Search

The microstructures and properties of powder metallurgy Ti-45Al-10Nb (at.%) alloys fabricated by vacuum hot pressing consolidation of milled powder have been investigated. Under the sintering condi...

Among refractory metals, tantalum has long been the primary material of use in high strain rate applications. Hot pressing (HP) is a technique to produce specimens with high density and homogeneous...

In this study the effect of veneer densification on the temperature change inside the plywood during the hot pressing step was analyzed. In addition, the shear strength of the plywood was determined. Rotary-cut birch veneer and phenol-formaldehyde resin were used to make the plywood samples. The multi-layers plywood structures made of densified and non-densified veneers with and without adhesive were investigated. Plywood products of 3, 5, 7, 9 and 11-layers were manufactured under laboratory conditions. It was found that the multi-layers plywood made of densified veneers was heated faster when compared to the plywood made of non-densified veneers. This will reduce the pressing time of plywood made of densified veneer by 2–29% depending on the number of veneer layers. The shear strength values of the plywood made of densified veneers were found two times higher than the normalized value of 1.0 MPa, meeting the EN 314-1 standard requirements. Findings of this work are useful for industrial applications to optimize the plywood production.

In this study, wear behavior of nanostructured Al and Al/2O3 nanocomposite samples prepared by an advanced technique called microwave- assisted hot press sintering process was investigated. The specimens were characterized by XRD analysis, pin-on-disk wear test and scanning electron microscopy observations. Compared to nanostructured Al, nanocomposite containing 4 wt-%Al2O3 showed a higher hardness of 175 HV and a lower wear rate of 7 × 10-3 mg m-1. Also, wear properties of hot-pressed samples were compared with those of nanocomposite conventionally prepared by Tavoosi et al. method. The results showed that contribution of ceramic particles in enhancing the wear resistance of nanocomposite can be eliminated by increased porosity content. Higher sintering temperature due to rapid heating rate of microwave-assisted hot press sintering method led to more densification and improvement in wear resistance in comparison with conventional method.

Herein, a type of biomass-based electric heating membrane (EHM) with excellent stability was fabricated; this was achieved by incorporating carbon nanotubes (CNTs) into the nanofibrillated cellulose (NFC) as a natural dispersant and a biological substrate, as well as via the control of ultrasonic dispersion, grammage, and encapsulation using poly(dimethylsiloxane) (PDMS) with hot pressing. NFC entangles with CNTs in the form of an intertwined network and non-covalent interactions to fabricate a flexible EHM with steady electric heating performance; this formation is attributed to not only their similar morphology and surface-active groups but also the use of NFC that avoids additional disturbances in the overlapped interface among CNTs as far as possible. The obtained steady resistance varies as low as 5.1% under energized operation. In the encapsulated EHM (EM), PDMS was anchored on its surface by using hot pressing and an intertwined structure to enhance flexibility and robustness. The encapsulated membrane can be used in low-voltage applications, which require flexibility, waterproofing, and insulation.

Refined wheat flours commercially produced by five different U.S. and Mexican wheat blends intended for tortilla production were tested for quality and then processed into tortillas through the hot-press forming procedure. Tortilla-making qualities of the flour samples were evaluated during dough handling, hot pressing, baking, and the first five days on the shelf at room temperature. The predominant variables that affected the flour tortilla performance were wet gluten content, alveograph W (220–303) and P/L (0.70–0.94) parameters, farinograph water absorption (57%) and stability (10.8–18.7 min), starch damage (5.43–6.71%), and size distribution curves (uniform particle distribution). Flours produced from a blend of Dark Northern Spring (80%) and Mexican Rayon (20%) wheat had the highest water absorption, and tortillas obtained from this blend showed the highest diameter and lowest thickness. The whitest and best textured tortillas were obtained from the flour milled from three hard types of Mex...

In this study the W/Cu and W/ZrC composites have been fabricated by hot-press and then their mechanical properties were compared in addition to their ablation resistance. To produce W-20vol.%Cu composite at first stage the elemental W and Cu powders were ball milled for 3 h in rotation speed of 200 rpm, in which 2% nickel was added in order to reduce the density. The mixed powders were hot-pressed for 1 h at 1400 °C and compact pressure of 30 MPa. Additionally W/40vol.%ZrC composite has been fabricated by hot-pressing of mixed W and ZrC powders in 30 MPa and 2200 °C for 1 h. Since these materials are used at elevated temperature applications, where ablation is the main source of material failure, after producing the composites their ablation resistance was evaluated in a real condition. The results show that not only W–ZrC composite is better than W–Cu composite in mechanical properties, but also in ablation resistance.

