Hot-pressed Samples Research Articles

Influence of the Uniaxial Hot-Pressing Sintering Condition on Bi4Ge3O12 Ceramic Scintillators

The production of high-density bismuth germanate (Bi3Ge4O12) ceramic scintillators by uniaxial hot pressing was investigated as a function of different applied pressure conditions. The X-ray diffraction showed that the sintering process was able to eliminate the undesirable secondary phase present in the nonsintered samples. The height changes from samples with higher applied pressure rate and applied pressure duration lead to a better relative density value, >95% for samples sintered under a pressure of 0.14 and 0.18 MPa. The radioluminescence results showed that all samples have the characteristic emission spectra of Bi3Ge4O12 and that the hot-pressed samples have higher radioluminescence emission efficiency.

Effect of Hot Isostatic Pressing and Powder Feedstock on Porosity, Microstructure, and Mechanical Properties of Selective Laser Melted AlSi10Mg

AlSi10Mg tensile bars were additively manufactured using the powder-bed selective laser melting process. Samples were subjected to stress relief annealing and hot isostatic pressing. Tensile samples built using fresh, stored, and reused powder feedstock were characterized for microstructure, porosity, and mechanical properties. Fresh powder exhibited the best mechanical properties and lowest porosity while stored and reused powder exhibited inferior mechanical properties and higher porosity. The microstructure of stress relieved samples was fine and exhibited (001) texture in the z-build direction. Microstructure for hot isostatic pressed samples was coarsened with fainter (001) texture. To investigate surface and interior defects, scanning electron microscopy, optical fractography, and laser scanning microscopy techniques were employed. Hot isostatic pressing eliminated internal pores and reduced the size of surface porosity associated with the selective laser melting process. Hot isostatic pressing tended to increase ductility at the expense of decreasing strength. However, scatter in ductility of hot isostatic pressed parts suggests that the presence of unclosed surface porosity facilitated fracture with crack propagation inward from the surface of the part.

Microstructure and mechanical properties of a hot pressing-dynamic partition treated steel

ABSTRACTThe microstructure and mechanical property of improved press-hardened steel with hot pressing combined dynamic partitioning (HP-DP) treatment are presented. Microstructure of the steel subjected to HP-DP treatment is featured by multi-martensite phases and the retained austenite (RA) phase with carbon content gradient. Compared with conventional hot-pressed samples, the HP-DP samples show better tensile property especially ductility. The effect of HP-DP parameters on the evolution of RA and mechanical property is then discussed. Finally, hot pressing of a double U-shaped part using both 22MnB5 steel sheet and the developed HP-DP steel sheet was carried out with exact control of part temperature at the end of hot pressing followed by air cooling.

Largely enhanced thermal conductivity of HDPE/boron nitride/carbon nanotubes ternary composites via filler network-network synergy and orientation

In recent years, hybrid fillers with different dimension are frequently used to improve the thermal conductivity of polymer/filler composites. While the combined effect of hybrid filler and orientation on the thermal conductivity of polymer/filler composites has rarely reported. In this work, high density polyethylene (HDPE)/boron nitride (BN)/carbon nanotubes (CNT) ternary composites were prepared by melt blending then hot rolled to obtain oriented sheets. The thermal conductivity and internal structure of the obtained sheets were investigated and compared with those obtained by hot-pressed sheets with random distributed structure. Two representative systems were used, the one is that BN content is low and forms the isolated dispersions (using HDPE/5BN/CNT composites with 5 wt% of BN as example), the other one is that BN content is high and forms network structure (using HDPE/25BN/CNT composites with 25 wt% of BN as example). For hot-pressed samples, no synergy between BN and CNT was found for HDPE/5BN/CNT system with BN dispersed in isolation in HDPE matrix, while an obvious increase of thermal conductivity was seen for HDPE/25BN/CNT system with BN network formation in HDPE matrix, and a 300% increase of thermal conductivity could be achieved as 3 wt% of CNT was added, compared with that of net HDPE. For hot-rolled samples, an increase of thermal conductivity was observed for both HDPE/5BN/CNT and HDPE/25BN/CNT ternary composites by adding CNT into the composites, suggesting the importance of filler orientation in the enhancement of thermal conductivity in polymer/filler composites with hybrid filler. The combined effect of hybrid filler and orientation could result in a further increase of thermal conductivity and 600% increase of thermal conductivity could be achieved. Finally, based on the analysis of internal structure of prepared samples as obtained by SEM observation, rheology and XRD measurements, a possible mechanism for the enhancement of thermal conductivity via hybrid and orientation was proposed. Our work is important and could shed light for the preparation of polymer composites with super thermal conductivity.

