Papers by Keyword: Hot Pressing

Abstract: Mycelium-based composite (MBC), as a new engineering biocomposite, is receiving numerous interests due to its environmental sustainability. The study aimed to address the challenge of optimizing the physical properties of MBC for a more efficient production process. The study investigated the impact of hot or cold pressing, different pressing temperatures (120 °C, 160 °C, and 200 °C), pressing pressures (low, medium and high) and sequences (before and after drying process) on the physical properties of MBC such as density, shrinkage, moisture content and hardness. Mycelium millets were mixed with kenaf, carbon carbonate, wheat bran and wheat flour. The pressing methods and sequences significantly affected the properties of the MBC. Cold pressing had no effect on reducing shrinkage and moisture content of MBC but improved density. Hot pressing increased hardness at higher temperature and pressure, with strong mycelium-substrate bonding and less porosity observed in SEM image. The post processing sequence involving drying followed by hot pressing at 200°C exhibited higher density, hardness, less shrinkage and controllable moisture content of MBC for better dimensional stability and quality control purpose. It was crucial to optimize MBC pressing techniques for specific applications and ensure that it satisfied the demanding standards of companies looking for sustainable alternatives and cost-effective production.

Abstract: Ni-YSZ cermet remains to be the most used anode material for solid oxide fuel cells (SOFCs), and metal-supported solid oxide fuel cells are considered as the third generation SOFCs which can possibly address the overpotential and ohmic losses due to thicker components of electrolyte-and anode-supported cells. This study investigates the low-temperature deposition of crystalline NiO-YSZ thin film anodic layers on stainless steel (SS316L) substrates via screen-printing and hot pressing. Results revealed that screen-printing and hot pressing of NiO-YSZ on SS316L substrates at only 700°C (100 MPa) successfully deposited a ~40-μm thin film with a cubic crystalline structure. The thin film can also be fully reduced to Ni-YSZ with a cubic crystalline structure for both Ni and YSZ. In addition, EDS mapping revealed a relatively homogenous distribution of the Ni-YSZ components.

Abstract: Copper/diamond composites show promise as potential thermal management materials for electronic devices due to their excellent thermophysical properties. In this study, copper/55vol%Ti-coated diamond composites were fabricated by hot pressing at 800oC and varying pressures of 300MPa, 400MPa, 500MPa, and 685MPa. The results illustrated that the thermal conductivity of the copper/Ti-coated diamond composites initially increased and then decreased as the pressing pressure increased. Among these hot-pressed composites, the composite hot-pressed at 500MPa exhibits the highest thermal conductivity of 466W/mK. This is attributed to the uniform diamond distribution, highly covered TiC interface on the diamond, and the strong interfacial bonding between the copper and the diamond. Hot pressing is a feasible alternative to fabricate copper/diamond composites with high relative density and high thermal conductivity, the pressing pressure plays a vital role in the microstructure and the final properties of the copper/Ti-coated diamond composites.

Abstract: In this study, the 2024 Al powder with different weight fractions of graphite is mechanically milled using a high-energy ball mill for 3 hours each in the nitrogen environment. The milled powder is compacted at an elevated temperature. X-ray diffraction is used to phase analysis of milled powder as well as compacted specimens. Optical microscopy is used for microstructural analysis and hardness measurements are done for the evaluation of mechanical properties. The hot compacted specimens are also tested for their wear properties. Results show that there is no new phase formed during mechanical milling. But, after hot compaction of the milled powder, Al₂Cu formed due to precipitation. No reaction is observed between the aluminum and the carbon (graphite) after milling as well as hot compaction. Microstructures of all hot compacted specimens are not showing pores, which, signifies full density after compaction. The formation of Al₄C₃ is not observed at any stage of processing. Therefore, graphite is uniformly distributed in all specimens, and the same is observed at grain boundaries of α-Al grains in the microstructures. Hardness increases with the addition of 1 wt.% graphite but it decreases with a further increase in graphite. The wear resistance of 2024 Al with 1 wt% graphite is the highest among all the compositions. The high hardness and wear resistance of 2024Al with 1 wt% graphite is the consequence of precipitation of Al₂Cu during hot compaction and the presence of graphite which creates hindrances in the metal matrix. The presence of free graphite in the vicinity of grain boundaries acts as a solid lubricant which improves wear resistance of 2024 Al.

