Effect Of Inclusion Size Research Articles

The size effect of crystalline inclusions on the fracture modes in glass–ceramicmaterials

The main parameters influencing the mechanical performance of glass–ceramicmaterials are the shape and mean size of the ceramic phase, i.e. the crystallineinclusions. The aim of the present work is twofold: first, to study the effect ofthe above parameters on the modes of fracture in two kinds of glass–ceramicmaterials by the use of the static microindentation technique; second, to interpretthe experimental results by the application of a simple physical model. It wasfound that reduction in the size of granularly shaped crystallite inclusions orreduction of the width of needle-like crystalline inclusions results in an increase of theextent of crack propagation, while the fracture mode shifts from intergranular totransgranular. These observations were successfully interpreted in terms of energeticarguments related to the size of the crystalline inclusions with respect to the widthof a disordered zone acting as an interface between them and the amorphousmatrix.

A molecular dynamics simulation study of inclusion size effect on polymeric nanocomposites

The elastic behavior of polymeric nanocomposites is investigated with molecular dynamics simulations. Inclusions are modeled as spherical nanoparticles. It is demonstrated with numerically performed tensile tests that Young’s moduli of nanocomposites are strongly affected by the size of the nanoparticle as well as by the interaction strength between polymer chains and the nanoparticle. The Young’s modulus of the nanocomposite is enhanced as the size of the nanoparticle decreases as long as the strength of polymer–nanoparticle interaction is stronger than or equal to that of the polymer–polymer interaction. The analysis of stresses on polymer monomers shows that the composite modulus enhancement by smaller nanoparticles is attributed to the stiffer layer of polymer of higher densities around the nanoparticle.

Finite-element simulation of inclusion size effects on copper shaped-wire drawing

The effects of inclusion size on copper shaped-wire drawing were investigated. For this purpose, an experimental investigation for optimal die half-angle was conducted. Based on experimental data of optimal die half-angle, the deformation and the hydrostatic stress of the copper shaped-wire that contain an inclusion were calculated by two-dimensional finite element analysis. As the FEA results, while the leading edge of the inclusion passed through the die, the necking due to inclusion wire drawing occurred on some parts of the copper wire surface in front of and near the leading edge of the inclusion. The effects of inclusion size on drawing stress, tensile stress in front of inclusion and contact compressive stress while copper shaped-wire drawing were carried out.

Effect of inclusion size on mechanical properties of polymeric composites with micro and nano particles

The effect of the particle size on the mechanical properties of polymeric composites reinforced with spherical particles was investigated. The size of particles varied from macro (0.5 mm) to nano (15 nm) scale. It was found that particle sizes at micro scale have little influence on the Young’s modulus of the composite and that Young’s modulus increases as the size of particles decreases at nano scale. It was also observed that tensile strength of the composite is significantly dependent on particle size. At 1 vol% loading, the tensile strength increased as the particle size decreased. However, the trend for the composite with alumina nanoparticles of 3% volume fraction was found to be opposite. TEM and SEM micrographs showed higher likelihood of poor dispersions in the composite with 3 vol% nanoparticles than that with 1 vol%. To understand the effect of the particle size in micron scale on the failure process, finite element analyses showed that total strain energy release rate for particle/matrix debonding growth decreases as particle size decreases and that sliding fracture mode becomes dominant as the debonding grows. It was found that interfacial fracture toughness does not depend on particle size but increases substantially when the sliding fracture mode prevails.

