Varying Sintering Time Research Articles

Effect of reinforcement and sintering on dry sliding wear and hardness of titanium – (AlSi)0.5CoFeNi based composite

Owing to its weight-to-strength ratio, titanium is a widely used material, especially in gas turbine engines. It possesses a high melting point and corrosion resistance, however, exhibits poor wear resistance. An improvement in its tribological properties can be accomplished by the addition of a suitable reinforcement in metal matrix composite (MMC). In this research, titanium MMCs were fabricated through mechanical alloying (MA) followed by vacuum arc melting of 95% titanium reinforced with 5% of (AlSi)0.5CoFeNi high entropy alloy (HEA). Compaction was later done at 1000 MPa, while specimens were heat-treated at sintering temperatures of 900 °C and 1000 °C, with varying sintering times of 1 h and 2 h at 10–4 millibar vacuum. Microhardness and sliding wear rate of reinforced HEA specimens exuded improvement when compared to the Ti 900 °C 2 h specimen. Owing to the reinforcement, a reduction in wear rate and more than 5% improvement in microhardness had been observed, at higher sintering temperatures. The improvement was attributed to the synergistic effect of sintering time and temperature during the density and wettability analysis which was supported by the morphological analysis.

Process Capability of Aerosol-Jet Additive Processes for Long-Runs Up to 10-Hours

Abstract Traditionally, printed circuit assemblies have been fabricated through a combination of imaging and plating-based subtractive processes involving the use of photo-exposure followed by baths for plating and etching in order to form the necessary circuitry on rigid and flexible laminates. The emergence of a number of additive technologies presents an opportunity for the development of processes for manufacturing of flexible substrates by utilizing mainstream additive processes. Aerosol-jet printing is capable of printing lines and spaces below 10 μm in width. The aerosol-jet system also supports a wide variety of materials, including nanoparticle inks, screen-printing pastes, conductive polymers, insulators, adhesives, and biological matter. The adoption of additive manufacturing for high-volume commercial fabrication requires an understanding of the print consistency and electrical mechanical properties. Little literature that addresses the effect of varying sintering time and temperature on the shear strength and resistivity of the printed lines exists. In this study, the effect of process parameters on the resultant line consistency and mechanical and electrical properties has been studied. Print process parameters studied include sheath rate, mass flow rate, nozzle size, substrate temperature, and chiller temperature. Properties include resistance and shear load to failure of the printed electrical line as a function of varying sintering time and temperature. The aerosol-jet machine has been used to print interconnects. Printed samples have been exposed to different sintering times and temperatures. The resistance and shear load to failure of the printed lines have been measured. The underlying physics of the resultant trend was then investigated using elemental analysis and scanning electron microscopy. The effect of line consistency drift over prolonged runtimes has been measured for up to 10 h of runtime. The printing process efficiency has been gaged as a function of the process capability index (Cpk) and process capability ratio (Cp). Printed samples were studied offline utilizing optical profilometry in order to analyze the consistency within the line width, height, and resistance, and shear load to study the variance in electrical and mechanical properties over time.

Enhancement of electrical energy storage ability by controlling grain size of polycrystalline BaNb2O6 for high density capacitor application

The present article focuses on the electrical energy storage capacity of BaNb2O6 (BN) ceramic material with varying sintering time duration of material synthesized by solid state reaction method. The crystal phase formation during calcination process was studied with high temperature x-ray diffraction, which confirms the formation of desired crystalline phase at temperature above 1100 °C. The associated micro-structural images reveal increasing trend of average grain size from 4.32 μm to 10.08 μm with raising sintering time. A decrease in Z′ with temperature confirms the occurrence of negative temperature coefficient (NTCR) behavior of BN ceramic similar to semiconductor material. The impedance spectroscopy provides the electrical equivalent circuit of investigated BN ceramic. Fitting of these data with three R and Q (CPE) elements connected in series revealed an important information regarding grain, grain boundary and electrode effects. The frequency dependent conductivity of the material follows the Jonscher’s power law and found increase in frequency exponent n from 0.51 to 0.92 for BN05 to BN50 that suggests shifting of ionic long-range translational motion to localized motion of ions/charge carriers. The activation energy, calculated from curve between relaxation time and inverse temperature, reduces from 0.59 eV to 0.33 eV for sample BN05 to BN50. The recoverable energy increases from 2.12 to 10.28 mJ/cm3 with sintering time interval whereas, the storage energy efficiency enhanced from 12.98% to 57.85%.

