Small Amount Of Porosity Research Articles

THE EFFECT OF SPIN COATING’S SPEED ON GRAPHENE-OXIDE’S LAYER TOPOGRAPHY AND QCM VISCOELASTICITY

Spin coating speed controls the deposition process, affecting the formation of the layer’s topography of graphene oxide and the viscoelastic properties of quartz crystal microbalance (QCM). In this work, the graphene oxide was deposited on the QCM surface by spin coating method with speeds ranging from 500 to 800 rpm. The layer’s surface topography was subsequently measured and analyzed using a roughness multiparameter, which included the area average (Sa), area roughness deviation (Sq), localized surface roughness (Sz), surface skewness (Ssk), and surface kurtosis (Sku). The Sa, Sq, and Sz, which were decreased as the spinning speed increased. The measurements indicated that the graphene oxide layer deposited at 500 rpm had a rough and clumpy texture, while at a high speed of 800 rpm, the layer had a much smoother texture. A detailed analysis using the Sku and Ssk parameters revealed that the clumpy texture in the 500 rpm sample contains tapered sharp graphene oxide structures and a small amount of porosity. On the other hand, the sharp structures were significantly reduced, and porosity was dominant in the sample deposited at high speeds of 700 rpm and 800 rpm. The effect of the spinning speed and the topography on the viscoelasticity was studied using an impedance analyzer. The impedance of the layer deposited at 500 rpm was relatively higher than that at 800 rpm. The frequency shift was also relatively significant for the sample deposited at low speed and was reduced at higher speed. The impedance analysis demonstrated that the layer’s viscosity is affected by its mass, roughness, texture, and porosity.

Theoretical investigation of reactive burn in a highly cracked energetic material

While energetic material reactive burn processes such as the buildup to detonation are well understood for energetic materials like PBX 9501 that contain small amounts of porosity, the same is not true for highly cracked energetic materials. This work addresses this shortcoming by performing theoretical reactive burn calculations where thin submillimeter thick cracks permeating a PBX 9501 system are explicitly modeled. We use the Scaled Uniform Reactive Flow (SURF) model for the reactive burn calculations. Before considering highly cracked structures, we first show that SURF closely reproduces reactive burn experiments done on pristine and single air gap PBX 9501. For all cases of this investigation, a high-pressure shock is introduced by way of a high velocity impact to initiate a detonation in our cracked PBX 9501 structures. Using fully three-dimensional simulations and the physics code PAGOSA, we investigate the reactive burn process in cracked structures that have a propensity to have cracks either aligned with or orthogonal to the direction of wave propagation. While each crack structure has the same net crack porosity, we demonstrate that the reactive burn produced differs for the two cases. We also provide crack structure metrics, beyond porosity, that characterize the average crack orientation relative to the direction of wave propagation. Simulation results are provided for several variants of cracked structures. At the highest crack porosity studied here we observed the breakdown of stable detonation propagation. This high porosity case was achieved by doubling the average crack width, leaving all other features of the crack network unchanged. We conclude with a synthesis of our simulation observations to make general comments regarding how crack networks can affect points on the PBX 9501 detonation pop plot.

The effect of pore shape on the Poisson ratio of porous materials

A brief review is given of the effect of porosity on the Poisson ratio of a porous material. In contrast to elastic moduli such as K, G, or E, which always decrease with the addition of pores into a matrix, the Poisson ratio may increase, decrease, or remain the same, depending on the shape of the pores, and on the Poisson ratio of the matrix phase, . In general, for a given pore shape, there is a unique critical Poisson ratio, , such that the addition of pores into the matrix will cause the Poisson ratio to increase if , decrease if , and remain unchanged if . The critical Poisson ratio for spherical pores is 0.2, for prolate spheroidal pores is close to 0.2, and tends toward zero for thin cracks. For two-dimensional materials, for circular pores, 0.306 for squares, 0.227 for equilateral triangles, and again approaches 0 for thin cracks. The presence of a “trapped” fluid in the pore space tends to cause to increase, and for the range of parameters that may occur in rocks or concrete, this increase is more pronounced for thin crack-like pores than for equi-dimensional pores. Measurements of the Poisson ratio therefore may allow insight into pore geometry and pore fluid. If the matrix phase is strongly auxetic, small amounts of porosity will generally not cause the Poisson ratio to become positive.

