Porosity Morphology Research Articles

Investigation and Comparison between Wear Properties of Powder Metallurgy (P/M) and Powder Forge (P/F) Product

In recent years powder metallurgy method P/M because of complicated parts production ability is used widely, but existence of porosities in this products will decrease mechanical properties in this method, but advanced powder metallurgy methods like powder forging P/F with having profits of powder metallurgy P/M because of visible reduce in porosities will decrease powder metallurgy problems. One of the mechanical properties that is effected by the porosity is wear properties ,in this research by comparison between two groups of specimen, that first group made by powder metallurgy method that had 14% amount of porosities and second group that made by powder forge method P/F that had less than 1% amount of properties and change in wear parameters in both of groups we survey wear properties and we compare wear rate and mechanism result is showing visible relation between wear properties and amount and morphology of porosities.

Microstructure and Properties of Multi-Function Micro-Plasma Sprayed Al<sub>2</sub>O<sub>3</sub> Coatings

Al2O3 coatings were fabricated by multi-functional micro-plasma spray through axial powder feed. The flight particle velocity and temperature were measured by SprayWatch-2i. With the rising of Ar flow, the velocity of Al2O3 particles increases, but the temperature of particles decreases gradually. Al2O3 coatings were analyzed by SEM and XRD. The microstructure of coatings is density, low porosity and uniform morphology. X-ray diffraction results show that α-Al2O3 is the main phase in the original Al2O3 powders, but Al2O3 coatings consist of γ-Al2O3 and a small amount of α-Al2O3. The microhardness and bonding strength of Al2O3 coatings were also measured, which is HV0.11183~1387 and 28.6MPa, respectively.

Mechanical Properties of Macroporous Biphasic Calcium Phosphate Bioceramics Fabricated Using a Porogen

Macroporous biphasic calcium phosphate bioceramics, for use as bone substitutes, have been fabricated by cold isostatically pressing and conventional sintering, using naphtalen or saccharose particles to produce macropores. The resulting ceramics, composite materials made of hydroxyapatite and b-tricalcium phosphate containing ~ 45% macropores and ~ 25% micropores, have been submitted to compression and three-point bending tests, toughness tests by single-edge-notched-bending, and spherical indentation tests. A new model is established to describe mechanical properties as a function of the amount and morphology of porosity, and propositions are made to optimise the fabrication procedure. Finally, those highly porous ceramics, although very brittle, exhibit a damage-tolerant contact behaviour, due to the compaction of the porous body under the indenter.

Tantalum oxide effect on the surface structure and morphology of the IrO2 and IrO2 + RuO2 + TiO2 coatings and on the corrosion and electrochemical properties of anodes prepared from these

Alterations in the phase composition, porosity, and surface morphology of coatings are examined following the insertion of a quantity of Ta2O5 into active coatings prepared from IrO2 or IrO2 + RuO2 + TiO2 (OIRTA). It is shown that even an insignificant concentration of Ta2O5 in a coating renders it substantially amorphous and leads to the appearance of a large number of wide protracted cracks in the coating. The latter extends the surface of anodes and boosts their apparent catalytic activity in the chlorine evolution reaction. In addition, this accelerates the diffusion of chloride ions toward the front surface of anodes, which noticeably reduces the overvoltage of the chlorine evolution reaction when manufacturing sodium chlorate. The coatings’ amorphization and the development of their surface substantially reduce the corrosion resistance of these anodes as compared with OIRTA.

X‐ray Microtomographic Characterisation of Porosity and its Influence on Fatigue Crack Growth

Cast Al alloys are seeing increasing use in transport applications due to their high strength‐to‐weight ratio at an acceptable cost compared to many ferrous alloys. Therefore, a quantitative characterisation of the pore distribution and its influence on the evolution of fatigue damage are required to predict the fatigue life of cast Al alloy components. In this investigation, X‐ray microtomography was used to characterise the 3D morphology of porosity in A356‐T6 specimens and to relate the porosity to fatigue behaviour.

Modelling the mechanical properties of microporous and macroporous biphasic calcium phosphate bioceramics

Macroporous biphasic calcium phosphate bioceramics, for use as bone substitutes, have been fabricated by cold isostatic pressing and conventional sintering, using naphtalen particles as a porogen to produce macropores. The resulting ceramics, composite materials made of hydroxyapatite and β-tricalcium phosphate (TCP) containing ∼45% macropores and with various microporosities, have been submitted to compression and three-point bending tests, toughness tests by single-edge-notched-bending (SENB), and spherical indentation tests. By combining two approaches at two different scales, one for closed porosity and one for open porosity, a model is established to describe mechanical properties as a function of the amount and morphology of porosity. The model assumes a quasi-continuous matrix containing macropores, the matrix being itself microporous, and considers that fracture always initiates on a macropore. The preliminary mechanical tests performed on the sintered ceramics tend to validate the modelling approach.