Grain size effect on structure and electrical properties of lead-free Na0.4K0.1Bi0.5TiO3 ceramics

Abstract Sodium potassium bismuth titanate ceramics (Na 0.4 K 0.1 Bi 0.5 )TiO 3 with grain sizes of 0.58, 0.93, 1.19 and 1.83 µm were prepared by varying sintering time. Grain size dependent structural and electrical properties of NKBT ceramics at morphotropic phase boundary composition have been investigated for the first time. Large internal compressive stress preclude the formation of tetragonal phase in sub-micron sized samples. Phase co-existence in 1.83 µm sample has been well modelled with rhombohedral ( R 3 m ) and tetragonal ( P 4 mm ) using Rietveld refinement. Relative permittivity increases with grain size and all the samples exhibits relaxor behavior. Strong coupling between grain boundary and domain walls hinder domain switching and polarization reversal. Hence reduction in the remnant polarization was observed in sub-micron sized samples. Excellent piezoelectric constant of 215 pC/N for sample with grain size of 1.83 µm is due to large amount of non-180° domain variants than that of samples with lowest grain size.

Al stabilized Li7La3Zr2O12 solid electrolytes for all-solid state Li-ion batteries

All Solid State Lithium Ion Batteries (ASS-LIB) have been attracting great attention due to their high temperature stability, energy density and safety. Cubic Li7La3Zr2O12 (LLZO) ceramic electrolyte is one of the most studied solid electrolyte because of its exceptionally high chemical stability against Li metal, air and moisture, thermal stability and very competitive ionic conductivity. In order to stabilize cubic LLZO, relatively high temperatures are required. On the other hand, it's possible to decrease sintering temperature and time with a stabilizer addition. In this study, 20–30 mol % Al containing LLZO electrolytes were prepared by solid state reaction method at varying sintering temperatures (1100 °C and 1150 °C) for varying sintering times (12 h and 24 h) and the characterization of resultant materials were carried out. XRD results showed that, small amount of other compounds such as LaAlO3 were present in the sample produced at 1100 °C–12 h along with the main phase of cubic LLZO structure. According to SEM images, the sintering temperature was found to be more effective than sintering time on the densification behaviour. Existing porosities were reduced when both sintering temperature and time were increased. Different amount of Al addition did not have an effect on the densification behaviour. Both intergranular and transgranular types of fractures were observed by SEM. Finally it was found that 30 mol % Al containing samples sintered at 1150 °C for 12 h showed mixed conductor behaviour, whereas for 24 h and 36 h pellets showed ionic conductor behaviour.

Processing and Properties of Textured Potassium Sodium Niobate [K,Na]NbO3 Ceramic Ribbons by Alginate Gelation Method

Random and <001> textured potassium sodium niobate – [K,Na]NbO3 (KNN) ceramics with 1 mole% CuO sintering aid were fabricated in ribbon form through a combination of novel alginate gelation process and templated grain growth methods using platelike sodium niobate ‐ NaNbO3 (NN) template particles. The platelike NN template particles were prepared by a two‐step molten salt synthesis method. Ribbons were drawn from alginate‐based slurries without or with 10 wt% NN template particles using 50 mm long slit nozzle with a rectangular orifice of 10 mm × 1 mm. Development of crystallographic texture as a result of varying sintering time and temperature was evaluated through the calculation of the degree of orientation as measured by the Lotgering factor (ƒ(001)) and an ƒ(001) of 0.81 was achieved. The electrical properties of textured ribbons were evaluated with polarization and strain versus electric field measurements.