Estimation of mechanical response of 2-phase oxide ceramic composites under high strain rate

The high strain-rate behaviour of ceramic composites (CCs) results from the complexity of their internal microstructure. The CCs are built of mixtures of different phases joined by various technological processes. Usually, CCs contain small amounts of porosity and technological defects. The phases can exhibit purely elastic behaviour or elastic–plastic one under a high level of loading. The paper describes experimental tests performed with Split Hopkinson Pressure (SHPB) of exemplary ceramic samples and proposes a correlation based on mesocrack formation with this type of loading. Therefore, a multiscale model of microcracking processes for high strain rate is proposed and related to time.

Investigation and characterization of brass joint fabricated by microwave hybrid heating process

Microwave energy is a novel technique for joining metals and composites in the field of manufacturing. In this paper, joining of bulk metallic material (Brass) is successfully carried out using microwave hybrid heating. Joint is formed at 480 sec exposure time with power 900 W and frequency 2.45 GHz. The joint is studied by using microstructural analysis, XRD, SEM, Tensile strength, Hardness and % elongation. Microstructural analysis reveals that small amount of porosity is observed and joint is clearly visible. Formations of various compounds which improve the mechanical properties of the joint are shown in XRD analysis. SEM analysis indicates the formation of dense joint with no cracks and voids. Tensile strength, hardness and percentage elongation were measured i.e. 292.67 MPa, 50 Hv and 7.30% respectively.

Low Critical Temperature at 10K on (Bi,Pb)-Sr-Ca-Cu-O Wire with the TiO<sub>2</sub> Doped Using Stainless Steel Tubes

Bi-type superconductor is a high-temperature superconductor with mainly applied in the field of electricity. Silver is used as a wire sheath which causes the price of this wire production to be high. In this study Bi(Pb)-Sr-Ca-Cu-O (BPSCCO) wires were made by using stainless-steel (SS316) tubes which is cheaper and is not change its properties by the temperature of the formation of BPSCCO at 860°C. The preparation of superconducting wire is done by the Powder-In-Tube method, sintering and withdrawing/ rolling process. TiO2 powder was added to analyze the effect on the formation of BPSCCO. Based on analyzing results, there is a dominant impurity phase that has been formed, namely Fe2.5Ti0.5O4. We found that in the use of stainless-steel tubes and the TiO2 powder (5wt%), 2223 phase was not formed. Although, small amounts of Bi2Sr2CaCu2O8 (2212) and Bi10Sr10Cu5O29 (2201) phases were found. Resistance versus temperature test using cryogenic equipment results indicate that there are symptoms of a low critical temperature around 10 K. 2212 and 2201 phases are thought to cause a low critical temperature in the samples, even though the decrease in electrical resistance does not reach zero. While the morphology of superconducting wire is quite well characterized from fairly even grains and only a small amount of porosity is formed.

Well-log-constrained porosity and permeability distribution in the Springbok Sandstone, Surat Basin, Australia

The Late Jurassic Springbok Sandstone in the Surat Basin, Australia, is highly heterogeneous in terms of lithology and hydrogeological properties. This heterogeneity is poorly defined in well logs, due, in part, to clay phases that do not exhibit a prominent gamma ray signature. The resulting uncertainties in the hydrogeological properties are propagated to uncertainties in the groundwater models of the Springbok Sandstone. Further, only a small amount of porosity and permeability data are publicly available and the discussion of petrophysical models for the Springbok Sandstone in the peer-reviewed literature has been limited. At the same time, accurately predicting the potential groundwater impact due to coal seam gas production from the underlying Walloon Subgroup is of significant societal and economic importance. This paper presents new porosity and permeability data from more than 50 core samples from the Springbok Sandstone alongside a review of existing data. Based on this dataset and wireline data from five study wells, a new petrophysical model for the formation is proposed. The results show that (1) the Springbok Sandstone is highly variable in terms of hydrogeological parameters, (2) this variability can be captured with a petrophysical model that draws on a full log suite (i.e. triple-combo) and (3) electrofacies classifications based on gamma-ray and bulk-density log cut-offs do not reflect this variability. This improved understanding of the Springbok Sandstone will contribute to best practice management of the water and hydrocarbon resources in the Great Artesian Basin.