Spark plasma sintering and hot pressing of ZTA-NbC materials – A comparison of mechanical and electrical properties

Zirconia toughened alumina can be made electrically conductive and thus electric discharge machinable by addition of a percolating dispersion of niobium carbide. In order to boost the productivity of the sintering process spark plasma sintering was tested at identical temperature and pressure but shorter dwell than in hot pressing. SPS sintering parameters for ZTA-NbC are developed and spark plasma sintered ceramics are compared to the hot pressed benchmark.During SPS a percolating NbC backbone of niobium carbide grains is formed which enhances electrical conductivity but impedes densification. Identical strength at however higher sintering temperature is achieved by SPS but the fracture resistance and hardness were always superior in hot pressed samples. The monoclinic content of zirconia grains in as fired SPS samples is higher despite smaller average grain size and the transformation toughening effect is less pronounced. SPS promises economic benefits due to shorter dwell and cooling cycles.

Mechanical properties of PLA-based composites for fused deposition modeling technology

To predict the mechanical behavior of 3D printed products, it is important to understand the composite material properties and the effect that parameters of 3D printing process have on the properties of these materials. The mechanical properties of PLA-based composite materials were studied in this work. The mechanical properties of the hot pressed samples were compared to those of the 3D printed samples. The elongation at break and the yield strength of the samples fabricated by 3D printing are decreased by 15–60% compared to those for the hot pressed samples. It has been found that the mechanical properties of 3D printed samples do not practically depending on the deposition scheme.

Thermoelectric properties of nanostructured bornite Cu5-xCoxFeS4 synthesized by high energy ball milling

Cobalt-substituted bornite Cu5-xCoxFeS4 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) solid solutions were synthesized by high energy mechanical alloying (MA) followed by hot pressing. X-ray diffraction (XRD) spectra revealed bornite as the pure phase for substitution level up to x = 0.08, whereas a trace amount of the secondary phase Co3S4 was detected for x = 0.1. The surface morphology of hot-pressed samples confirmed their nanostructured nature, with grains sizes smaller than 50 nm. As expected, the electrical resistivity and Seebeck coefficient increased with an increase in the Co substitution level up to x = 0.04, as a results of a decrease in the hole concentration induced by substitution of Cu+ by Co+2. The combined effect of adjusting resistivity and Seebeck coefficient leaded to power factors up to 0.3 mWm−1K−2 at 590 K for Cu4.96Co0.04FeS4, which is 20% higher than the values measured from pure bornite Cu5FeS4. The total thermal conductivity decreased with increasing the substitution level up to x = 0.04, reaching a minimum thermal conductivity of 0.22 W/mK for x = 0.04 at 473 K, which is the lowest value reported for bornite in all temperature ranges. A maximum thermoelectric figure-of-merit ZT ≈ 0.5 was attained at 590 K for Cu4.96Co0.04FeS4.

