Densification Of Material Research Articles

Influence of the Thermal Conditions of Fabrication and Treatment on the Optical Properties of In2O3 Films

In2O3 films on Al2O3 (012) substrates are fabricated by dc magnetron sputtering at various temperatures (20–600°C). The effect of annealing and the substrate temperature on the film properties are studied by the ellipsometric method and the optical transmission method. Refractive-index profiles are constructed and band gaps for direct and indirect transitions are found. It is established that annealing leads to densification of the film material and unifies the refractive index. Annealing also decreases and unifies the energies of band-to-band transitions, which can be explained by lowering the influence of barriers in annealed films. However, the band gap for direct transitions varies greater than for indirect transitions. This fact can be associated with the mechanism of indirect transitions, notably, the participation of phonons facilitates interband transitions even if they are hindered by extra barriers caused by grain boundaries. The latter can be indirect evidence of the actuality of indirect transitions in indium oxide.

Influence of Nb content on the microstructure and deuterium retention of W–Nb alloys

W–Nb alloys were prepared using machine milling and spark plasma sintering. Field–emission scanning electron microscopy, high–resolution transmission electron microscopy were used to characterize the samples. Thermal desorption spectroscopy was used to measure the deuterium retention. Results indicated that the interdiffusion between W and Nb occurred during high temperature sintering and formed Nb(W) solid solution. The grain size decreased with Nb content increased, and porosity of W–Nb alloys was decreased significantly compared to W bulk. Hence, Nb alloy had a significant effect on promoting W-based material densification. The microhardness increased as Nb content increased, which was ascribed to fine grain and low porosity. D retention in W–Nb alloys was higher than that in pure W (D2+ flux ∼ 1021m−2 s−1, ion energy ∼5 KeV).Total D retention increased as Nb content increased, which was ascribed to the density of grain boundaries that increased as Nb content increased and higher affinity between Nb and D.

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AbstractIn_2O_3 films on Al_2O_3 (012) substrates are fabricated by dc magnetron sputtering at various temperatures (20–600°C). The effect of annealing and the substrate temperature on the film properties are studied by the ellipsometric method and the optical transmission method. Refractive-index profiles are constructed and band gaps for direct and indirect transitions are found. It is established that annealing leads to densification of the film material and unifies the refractive index. Annealing also decreases and unifies the energies of band-to-band transitions, which can be explained by lowering the influence of barriers in annealed films. However, the band gap for direct transitions varies greater than for indirect transitions. This fact can be associated with the mechanism of indirect transitions, notably, the participation of phonons facilitates interband transitions even if they are hindered by extra barriers caused by grain boundaries. The latter can be indirect evidence of the actuality of indirect transitions in indium oxide.

Densification and Microstructure of Fluorapatite Sintered with Alkaline and Alkaline-Earth Additives

A study was performed to investigate the effect of some selected sintering additives on the densification and microstructure of fluorapatite (FAp, Ca10(PO4)6F2). The sintering aids, used for improving the material densification at lower than 1080℃ temperature, were classified according to their cations as alkaline such as Li2CO3, NaF, Na2CO3, Na3PO4, KCl, K2CO3, and alkaline-earth such as CaF2, CaCl2 and MgCl2. Amounts of 0.1; 1 and 3 wt% were vigorously homogenized with FAp powders then the solid mixture was pressurelessly sintered under argon flow with 10℃ . min-1 heating and cooling speed. The density of each sintered material was determined by calculation of the pellet dimension and weight, the crystalline phases were identified using X-ray diffraction (XRD) and the phase morphology was examined by scanning electron microscopy (SEM). The dependence of densification and microstructure on sintering temperature range 900℃ - 1000℃ and amount of sintering aids was studied. It was found that all sintering additives were able to ameliorate the sintrability of the material at temperatures 900℃ and 1000℃. Maximums of about 96% were reached with adequate amounts and sintering temperatures. An exception was found with KCl which had no effect on the density. The microstructures of sintered specimens strictly follow the densification ratios and the sintering mechanism depended on the melting point of the additive.

Study on quasi static and dynamic mechanical properties of chemical foaming concrete

Chemical foaming concrete is a kind of new building material. In this paper, the quasi-static conditions of foam concrete and dynamic mechanical properties under impact dynamic conditions are studied. This paper also analyzes in detail the damage mechanism, deformation characteristics and energy absorption characteristics of the foam concrete under compression and stretch conditions. The results indicate that, the lower the density is, the less the cells on the surface and the inside of the concrete material is, and the larger the diameter of the pores is. When the density increases, the number of cells increases as well, and the diameter of the pores decrease gradually. The whole process of uniaxial compression of foam concrete is divided into three stages, that is, the material's elasticity and plasticity stage, platform stage and material densification stage. In the initial stage of stretch and compression, the stress-strain curve of foam concrete increases linearly basically. In platform stage, the foam concrete is mainly absorbing the energy, and there are both strain- softening and strain-hardening behaviors in this stage at the same time. The greater the density of the concrete, the earlier the densification stage occurs. The research on the impact dynamic properties of foam concrete shows that the dynamic strain rate is obviously positively correlated with the impact velocity, i.e., the greater the impact velocity, the greater the strain rate. The dynamic stress-strain curve of foam concrete is almost the same as that of static curve. It is also divided into three stages: linear elastic stage, material yield stage and material failure stage.