Forging of Hierarchical Multiscale Capabilities for Simulation of Energetic Materials

AbstractWe present new capabilities for investigation of microstructure in energetic material response for both explicit large‐scale and multiscale simulations. We demonstrate the computational capabilities by studying the effect of porosity on the reactive shock response of a coarse‐grain (CG) model of the energetic material cyclotrimethylene trinitramine (RDX), the non‐reactive equation of state for a porous representative volume element (RVE) of CG RDX, and utilization of available supercomputing resources for speculative sampling to accelerate hierarchical multiscale simulations. Small amounts of porosity (up to 4 %) are shown to have significant effect on the initiation of reactive CG RDX using large‐scale reactive dissipative particle dynamics simulations. Non‐reactive RVEs are shown to undergo a porosity‐dependent pore collapse at hydrostatic conditions, and an existing automation framework is shown to be easily modified for the incorporation of microstructure while retaining reliable convergence properties. A novel predictive sampling method based on use of kernel density estimators is shown to effectively accelerate time‐to‐solution in a multiscale simulation, scaling with free CPU cores, while making no assumptions about the underlying physics for the data being analyzed. These multidisciplinary studies of distinct yet connected problems combine to provide methodological insights for high‐fidelity modeling of reactive systems with microstructure.

The Effect of Tool Rotation Speed on Mechanical Properties of Friction Stir Spot Welded (FSSW) AA7075-T6 Aluminium Alloy Sheets

In this study, the effect of tool rotation speed on the mechanical and metallurgical properties of friction stir spot welded (FSSW) AA 7075-T6 aluminum alloy plates was investigated. Aluminum alloy plates were joined by FSSW using welding parameters consisting of three different rotation speeds of 1040, 1320 and 1500 rpm and a constant insertion depth of 3.2 mm. In spot welded specimens, the highest tensile strength value (6200 N) was obtained in plates welded at a tool rotation speed of 1500 rpm. The data obtained from the metallographic analysis are compatible with the tensile test results. Metallographic investigations demonstrated that there was a small amount of porosity in the welding zone of the specimens jointed at 1500 rpm.

Evaluation of solidification and microstructure in laser cladding Inconel 718 superalloy

The development of directional or completely equiaxed microstructures by the laser cladding process can determine the final properties and applications of Inconel 718 alloys. The main purpose of this study is to investigate the effect of laser cladding process parameters on the solidification and final microstructure of Inconel 718 alloy. In this study, Inconel 718 powder was cladded on the Inconel 718 substrate by Nd: YAG laser using laser power of 150–300 W, scanning rate of 4–6 mm/s and powder feeding rates of 150, 200, 250, 300 and 400 mg/s and the effect of them on the solidified microstructure at three zones of the interface, middle and surface of coating was studied. The dendritic secondary arms spacing was calculated and the cooling rate was determined in each zone. The structural defects including cracks, porosity and segregation and finally phase analysis were examined. The results showed that with increasing laser power from 150 to 300 W and also laser scanning rate from 4 to 6 mm/s due to decrease in the G/R ratio, so that the more part of microstructure was equiaxed. In addition, by taking distance from the interface, the dendrite secondary arms spacing decreased from 1.08 to 0.98 and the cooling rate increased from 2.3649 × 104 k/s to 3.2641 × 104 k/s. With increase in the powder feeding rate the equiaxed zone increases. However, the effect of the powder feeding rate cannot be directly and specifically determined. The all samples were free crack but, the small amount of porosity was observed in cladding sample. Results showed that between the laser parameters and the percent of porosities were not exist of the clear relation.