Effect of Production Route on the Microstructure and Mechanical Properties of Cu–SiC $$_{\mathrm{p}}$$ p Composites

In this study, Cu matrix composite materials reinforced with SiC particles \((\hbox {SiC}_{\mathrm{p}})\) at different contents were produced by two different powder metallurgy (PM) processes, being traditional sintering and hot pressing. For the composites to be produced, 5–25% \(\hbox {SiC}_{\mathrm{p}}\) by weight was added to pure Cu powder at different contents and powder mixtures were prepared. The mixtures prepared in the production with traditional sintering were shaped by 500 MPa pressure, and green compacts were sintered at different temperatures to determine the optimum sintering conditions. The specimen production with the hot pressing process was performed by keeping the prepared powder mixtures at \(880\,^{\circ }\hbox {C}\), under 20 MPa pressure for 5 min using a graphite mold. The density, microstructure and mechanical properties of the composites produced were examined. The microstructure examinations were performed with the scanning electron microscope, energy distribution spectrometer and X-ray analysis. Characterization techniques such as hardness measurements, 3-point bending test and impact test were used for the determination of mechanical properties. Increased SiCp content caused a decrease in relative density values for both samples produced through traditional sintering method and hot-pressed samples. Considerably high relative density values were achieved with the hot pressing process compared to traditional sintering. The microstructure examinations showed that in the composites produced, the \(\hbox {SiC}_{\mathrm{p}}\) reinforcement phase dispersed homogeneously in the Cu matrix that comprised of relatively small and equiaxed particles. The mechanical tests showed that hardness increased remarkably with the increasing \(\hbox {SiC}_{\mathrm{p}}\) content while bending strength and impact energy values decreased.

Effect of consolidation techniques on the properties of Al matrix composite reinforced with nano Ni-coated SiC

Abstract Al /Ni-SiC composite was prepared via powder metallurgy technique. SiC particles were coated with 10 wt% nano nickel by electroless deposition, then mixed by three percents (5, 10 and 15 wt%) with Al powder in a ball mill using 10:1 ball to powder ratio for 5 h. Three types of sintering techniques were used to prepare the composite. Uniaxial cold compacted samples were sintered in a vacuum furnace at 600 °C for 1 h. The second group was the vacuum sintered samples which were post-processed by hot isostatic press (HIP) at 600 °C for 1hr under the pressure of 190 MPa. The third group was the hot pressed samples that were consolidated at 550 °C under the uniaxial pressure of 840 MPa. The results showed that the hot pressed samples have the highest densification values (97–100%), followed by the HIP samples (94–98%), then come the vacuum sintered ones (92–96%). X-ray diffraction analysis (XRD) indicated the presence of Al and Al3Ni, which means that all SiC particles were encapsulated with nickel as short peaks for SiC were observed. Hardness results revealed that HIP samples have the highest hardness values. The magnetization properties were improved by increasing SiC/Ni percent, and HIP samples showed the highest magnetization parameter values.

High-temperature formation phases and crystal structure of hot-pressed thermoelectric compounds with chalcopyrite-type structure

In this study, we introduced the temperature-dependent formation phases and crystallographic parameters of hot-pressed silver gallium telluride AgGaTe2 and copper gallium telluride CuGaTe2 with chalcopyrite structure from 300 to 800 K. These two compounds are potential thermoelectric materials in the intermediate temperature range; however, the temperature-dependent formation phases and crystallographic parameters of hot-pressed samples have not yet been analyzed in detail. The crystal structure analysis based on synchrotron X-ray diffraction (SXRD) measurements clarifies that impurity phases such as Te and Ag2Te in the AgGaTe2 matrix and Te and CuTe in the CuGaTe2 matrix appear at some temperature regions above 300 K. The existence of such impurity phases could be correlated with the increases of the electrical resistivity and Seebeck coefficient of the samples after multiple measurement cycles of the temperature-dependent transport properties from 300 to 800 K. The tetragonal lattice parameters a and c, tetragonal lattice volume, thermal expansion coefficients, tetragonal distortion, anion displacement parameter, and isotropic displacement parameter of the hot-pressed AgGaTe2 and CuGaTe2 were also analyzed. These crystallographic parameters are expected to substantially affect the thermoelectric properties of AgGaTe2 and CuGaTe2. Our results provide prospect of the long-term high-temperature stability and clues of the detailed analysis on the transport properties of hot-pressed AgGaTe2 and CuGaTe2, which should aid their development for thermoelectric applications.

