Papers by Keyword: Densification

Abstract: Titanium matrix composites (TMCs) have found extensive application in aerospace, biomedical, and military sectors due to their exceptional strength-to-weight ratio and wear resistance at ambient and elevated temperatures. Nevertheless, conventional production methods often face a compromise between cost and performance, thus limiting the suitability of this material for broad utilization in engineering contexts. Recent research findings indicate that the utilization of manufacturing techniques such as hydrogen assisted blended elemental powder metallurgy (HABEPM) with the incorporation of a double press-and-sinter option, as well as the sintering of powder blends that have been preliminarily activated through milling, can both serve as economically viable methods for the production of highly dense TMCs with satisfactory mechanical properties. Both methods guarantee the activation of sintering in powders, resulting in notable improvements in density and a more refined and uniform microstructure compared to porous and nonuniform composites obtained through traditional vacuum sintering of powder blends. This study provides novel insights into the design and production of cost-effective and environmentally friendly TMCs with determined mechanical properties.

Abstract: In this work, the molecular dynamics simulation method is employed to understand the sintering behaviour and mechanical properties of the Invar alloy. The densification behaviour of Invar alloy nanoparticles with different sizes at a fixed sintering temperature is investigated. The influence of external pressure is also simulated. Finally, the uniaxial tensile test is employed to study the mechanical response of the sintered product. The results show a qualitative relationship between particle size, external pressure, densification, and mechanical properties. Smaller particle sizes and higher external pressure promote densification. The uniaxial tensile results show that the sintered structure has a lower Young’s modulus than the bulk crystal because of the porosity, and the sample with high porosity has a low value of mechanical strength.

Abstract: This paper focuses on the computational modeling of the crashworthiness performance of designed foam-filled thin-walled tubular structures under quasi-static compression loading. The studied foam sample is designed in SolidWorks using the ‘sphere subtraction method’ and implemented as a filler material in the thin-walled tube. The quasi-static compression was simulated by Abaqus software. The foam porosity is manipulated to enhance the crashworthiness performance of empty tubes. The deformation mode and energy absorption capability of the analyzed structures are introduced in detail. The numerical results showed that foam-filler material could change the deformation mode and improve stability during the compression process of thin-walled tubular structures. The number of lobes significantly increases when introducing the foam filler to the tube. These folds are affected by the foam porosity. Results also indicate that the total crushing load of the foam-filled tube is also a function of foam porosity, the mechanical response of the foam-filled tubes tended towards the response of the empty tube for a high porosity (P >85%), while for low porosity (P<85%) the mechanical response of the foam-filled tubes exhibits the three universal deformation characteristics of foams, namely, initial linear stage, extended plateau stage, and final densification stage. The main mechanical properties: collapse stress, plateau stress, and densification strain were obtained via the energy-efficient method for different configurations. The calculated mechanical properties exhibited a strong dependence on foam porosity. To give a quantitative description of the obtained quasi-static compressive properties, these properties are expressed as a function of foam porosity. The proposed formulas can easily recover the quasi-static compressive properties of the empty tube in the case of the absence of foam. The control of the compressive performance of foam-filled tubes as a function of porosity allows for finding an optimum geometry with a predefined foam porosity value adjusted for a given application.

Abstract: The volumetric changes and variable porosity due to the concentration expansion of the solid phase in the synthesis of zirconium nitride (ZrN) are studied. The model of two-stage reactor based on spark plasma sintering (SPS) is proposed. At the first stage the synthesis for the given kinetics is simulated. At the second stage the densification of ZrN using the Olevsky’s sintering model [1-5] is applied. The synthesis and densification processes using the prescribed heat sources, at the given positions inside the reactor is simulated. The generalization of the two-temperature model [6] and the formula of the porosity in the densification using calculation of the solid concentration expansion and thermal dispersion is proposed. The concentration expansion coefficients in the process of zirconium nitrogenating at a given initial density values and coefficients of expansion of reagents .is studied The temperature at the stage of ZrN synthesis and porosity variation at the stage of densification are in satisfactory agreement with experimental results [2,7,8]

Abstract: Powder metallurgy (PM) is an alternative approach to ingot metallurgy (IM) in the production of metal products. It is of paramount importance for PM to be able to produce fully dense products for it to make headway in becoming an equal alternative to IM and be a better option economy-wise. Cold rolling is an inexpensive post-sintering densification option that enables the lowering of sintering conditions. Experiments were carried out in this study to investigate cold rolling parameters on the densification of titanium brown compacts with a starting relative density of 89.3 %. The highest relative density obtained during the cold rolling experiments was 97.7 % without any annealing. It was found that the density increases with an increase in the percentage reduction of cold rolling. High percentage reductions reduce the number of roll passes needed to increase the density up to a limit where the brown compacts become susceptible to severe rolling defects. It was also found that the total increase in density increases with a decrease in cold rolling speed. An increase in the relative density of 8.36 % was observed at the cold rolling speed of 1 rpm, whereas the highest increase recorded at 10 rpm was 5.83 %.