Metal matrix composites (MMCs) are engineering materials in which a hard ceramic component is dispersed in a ductile metal matrix in order to obtain characteristics such as hardness and corrosion resistance. Corrosion resistance is one of the important properties of nanocomposites; however, the corrosion mechanism of the Al- SiC nanocomposite has not yet been determined. .In this study, bulk Al-5% SiC nanocomposite was prepared using mechanical alloying and the hot press method. Corrosion behavior was then investigated using EIS techniques such as Nyquist and the Bod diagram. A larger charge transfer resistance was found for the Al- SiC nanocomposite by the EIS diagrams, confirming its corrosion resistance in a 3.5wt% NaCl solution.

Nanocellulose (NC) has been spotlighted as a new building block of future materials since it has many advantages, such as being lightweight and environment-friendly and having high mechanical properties and heat resistance. However, the use of NC requires an upscale manufacturing process to maintain its advantageous properties. Herein, the process of assembling NC into a macro-scale bulk material was developed through a combination of steam treatment and hot press molding. The steam treatment was applied to an NC paste to energize the hydroxyl groups in the cellulose, followed by two stages of hot press molding, which helped in the self-assembly of NC without adhesives. Cellulose nanocrystals were used as the NC, and circular disk shape specimens were prepared. The mechanical properties of the prepared bulk material were higher than typical engineering plastics. In addition, an end mill machining test of the NC bulk material showed its machinability. This paper showed the processing feasibility of NC bulk material, which can substitute plastics.

FeAl intermetallic compound with different contents of rare earth oxide La2O3 addition was prepared by hot pressing the mechanically alloyed powders. Effect of La2O3 on microstructure and high-temperature wear property of the sintered FeAl samples was investigated in this paper. The results showed that 1 wt.% La2O3 addition could refine the microstructure and increase the density of the FeAl intermetallic compound, and correspondingly improved the high-temperature wear resistance. SEM and EDS analyses of the worn surface indicated that micro-ploughing and local melting combined with oxidation were the dominant wear mechanisms.

Magnesium and its alloys have become attractive materials in automotive and aerospace fields because of their low density and high strength. However, their application is greatly limited by their poor deformation capacity. Powder metallurgy technology can reduce the deformation and processing of magnesium alloys during the preparation process to alleviate this problem because of its near net shape machining characteristics. In this paper, a high-performance AZ31 magnesium alloy was prepared via vacuum hot-press sintering. The effects that sintering temperature has on the structure and mechanical properties of the as-sintered alloy were investigated. The results indicate that the sintered microstructure is composed of approximately equiaxed α-Mg crystal grains, and nanoscale Al-Mn phases precipitated in the crystals and particle boundaries. At an optimal sintering temperature of 535 °C, the average tensile strength, compressive strength, elongation, and fracture strain of the sample are 247.10 MPa, 391.35 MPa, 22.27%, and 24.17%, respectively. In addition, the reasons for the high strength and favorable elongation of the AZ31 magnesium alloy that was sintered via vacuum hot pressing were also analyzed. This is mainly because pressure is applied during the sintering process; this eliminates pores and breaks the oxide film on the powder surface, thereby forming a good metallurgical bond between the powders.

Mo, Si and B 4 C powders were used to fabricate 0.4MoB-0.1SiC- x MoSi 2 composites by self-propagating high-temperature synthesis (SHS) and hot pressing (HP). The effects of MoSi 2 content ( x = 1, 0.75, 0.5 and 0.25) on phase composition, microstructure and properties of the composites were investigated. The results showed that the 0.4MoB-0.1SiC- x MoSi 2 composite exhibited Vickers hardness of 10.7–15.2 GPa, bending strength of 337–827 MPa and fracture toughness of 4.9–7.0 MPa m 1/2 . The fracture toughness increased with the increasing volume fraction of MoB and SiC particles which were promoted by the toughening mechanisms, such as crack bridging, cracks deflection and crack branching. Moreover, the electrical resistivity showed an increasing trend with decreasing volume fraction of MoSi 2 .

In this work, Bi 0.85 Sm 0.15 Fe 0.97 Sc 0.03 O 3 ceramics were prepared by rapid hot pressing. Their crystal structures, dielectric and multiferroic properties were studied with an emphasis on microscopic ferroelectric and ferromagnetic domains characterizations. X-ray diffraction data revealed a diphase structure consisting of rhombohedra R 3 C and orthorhombic Pbnm . The ferroelectric polarization and magnetization measurements showed the ceramics， possessing simultaneously a giant remanent polarization of 42.36 μC/cm 2 and a high remanent magnetization of 0.134 emu/g at room temperature. Moreover, the regularly striped ferroelectric and ferromagnetic domain structures have been identified and analyzed by combining transmission electron microscopy and piezoresponse/magnetic force microscopy.