Synthesis of Tin-Doped FeVSb Half-Heusler System by Mechanical Alloying and Evaluation of Thermoelectric Performance

In the current work, we tried to investigate and compare the thermoelectric performance of the FeVSb1−xSnx (x = 0.0–0.05) half-Heusler system. The elemental mixture was formulated and subjected to mechanical alloying, and subsequently consolidated using vacuum hot pressing. X-ray diffractometry analysis was used to observe phase transition during the process, and scanning electron microscopy was utilized for microstructure analysis. After vacuum hot pressing, a near single phase of FeVSb1−xSnx (x = 0.0–0.05) was observed with small portions of second phases. The vacuum hot-pressed samples were analyzed to study the thermoelectric properties as a function of temperature up to 980 K. The n-type conduction was confirmed from Seebeck and Hall coefficients in the test range. In addition, the electrical conductivity showed combined conduction behavior in the test range, while the thermal conductivities showed abnormal behavior. Mass fluctuation scattering and changing in carrier concentration might have taken place during doping. The Seebeck coefficient and electrical conductivity of the system also decreased after doping. Dimensionless figure of merit values were calculated and compared with the results of analogue studies. The maximum ZT value was obtained for x = 0.01 at 553 K.

Spark plasma sintering versus hot pressing – densification, bending strength, microstructure, and tribological properties of Ti5Al2.5Fe alloys

ABSTRACTTi5Al2.5Fe alloys were fabricated by the spark plasma sintering (SPS) and hot pressing (HP) pressure-assisted sintering techniques from pre-alloyed powders with a particle size of about 200 μm. The powders were sintered at 850 °C for two different holding times (5 and 8 min) and heating rates (50 and 150°C min−1) at 25 MPa. The maximum relative densities were 99.70 and 98.78% for SPS and HP samples, respectively. All the alloys prepared by the SPS process had significantly higher bending strengths (1825–2074 MPa) than the alloys prepared by the HP process (648–1330 MPa). A decrease in the heating rate from 150 to 50°C min−1 enhanced the wear resistance of the Ti5Al2.5Fe alloys prepared by both the SPS and HP processes.

Mechanical Alloying and Hot Pressing of Ti-Zr-Si-B Powder Mixtures

This work discusses microstructure evolution during ball milling and hot pressing of Ti-xZr-10Si-5B (x = 2 and 5 at. %) and Ti-xZr-20Si-10B (x = 5, 7, 10, 15 and 20 at. %) powder mixtures. Mechanical alloying was carried out in a ball mill using stainless steel balls and vials, 300 rpm and a ball-to-powder ratio of 10:1. Powders milled for 600 min were then hot-pressed (25 MPa) under vacuum at 1100 °C for 60 min. As-milled and hot-pressed samples were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and energy dispersive spectrometry (EDS). Peaks of Si and Zr disappeared in powders milled for 60 and 180 min, respectively, while the lattice parameters and cell volume of α-Ti were varied during ball milling up to 300 min indicating that supersaturated solid solutions were achieved. Ti6Si2B dissolving up to 10 at. % Zr was found in microstructure of hot-pressed Ti-xZr-10Si-5B (x = 2 and 5 at. %) and Ti-xZr-20Si-10B (x = 2, 5, 7 and 10 at. %) alloys. The amount of TiB and Ti5Si3 was preferentially increased whereas the Ti3Si formed in microstructure of the hot-pressed Ti-15Zr-20Si-5B and Ti-20Zr-20Si-10B alloys.

Influence of the fabrication process of copper matrix composites on cavitation erosion resistance

Copper matrix composites reinforced with ZrB2 particles were produced in two ways: by hot pressing (HP) and laser-sintering process. Powder mixture Cu-Zr-B was mechanically alloyed before densification processes. Variations in the microstructure of treated samples obtained during cavitation test were analyzed by scanning electron microscopy (SEM). Cavitation erosion resistance was investigated with the standard test method for cavitation erosion using vibratory apparatus. Changes in mechanical alloying duration show a strong influence on cavitation erosion resistance of Cu–ZrB2 composites regardless the number of reinforcements. Laser-sintered samples show better cavitation erosion resistance than hot-pressed samples.