Experimental Study on Pore-Defect by Selective Laser Melting of 316L Stainless Steel

With different process parameters (laser power, scanning speed and scanning distance),the low-time defects of forming part were studied by microscope,including air bubble, pore, micro-crack and macro-crack. The formation mechanism of pore-defect was analyzed. The micro-structure and composition of the pore-defect were studied by means of SEM and EDS. The results showed that the porosity mainly included circular air porosity, irregular process porosity and oxide inclusion.Linear energy density (E=P/v) was introduced as synthetic parameter.According to analysis and test verification, the optimum technological parameters of 316L stainless steel were laser power 190-210KW, laser speed 800-1000mm/s and scanning interval 0.9-0.11mm,and the linear energy density was about 200J/m. There were no cracks, no bubbles, a small amount of porosity, and the product density reached 99.7%.

Effect of Linear Energy Density on Bubble-Defect of 316L Stainless Steel by Selective Laser Melting

In the experiments of different process parameters (laser power, scanning speed and scanning distance),the low-time defects of forming part were studied by microscope,including air bubble, pore, micro-crack and macro-crack. The formation mechanism of bubble-defect was analyzed.Linear energy density (E=P/v) was introduced as synthetic parameter.According to analysis and test verification, the optimum technological parameters of 316L stainless steel were laser power 190-210KW, laser speed 800-1000mm/s and scanning interval 0.9-0.11mm,and the linear energy density was about 200J/m. There were no cracks, no bubbles, a small amount of porosity, and the product density reached 99.7%.

Crystallographic texture study of pulsed laser deposited Cr2O3 thin films

Chromium oxide thin films of thickness ~140 nm were grown on c-plane (0001) and a-plane (112¯0) sapphire substrates by Pulsed Laser Deposition (PLD) technique. The films of Cr2O3 on Si (100) substrates have been synthesized at an optimized oxygen partial pressure of 2 Pa with varying substrate temperature in the range of 473-973 K. It was observed that the films deposited at temperatures ≥673 K are crystalline as confirmed by X-Ray Diffraction (XRD) studies. The X-Ray Photoelectron Spectroscopy (XPS) profile showed that the films were grown with Cr3+ oxidation state. Atomic Force Microscopy (AFM) revealed smooth, uniform surface morphology with small amount of porosity. The epitaxial nature of the film on sapphire substrate and crystallographic orientation of the Cr2O3 over Si substrate were studied using rocking curve, ϕ (Phi) scan and pole figure measurement. Pole figure analysis suggested that the films deposited on Si substrate were fiber textured. Rocking curve Full Width at Half Maximum (FWHM) for Cr2O3 (0006) and Cr2O3 (112¯0) was about 0.1° and 0.06° respectively, which indicate the good quality of crystalline film. High Resolution X-ray Diffraction (HRXRD) with reciprocal space mappings (RSM) measurements indicate that the films grown on sapphire substrates are in relaxed state.

Large-sized La$lt;inf$gt;2$lt;/inf$gt;O$lt;inf$gt;3$lt;/inf$gt;-TiO$lt;inf$gt;2$lt;/inf$gt;-SiO$lt;inf$gt;2$lt;/inf$gt; Amorphous Oxide Fabricated by Hot Press Sintering

La2O3-TiO2 amorphous oxide has prospective applications because of its remarkable optical properties. However, due to its poor glass-forming abilities, it is difficult to prepare this material in a traditional way. The containerless solidification method can overcome this shortcoming, but the formed material size is generally restricted to be less than 10 mm. In order to obtain large-sized La2O3-TiO2 amorphous oxide, a small amount of SiO2 was added to the La2O3-TiO2 oxide system to form the amorphous oxide powders by aerodynamic levitation furnace. Subsequently, the high-density La2O3-TiO2-SiO2 materials were fabricated by vacuum hot press sintering. Compositions and microstructure properties were systematically studied by XRD and SEM. The results showed that SiO2 could improve the glass-forming ability of La2O3-TiO2. The raw powders made by aerodynamic levitation furnace were completely non-crystal, while the sintered samples had weak crystallization, which affected fully densification of sintered samples. There was a small amount of porosity in the high-density product made by vacuum hot press sintering. In addition, sintering densification mechanism of the La2O3-TiO2-SiO2 amorphous powders was analyzed. Finally, the optical property of hot pressed La2O3-TiO2-SiO2 material was investigated. It is found that La2O3-TiO2-SiO2 material still kepts high refractive index of above 2.2 in the visible light region. Small amount addition of SiO2 species improves the glass-forming abilities, yet decreases the refractive index slightly.