The purpose of this study was to investigate the improvement in the hydrophobicity of cellulose through gas grafting treatment with long chain fatty acid chloride using high pressure during pressing at high temperature. To do this, the gas grafting treatment was performed on the cellulose sheet using a hot pressing method, and then the hydrophobization effect was analyzed. It was found that the gas grafting treatment by hot pressing using high pressure during pressing at high temperature produced cellulose sheets of high hydrophobicity. Especially, it was notable that the hydrophobization efficiency enhanced with an increase of the pressing pressure. In addition, the gas grafting efficiency was improved when polyvinyl alcohol (PVA) was coated to obtain high resistance to air permeability. These results indicate that protecting the loss of fatty acid gas by coating of polyvinyl alcohol (PVA) on the cellulose sheet surface contributed to the improvement of gas grafting efficiency.

Bulk Al/4wt-%Al2O3 nanocomposites were prepared by consolidating nanocomposite powders using pressureless microwave sintering, microwave-assisted hot press sintering and conventional hot pressing techniques. Microstructural observations revealed that the microwave- assisted hot press sintering at different sintering temperatures of 400°C and 500°C resulted in more densification and smaller grain size for Al/Al2O3 nanocomposite as compared with the conventional hot pressing. Moreover, the application of pressure in microwave sintering process led to more densification and grain growth. Mechanical properties resulting from microhardness and nanoindentation tests were also compared between three-method processed samples. It was found that the microwave-assisted hot-pressed sample exhibited higher hardness and elastic modulus in comparison with microwave-sintered and conventional hot-pressed samples. The improvement in the mechanical properties can be ascribed to lower porosity of microwave-assisted hot-pressed sample.

A hot-press method was used for MgB 2 bulk samples, and the densification samples were prepared by the varying applied pressure. The critical current density J c of the sample was measured and the pressure and temperature dependences of J c were systematically investigated. The density of the bulk samples have improved by applying pressure in the direction of thickness of the sample while heating, and the density increased with the rise in the hot press pressure. In the sample processed at 400 kg/cm 2 and 730 °C, J c was around 9.7 × 10 5 A/cm 2 at 20 K, 2 T, which is at least three times the value of sample without hot pressing. The results suggest that densification of the sample by hot pressing contributes to the J c improvement in the MgB 2 bulk.

The hot press method was employed for the synthesis of a new family of the high T c superconductor (CuTl)Ba 2 Ca n −1 Cu n O 2 n +4− y . By varying the starting composition of the samples, the optimum preparation conditions for the Cu 1− x Tl x Ba 2 Ca 2 Cu 3 O 10− y ( x =0.25–0.75) phases were studied. The highest T c (121 K) sample of (Cu 0.3 Tl 0.7 )-1223 was obtained by hot press sintering at 1000°C for 3 h. Highly oriented (Cu 0.3 Tl 0.7 )-1223 samples along the c -axis were obtained by the same way.

In this paper, Microwave-Assisted Hot Press (MAHP) process in a multimode microwave furnace using double-action compaction for two samples including Al–Al 2 O 3 composite and Alumina ceramic was simulated. Firstly, cold press process for two samples was simulated. The constitutive relations of porous compacts during the compaction process were derived with respect to the yield criterion of Gurson–Tvergaard–Needleman (GTN) model. Secondly, to simulate the microwave heating process, a frequency domain calculation was used to calculate the electromagnetic field in the furnace. Then, the temperature variation of samples was calculated according to the dielectric permittivity and thermal parameters. The result was that the difference between such parameters as permittivity and conductivity, in different powder systems led to different times needed to reach the required temperature for the hot pressing process. Furthermore, compared to Alumina ceramic, more heating uniformity of the composite specimen was seen. Finally, by using green density distributions and temperature gradient extracted from microwave heating process, the hot press process of two compactions was simulated. In the process of compaction, Von Mises stress, density distributions resulted. For hot-pressed Alumina ceramic, the Mises stress at the corners of the compact reached 45% to 50% of the applied pressure and decreasing towards the center of the circumference of the compact. However, for hot-pressed Al–Al 2 O 3 composite, the value at the corners of the compact was about 25% of applied pressure. Also, Alumina ceramic specimen during the hot press had a relative density of 96% in the outside region and a relative density of 95% in the central region where this number for Al–Al 2 O 3 composite compact was derived to be 98% in central region.

Thin-layer thermal pressing is an innovative method that has the potential to further eliminate moisture content in liquid form from mechanical dewatering of sludge. Here, the dewatering performances of treated sludge are evaluated. The results demonstrate that the hot-press treatment is able to effectively reduce the moisture content of dewatered sludge with a thickness of less than 5 mm. A preliminary survey of the hot-press mechanisms for thin-layer sludge has also been conducted, by analysis of extracellular polymeric substance extracted from treated sludge. It can be deduced that hot pressing leads to cell damage in sludge by increased cell lysis.