Abstract: This work presents the investigation of nanopowders from magnesium aluminum spinel doped with Cr³⁺. Different synthesis conditions were used to determine the influence on lattice parameter. The following synthesis parameters varied: time of calcination, cold pressing and alternative precursor of Cr³⁺. The nanopowders properties were measured by XRD, optical transmission and EDX spectroscopy. The determined average size of synthesized nanoparticles is around 70 nm. Ceramic samples are given by hot pressing and studied by transmission spectroscopy and luminescent spectroscopy. The excitation and emission spectra demonstrates ²E - ⁴A₂ (687 nm), ⁴A₂ - ⁴T₁ (400 nm) and ⁴A₂ - ⁴T₂ (532 nm) transitions.

Abstract: In this paper, we present the development of new types of boron carbide-based ceramics. Boron carbide is applied in the electronics and nuclear industries as well as for production of the grinding and abrasive materials, protective plates for body armor. The interaction of boron carbide with chromium nano-oxide additives (1-5 wt.%) during sintering was studied by mass spectrometry. It is shown that the formation of chromium nano-boride takes place at the stages of formation of metallic chromium, the lowest chromium boride and chromium carbide. The maximum solubility of chromium in the boron carbide lattice was found to be 0.5 wt.%. A composite material based on boron carbide, В₄С with CrB₂ nano-inclusions, was prepared. The bending strength and modulus of normal elasticity were equal to 44.6 MPa and 449.5 GPa, respectively. Micro-hardness and residual porosity were determined to be 40 GPa and 5-7 %.

Abstract: The optimal modes (temperature, time, pressure force) of spark plasma sintering (SPS) and hot pressing of boron carbide obtained by various methods are determined. The initial powders were obtained from soot and amorphous boron by the mechanochemical synthesis method, by the high-temperature synthesis (SHS) method and by the carbon reduction method. The structure and the properties of SPS sintered and hot-pressed boron carbide blanks were determined. The highest value of the relative density was achieved during SPS sintering of blanks from B₄C powders obtained by mechanosynthesis and SHS methods. It was found out the optimal conditions for sintering blanks from B₄C powder obtained by mechanosynthesis. The density value reaches 99.0 rel.% at 1500 °C/25 MPa and sintering time of 45 min. For powders obtained by the SHS method, the density of sintered blanks is 98.5 rel.%. at 1800 °C/30 MPa with sintering time of 45 min. The highest value of the relative density was achieved during the hot pressing of blanks from B₄C powders obtained by mechanosynthesis.

Abstract: The aim of this paper was to determine the influence of the mechanical and thermal parameters of the matrix materials on their retentive properties. The term ‘matrix retention’ denotes the capacity of a metallic matrix material to retain diamond particles at the surface of a diamond tool during working. The bonding is obtained during cooling after the hot pressing process. Proper mechanical bonding depends on elastic and plastic properties of the matrix. The model of a diamond particle embedded in a metallic matrix was created using Abaqus software. The analysis has indicated the mechanical parameters that are responsible for the retention of diamond particles in a matrix.

Abstract: The objective of this paper is to study Fe65Nb-Cu metal matrices, thus varying the content of the pre-alloyed Fe65Nb powder from 10% to 100%. Therefore, powders of Fe65Nb and Cu were used, innovating in the chemical composition of the commonly used matrices. The objective is to evaluate the substitution of Co (toxic element, commonly used) by Nb (98.2% of reserves are Brazilian). For the sintering of the samples it was used hot pressing technique. The parameters were set at: 850°C / 35MPa / 3min. The sintered bodies underwent SEM/EDS analysis and density and porosity measurements were performed. From the results it is possible to say that the compositions of (10% and 30% Fe65Nb) presented the best physical and mechanical properties. The relative density decreases for the compositions with 40%, 50% and 60% Fe65Nb is justified by the presence of fragile particles in metal matrices, since they require more energy in order to efficiently transport matter (diffusion) in a solid state.

Abstract: This paper introduced a new method for fabricating aluminum foam sandwich (AFS) panel with large scale dimension. The foamable Al-based precursor was prepared by optimized FORMGRIP foaming method which was developed from melting process. The blowing agent was specially modified to increase the decomposition temperature. To avoid surface oxidation, the mild cover sheets were aluminized by cold spraying technique. An optimized hot pressing technique was designed and showed great advantages in the bonding of the precursor to the cover sheets at low temperature. The precursor and the cover sheet was successfully bonded by using a specially designed hot pressing apparatus via diffusion bonding. It is shown that the pre-bonding in the three-layer composite is beneficial to the formation of metallurgical bonding surface in AFS. The foaming and bonding process was carried out simultaneously. This approach for manufacturing AFS may have particularly importance on applying the AFS panels to industrial applications.