Effect of inclusion size on mechanical properties of alumina toughened cubic zirconia

The relationship between alumina inclusion size and mechanical properties of particulate cubic zirconia-alumina composites was studied. The composites of the diverse size and content of alumina inclusions and of the nearly constant size of zirconia grains were used. Physical mixtures of the 8 mol% Y2O3-ZrO2 nano-powder and the γ-Al2O3 or α -Al2O3 micro-powder were cold isostatically pressed and then pressurelessly sintered for 2 h at 1300∘C in air. The γ -Al2O3 and α -Al2O3 powder was composed of the particles of 0.17 and 0.36 μ m in size, respectively. Crystallites of the zirconia powder had the size of 6 nm. Microstructural features of the composites have been characterised quantitatively. Hardness, critical stress intensity factor and bending strength of the composites was measured and correlated with the microstructural features. Depending on the size and content, the alumina inclusions influenced strength of the composites by influencing their fracture toughness and the presence of flaws of critical size. An increase in size of the alumina inclusions was accompanied by the increase of fracture toughness due to the additional contribution of large alumina inclusions to the crack deflection mechanism. It was found that decreasing the alumina inclusion size significantly below the cubic zirconia matrix grain size (more than 3 times) did not lead to the increased values of fracture toughness of the composites. The highest increase in fracture toughness (up to 3.9 MPa⋅ m0.5) has been found when the inclusion size was comparable to the matrix grain size.

The effect of inclusion size on the local conditions for void nucleation near a crack tip in a mild steel

The local conditions for void initiation are determined for individual MnS-inclusions near the crack tip in a mild steel St37. First, the crack tip opening displacement at the moment of void initiation, CODvi, is measured by quantitative fracture surface analysis; subsequently, the maximum interfacial stress, σmaxinterf, is calculated from models by Argon et al. [Metall Trans 1975;6:825] and Beremin [Metall Trans 1981;12:723]. A strong effect of the size of the MnS-inclusions on the CODvi- and the σmaxinterf-values is revealed.

Non‐stoichiometry and non‐homogeneity in InN

It is shown that the wide variation of apparent band-gap observed for thin films nominally referred to as InN is strongly influenced by variations in the nitrogen:indium stoichiometry. InN samples grown by remote plasma enhanced chemical vapour deposition show a change in band-gap between 1.8 and 1.0 eV that is not due to the Moss-Burstein effect, oxygen inclusion or quantum size effects, but for which changes in the growth temperature result in a strong change in stoichiometry. Material non-homogenity and non-stoichiometry appear to be general problems for InN growth. Excess nitrogen can be present at very high levels and indium rich material is also found. This work shows that the extent of the Moss-Burstein effect will have to be reassessed for InN. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of reduction ratio, inclusion size and distance between inclusions on wire breaks in Cu fine wiredrawing

The presence of an inclusion in wire makes wire breaks easy to occur even with a high reduction ratio. The investigation presented here is mainly aimed at determining the reduction ratio when size of an inclusion, application of back tension and distance between inclusions are considered. In order to investigate the effect of back tension on wire breaks, the applied back tension in a slip type continuous drawing machine is calculated quantitatively using some parameters such as diameter and peripheral speed of capstan and coiling number. The effect of an inclusion size and reduction ratio on wire breaks is investigated when quantitatively calculated back tension being 28% of drawing force is applied. The size of an inclusion varies 5, 7 and 10 μm, the reduction ratio varies 10, 13 and 16%, the distance between inclusions is set to be 0.25 and 0.5 mm, respectively. Conical dies with a half angle α of 7°, which is the value generally used in commercial production. As the FEM code, the commercially available software DEFORM-2D is used. Copper is used for fine wire drawing process that initial diameter is 1 mm and final diameter is up to 50 μm. Accumulated strain and mean stress are simultaneously calculated to obtain damage value in the multistage wiredrawing. The defects of central burst type are generated at a smaller total reduction ratio with decreasing unit reduction ratio and with increasing inclusion size. Furthermore, damage value rises because the tensile stress in deformation zone increases by applied back tension. The distance between inclusions would not affect wire breaks because the distance is expanded excessively through multistage wiredrawing.