Alumina/Aluminum Composite Fabricated by Freeze and Dry Process with Water-Soluble Polymer Slurry

To clarify the effects of parameters of porous ceramics form on the characteristics of composites fabricated by high-pressure infiltration, Alumina forms with different porosity (15~70vol %) and pore morphology were fabricated by Freeze and Dry Process and Partial Sintering Process. Alumina/aluminum composites were made by the squeeze casting. The composites contained the different volume fraction of aluminum depending on the initial porosity of the ceramics form. The coefficient of thermal expansion (CTE) and thermal conductivity of composites were measured. The results indicated clearly that variation of the structure of porous ceramics form fairly affected CTE but the effects on thermal conductivity were small.

Control of Porosity and Composition in Large-Area YBCO Films to Achieve Micrometer Thickness and High<tex>$J_rm c$</tex>on Sapphire Substrates

Relatively thick YBCO thin films (thickness d>0.5 /spl mu/m) ideal for fault current limiter as well as microwave applications have been successfully prepared by large-area pulsed laser deposition (PLD) on CeO/sub 2/-buffered sapphire substrates. The attainment of an unusually high film thickness (up to 2.0 /spl mu/m) without microcracking is attributed in part to the presence of pores correlated with yttrium-rich composition in the films. The effect of using YBCO targets with varied Y:Ba:Cu ratios on film porosity and surface morphology was investigated in detail. Using the optimum target composition, uniform critical current densities (J/sub c/) ranging from /spl sim/4.5 MA/cm/sup 2/ at d/spl sim/0.23 /spl mu/m to /spl sim/1.75 MA/cm/sup 2/ at d/spl sim/0.6 /spl mu/m have been achieved. Characterization of a film with d/spl sim/0.5 /spl mu/m showed low microwave surface resistance values [R/sub s/(77.3 K)/spl ap/2.09 m/spl Omega/ and R/sub s/(20 K)/spl ap/227 /spl mu//spl Omega/ at 22 GHz] comparable to the best YBCO films reported by other studies.

Corrosion behaviour of a pressure die cast magnesium alloy

High pressure die casting is the most important production method for casting magnesium alloy components, and uniformity of appearance is an important criterion for acceptance of a component by customers. This paper investigates the influence of uniformity in surface appearance of diecast AZ91D plates on their corrosion behaviour. Through immersion, hydrogen collection and weight loss measurements it was found that corrosion is more likely to occur on the areas of the plate that appear to be darker, leading to a non-uniformly corroded surface. Microstructural analysis showed that the non-uniformity in appearance is related to a difference in the morphology and distribution of porosity across the surface of a diecast AZ91D plate. The darker areas of the surface are high in porosity which breaks the continuity of the β-phase network and provides shortcut paths for corrosion from the surface to the interior of the casting. The brighter shiny areas of the surface are much less porous, with isolated pores being confined by corrosion resistant β-precipitates thus reducing the corrosion rate.

Correlations between the surface morphology and electronic properties of porous multilayer structures with quantum InGaAs layers

The conducting properties of the porous two-dimensional InGaAs layers embedded in GaAs or InAlAs porous dielectric matrix are discussed. The influence of the electrochemical etching time of samples, their porosity and surface morphology on the optical and electrophysical characteristics of the structures with a low-dimensional electron gas has been investigated. The change of a surface structure morphology during an etching process was studied by a scanning probe microscopy (SPM). Using this method we estimated a range of a porosity, width and depth of pores formed in a sample as function of the time etching. We considered both the InGaAs layers located nearest a sample surface when the pores intersected a layer plane, and a case for the InGaAs layers lying under a layer of a porous material. In all these cases the precise correlation between a surface morphology and a conductivity of a two-dimensional electron gas in a layer was traced.

Closed-Cell Metal Foams Manufactured from Bulk Metal and Alloy Sheets through ARB Process

Aluminum foams having extremely low densities offer a large potential for lightweight structural materials. New manufacturing process without expensive aluminum alloy powder has been developed using conventional bulk aluminum alloy sheets. Preform plate containing blowing agent particles is first manufactured through accumulative roll-bonding (ARB) process. By heating the preform plate, closed-cell aluminum foams having various porosity and cell morphology are produced. It was revealed that ARB processing condition is significantly important to produce suitable aluminum foam with high porosity and uniform pore distribution. Present manufacturing process also possesses a potential to apply to many other metal and alloy foams.