Investigation of the Dielectric Function of Solution-Processed InGaZnO Films Using Ellipsometry

The optical properties of InGaZnO (IGZO) films grown through the sol-gel process as a function of sintering time were investigated with spectroscopic ellipsometry (SE). The IGZO precursor sol was prepared by mixing In nitrate, Ga nitrate, and Zn acetate at a molar ratio of In:Ga:Zn = 3:1:1. The solution was deposited on a SiO2/Si substrate via spin coating. Sintering was performed at 400 degrees C for 1-15 h in an ambient atmosphere. The optical properties were measured over the range 1.12-6.52 eV via variable angle SE, at room temperature. The angle of incidence was varied from 50 to 70 degrees in 5 degree steps. To extract the pure optical properties of IGZO, multilayer-structure calculation with Tauc-Lorentz dispersion relation for IGZO was performed. The changes in the dielectric function of the IGZO films with varying sintering time were observed. The resultant optical properties can be related to the concentration of oxygen vacancies in the material, which can be controlled by the sintering time.

Effect of heat treatment on physical and electrical characteristics of conductive circuits printed on Si substrate

Printed electronics is expected to increase its market share significantly in near future on account of its high material usage efficiency, environmental friendliness, the avoidness of expensive process steps, and the ability to rapidly change circuit designs in real time in a highly cost effective fashion. Herein, we tried to examine the physical characteristics of the two types of selected Ag nanopastes and electrical characteristics of screen printed Ag patterns on a Si substrate sintered at 200 °C for varying sintering times. The first type of the paste had no binder material and the second one was formulated with an addition of a polymeric binder. They had different thermal behaviors, i.e., the paste with a binder showed a continuous small reaction well beyond the temperature for the main reaction of the paste without any binder. The microstructure of the Ag tracks after sintering was also different between the two cases, which verified the poor electrical characteristics of the paste containing a binder than the one without any binder. We also measured the insertion losses of the Ag tracks with a design for the high frequency transmission, and the observed electrical behaviors were discussed with the physical properties of the pastes measured in this study.

The effect of powder sintering method on the densification and microstructure of pewter alloys

Pewter alloys made from tin, copper and antimony powders were sintered using microwave and conventional vacuum sintering. Three different compositions of the pewter alloy were used; 91Sn6Cu3Sb, 94Sn4Cu2Sb and 97Sn2Cu1Sb. The effect of densification and microstructure of the pewter alloys from varying sintering time and sintering mode were examined and compared. Samples were compacted at 40kN and sintered at 220°C. Samples in the conventional furnace were sintered 60 minutes and 120 minutes, while samples in the microwave furnace were sintered for 15 and 30 minutes. Samples sintered at longer sintering times resulted in higher density for both sintering methods. Microwave sintering produced samples with slightly smaller grain size than the conventionally sintered samples resulting in a better densification. There were no new phases formed from the sintering of pewter alloy.

Cold Plasma Modification Effects on the Water Flow through Sintered UHMWPE Membranes

The effects of cold plasma surface modification on the pore size and permeated water flow through sintered UHMWPE membranes were investigated. Two different UHMWPE, having the same average particle size (180 µm) but different molecular weights (3 × 108 and 7 × 108 g/mol) were used to manufacture the membranes. The membranes were sintered at 200°C at varying sintering times (60, 75 and 90 minutes), and were characterized by SEM, contact angle and permeated water flow rate. Surface modification was performed with the application of methane plasma for 60 min. For the untreated membranes, increased sintering times led to flow reduction, and this behavior was more significant for the membrane manufactured with the lower molecular weight polymer. These results were associated with pore size reduction and increased compaction of the samples sintered for longer times. Plasma surface modification led to significant water flow reduction through the membranes. A 90% flow decrease was measured for the membranes manufactured with the higher molecular weight polymer, sintered for 60 minutes. This behavior was attributed to higher surface tension on the walls, lowering the permeate water flow rate. SEM analysis and contact angle measurements showed plasma modification to successfully modify membrane surface characteristics and likely to promote pore size reduction.