Size effect of hematite and corundum inclusions on the efflorescence relative humidities of aqueous ammonium nitrate particles

The influence of relative humidity (RH) and mineral dust inclusions on the physical state of NH4NO3/H2O particles is investigated through infrared aerosol flow tube experiments. Neat submicron aqueous particles do not effloresce, while those bearing mineral inclusions ranging from 150 to 400 nm in diameter effloresce between 3 and 10% RH at 298 K. NH4NO3/H2O coatings are achieved on hematite (α‐Fe2O3), corundum (α‐Al2O3), mullite (Al6Si2O13), and amorphous silica (am‐SiO2) through a HNO3 vaporization‐condensation technique followed by neutralization with NH3. The extent of internal mixing in the aerosol ranges from 7 to 27% depending on the mineral dust diameter. The size‐dependent efflorescence results are successfully rationalized within the framework of an active‐site model, and the physical parameters obtained from the model optimization are consistent with previous work on the efflorescence of (NH4)2SO4/H2O by these mineral dusts. Evidence is presented for a mechanism of heterogeneous nucleation that proceeds by chemisorption of nitrate at the surface of the oxide minerals followed by epitaxial germ formation of crystalline NH4NO3, all of which is driven by the saturation of the aqueous solution with respect to the solid.

Arc generation from sputtering plasma-dielectric inclusion interactions

Arcing during sputter deposition and etching is a significant cause of particle defect generation during device fabrication. In this article we report on the effect of aluminum oxide inclusion size, shape, and orientation on the propensity for arcing during sputtering of aluminum targets. The size, shape, and orientation of a dielectric inclusion plays a major role in determining the propensity for arcing and macroparticle emission. In previous studies we found that there is a critical inclusion size required for arcing to occur. In this article we used high-speed videos, electric arc detection, and measurements of particle defect density on wafers to study the effect of Al2O3 inclusion size, shape, and orientation on arc rate, intensity, and silicon wafer particle defect density. We found that the cross-sectional area of the inclusion exposed to the sputtering plasma is the critical parameter that determines the arc rate and rate of macroparticle emission. Analysis of the arc rate, particle defect density, and the intensity of the optical emission from the arcing plasma indicates that the critical aluminum oxide inclusion area for arcing is 0.22±0.1 mm2 when the sputtering plasma sheath dark-space λd, is 0.51 mm. Inclusions with areas greater than this critical value readily induce arcing and macroparticle ejection during sputtering. Inclusions below this critical size do not cause arcing or macroparticle ejection. When the inclusion major axis is longer than 2λd and lies perpendicular to the sputter erosion track tangent, the arcing activity increases significantly over the case where the inclusion major axis lies parallel to the erosion track tangent.

Measurements of the critical inclusion size for arcing and macroparticle ejection from aluminum sputtering targets

Arcing during sputtering is a significant cause of defect generation during sputter deposition of thin films. We studied the effect of dielectric inclusion size on the propensity for arcing while sputtering aluminum targets in argon at power densities ranging from 8 to near 60 W/cm2. We found that there is a critical inclusion size required for arcing to occur. The critical size for an Al2O3 inclusion in an aluminum-sputtering target in an argon plasma is 440±160 μm. Inclusions with sizes above this critical value readily induce arcing and macroparticle ejection during sputtering. Inclusions below this critical size do not cause arcing or macroparticle ejection. We also found that the inclusion critical size was not sensitive to the sputtering power density. When the inclusion size exceeds the critical value the plasma boundary over the inclusion is deformed by the charge accumulating on the dielectric inclusion and the plasma positive column diffuses toward the target leading to a bipolar arc. Inclusions below the critical size do not distort the dark space to an extent great enough to permit bipolar arc formation. Our proposed model predicts that the critical inclusion size depends upon the sheath thickness, which ranged between 300 and 600 μm for the experimental conditions used in this study.