Friction-stir processing of a cold sprayed AA7075 coating layer on the AZ31B substrate: Structural homogeneity, microstructures and hardness

In this study, the cold gas dynamic spraying (CGDS) process was employed to modify the surface of AZ31B magnesium alloy with an aluminum-zinc alloy (AA7075). Friction-stir processing (FSP) was subsequently applied as a solid-state localized surface modification technique to improve the structure and integrity of the cold sprayed layer, by enhancing densification, homogeneity, and microstructural features of the as-deposited material. The structure of precipitates and grains were also refined due to the applied severe plastic deformation during FSP, which ultimately affects the indentation hardness resistance of the processed AZ31B-AA7075 bi-metallic structure. Microscopy indicated slight grain coarsening within the AZ31B substrate occurred simultaneously with refinement of the AA7075 coating, along with significant hardness improvements of ~80% and 30% respectively for each region in terms of Vickers hardness after FSP.

Anisotropic elastic-plastic deformation of paper: Out-of-plane model

Laminated paperboard and paper is widely used in packaging products. Its out-of-plane properties play a crucial role in converting paperboard to a carton through the creasing and folding process. The aim of this study is to describe the out-of-plane mechanical response with an elastic-plastic model based on the observed experimental behavior. The model was derived from a thermodynamic framework and was based on the multiplicative split of the deformation gradient in the context of hyperelasticity. A structural tensor-based approach was applied to model the elastic deformation, while a multi-surface based yield criterion was adopted to describe the plastic behavior. The model considers both material densification and internal friction effects, which were observed experimentally. According to the experimental behavior, a quadratic yield locus under pure shear loading was assumed in the model. Finally, the model was validated with a cylinder compression test and found to capture the highly anisotropic, elastic-plastic behavior accurately.

Effect of Mixing Modes and Nano Additives on the Densification and Sintering Behavior of Tungsten Material Under Spark Plasma Sintering

The influence of 0.5 wt% nano tungsten and different mixing (turbular and magnetic mixing) on the densification, microstructure, microhardness and dilatometric properties, of tungsten materials was investigated under spark plasma sintering. The dilatometric analysis confirms that sintering process was started at 1100 °C for magnetic mixed samples but there were no sign of sintering for samples after turbular mixing. Nano tungsten and magnetic mixing increased the density of tungsten up to 98.5% at 1400 °C with the increased micro hardness value of 592 HV. The major impact after magnetic mixing is morphology changes in tungsten, development of active sites on the surface, breakdown of agglomerates and even distribution of nanoparticles throughout the bulk tungsten powder. This facilitates the mass transfer between nano tungsten and bulk tungsten which results in the increase in the Laplace force which plays an important role in mass transfer diffusion process during sintering. As a result, it leads to an enhancement of densification process of tungsten powder mixture during sintering and, hence a decrease in the sintering temperatures. Thus, this is a novel approach to use magnetic mixing and nano tungsten to improve densification and sintering behavior of tungsten under spark plasma sintering.

On the die compaction of powders used in pharmaceutics

Die compaction is widely used in the compaction of pharmaceutical powders (tableting). It is well known that the powder densification is a result of particle rearrangement and particle deformation. The former is considered to be the governing mechanism of densification in an initial stage of compaction and the latter is regarded as the governing mechanism in the compaction at the higher pressure range. As a more realistic assumption, one can consider that a simultaneous performance of both the rearrangement and deformation mechanisms takes place from the beginning of compaction. To mathematically formulate this assumption, a piston equation is presented where the material relative density is given as a function of the applied pressure on the powder. From the equation, it is possible to obtain the contribution of each mechanism to the material densification at each value of the applied pressure. In the continuation, the piston equation is applied to the tabletting of some pharmaceutical powders. These are the powders of Ascorbic Acid, Avicel® PH 101, Avicel® PH 301, Emcompress®, Sodium Chloride, and Tablettose® whose tableting results have been previously published in the literature. The results show the piston equation as a suitable approach to describe the tabletting of pharmaceutical powders.