Osteogenic differentiation of dura mater stem cells cultured in vitro on three-dimensional porous scaffolds of poly(ε-caprolactone) fabricated via co-extrusion and gas foaming

A novel scaffold fabrication method utilizing both polymer blend extrusion and gas foaming techniques to control pore size distribution is presented. Seventy-five per cent of all pores produced using polymer blend extrusion alone were less than 50 μm. Introducing a gas technique provided better control of pore size distribution, expanding the range from 0–50 to 0–350 μm. Varying sintering time, annealing temperature and foaming pressure also helped to reduce the percentage of pore sizes below 50 μm. Scaffolds chosen for in vitro cellular studies had a pore size distribution of 0–300 μm, average pore size 66 ± 17 μm, 0.54 ± 0.02% porosity and 98% interconnectivity, measured by micro-computed tomography (microCT) analysis. The ability of the scaffolds to support osteogenic differentiation for subsequent cranial defect repair was evaluated by static and dynamic (0.035 ± 0.006 m s −1 terminal velocity) cultivation with dura mater stem cells (DSCs). In vitro studies showed minimal increases in proliferation over 28 days in culture in osteogenic media. Alkaline phosphatase expression remained constant throughout the study. Moderate increases in matrix deposition, as assessed by histochemical staining and microCT analysis, occurred at later time points, days 21 and 28. Although constructs cultured dynamically showed greater mineralization than static conditions, these trends were not significant. It remains unclear whether bioreactor culture of DSCs is advantageous for bone tissue engineering applications. However, these studies show that polycaprolactone (PCL) scaffolds alone, without the addition of other co-polymers or ceramics, support long-term attachment and mineralization of DSCs throughout the entire porous scaffold.

Synthesis, structure and electrical properties of Li 1 + x + ySc xY yTi 2 − x − y(PO 4) 3 ( x = 0.15–0.3, y = 0.01–0.15) ceramics

The powder of Li 1 + x + y Sc x Y y Ti 2 − x − y (PO 4) 3 ( x = 0.15–0.3, y = 0.01–0.15) has been synthesized by solid phase reaction. The structure of the compounds was determined by X-ray diffraction patterns from the powder. The compounds belong to the rhombohedral symmetry (space group R3¯c) with Z = 6 formula units in the lattice. Ceramic samples were sintered in air at temperature T s = 1523 K varying sintering time ( t s) from 1 to 5 h. The element compositions of ceramics were defined by XPS. The complex impedance ( Z˜), electric conductivity ( σ˜), dielectric permittivity ( ɛ˜) of the ceramics in frequency range (10 6−1.2 · 10 9) Hz and temperature range (300−600) K were carried out. Two relaxation dispersions of the electric parameters were found for all compounds. The dispersions are caused by the ion transport in grains and grain boundaries of the ceramic samples. The values of the bulk ( σ b), grain boundaries ( σ gb) conductivities, their activation energies, and dielectric permittivity are dependent on stoichiometric parameters x, y and sintering conditions of the ceramics.

Synthesis and characterization ofLi1/3Ce2/3PO4 and LiCe2/3PO4 ceramics

Li1/3Ce2/3PO4 and LiCe2/3PO4 compounds were synthesized by a solid state reaction and studied byx-ray diffraction and thermogravimetric analysis. At room temperaturethe investigated compounds exhibit monoclinic symmetry (space groupP 21/n) with four formula units in the lattice. The compounds are stable up to 1200 K inair and show no weight loss. The ceramic samples were fabricated with varyingsintering times. The surfaces of the ceramics were studied by scanning electronmicroscopy. The increase of sintering time of the ceramics leads to an increase of thegrain size of the materials. The results of an x-ray photoelectron spectroscopystudy have shown that the external electric field changes the Li amount on thesurfaces of the ceramic samples. The electric properties of the samples wereinvestigated by complex impedance spectroscopy in the frequency range from 50 to1.2 × 109 Hz in the temperature range from 300 to 650 K. Varying the sintering time of the ceramicsaffects the values of the total conductivity, activation energy, dielectric permittivity anddielectric losses of the ceramics.