The size effect of hematite and corundum inclusions on the efflorescence relative humidities of aqueous ammonium sulfate particles

Mineral dusts inside aqueous atmospheric particles provide surfaces that induce crystallization during episodes of decreasing relative humidity (RH). Submicron aqueous ammonium sulfate particles containing hematite (α‐Fe2O3) and corundum (α‐Al2O3) inclusions are investigated in an aerosol flow tube at 298 K. As compared to 35% RH where homogeneous nucleation is rapid, the heterogeneous nuclei regulate the RH from 35% up to 60% RH as the inclusion size varies from 50 to 450 nm. The strong size dependence can be rationalized by an active site model. Model optimization yields 1010.4 sites cm−2 and m < 0 for α‐Al2O3 and 109 sites cm−2 and m=0.04 for α‐Fe2O3 particles.

Effect of Inclusion Size on the Nucleation of Acicular Ferrite in Welds.

Low-carbon steel weld with a high density of oxide inclusions prepared using a experimental metal-cored wire has been examined to study the effect of inclusion size on the formation of acicular ferrite, and to understand the role of inclusion in the nucleation of ferrite lath. Depending on the ferrite morphology associated with inclusions, a total of 282 inclusions observed under TEM could be classified into two groups, i.e. the non-nucleant and the nucleant. Experimental results showed that the group of inclusions acted as nucleant were appreciably larger in size compared with those of non-nucleant resulting in the increased probability of nucleation with the increase of inclusion size, even though the chemical and structural natures appeared to be the same. The group of nucleant-inclusion was further divided into two types depending on the degree of nucleation, which was evaluated by the number of ferrite lath nucleated. Statistical analysis performed on inclusion size indicated that the larger the inclusion size is the more ferrite laths could be nucleated. Those laths nucleated from a large single inclusion have grown in many different radial directions and mostly had a different crystallographic orientation from those of adjacent ferrite laths. As a result of this study, it is demonstrated that larger inclusions are indeed more potent nucleation sites when compared with those of smaller size. Thus it could be concluded that the provision of the inclusion surface as for the inert surface for the heterogeneous nucleation of acicular ferrite lath would be the principal role of inclusions playing in the weld metal of low alloy steels. Other possible mechanisms were also considered, but they were unlikely to be operated in the present weld metal system.

Effect of SiC volume fraction and particle size on the fatigue resistance of a 2080 Al/SiC p composite

The effect of SiC volume fraction and particle size on the fatigue behavior of 2080 Al was investigated. Matrix microstructure in the composite and the unreinforced alloy was held relatively constant by the introduction of a deformation stage prior to aging. It was found that increasing volume fraction and decreasing particle size resulted in an increase in fatigue resistance. Mechanisms responsible for this behavior are described in terms of load transfer from the matrix to the high stiffness reinforcement, increasing obstacles for dislocation motion in the form of S’ precipitates, and the decrease in strain localization with decreasing reinforcement interparticle spacing as a result of reduced particle size. Microplasticity was also observed in the composite, in the form of stress-strain hysteresis loops, and is related to stress concentrations at the poles of the reinforcement. Finally, intermetallic inclusions in the matrix acted as fatigue crack initiation sites. The effect of inclusion size and location on fatigue life of the composites is discussed.

Effects of Shape and Size of Inclusions on the Sintering of ZnO—ZrO2 Composites

The densification behavior and microstructure development of ZnO matrices containing rigid Zro2 inclusions were studied, with special emphasis on the effect of inclusion shape and size. The inclusions retarded the densification of the matrix, regardless of the inclusion shape and size. For large inclusions with diameters of 10 μm, dense regions developed between inclusion particles. The inclusion particles and dense regions formed a continuous network, which constrained the densification of the composites. The inclusion shape had a small effect on the development of dense regions. Severe retardation in densification was observed for compacts containing inclusions with diameters of 10 μm. In these cases, dense regions between inclusion particles did not develop. The formation of the continuous network cannot be applicable to small inclusions as an origin of retardation of densification.

The second Stekloff eigenvalue of an inclusion and new size effects for composites with interface thermal barriers

Two-phase particle reinforced composites are considered. We treat the case when there is an interfacial thermal barrier between phases. We obtain the geometric criterion that determines when the effects of the interfacial thermal barrier overcome the benefits of a highly conducting reinforcement. This criterion is general and applies to any reinforcement with Lipschitz continuous boundary. It is given in terms of the second Stekloff eigenvalue of the reinforcement. This result is used to predict size effects for a general class of inclusion shapes.