Dual phase amorphous carbon ceramic achieves theoretical strength limit and large plasticity

Ceramics are widely used as engineering materials due to their high strength; however, their lack of plasticity is a major drawback. We report that dual-phase amorphous carbon (a-C) reveals high yield strength of ∼E/11 (E is elastic modulus, and E/10 is theoretical limit for ideal material) and large plasticity of ∼70% at room temperature in uniaxial compression tests. To the best of our knowledge, this report describes the first time since 2006 that the experimental yield strength has been determined to agree with the theoretical prediction. Pillars with diameters smaller than 427 nm deform homogeneously and show plasticity comparable to that of metals. The mechanism for such unusual properties of a-C is explored using high-resolution transmission electron microscopy (TEM) and Raman spectroscopy. The results indicate that the near-ideal strength is ascribed to the limitation of both the size and the number of defects with the smaller sample size. Large plasticity is accompanied by material densification and phase transformation at compressive stress. This finding widens the possible application of strong-and-plastic ceramic films for both biomedical and micro/nano-electromechanical systems (MEMS/NEMS).

Research Progress on Plastic Processing Techniques of Particulate Reinforced Aluminium Matrix Composites

Particulate Reinforced Aluminium Matrix Composites (PRAMCs) have been widely applied in military and civilian areas such as aviation, aerospace, advanced weapon applications and electrical industries due to their good mechanical properties at elevated temperature, low thermal expansion coefficient, excellent wear resistance and low production cost. The main preparation techniques of the PRAMCs include stir casting, powder metallurgy, pressureless infiltration and spray deposition. However, the problems such as low densification and particle cluster encountered in these techniques often reduce the material properties. It has reported that the homogeneity of the distribution of particulate reinforcements in metal matrix can be improved by plastic processing, thus enhancing the material densification. This paper summarized recent progress in the plastic processing methods of the PRAMCs, with an emphasis on the spinning technique. The effects of various process parameters on the material properties were discussed in detail. A summary of research progress on the numerical simulation of plastic processing of the PRAMCs was presented. In the end, an outlook was given on the prospect of the PRAMCs’ development.

Numerical and experimental analysis of the Young’s modulus of cold compacted powder materials

We present co-designed experimental, theoretical, and numerical investigations aiming at estimating the value of the Young’s modulus for cold compacted powder materials. The concept of image-based modeling is used to reconstruct the morphology of the powder structure with high fidelity. Analyses on aluminum powder pellets provide significant understanding of the microstructural mechanisms that preside the increase of the elastic properties with compaction. The role of the stress percolation path and its evolution during material densification is highlighted.

Structural Reliability of Cathode Contact Materials in Planar SOFCs

Despite significant developments in material and stack design technologies to enhance performance, the long-term mechanical reliability of solid oxide fuel cells remains an issue. The contact between electrodes and interconnects (especially the cathode side) was identified as one of the weakest links in present generation planar solid oxide fuel cells. Computational modeling was used to gain valuable insights on the cathode contact sintering mechanics and bond reliability. A continuum viscous sintering model was incorporated into a commercial finite element analysis code to simulate contact material densification and evaluate the bond and stack mechanical reliability due to stresses resulting from the contact layer sintering. The parameters required for the cathode contact material constitutive model were extracted from experiments conducted for the contact material development at PNNL. The effects of contact layer thickness and sintering conditions like temperature and pressure on the stack stresses and reliability were investigated.

Cavity Formation Modeling of Fiber Fuse in Single-Mode Optical Fibers

The evolution of a fiber-fuse phenomenon in a single-mode optical fiber was studied theoretically. To clarify both the silica-glass densification and cavity formation, which have been observed in fiber fuse propagation, we investigated a nonlinear oscillation model using the Van Der Pol equation. This model was able to phenomenologically explain both the densification of the core material and the formation of periodic cavities in the core layer as a result of a relaxation oscillation.

Elastic stress field model and micro-crack evolution for isotropic brittle materials during single grit scratching

Abstract An analytical model for the elastic stress field in isotropic hard and brittle materials during scratching is presented. The model considers the entire elastic stress field and the effect of material densification that was ignored in past studies, and is developed under a cylindrical coordinate system to make the modeling process simpler. Based on the model's predictions, the location and sequence of crack nucleation are estimated and the associated mechanisms are discussed. A single grit scratching experiment with an increasing scratch depth up to 2 µm is conducted for two types of optical glasses representing isotropic brittle materials: fused silica and BK7 glasses. It is found that the model's predictions correlate well with experimental data. Median cracks are found to be formed first during scratching, and the corresponding depth of the scratch sets the basis for determining the critical depth for brittle to ductile machining. Lateral cracks are initiated in the plastic yielding region and deflect to the work surface to cause material removal, while Hertzian cracks interact with lateral cracks to help remove lateral-cracked material. Furthermore, it is found that, owing to its open network molecular structure, fused silica has a much worse ductile machinability than the BK7 glass.