Mechanical Properties of Porous MSQ Films: Impact of the Porogen Loading and Matrix Crosslinking.

AbstractSemiconductor industry needs a continuously improvement of integrated circuits performance and an increase of integrated density on silicon. The 2004 ITRS Roadmap underlines the need of dielectric material for ILD with dielectric constant (k) lower than 3 for the 90 nm node and than 2.4 for the 45 nm node. In this work, porous films with k value lower than 2.2 were processed using a porogen approach. Firstly, a material composed of a methylsilsesquioxane (MSQ) matrix and of organic nanoparticles (called porogen) is deposited and baked. Then, this composite is thermally cured to allow the porogens degradation and matrix crosslinking. Different k values were obtained by varying the porogen loading in the composite. Mechanical properties of composite and porous films (before and after porogen removal respectively) were investigated using nanoindentation and FTIR analysis for different porogen loadings (between 0 and 40 %). The composite modulus is higher than the porous film modulus for high porogen loading. This result is interpreted in term of matrix crosslinking. Mechanical properties were also modelized using foam mechanical models. For high porosity level, the best Young modulus fitting is obtained with tetrakaidecaedric cells, which seems in good agreement with porosity morphology.

Microstructural evolution of AS21X HPDC alloy during thermal treatment

The microstructure of a High Pressure Die Cast Magnesium (HPDC) AS21X alloy was investigated after various heat treatments. The material, supplied in the as cast state, consisted of Mg-α grains separated by intermetallic particles such as Mg17Al12, Mg2Si and Al–Mn. The alloy was subjected to solution treatment at 415° C for times ranging from 0.5 to 48 h and to aging to assess grain growth stability and precipitation hardening. Light microscopy showed that Mg-α grains increase slightly in size whereas intermetallic particles do not disappear but assume a more rounded shape. Static precipitation and/or dissolution were followed by electrical conductivity, hardness measurements and X-ray diffractometry. Tensile properties at room temperature were evaluated on both the as cast and solution treated samples. Density was used as an indicator of porosity to explain the scatter in elongation to fracture data. Study of the fracture surfaces revealed the morphology of porosity and the otherwise ductile fracture failure mechanism.

Hemispherical transition of seismic attenuation at the top of the earth's inner core

In contrast to the liquid outer core, the earth's inner core is mostly solid, and its composition is more pure iron. Based on dynamic arguments related to the freezing process of the inner core, and the observation of much lower P-wave quality factor in the inner core ( Q α<450) than in the outer core ( Q α>10,000), it has been suggested that a mushy layer with liquid inclusions may exist at the top of the inner core. On the other hand, seismic measurements indicate that Q α increases towards the center of the inner core. We here present estimates of Q α in the depth range 32–110 km beneath the Inner Core Boundary (ICB), based on the measurement of PKIKP/PKiKP amplitude ratios after a narrow band-pass filtering (0.7–2.0 Hz). Our measurements indicate that there are pronounced hemispherical differences in the values of Q α (∼335 and ∼160 in the western (180°W to 40°E) and eastern (40°E to 180°E) hemispheres, respectively), and in the depth of transition from decreasing to increasing Q α (<32 km beneath the ICB in the eastern hemisphere and ∼85 km in the western hemisphere). Below 85 km, the hemispherical pattern disappears. We also confirm the existence of a correlated hemispherical pattern in P velocity down to 85 km. The P velocity and Q α variations are compatible with an interpretation in terms of small hemispherical variations of temperature at the top of the inner core and their influence on the morphology of porosity and connectivity of liquid inclusions in the mushy zone. The disappearance of the differences in Q α beneath 85 km provide constraints on the likely depth extent of the mushy zone.

The influence of strontium on porosity formation in Al-Si alloys

Strontium modification is known to alter the amount, characteristics, and distribution of porosity in Al-Si castings. Although many theories have been proposed to account for these effects, most can be considered inadequate because of their failure to resolve contradictions and discrepancies in the literature. In an attempt to critically appraise some of these theories, the amount, distribution, and morphology of porosity were examined in sand-cast plates of Sr-free and Sr-containing pure Al, Al-1 wt pct Si, and Al-9 wt pct Si alloys. Statistical significance testing was used to verify apparent trends in the porosity data. No apparent differences in the amount, distribution, and morphology of porosity were observed between Sr-free and Sr-containing alloys with no or very small eutectic volume fractions. However, Sr modification significantly changed the amount, distribution, and morphology of porosity in alloys with a significant volume fraction of eutectic. The addition of Sr reduced porosity in the hot spot region of the casting, and the pores became well dispersed and rounded. This result can be explained by considering the combined effect of the casting design and the differences in the pattern of eutectic solidification between unmodified and Sr-modified alloys.