Dependence of the fatigue limit of rail steels on stress intensity factor near inclusions

The fatigue limits of four rail steels were evaluated with multiple specimens under bending. Inclusion volume and average size were quantitatively measured using an image analyzer in an attempt to correlate these parameters with the fatigue limit. However, no direct relationship was found between the fatigue limits and the elongated inclusion content and average size. Hence, the stress intensity factor at the elongated inclusion tip is considered as a parameter which governs fatigue crack initiation. A theoretical model for the estimation of fatigue limits of the rail steels was developed from the consistency in principle between the definition of the fatigue limit and the fatigue crack propagation threshold. In this model, the stress intensity factor at the inclusion tip was evaluated by taking into account a traction stress at the interface between the inclusion and the matrix. Furthermore, a correction for closure effects was made to obtain the true threshold. The proposed model takes into account the effect of inclusion size and the elastic modulus relative to the matrix, as well as the matrix resistance to crack propagation. As a consequence, a comparison was made between the theoretical values and the experimental values of the fatigue limits.

Sintering, Creep, and Electrical Conductivity of Model Glass‐Matrix Composites

The sintering, creep, and electrical conductivity of model glass‐matrix composites were investigated as functions of inclusion content and size. The composites consisted of spherical soda–lime glass particles and spherical nickel inclusions. At inclusion volume fractions below 10 vol% there was no inclusion size effect on the creep viscosity. Above 10 vol% there was an inclusion size effect, with the viscosity increasing significantly with decreasing inclusion size. The increase in electrical conductivity commenced at lower inclusion volume fractions as the inclusion size decreased. The data indicate that interactions between the inclusions might be responsible for the observed inclusion size effect. The sintering rates of the composites were compared with the predictions of Scherer's self‐consistent model. Good agreement was obtained when the measured creep viscosity was used in the model equations.

Factors Controlling the Sintering of Ceramic Particulate Composites: I, Conventional Processing

The effect of processing and material parameters on the sintering and coarsening of model composites consisting of a fine‐grained ZnO matrix and coarse, rigid, inert particulate inclusions of ZrO2 was investigated. The green composites were formed by two methods: (i) mixing the matrix and inclusion powders in a ball‐mill followed by die‐pressing and (ii) slip casting. For both forming methods, the inclusions caused a significant reduction in the density and the grain size of the composite matrix but had almost no effect on the grain size vs density relationship. The effects of inclusion volume fraction and sintering temperature were somewhat independent of the forming method. However, for the slip‐cast composites, the effect of inclusion size was less severe and the packing of the matrix phase immediately surrounding the inclusion showed some improvement. The sintering kinetics and microstructural observations indicated that two main factors controlled the sintering of these composites: (i) interactions between the randomly distributed inclusion particles that created a constraint on the matrix and (ii) the packing of the matrix, especially in regions immediately surrounding the inclusion particles.

Inclusion size effect on the fatigue crack propagation mechanism and fracture mechanics of a superalloy

Low cycle fatigue life of nickel-base superalloys is enhanced as a consequence of inclusion reduction in the melt process; however, the functional dependencies between fatigue characteristics and inclusions have not been well investigated. In this study, the propagation mechanism of the fatigue crack initiated from inclusions is examined in fine-grained IN718, which is a representative turbine disc material for jet engines. There is a faceted-striated crack transition on the fracture surfaces. This faceted-striated transition also appears in theda/dN vs crack length curves. It is observed that the faceted crack propagation time can be more than 50 pct of total lifetime in the low cycle fatigue test. The significance of inclusion size effect is explained on the premise that the faceted fatigue crack propagation time scales with the inclusion size, which is taken as the initial crack length. A predictive protocol for determining inclusion size effect is given.