Abstract: In this study, carbon nanotube films, densifying with ethanol/water, acetone/water, acetic acid/water, sulfuric acid/water with volume rate of 4:1 and following rolling process, were manufactured. Afterwards, the electrothermal, mechanical properties and performance stability of these carbon nanotube films were investigated, along with mechanism analysis. Based on our investigations, the ability of rapid electrothermal response within 5 second, higher steady-state temperature of above 120~160°C at low input voltages of 5V, excellent cycling stability of electrical heating are reported by the aforementioned methods, revealing better outcome as compared with previous reports of congeneric carbon nanotube films. The electrothermal and mechanical properties of treated carbon nanotube films were superior to carbon nanotube film pressed from carbon nanotube aerosol, and the best outcomes could be synchronously achieved at an immersion of 0.5h in solvents and rolling. The consequences, which are attributable to treatments by the first three mixed solvents as well as rolling, were similar, however, the electrical and electrothermal properties of carbon nanotube film treated with sulfuric acid/water and rolling were significantly improved comparative to others due to p-type doping and purification, which could enhance the electrical conductivity of carbon nanotube film, while the mechanical property was not degraded compared to films treated by other ways. Particularly, electrical and mechanical properties of carbon nanotube films were unchanged through repeated electrical heating owing to the stability of their structure and morphology, which contributed to exceedingly stable electrothermal property and established foundation for application as heater with long-term stability. Lastly, we have also proposed the mechanism concerning performance stability of electrical heating film.

Abstract: The recent surge in interest in the densification of calcium phosphate powders needs consideration of all the influencing factors. Spark plasma sintering with the primary contribution from the spark plasma and cold compaction that densifies from the large compaction pressures were considered. X-ray diffraction and Fourier transform infra-red spectroscopy characterized the powder and tablet to confirm the retention of the amorphous phase. Density was measured using the Archimedes method and the microstructure was viewed by scanning electron microscopy. The densified tablets were indented by nanoindentation to determine the hardness and elastic modulus. Reports on the density showed that the smallest contribution to density arose from vacuum, a marginally higher densification from the spark plasma effect, but the largest densification arose from the use of significantly higher pressures. Nanoindentation showed a small difference in elastic modulus between tablets densified at 25 °C and 200 °C, but a larger difference in the hardness.

Abstract: Jet grading technology is an efficient process in different industries. In this research, tungsten powder with different particle size distribution was used as a raw material to produce tungsten products via isostatic pressing as well as sintering. The mechanism of jet grading and the morphology and particle size distribution of different precursors were analyzed. The results showed that jet grading technology had remarkable effect on tungsten powder classification. The appropriate grading treatment was helpful to the formation of tungsten products with high performance. After jet grading and the following process like pressing and sintering, the tungsten products with better properties were manufactured which was used fischer particle size of 3.0~3.5μm as the raw material. The obtained products’ density was 18.77g/cm³ and its hardness was 372.15HV_0.3.

Abstract: This study aims to investigate the effects of powder particle size on the densification and microhardness properties of spark plasma sintered superalloy. Three particles size ranges of nickel were used in this study, namely, (3-44, 45-106 and 106-150 μm), and this is the matrix in the IN738LC superalloy composition (powder), used in the study. The effects of the particle size were examined at a specific applied temperature and pressure. The transitioning stages during the sintering process of the green powders to the formation of the sintered alloy were analyzed and given as the particle rearrangement stage, the localized deformation stage and the neck formation/grain growth stage. There was the formation of γ, γ' and a solid solution within the microstructure of the sintered alloys. The effect of particle size was more pronounced on the grain sizes obtained, while the phases formed is the same for the three alloys. The results indicate that the nickel particle size (>60% of the total composition) has a significant influence on the densification, porosity, grain size and hardness properties of the IN738LC sintered alloy. Finer nickel particle size resulted in a sintered product with smaller grain size (9 µm), reduced percentage porosity (3.9%), increased relative density (96.1%) and increased hardness properties (371 Hv).

Abstract: A study was carried out on the behavior during the sintering of Al₂O₃ ceramics with pre-sintering of the additives Nb₂O₅ and LiF at different temperatures. It was observed through XRD and DSC the formation of the LiNb₃O₈, Nb₃O₇F and LiNbO₃ phases during the pre-sintering of the additive powders and the formation of the LiAl₅O₈, AlNbO₄ phases during the sintering of the samples The samples showed densities around 91% of the theoretical density, and pre-sintered samples showed low growth in grain size.