Correlation Between Spraying Conditions and Microcrack Density and Their Influence on Thermal Cycling Life of Thermal Barrier Coatings

It is generally known that the porosity of thermal barrier coatings is essential to guarantee a sufficiently high strain tolerance of the coating during thermal cycling. However, much less is known about the influence of the specific morphology of porosity, such as microcracks and typically larger pores, on the performance of the coatings. Both features are usually formed during plasma spraying of yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs). In this investigation, the influence of microcracks on the thermal cycling behavior was studied. The amount of microcracks within YSZ thermal barrier coatings was changed by changing the powder-feeding rate. Only small changes of the total porosity were observed. Mercury porosimetry served as a tool to investigate both the amount of microcracks and pores in the coating. Additionally, microcrack densities were determined from metallographical investigations. A linear dependence between the amount of fine pores determined by Hg porosimetry and the crack density was obtained for one set of coatings. Thermal cycling TBC specimens with different microcrack densities were produced and tested in a gas burner test facility. At high surface temperatures (above 1300 °C), failure occurred in the ceramic close to the surface. Under these conditions, the samples with increased horizontal microcrack densities showed a significant increase of thermal cycling life.

Effect of micro- and macroporosity of bone substitutes on their mechanical properties and cellular response.

The control of porosity morphology and physico-chemical characteristics of calcium phosphate bone substitutes is a key-point to guaranty healing success. In this work, micro- and macroporosity of materials processed with 70% Hydroxyapatite (HAP) and 30% beta-tricalcium phosphate (beta-TCP) were controlled by sintering temperature and porogen addition, respectively. Porosity was quantified by scanning electron microscopy (pore size) and mercury intrusion porosimetry (interconnection between pores). The content of macrointerconnections and their size were dependent on porogen content, shape, and size. Mechanical properties (compressive strength) were strongly dependent on macroporosity size and content, on the basis of exponential laws, whereas microporosity ratio was less influent. Relying on those results, three types of materials with contrasting porous morphologies were processed and assessed in vitro, in primary culture of human osteoblasts and fibroblasts. With both types of cells, an exponential cellular growth was effective. Cells colonized the surface of the materials, bridging macroporosity, before colonizing the depth of the materials. Cell migration across and into macroporosity occurred via the emission by the cells of long cytoplasmic extensions that hanged on microporosity. Both macroporosity and macrointerconnectivity size influenced the penetration of cells. An interconnection size of 15 microm appeared to be effective to support this invasion without bringing down mechanical strength.

Simulation of the three-dimensional morphology of solidification porosity in an aluminium–silicon alloy

A novel extension of the cellular automata technique for microstructural modelling is presented, allowing simulation of the evolution of the complex three-dimensional morphology of porosity during the solidification of an aluminium–silicon alloy. The complex morphology arises due to the restriction of the growth of the pores by the developing solid phase. The model predicts the average properties of the porosity formed, together with the distribution in size and morphology. The model is used to determine the influence of a variety of applied conditions (e.g. thermal history, pressure, hydrogen content) and material properties (nucleation behaviour, alloy composition) upon the pore morphology, as characterized by the average and extreme dimensions. The relative magnitude of the effect of each parameter and the interactions between parameters upon the porosity are statistically analysed. The simulated pore size shows the largest sensitivity to applied pressure, hydrogen content and solidification time, together with interactions between solidification time and pressure. These results are in good agreement with previously reported experimental behaviour.

Ultrafiltration Membrane Made with Mesoporous MSU-X Silica

A new membrane synthesized onto a commercial tubular support was prepared by the directed synthesis of ordered mesoporous MSU-type silica through an interfacial reaction between a silica condensation catalyst (NaF) and new hybrid micellar building units made of silica precursors and nonionic surfactants. This membrane exhibits a specific permeation behavior toward PEO polymers that can be explained by the porosity morphology and silica charge pH dependence.

Image analysis investigation of the effect of the process variables on the porosity of sintered chromium steels

Image analysis is used to study the effect of compaction and sintering temperature on the porosity morphology of chromium steels. The pore morphology was described by means of two parameters, f circle and f shape, which have different geometrical meanings. The results have been interpreted with reference to an elliptical geometry, which represents the theoretical shape to which porosity tends. High sintering temperature improves f circle more than f shape, while warm compaction does not have a significant effect. But, if the largest pores are considered, a synergic effect of sintering temperature and warm compaction arises. f circle seems to be more suitable than f shape for evaluating the effect of the process variables on the evolution of the pore morphology.