Self-propagating high-temperature synthesis of barium titanate and subsequent densification by spark plasma sintering (SPS)

This paper describes the self-propagating high-temperature synthesis (SHS) of perovskitic oxides, specifically BaTiO 3, and their subsequent densification by spark plasma sintering. With the final goal of obtaining dense nanostructured materials, SHS products were mechanically treated at different milling time conditions, before densification. It was found that the grain size of ball milled powders decreases with increasing milling time, this effect being more evident at early stages of milling. Depending upon the ball milling (BM) conditions adopted, crystallite size in the range 15–70 nm was obtained. After milling for 5 h, the resulting powders (20–30 nm) were sintered by SPS, at 700 A, for different periods of time. By properly varying sintering time in the interval 70–140 s, it is possible to obtain products with relative density in the range 66–99%, respectively. In particular, grain growth during sintering was found to be limited (below 50 nm) if the electric current is applied for time intervals equal to or less than 100 s. The observed dielectric properties are typical of a nanocrystalline BaTiO 3 ceramic.

Influence of microstructure on oxygen transport in perovskite type membranes

The influence of bulk microstructure (grain size distribution, grain boundary length) on the oxygen transport properties of permeation membranes has been investigated. For this purpose, La0.5Sr0.5FeO3-δ samples with different microstructures were prepared by varying sintering time and temperature. Average grain sizes, which ranged from 0.20 to 1.43 μm, were determined by SEM analysis. The oxygen transport properties of the samples were characterised by permeation measurements as a function of temperature in an air/argon oxygen partial pressure gradient. The fluxes presented a change in activation energy, which was attributed to a change in the rate limiting step, from bulk diffusion at lower temperature (< 850°C) to surface limitation at higher temperature (> 900°C). Only transport through the bulk was influenced by the microstructure, with the highest flux for the smallest grains. At 800°C, the fluxes were respectively 0.06, 0.03 and 0.01 μmol cm-2 s-1 through ≈ 1 mm thick samples with average grain sizes of 0.20, 0.63 and 1.43 μm respectively. This would imply that oxygen transport occurs more rapidly along grain boundaries than through the bulk. Grain boundary structure and composition were analysed by TEM.

SANS investigation on evolution of pore morphology for varying sintering time in porous ceria

Precipitates of ceria were synthesized by homogeneous precipitation method using cerium nitrate and hexamethylenetetramine at 80°C. The precipitates were ground to fine particles of average size ∼0.7 μm. Circular disks with 10 mm diameter, 2 and 3 mm thickness were prepared from the green compacts by sintering at 1300° C for three different sintering times. Evolution of the pore structures in these specimens with sintering time was investigated by small-angle neutron scattering (SANS). The results show that the peak of the pore size distribution shifts towards the larger size with increasing sintering time although the extent of porosity decreases. This indicates that finer pores are eliminated from the system at a faster rate than the coarser ones as sintering proceeds and some of the finer pores coalesce to form bigger ones.

Linear and nonlinear magnetic responses of weakly sintered YBa 2Cu 4O 8 ceramics of sub-micron scale grains

Weakly sintered ceramic samples of YBa 2Cu 4O 8 (124) are prepared as systems of Josephson-coupled sub-micron grains, with varying sintering time. The obtained ceramic systems are studied by observing fundamental and harmonic magnetic responses. Each specimen shows characteristic temperature dependence of the responses caused by intergrain ordering. The ordering temperature estimated by singular peak of the nonlinear response changes consistently with the sintering time, indicating that the coupling strength is systematically changed. Furthermore, dual anomalies of the nonlinear response are found. The results suggest that two different origins of nonlinear response inhere in the intergrain ordering.