Wire EDM of ZTA-NbC Dispersion Ceramics – The Influence of ED Machining on Mechanical Properties

Zirconia toughened alumina (ZTA) ceramics are well known for their good mechanical properties such as high hardness and bending strength and moderate fracture resistance. By adding an electrically conductive phase, such as a transition metal carbide, ceramics can be machined by electrical discharge machining (EDM).In this study the influence of electrical discharge machining on the mechanical properties of ZTA-NbC was investigated. Hot pressed samples were wire electrical discharge machined to obtain bending bars for mechanical characterization. Machining included the main cut and four subsequent trimming operations. Machined and polished samples were characterized with respect to bending strength and Weibull modulus to elaborate the influence of the individual machining steps on strength reliability of the material. Moreover surface morphology and surface roughness of the machined samples were studied by SEM and white light interferometry.It was found out that the ED machining affects the average values of bending strength and the scattering of the data described by the Weibull Modulus. While Weibull modulus and thereby reliability evidently rises with increasing number and refinement of machining operations, while bending strength showed an intermediate strength minimum after the 1st trimming operation. Subsequent trimming steps partly recover the bending strength.

A Structure and Durability Comparison of Membrane Electrode Assembly Fabrication Methods: Self-Assembled Versus Hot-Pressed

The most common means of fabricating membrane electrode assemblies (MEAs) for polymer electrolyte fuel cells (PEFCs) involves a hot-press step. The conditions used to perform the hot-press impacts the performance and durability of the fuel cell. However, the hot-press process is not essential for achieving operational MEAs and some practitioners dispense with the hot-press stage altogether by using a self-assembled approach. By performing the integration of the components in-situ during fuel cell assembly, there is the potential to lower the cost and time of manufacture. This study investigates the electrochemical performance and mechanical microstructure of MEAs that were either hot-pressed or self-assembled (non-hot-pressed) and compared at beginning-of-test (BOT) and end-of-test (EOT), following accelerated stress testing. Hot-pressed and self-assembled MEAs were found to show negligible difference in their performance and almost identical performance degradation. X-ray computed tomography (X-ray CT) showed distinct differences in the microstructure of the electrodes. In addition to a crack network in the catalyst layer, the self-assembled samples exhibit indentations that were not present in the hot-pressed sample. It was concluded that in-situ assembly of MEAs could be a suitable means of fabricating PEFC MEAs.

Effect of processing parameters on microstructural properties of lead magnesium niobates

The synchrotron powder X-ray diffraction (XRD) and subsequent detailed Rietveld analysis of lead magnesium niobate (PMN) samples were performed to study the microstructural properties of polar nanoregions (PNRs) of the R3m phase. PMN samples were synthesized under different sample processing conditions. The line profile broadening analysis of room-temperature synchrotron powder XRD patterns was performed using the multi-phase Rietveld refinement method for isotropic microstructural evaluation of different PMN samples. The two phases of perovskite PMN considered in the Rietveld refinement approach for satisfactorily fitting the XRD patterns are the paraelectric cubic phase (Pm\overline 3m) and the local rhombohedral phase (R3m) which corresponds to the PNRs. It is observed that the contributions of the Gaussian component of size broadening of the polar rhombohedral phase (R3m) and the Lorentzian component of strain broadening of the paraelectric cubic phase (Pm\overline 3m) are apposite for satisfactory Rietveld refinement of the synchrotron XRD data for all PMN samples. The volume-average crystallite size of PNRs (R3m phase) is almost invariant (approximately 12 nm) with increasing processing temperature while their weight percentage increases. The values of the apparent microstrain in the paraelectric cubic phase (Pm\overline 3m) are larger for hot-pressed samples.