Processing conditions are one of the factors that significantly influences the properties and characteristics of the polymer matrix composites products. Therefore, the suitable processing parameters must be selected in order to yield the optimum properties of the composite products. In this work, Box-Behnken Design (BBD) was selected as experimental design approach. Biodegradable composites from unidirectional long kenaf fibre reinforced polylactic-acid were fabricated by hot pressing method. Response surface methodology (RSM) and analysis of variance (ANOVA) were used to optimize as well as determine the significance of the factors affecting the tensile strength. Three factors studied were pressure, temperature and heating time at three different levels. The experimental results showed that all three factors are the significant processing parameters affecting the strength of composite. The combination of hot pressing parameters for optimum tensile strength was 200 o C temperature, 3MPa pressure, and heating time at 8 minutes. Confirmation runs test yield error less than 7% verified the validity of the model.

Based on the hot-pressing sintering process, the kinetics of hot-pressing sintering crystal grain growth and the hot-pressing sintering densification kinetics, the mixing ratio of the raw material powder and the hot-pressing sintering system are designed. The pressure is maintained at 30 MPa from the temperature rise to the end of the sintering process, and wait until the temperature reaches the corresponding hot pressing sintering temperature (1200°C~1400°C), keep the corresponding time for 1.5h~4.5h, stop heating and depressurize, and the alloy billet is cooled to room temperature with the furnace. The main phases of Ti2AlNb powder and hot pressing sintering process are TiAl and Ti3Al.

In this study, aluminum alloyAA6061-T6 was joined by a hot press process with three types of material; polyamide PA 6.6 (nylon), 1% carbon nanotube/PA6.6 and 30% carbon fiber/PA6.6 composites. Three parameters were considered in the hot pressing; temperature (180, 200 and 220°C), pressure (2, 3, 4, 5 and 6 bar) and time of pressing (1, 2, 3, 4 and 5 minutes for 200ºC, and 0.25, 0.5, 0.75, 1 and 1.25 minutes for220ºC). Applied pressure has great effect on shear strength of the joint, corresponding to bonding time and temperature. Maximum shear strength was 8.89MPa obtained for PA6.6 at bonding conditions of 4 bar, 220ºC and 0.75 minute. For 30% carbon fiber/PA6,6 shear recorded was 8MPa at 4 bar, 220°C and 1 minute, while 1% carbon nanotube/PA6.6 was registered at 8MPa at 4 bar, 220ºC and 0.75 minute. Mechanical interlocking of polyimide in anodizing surface is 8μm approximately. The melting point and glass transmission temperature of polyimide and composites are decreased after hot pressing.

An investigation was carried out on the influence of a number of relevant factors which, in the case of hot press gluing i.e. conduction gluing (CG) and high-frequency (HF) gluing of peeled beech veneer (Fagus silvatica L.) to produce veneer boards, result in a permanent thickness loss of the boards. Using both types of gluing, four different thicknesses of veneer, four different veneer humidities, and four different gluing pressures were varied to make a large number of different combinations. Gluing of a total of 384 test boards 500×200 mm, with a thickness of approximately 15 mm, was carried out using urea-formaldehyde glue at a temperature of 120 °C. The gluing lasted for 8 minutes for hot press gluing, and 5 minutes for the HF method. The results of the tests showed that the interdependencies noted between the effects of the studied factors were similar for both methods of gluing. Influence of humidity on thickness loss was greater in the case of HF gluing and premanent thickness loss was greater for high frequency gluing.

The hot press moldability of bamboo powder without additives was investigated in this study. Bamboo powder was hot pressed into self-bonded cylindrical moldings at temperatures of 160 to 200 oC and pressing times of 1 to 20 min at a punch surface pressure of 200 MPa. After pressing, the color, density and bending properties of the moldings were evaluated. The bending strength, bending elastic modulus and density were found to increase with an increase in temperature, and moldings having good mechanical properties were obtained at a temperature of 200 oC. With respect to the influence of hot pressing time on moldability, a maximum bending strength of 34 MPa was achieved for a time of 10 min at a temperature of 200 oC. In addition, we removed moldings from the mold after cooling to 100 oC or less in order to improve the surface texture and density of the moldings. The results showed a cooled molding had a good surface texture (resembling plastic) and a bending strength of 53 MPa.

(Pb0.87Ba0.1La0.02)(Zr0.68Sn0.24Ti0.08)O3 anti-ferroelectric ceramics with various amounts of excess PbO have been fabricated by the conventional solid-state reaction process and the hot-press sintering method, and the dependence of microstructure, ferroelectric and dielectric properties on sintering approaches and lead volatilization conditions has been studied. When an appropriate quantity of excess PbO is added, the lead volatilization effect can be compensated and the content of pyrochlore phase is decreased. Hot-pressed anti-ferroelectric ceramics exhibit much higher densities than conventionally sintered samples. The spontaneous polarization and maximum dielectric constant of the AFE ceramics decrease when the hot-press sintering method is used. The dielectric loss can be obviously reduced by using the hot-press sintering method and adding a proper amount of excess PbO. The systemic investigation of the lead volatilization effect and the hot-press sintering method will contribute to the development of high properties of anti-ferroelectric ceramics in practical applications.