Effects of sintering conditions on mechanical properties of mechanically alloyed tungsten heavy alloys

The effects of sintering conditions on the microstructural evolution and mechanical properties of mechanically alloyed tungsten heavy alloys were investigated. W, Ni and Fe powders were mechanically alloyed in a tumbler ball mill at a milling speed of 75 rpm, ball-to-powder ratio of 20∶1 and ball filling ratio of 15%. The mechanically alloyed powders were compacted and solid-state sintered at a temperature of 1300°C for 1 hour in a hydrogen atmosphere. The solid-state sintered tungsten heavy alloy was subsequently liquid-phase sintered at 1470°C with varying sintering times from 4 min to 90 min. The solid-state sintered tungsten heavy alloy showed fine tungsten particles of 3 μm in diameter and high relative density above 99%. The volume fraction of the W-Ni-Fe matrix phase was measured, as 11% and tungsten/tungsten contiguity was 0.74 in solid-state sintered tungsten heavy alloys. Mechanically alloyed and two-step sintered tungsten heavy alloys showed tungsten particles of 6–15 μm and a volume fraction of the W-Ni-Fe matrix phase of 16% and tungsten/tungsten contiguity of 0.40. The solid-state sintered tungsten heavy alloy exhibited a yield strength of about 1100 MPa due to its finer tungsten particles, while it showed low elongation and impact energy due to its large tungsten/tungsten contiguity. The yield strength of two-step sintered tungsten heavy alloys increased with the decreasing of tungsten particle size and volume fraction of the W-Ni-Fe matrix.

Effects of Sintering Conditions on Mechanical Properties of Mechanically Alloyed Tungsten Heavy Alloys

The effects of sintering conditions on the microstructural evolution and mechanical properties of mechanically alloyed tungsten heavy alloys were investigated. W, Ni and Fe powders were mechanically alloyed in a tumbler ball mill at a milling speed of 75 rpm, ball-to-powder ratio of 20∶1 and ball filling ratio of 15%. The mechanically alloyed powders were compacted and solid-state sintered at a temperature of 1300°C for 1 hour in a hydrogen atmosphere. The solid-state sintered tungsten heavy alloy was subsequently liquid-phase sintered at 1470°C with varying sintering times from 4 min to 90 min. The solid-state sintered tungsten heavy alloy showed fine tungsten particles of 3 μm in diameter and high relative density above 99%. The volume fraction of the W-Ni-Fe matrix phase was measured, as 11% and tungsten/tungsten contiguity was 0.74 in solid-state sintered tungsten heavy alloys. Mechanically alloyed and two-step sintered tungsten heavy alloys showed tungsten particles of 6–15 μm and a volume fraction of the W-Ni-Fe matrix phase of 16% and tungsten/tungsten contiguity of 0.40. The solid-state sintered tungsten heavy alloy exhibited a yield strength of about 1100 MPa due to its finer tungsten particles, while it showed low elongation and impact energy due to its large tungsten/tungsten contiguity. The yield strength of two-step sintered tungsten heavy alloys increased with the decreasing of tungsten particle size and volume fraction of the W-Ni-Fe matrix.

An optimum heating program for fabricating multifilamentary Bi-2223/Ag tapes

Ag-sheathed multifilamentary Bi-2223 tapes have been fabricated by a conventional powder-in-tube method with an optimum final heating program. Many heating programs were done by varying sintering time (ts), post annealing time (tp) and cooling rate (R) from sintering temperature to post annealing temperature. It is found that Jc has been increased by a factor 1.5 to 2 at 0T over the normally processed tapes, with the ΔT=(Ts-Tp)=10°C and R=0.3°C per hour conditions. XRD indicate that these tapes have a high degree of phase purity, and well-aligned grains. The typical value of Jc is 2.0–2.5×104A/cm2.