Sintering behavior, microstructure and thermoelectric properties of calcium cobaltite thick films for transversal thermoelectric multilayer generators

The sintering behavior and the thermoelectric performance of Ca3Co4O9 multilayer laminates were studied, and a multilayer thermoelectric generator was fabricated. Compacts and multilayer samples with anisotropic microstructure and residual porosity were obtained after conventional sintering at 920°C, whereas dense and isotropic multilayer samples were prepared by firing at 1200°C and reoxidation at 900°C. A hot-pressed sample has a dense and anisotropic microstructure. Samples sintered at 920°C exhibit low electrical conductivity due to the low density, whereas the Seebeck coefficient is not sensitive to preparation conditions. However, thermal conductivity of multilayers is very low, and, hence acceptable ZT values are obtained. A transversal multilayer thermoelectric generator (TMLTEG) was fabricated by stacking layers of Ca3Co4O9 green tapes, AgPd conductor printing, and co-firing at 920°C. The TMLTEG has a power output of 3mW at ΔT=200 K in the temperature interval of 25°C to 300°C.

Preparation of super-high strength nanostructured B4C reinforced Al-2Cu aluminum alloy matrix composites by mechanical milling and hot press method: Microstructural, mechanical and tribological characterization

In this research, super-high strength nanostructured B4C reinforced Al-2Cu aluminum alloy matrix composites produced by mechanical milling and hot press method. Nanostructured Al-2Cu powder containing 4, 6 and 10 wt.% B4C reinforcement particles synthesized using a high-energy attritor under argon atmosphere. Results showed that with increasing the content of B4C particles the matrix grain size decreased. Since the compressibility of mechanically milled powders is very low, hot press processing used for consolidation of nanostructured Al-2Cu/B4C powders. The hot pressed Al-2Cu/10 wt.%B4C nanocomposite, when tested in compression, exhibited extremely high strength (1.1 GPa) which is 735 MPa higher than that of coarse grain Al-2Cu sample. Moreover, the hardening capacity (Hc) of hot pressed nanocomposites decreased with the increase in the content of B4C particles. According to Orowan strengthening mechanism, since B4C particles act as a barrier to the dislocations movement, the increase of B4C particles leads to the increase of barriers and as a result, ΔσOrowan increases. Therefore, the strength of composite increases but work hardening capacity (Hc) decreases. The results of wear test indicated that wear rate and friction coefficient declined gradually as the B4C particles fraction increased. Based on this result, hot-pressed sample containing 10 wt.% B4C showed the lowest wear rate and friction coefficient (1.9 × 10−5 mm3/m and 0.48 respectively).

Comparison of hot pressing and spark plasma sintering in the densification behavior of indium tin oxide‐borosilicate glass composites

AbstractThe goal of this study was to fabricate borosilicate glass matrix composites with high optical transmittance and high conductivity by forming percolated segregated networks of indium tin oxide (ITO) in the microstructure. ITO nanoparticles and borosilicate glass microspheres were mechanically mixed with ITO concentrations varying from 0 to 2.99 vol%. The mixes were then consolidated using either hot pressing (HP) or spark plasma sintering (SPS). The effects of changing sintering methods, along with varying other processing parameters such as heating rate, maximum temperature, and applied pressure, had surprising and unanticipated effects. Ac impedance spectroscopy (IS), SEM, and EDS results indicated the successful formation of a grain‐like microstructure of the sintered glass using both HP and SPS processing, with the ITO particles segregated to the boundary regions in all samples. IS results indicated percolation threshold values between 0.154 and 0.307 vol% ITO in the HP samples and between 0.307 and 0.764 vol% ITO in the SPS samples, with resistivities as low as 29 (Ω·cm) at 2.99 vol% ITO. Optical properties were dominated by impurities and light scattering at defects such as pores. Contrary to conventional belief, it was found that samples made using SPS required far higher temperatures to fully densify, with all other processing conditions being the same, compared with HP. This behavior was confirmed through repeat tests using different SPS equipment and a wide range of processing conditions.