We present data on the heavy fermion compound CeAl 3 as a potential p -type thermoelectric material at cryogenic temperatures. Samples of CeAl 3 were synthesized by arc-melting, ball milling and hot pressing the nano-powder at different temperatures. Thermal conductivity ( κ ), Seebeck coefficient ( S ), electrical resistivity ( ρ ) and Hall coefficient ( R H ) of the samples were measured at temperatures ranging from 5 to 330 K. The thermoelectric properties of this compound are highly dependent on the hot-pressing (HP) temperature. The thermal conductivity increases with increase in HP temperature which is compensated by increased power factor ( S 2 ρ − 1 ). As a result the samples with higher HP temperatures exhibit higher ZT values. The highest ZT value of 0.016 at 55 K was observed for the sample hot-pressed at 800 °C. The Hall coefficient data reflects an increase in carrier concentration and a decrease in carrier mobility with decreasing hot pressing temperature.

In the present study, coating of some magnesium alloys including AZ31 and AZ91 were studied using different techniques namely anodizing, electroless and hot press cladding. AZ91 alloy was coated using anodizing process using three types of environmental friendly electrolytes; the first based on sodium silicate, the second based on sodium hydroxide-boric acid-borax and the third on sodium silicate-potassium hydroxide-sodium carbonate-sodium tetra borate. Characterization of the anodizing layer was achieved by determination of surface morphology, microstructure, phase analysis, coat thickness, adhesion and corrosion resistance. It was found that the anodic film thickness increases with increasing the current density, anodizing voltage and deposition time until the deposition stops due to the formation of a thick anodic film. The range of the anodic film thickness is 28 42 µm.Optimization of the anodizing conditions - current density and deposition time was determined for each electrolyte. A corrosion efficiency ranging from 94% to 97% was reached; the highest value corresponding to the third electrolyte. Another study is the electroless Ni plating technique with zinc pre-treatment applied on several magnesium alloys and the effect of pre-treatment and post heat treatment on the coat characteristics. The surface morphology, surface roughness, thickness of the layer, EDX analysis, adhesion, hardness and corrosion resistance are covered in this part. The electroless layer thickness is about 6 µm. The results showed good bond quality of the coat maintaining good corrosion behaviour of electroless Ni-P based on potentiodynamic polarization tests in chloride solution where it was improved after heat treatment process. On the other hand, AZ31 was covered by a commercial pure aluminum sheet by hot pressing. The influence of the applied pressure, holding time and temperature on the bond characteristics was studied. The experimental investigation has revealed a good bond quality due to the effective mutual diffusion of Mg and Al. The phase analysis resulted in the formation of two equilibrium phases namely; Mg17Al12and Mg2Al3. The corrosion resistance of AZ31 is enhanced as a results of this process by 98.6%. Further points will be covered.Keywords: Magnesium alloys; Coating; Anodizing; Electroless; Hot press cladding; environmental friendly electrolytes; corrosion

Hot Press Forming (HPF) of Tailor Welded Blank (TWB) was investigated with particular focus on the formability and phase transformation of the constituent base materials. Dilatometric analyses were conducted to study strength differentials for various cooling rates after heat treatment. U-draw bending tests were performed to evaluate the influence of a number of process parameters, namely, blank and tool temperatures, and cooling time, on the mechanical properties of the product. Formability at elevated temperature was assessed using forming limit diagrams for each monolithic material under realistic hot press forming conditions. Lab-scaled forming tests of a newly designed B-pillar were carried out to evaluate the formability of TWB under an actual hot press forming process. Finally, coupled thermomechanical finite element simulations, which utilize flow stresses and forming limit diagrams determined under realistic HPF conditions, were carried out. In particular, finite element simulation results for the weld-line displacement and thinning of the TWB were compared to experimental data for validation purpose.

The dense layered ternary Ti2AlN ceramics were successfully synthesized by a combination of mechanical alloying and hot press sintering from the mixture of Ti and Al in nitrogen milling atmosphere. The phase transformation and morphology characteristics in mechanical alloying and subsequently hot press sintering were studied by using XRD and SEM as well as EDS. The results show that Ti(Al,N) amorphous powders were synthesized successfully by mechanical alloying. When the as milled powders were hot pressed at 1200 °C for 1 h, full dense and highly pure layered ternary Ti2AlN ceramic was synthesized.

High coercivity, fully dense anisotropic permanent magnets of submicron grain sizes were produced by rapid hot-press consolidation of hydrogenation–disproportionation–desorption–recombination (HDDR) processed Nd–Fe–Co–B powders. In the hot-press process, the coercivity of the consolidated material showed a sharp minimum prior to full densification. Thereafter, it reached a value 25% higher than that of the initial powder. Scanning electron microscopy and transmission electron microscopy observations revealed that the variation in HcJ was caused by a redistribution of Nd along the grain boundaries during hot pressing and that the high coercivity was attributable to the formation of thin, continuous Nd-rich phase along the grain boundaries.