Effects of post-processing on cyclic fatigue response of a titanium alloy additively manufactured by electron beam melting

To establish the benefits of electron beam melting (EBM) for the fabrication of Ti–6Al–4V alloy components, it is necessary to properly understand the fatigue performance of the alloy. In the present study, we investigated the high-cycle fatigue behaviors of EBM-fabricated Ti–6Al–4V alloy component samples and systematically assessed their correlation with the microstructure, porosity, and (quasistatic) tensile properties of the material. The associated texture evolution and elemental distributions of the components were also examined. The employed samples were post-processed by hot isostatic pressing (HIP) and heat treatment (HT) at 920°C for 2h with and without the application of 100-MPa gas pressure, respectively. The as-built samples consisted of fine acicular α (hcp) microstructures, attributable to the β (bcc) → α′ (hcp) martensitic transformation during the EBM process, and these microstructures were coarsened by the HIP and HT processes. However, the fatigue properties of the HIP samples were found to be superior to those of the other samples despite the coarsened microstructure and reduced tensile strength. Notably, a small amount of porosity was observed in the as-built and HT samples, although all the samples were almost fully dense, having relative densities of ~100%. The pores were found to act as crack initiation sites, with the defects having a greater effect on the fatigue properties of the samples than the microstructures. Optimization of the parameters of both the EBM process and the raw powder production process is required to enhance the performance of EBM-fabricated Ti–6Al–4V alloy components.

Investigation of Stainless Steel Joint Fabricated Through Microwave Energy

In this paper, the microwave heating has fabricated joints of stainless steel (SS). Ni-based powder (EWAC 1002 ET) is used to join the stainless steel. The characterization of joint has been carried out through microstructural analysis, X-ray diffraction analysis, tensile strength, elongation, and microhardness. Microstructure analysis reveals that the joint is clearly visible. There are no cracks at the joints. Very small amount of porosity has been observed. Hardness decreases toward the joint. As the exposure time and percentage of nickel-based powder increase, tensile strength also increases. Tensile strength, elongation, and microhardness of joint are 323.16 MPa, 11.30%, and 145.3 Hv, respectively.

Porosity in Disk Shape Spray Formed Al-Si-Pb Alloy Preform

Spray forming technique was employed to produce a disc shape preform of Al-Si-Pb alloys. Porosity of this disc was investigated as a function of lead content and the distance from centre to periphery of the disc. The porosity decreases with distance from centre to periphery for all compositions of lead. The decay rate in porosity increases with the increase in lead content. Also the decay rate in porosity decreases towards the periphery of the deposit. The areas having large and small amount of porosity were observed in the microstructure of Al-Si-Pb alloys. The large and small amount porosity areas belong to the lead and aluminum rich areas, respectively.

A further simulation study on the dual role of porosity in solid-particle erosion of materials

► We investigate effects of porosity on solid-particle erosion of pure metal, ceramic, and composite materials (MMC and CMC) using a dynamic wear simulation model. ► A small amount of porosity has a positive effect on the erosion resistance of metal but the beneficial effect diminishes as a reinforcing phase is added. ► Pores play a dual role: providing preferential sites for crack nucleation but may force cracks to zigzag with elevated energy dissipation . ► Porosity is always detrimental to ceramic materials, which are hard and brittle. Previously we investigated the effect of porosity on solid-particle erosion of metal–matrix composites (MMCs) using a dynamic wear simulation model and demonstrated a positive effect of porosity on the resistance of MMCs to erosion when the amount of pores was small. We have extended this work to other materials, including pure metal, ceramic, and ceramic–matrix composites (CMCs), in order to obtain a general view of the role that porosity plays in solid-particle erosion processes for a wider range of materials. In this work, we simulate the performance of Cu, TiC–Cu, AlMgB 14 , TiB 2 , and AlMgB 14 –TiB 2 , which contain different amounts of porosity. It is demonstrated that a small amount of porosity has a positive effect on the erosion resistance of the metal but the beneficial effects diminish as the reinforcing phase is added. It appears that pores play a dual role: providing preferential sites for crack nucleation but forcing cracks to zigzag with elevated energy dissipation. Thus, a beneficial effect of porosity exists as long as the dual role is in an appropriate balance. However, porosity is always detrimental to ceramic materials, which are hard and brittle, susceptible to defects with low capability to absorb deformation energy, since the crack propagation in brittle materials only needs a small amount of input energy to generate fracture surfaces with little associated plastic deformation.

