of Al³⁺ ion vacancies in the Na⁺–β/β″-alumina. These vacancies promoted stabilization of the β″-alumina phase and densification by providing a diffusion path for Al³⁺ ions. The presence of Fe and Ti in the alumina increased the grain boundary diffusivity, thereby improving the mass transport. Thus, anisotropic grain growth occurred with increasing dopant content. However, excessive liquid-phase formation during sintering occurred when the amount of Ti was greater than 2.0 mol%, and the lowered sintered density decreased the ionic conductivity of the Na⁺-β/β″-alumina because the ionic conductivity behavior has a closer relationship to the trend of sintered density. The highest ionic conductivities of the Fe- and Ti-doped sintered specimens were 1.4 × 10^-1 S/cm (10.0 mol% Fe-doped) and 1.6 × 10^-1 S/cm (1.5 mol% Ti-doped) at 350 °C.     

An industrially feasible pathway for preparation of Mo nanopowder and its sintering behavior

In this study, a low-cost, efficient and industrially feasible pathway was developed to prepare Mo nanopowder via a two-stage carbothermic reduction of commercial MoO₃ with carbon black at 600 °C and 1050 °C, respectively, followed by deep hydrogen reduction at 800 °C. The sintering behaviors of the prepared Mo nanopowder and micron commercial Mo powder containing different amounts of Mo nanopowder were investigated in the temperature range of 1000 °C–1600 °C. At 1200 °C, the Mo nanopowder was sintered to near-fully densified compact with a relative density of about 95.8%, which was much higher than the value of 70% for commercial Mo powder. For the nanopowder, the grain size dramatically increased when the sintering temperature increased. The hardness of sintered nanopowder at 1200 °C (relative density, 95.8%; average grain size, 1.88 μm) was about 254 HV0.1, which was much higher than the value of 182 HV0.1 as sintering commercial micron sized Mo at 1600 °C (relative density, 93.9%). The addition of Mo nanopowder into micron Mo can noticeably activate its sintering and improve its hardness.     

Fabrication and structure characterization of ITO transparent conducting film by sol-gel technique

Using In（NO3）3·5H2O and acetylacetone as raw materials and anhydrous SnCl4 as dopant, the transparent conducting indium tin oxide（ITO） films were prepared by sol-gel and dip-coating technique. The phase transformation, structure properties and physical properties （sheet resistance and transmittance） of the films were investigated by DTA-TG, XRD, SEM, four-probe method and UV-Vis spectrometry. The results indicate that it is feasible to fabricate 1TO films on the quartz substrates by sol-gel technique, and the ITO films are formed by accumulating of particles with the size of several decades of nanometers. The prepared ITO film has cubic bixbyite structure, and （111） is its preferred plane. After five-times dip-coating, the 1TO film has a thickness less than 150 nm, a sheet resistance of 110Ω/□, a resistivity of 1.65×10^-3Ω· cm and a transparency of 90% .     

Effects of TaC and TiC addition on the microstructures and mechanical properties of Binderless WC

WC ceramics were sintered using a resistance-heated hot-pressing machine in the temperature range of 1600–1800 °C for TaC addition and at 1800 °C for TiC addition. Dense WC ceramics containing 0–2 mol% TaC at 1800 °C, 1–2 mol% TaC at 1700 °C, and 0–6 mol% TiC were obtained. A small addition of 1–2 mol% TaC at 1700 °C improved the sinterability of WC. The W₂C- and TaC-type solid solutions, (W, Ta)₂C and (Ta, W)C, were produced during the sintering process. The added TaC and TiC fully changed to the solid solutions of (Ta, W)C for dense TaC-added WC ceramics and (Ti, W)C for TiC-added WC ceramics. TiC inhibited the grain growth of WC in WC ceramics. The hardness of TaC-added WC ceramics sintered at 1700 °C increased from 19 GPa with no TaC addition to 25.1 GPa with 1 mol% TaC. The hardness of TiC-added WC ceramics sintered at 1800 °C differed only slightly from that without TiC addition, ~24 GPa. The relationship between the hardness of dense TaC- and TiC-added WC ceramics and WC grain size was similar to that for pure WC. The fracture toughness of the TaC-added WC ceramics at 1700 °C increased from 5.7 MPa m^0.5 without TaC addition to 6.7 MPa m^0.5 at 1 mol% TaC.     

Deoxidation and subsequent densification of sintered titanium by Ca deoxidizer

In this study, a sintering process involving simultaneous deoxidation and sintering was developed, using the vapor of a deoxidizer (Ca) to produce low-oxygen, high-density titanium. Compared to a series of reference titanium powder samples, the bodies sintered with Ca exposure had an ～1,400 ppm lower oxygen content, resulting in an ～2% increase in their density. This appears to be the result of decreased surface oxidation on the titanium, as increased oxidation suppresses densification at high sintering temperatures. The effect of the Ca deoxidizer was a lower oxidation, thereby increasing the sintered density. The Vickers hardness of sintered bodies from both experiments increased from an initial value of ～249 Hv at 900 °C to ～286 Hv at 1,400 °C, respectively. Moreover, both experiments revealed a tensile strength of ～170 MPa at 900 °C that finally increased to ～218 MPa at 1,400 °C. Meanwhile, the bodies sintered with Ca, the elongation was on average over 1% higher than contrary samples.     

Enhanced sintering of an Fe-Ni-P coated composite powder prepared by electroless nickel plating

An Fe-8.2 % Ni-6.0 % P powder was prepared by electroless nickel plating on a carbonyl iron powder, where phosphorous appeared as a contaminant of the plating process. Because of the high phosphorous concentration, persistent liquid phase sintering was effective at temperatures higher than 1000 °C. The sintered microstructure was dramatically different from the conventional approaches, where a low concentration of phosphorous was added in the form of Fe₃P. Sintering the alloy at a temperature as low as 1050 °C for 30 min yielded a sintered density of 98.6% theoretical and rounded grains having an average grain size of 53 μm. The rounded grains were surrounded by a large volume fraction of intergranular (Fe,Ni)₃P phase, arising from the high phosphorous concentration, which slightly deteriorated the magnetic saturation but significantly increased the electrical resistivity of the alloy. Generally speaking, the magnetic saturation of the sintered alloy was improved with respect to the iron-phosphorus, iron-nickel, or iron-silicon alloys fabricated by powder processing.     

Characterization of Ni-W solid solution alloy powders and sintered compacts synthesized via mechanically activated hydrogen reduction of NiO-WO3 mixtures

Blended nickel oxide — tungsten oxide powders corresponding to the compositions of 70 wt% nickel — 30 wt% tungsten were mechanically alloyed (MA’d) for different durations such as 0 h, 6 h, 12 h and 24 h and reduced/alloyed at 550 °C for 1 h followed by 600 °C for 0.5 h under hydrogen (H₂) atmosphere. H₂ reduction of the MA’d fine oxide powders resulted in the fabrication of nanocrystalline Ni(W) solid solution alloy powders, whereas a mixture of Ni and WO₂ powders were obtained via hydrogen reduction of asblended oxide mixtures, which revealed the activation of the reduction process by MA. Obtained powders were sintered at 1300 °C for 1 h under H₂ and Ar gas flowing conditions. X-ray diffraction patterns taken from the sintered samples revealed the presence of the Ni(W) solid solution phase for all samples, whereas the presence of elemental W phase was observed in the sintered as-blended and reduced powders. The lowest relative density value of 92.04% and microhardness value of 1.27 GPa were measured for the sintered as-blended and reduced powders, which increased to between 97.62% and 98.72% and 2.19 GPa and 2.23 GPa, respectively, with the applied MA.