The effect of Al as a sintering additive to TiN was investigated and mechanical properties such as flexural strength and Vickers hardness were studied.

BiFeO3 represents the most extensively investigated multiferroic due to its fascinating ferroelectric domain structures, large polarization, and multiferroic coupling, among many other emergent phenomena. Nevertheless, much less concern with the piezoelectricity has been raised while all these well addressed properties are identified in thin film BiFeO3, and bulk ceramic BiFeO3 has never been given priority of attention. In this paper, we report our experiments on the ferroelectric and piezoelectric properties as well as domain structures of BiFeO3 bulk ceramics synthesized by rapid hot-press sintering. It is revealed that these properties are strongly dependent on the microstructural quality, and the largest piezoelectric coefficient d33 = 55 pC/N with electric polarization as large as 45 μC/cm2 is obtained for the sample sintered at 800 °C, while they are only 30 pC/N and 14 μC/cm2 for the samples sintered in normal conditions at 800 °C. The two-level hierarchical stripe-like and irregular dendrite-like domain structures are observed in these hot-press sintered samples. It is suggested that the enhanced piezoelectric property is ascribed to the two-level hierarchical stripe-like domain structure which may respond more easily to electrical and strain stimuli than those irregular dendrite-like domains. The enhanced remnant polarization should be owing to the improved sample quality and large grains in the properly hot-press sintered samples.

The effects of deformation temperature on texture and thermoelectric properties of p-type Bi0.5Sb1.5Te3 sintered materials were investigated. The sintered materials were prepared by mechanical alloying and hot-press sintering. The hot-press deformation was performed at 723 K and 823 K by applying mechanical pressure in a graphite die. Then, the materials were extruded in the direction opposite to the direction of applied pressure. X-ray diffraction and electron backscattered diffraction patterns showed that the hexagonal c-plane tended to align along the extruded direction when the samples were deformed at high temperatures. The thermoelectric power factor was increased by high-temperature hot-press deformation because of the low electrical resistivity that originated from the c-plane orientation.

A series of boron carbide (B 4 C) matrix composites with different contents of Al, were synthesized by reaction hot-press sintering with milled B 4 C and pure metallic Al powder at 1600 °C for 1 h. X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) were used to identify the phase constituent of the milled powders and the composites. The results have shown that parts of B 4 C and Al particles were oxidized to boron oxide (B 2 O 3 ) and alumina (Al 2 O 3 ) during the milling. Thermit reaction occurred and B 2 O 3 was reverted during hot-press sintering. A ternary phase of Al boron carbide (Al 8 B 4 C 7 ) was found in the composites, and the B 4 C transformed to a rich boron phase (B 6.5 C) because of the superfluous boron in the system.

Textured hexagonal boron nitride (BN) composite ceramics with mullite as sintered additive were fabricated by hot-press sintering under different pressures. The degrees of texture and the microstructures of these materials were evaluated using X-ray diffraction, pole figures and scanning electron microscopy. The results showed that the hexagonal BN composite ceramics have obvious directional orientation. The preferred orientation of the c-axis of hexagonal BN grains was along the direction of pressure, and the sintering pressure influences texture formation.

In this paper, the effect of reactive hot press sintering (RHPS) parameters, such as milling time, hot pressing temperature, and heat treatment, on phase constitution, microstructure, and room temperature mechanical properties of a multicomponent Nb-16Si-22Ti-2Hf-2Al-2Cr alloy prepared from ball milled powder mixture is investigated. Evaluation of the microstructure revealed that all as-sintered and heat-treated samples mainly consisted of particles of Nb and Ti solid solutions (NbSS and TiSS), as well as a niobium silicide β-Nb5Si3 matrix, with a small quantity of Hf solid solution particles (HfSS). By sintering at 1773 K and 1873 K (1500 °C and 1600 °C), most of the NbSS phase in the samples prepared from 5 and 10 ball milled powder mixtures showed a narrow strip morphology. Upon increasing the milling time to 20 hours, the morphology changed to a near-equiaxed shape, which became finer with increased milling time. In contrast, the TiSS phase in all as-sintered samples more or less had a near-equiaxed shape. Spheroidizing tendency took place in both NbSS and TiSS phases during an annealing heat treatment at 1773 K (1500 °C) for 50 hours. Interestingly, when the milling time was extended from 5 to 20 hours, the volume fractions of the β-Nb5Si3 and TiSS phases increased, whereas that of the NbSS phase decreased. This resulted in the reduction of the fracture toughness KQ and an enhancement of the Vickers hardness Hv of the bulk as-sintered and heat-treated samples. A fractography analysis was also carried out to elucidate the fracture behavior of phases, with particular emphasis on the interaction between phases and cracks.