분말 혼합 공정으로 만들어진 은계 삽입금속의 특성

Ag계 분말 삽입금속을 볼 밀링법으로 제조하였다. 밀링공정의 변수들은 밀링시간을 제외하고는 일정하게 하였고 밀링 시간은 24, 48, 72시간들로 정하였다. 밀링에 의해 제조된 삽입금속들은 SEM관찰, DSC분석, 퍼짐성, 젖음성 시험을 통해 평가하였다. 삽입금속들의 브레이징부 특성은 상용금속에 비하여 우수하였다. 48시간 동안 밀링한 삽입금속이 퍼짐성과 젖음 특성이 가장 우수한 조건임을 나타냈다. 또한 브레이징부는 작은 양의 기공을 포함하고 있지만 안정적인 미세조직을 보였고 미세경도는 138VHN으로 나타났다. 【Powder type Ag system insert metals were manufactured by ball milling process. The variables of milling process were constant except the milling time. The milling times were selected for 24, 48 and 72 hours. The insert metals made by milling process were evaluated by performing scanning electron microscope, DSC(differential scanning calorimetry) analyses, spreading test and further in terms of wettability test. The selected insert metals that have the good characteristics compared to commercial insert metals were applied to make the brazed joints. The characterizations of those brazed joints were also conducted by microstructural observations. The results indicated that milling time of 48 hours for making powder type insert metals was the best condition showing the good spreadibility, low wetting angle. The brazed joints that applied the 48 hours milled insert metal were very sound condition indicating the stable microstructure in spite of containing small amount of porosity and the microhardness value of the joint was about 138VHN.】

Influence of spark plasma sintering temperature on sintering behavior and microstructures of dense bulk MoSi 2

Spark plasma sintering was employed to synthesize high-density bulk MoSi 2 in one step, using Mo and Si element powders as starting materials. Influence of sintering temperature on sintering behavior and microstructures of MoSi 2 were investigated. The sintering behavior at whatever temperature (1473, 1673 and 1873 K) is characterized by four stages, i.e., initial expansion, slight shrinkage, abrupt shrinkage and slight expansion. The maximum shrinkage displacement increased with increasing sintering temperature. When the sintering temperature reaches 1673 K or 1873 K, the second phases, i.e., SiO 2 and Mo 5Si 3/Mo 4.8Si 3C 0.6, were uniformly distributed in the synthesized MoSi 2 matrix accompanied with a small amount of porosity. Most of SiO 2 and Mo 5Si 3/Mo 4.8Si 3C 0.6 particles were concentrated at grain boundaries. The relative density of the products (atomic ratio: Mo/2.00Si) was improved tremendously from 89% to 98.2% over the range 1473–1673 K, and much smaller enhancement up to 99.0% was achieved from 1673 to 1873 K. At the same time, the grain size and amount of second phase particles (mainly Mo 5Si 3/Mo 4.8Si 3C 0.6) consistently increased with increasing temperature over 1473–1873 K. However, the use of a slight excess of Si (e.g., atomic ratio: Mo/2.06Si) at 1673 K resulted in dense products of MoSi 2 nearly free of Mo 5Si 3/Mo 4.8Si 3C 0.6, with the relative density of 99.2% and the average grain size of 5–10 μm. Thereby, in order to pursue an equilibrium among densification, microstructural refinement and formation of second phases, the most suitable sintering temperature and stoichiometry for fabrication of MoSi 2 by SPS are recommended to be 1673 K and a hyperstoichiometry of Mo/2.06Si in the present work.