Enhancement of densification and sintering behavior of tungsten material via nano modification and magnetic mixing processed under spark plasma sintering

In the present study, the influence of nano additives (Ni, Fe) and different mixing (turbular and magnetic) on the densification, microstructure and micro-hardness of the tungsten material under spark plasma sintering is analyzed. After turbulent mixing the nanoparticles are distributed widely in the W interparticle gaps but after magnetic mixing the nanoparticles are distributed not only on the gaps of the W particles but also on the broken surfaces. Ni incorporated tungsten materials achieved the maximum density of 98.3% at 1400 °C (turbular mixing) and 97.9% at 1300 °C (magnetic mixing). Fe incorporated tungsten material showed density of 97.7% at 1600 °C and 97.2% at 1400 °C after turbular and magnetic mixing. The influence of nanoparticles in the densification process was explained by Laplace force, boundary slip and Agte-Vacek effect. The microstructural analysis showed that nano-modification reduced the degree of porosity, and provides a compact material at low temperatures. X-ray fluorescence analysis reveals that magnetic mixing shows more uniform distribution of nanoparticles than turbular mixing. The nanoparticles incorporation increased the micro hardness of tungsten material. Hence, it is clear that magnetic mixing and nano modification greatly improved the densification and sintering behavior of the tungsten material.

Constitutive modeling of indentation cracking in fused silica

AbstractFused silica shows three distinct regimes during nanoindentation, that is, plastic deformation, inelastic densification, and cracking. Cohesive zone FEM is used to study these regimes for different indenter geometries. In a three‐dimensional model, the median/radial cracking is considered by introducing cohesive element planes that are aligned along the indenter edges perpendicular to the indented surface. In addition to comparing indentation cracking data with experimental data, the role of densification on indentation crack growth is critically examined using a pressure independent von Mises and a pressure dependent Drucker‐Prager Cap constitutive model. The results show that the Drucker‐Prager Cap model delivers an accurate description of the elastic‐plastic deformation conditions for all examined indenter geometries. Material densification leads to shorter crack lengths and thus the approach by Lawn et al. (J Am Ceram Soc, 1980;63:574‐581) results in larger indentation‐based fracture toughness values. Once the crack was initiated its propagation is comparable for blunt indenter geometries (Berkovich), while densification leads to a slower crack propagation for sharper indenter geometries.

A novel tri-layer nanoindentation method to measure the mechanical properties of a porous brittle ultra-low-k dielectric thin film

The mechanical properties of two porous ultra-low-k (ULK) dielectric thin films (porous carbon-doped silicon dioxide (pSiCOH); and octamethylcyclotetrasiloxane (OMCTS)) were measured by nanoindentation. Since a direct contact of a nanoindentation tip with a thin and brittle ULK film will likely induce damage to the film and thus alters its mechanical response, the mechanical properties measured from direct nanoindentation on an ULK film do not necessarily represent the behavior of an ULK thin film in service condition. To circumvent this difficulty, a novel tri-layer configuration was used for sample preparation. In this method, a thin layer of tetraethyl orthosilicate (TEOS) silica was deposited on an ULK thin film to protect it from direct contact with a nanoindenter tip. A nanoindenter tip was in contact with TEOS coating on the layered film in nanoindentation, and the collected data was subsequently analyzed by finite element analysis. The Ogden hyperfoam model was used as the constitutive law for the ULK film in simulations, and found to be appropriate. Results indicate that the linear elastic model is only applicable for very small strains. At large strains the ULK films show nonlinear behavior due to densification of the porous ULK material under compaction. The moduli for the pSiCOH and OMCTS dielectric films were determined as 2.6 GPa and 5.2 GPa, respectively.

Analysis of the Energy Efficiency of the Shredded Wood Material Densification Process

This work presents the results of experimental tests of the shredded wood material densification process with the use of a machine operating by means of piston technology. These results were confronted with the results of FEM analysis of the analogical working system of the densification machine. Experimental tests have been performed in order to facilitate building the numerical model. They made it possible to set change characteristics of the main mechanical parameters of the material under investigation. This work presents the values of coefficient of friction and shear stresses of the densified material as function of temperature. Based on the test results an attempt has been made to define important factors that have the biggest impact on the efficiency of the densification process.

Producing composite materials based on ZrB2, ZrB2-SiC

The effect of mechanical treatment by planetary ball milling on the properties of hot pressed ZrB2 - SiC ceramics was studied. It has been shown that material densification after mechanical treatment is finished at initial stages of sintering process. Addition of SiC causes a substantial increase in density of the sample to 99% of the theoretical powder containing 20% of silicon carbide, in comparison with samples ZrB2 density not exceeding 76%. It has been shown that all defects which were accumulated during mechanical treatment anneal in hot pressure process and there are no any changes of CDD values in sintered ceramics.