The purpose of this study was to modify Italian poplar (Populus euramevicana cv. ‘I-214’) wood with urea-formaldehyde prepolymer followed by hot pressing. The timbers were impregnated with urea-formaldehyde prepolymer using a pulsed-dipping machine and cured in a hot press. The results showed that the timbers could be easily compressed and cured at temperatures between 90°C and 120°C. The characteristics and quality of the modified wood were up to A grade according to Chinese Standard GB/T 6491‐1999. The air-dried density of modified wood was improved by 58 percent, and the hardness in the transverse, tangential, and radial directions was increased by 67, 210, and 160 percent, respectively. The bending strength was improved by 78 percent; the bend elastic modulus was improved by 66 percent. The water absorption of treated wood decreased relative to that of the untreated timbers. Fourier transform infrared spectroscopy of the modified wood showed a significant reduction in the C=O absorbance at 1,...

The sintering temperature of lead-basedanti-ferroelectric (AFE) ceramics is always as high as1230°C,which leads to the volatilization of lead and deterioration of performance. In order to bring down the sintering temperature and preventthe deterioration of electrical properties of AFE ceramics, Pb0.87Ba0.1La0.02(Zr0.68Sn0.26Ti0.06)O3(PBLZST) AFE ceramics with various amount of 0.5PbO-0.5B2O3 glass have been fabricated by the hot-press sintering method. The sintering temperature of AFE ceramics is reduced to 1150°Cand the density of all samples is enhanced.When the content of glass addition is 0.1 wt.%, the high density of 8.17 g/cm 3 is obtained. And when the content of glass addition is 0.3 wt.%, the saturate polarization of 42.4 μC/cm 2 is achieved.The combination of glass addition and the hot-press sintering method reduced the sintering temperature and simultaneouslypromoted the density and saturate polarization of PBLZST AFE ceramics.

In the present investigation, magnesium alloy AZ31 sheet was covered by a commercial pure aluminium sheet by cladding using hot pressing. The influence of the applied pressure, temperature and holding time on the bond characteristics was studied. Microstructure examination of bonded specimens was experimentally investigated by optical microscope, SEM and EDX. The experimental investigation has revealed a good bond quality due to the effective mutual diffusion of Mg and Al. The phase analysis resulted in the formation of two equilibrium phases namely; Mg17Al12 and Mg2Al3. The initiation and growth mechanisms of the diffusion layers were determined by empirical equations and compared with the experimental results. It was observed that the growth kinetics obeyed a parabolic equation of the second order. Moreover, Arrhenius equation for the bonded couple AZ31/Al is derived to show the rate of diffusion layer growth. In der vorliegenden Untersuchung wurde Magnesiumlegierungsblech AZ31 mit einem kommerziellen reinen Aluminiumblech durch Heispressen diffusionsbeschichtet. Der Einfluss des angelegten Drucks, Temperatur und Haltezeit auf die Bindungseigenschaften wurde untersucht. Die Mikrostruktur geklebter Proben wurde experimentell mit einem optischen Mikroskop, Rasterelektronenmikroskop (REM) und durch energiedispersive Rontgenspektrometrie (EDX) untersucht. Die experimentelle Untersuchung hat eine gute Bindungsqualitat aufgrund der effektiven gegenseitigen Diffusion von Mg und Al offenbart. Die Phasenanalyse fuhrt zur Bildung von zwei Phasen, namlich Gleichgewicht Mg17Al12 und Mg2Al3. Die Einleitungs- und Wachstumsmechanismen der Diffusionsschichten wurden durch empirische Gleichungen bestimmt und mit den experimentellen Ergebnissen verglichen. Es wurde beobachtet, dass die Wachstumskinetik einer parabolischen Gleichung zweiter Ordnung gehorcht. Daruber hinaus wird die Arrhenius-Gleichung fur die verbundenen Werkstoffe AZ31/Al abgeleitet, um die Rate des Diffusionsschichtwachstums zu zeigen.

GaAs-polymer composite varistors are prepared using hot pressing method at a temperature of 130 °C and different pressures and their current–voltage characteristics are investigated. The results show that these varistors can be used to protect circuits from 35 V up to 52 V over voltages. In addition, it is found that the varistor breakdown voltage and its nonlinearity as well as its impurity band gap increase by increasing sintering pressure while the corresponding barrier height decreases. Each sample has hysteresis which increases through the increase in sintering pressure. This causes the varistors to have lower lifetime due to their high degradation. These results are both investigated and analyzed using SEM micrographs.

Sodium superionic conductor, NASICON ceramic (Na1+xZr2SixP3-xO12, x=2), was hot-press sintered under different temperatures and the electrical properties of the obtained different samples were investigated. Results show that the relative density of the ceramics can be improved by hot-press process efficiently and the crystal size of the samples are closely related to sintering temperature. With the increase of sintering temperature, both the density and the crystal size of samples increase obviously, resulting in the increase of ionic conductivity of samples as the sintering temperature. When the sintering temperature reaches 1150oC, the ionic conductivity of sample is as high is 3.6×10-3S/cm, which is obviously higher than that of sample sintered at 1000oC (2.13×10-3S/cm). As the frequency increase, the real parts and the imaginary parts of complex dielectric constants for all the samples decrease in 8.2 GHz~12.4GHz frequency band. The ceramics obtained at the higher temperature possess the higher dielectric constant.

Fe 3 O 4 and Mo and were added to hot-press sintered Si 3 N 4 ceramics to improve their lipophilic and mechanical properties. The bending strength, relative density, hardness and fracture toughness of Si 3 N 4 ceramics with addition of Fe 3 O 4 and Mo were improved by hot-press sintering compared with samples prepared with the pressureless process. In particular, the bending strength and relative density were improved to about 200% and 104%, respectively. Both the macro- and micro-lipophilicity of Fe 3 O 4 - and Mo-added ceramics were improved when prepared with the hot-press process, compared with those prepared with the pressureless process. This can be attributed to the addition of Fe 3 O 4 , and the formation of MoO 3 and Si 2 N 2 O during hot-press sintering. The lower friction coefficient and high wear resistance of Fe 3 O 4 - and Mo-added ceramics have been achieved by applying the hot press process. The high wear resistance is considered to be due to the improvement of hardness and fracture toughness, which decreased the loss of particles during the wear test.

In this work, we report the successful and efficient transfer process of two- dimensional (2-D) vertically aligned carbon nanotubes (CNTs) onto polyethylene terephthalate (PET) substrate by hot pressing method with an aim to develop flexible sensor devices. Carbon nanotubes are synthesized by cold wall thermal chemical vapor deposition using patterned SiO2 substrate under low pressure. The height of the pattern of CNTs is controlled by reaction time. The entire growth and transfer process is carried out within 30 min. Strong adhesion between the nanotube and polyethylene terephthalate substrate was observed in the post-transferred case. Raman spectroscopy and scanning electron microscope (SEM) studies are used to analyze the microstructure of carbon nanotube film before and after hot pressing. This technique shows great potential for the fabrication of flexible sensing devices. We report for the first time, the application of patterned microstructure developed by this technique in the development of gas sensor and optoelectronic device. Surface resistive mode is used for detection of ammonia (NH3) gas in the sub-ppm range. An impressive photoconducting response is also observed in the visible wavelength. The reproducibility of the sample was checked and the results indicate the possibility of use of carbon nanotube as gas sensor, photodetector, CCDs etc.

Nano laminated bulk Ti₃SiC₂ was synthesized by hot press process using TiCx/Si powder mixture at the temperature range of 1300℃~1500℃. pure Ti₃SiC₂ was synthesized by a hot pressing above 1400℃, while unreacted TiCx were remained in bulk Ti₃SiC₂ which synthesized below 1400℃. The sintering density of bulk Ti₃SiC₂ were varied with the amount of TiCx. It was found that the mechanical properties and micro structures of bulk Ti₃SiC₂ were closely related to the amounts of TiCx which was controlled by the hot pressing temperature. The TiCx increase the flexural strength of bulk Ti₃SiC₂, while the fracture toughness and thermal shock resistance of bulk Ti₃SiC₂ were decreased with the content of TiCx. The plastic deformations of bulk Ti₃SiC₂ were appeared above 1000℃.

Nano-Fe particles coating Al2O3 composite powders were prepared by heterogeneous precipitation method with nanometer -Al2O3 and Fe(NO3)3•9H2O as raw materials. The composite powders were analyzed by DSC-TG, XRD,SEM and Zeta potential. Results showed that Fe coating Al2O3 nanometer composite powders were obtained in the condition of being sintered at 500°C for 30min and reduced at 700°C for 1h in H2. The coating Fe nanometer particles are in the shape of sphericity with diameter about 30nm and the dispersion of the powders is uniform. Al2O3/Fe composite ceramics were obtained by hot-pressing (30MPa). The mechanical properties of the composite were investigated after hot press at different temperatures. With the increasing of Fe content in composite ceramics, the hardness of the composite is decreased. Fracture toughness of 10mol%Fe content is 5.62MPa after sintered at 1400°C, which is increasing 57% high than that of monolithic Al2O3 ceramics.

The thermo-mechanically induced microstructure changes occurring in a type 1 aluminized coating on hot press forming (HPF) steel were studied in detail. The formation of intermetallic phases at the soaking temperature prior to die quenching revealed that the coating matrix consists mainly of FeAl2 intermetallic phase by the time the press forming carried out. Kirkendall void formation was observed to take place. The thermal oxidation of aluminized coating during HPF was found to be limited, with the coating acting as an effective barrier for the oxygen during heating. The deterioration caused by the high temperature plastic deformation was shown to lead to coating cracking without loss of adhesion. The steel surface was oxidized where it was exposed between the coating segments.