Size Distribution Of Oxide Particles Research Articles

Uncertainty and statistics of dislocation-oxide interactions on strength and creep failure of oxide dispersion strengthened steels

Oxide dispersion strengthening (ODS) steels exhibit excellent mechanical and creep properties due to the nanoscale oxide particles as barriers to dislocation motion, for the great application potentials to structural components of advanced nuclear power plants. However, the classical ODS model described by the Orowan mechanism or cutting mechanism only depends upon a single average size, ignoring uncertainty and statistics of dislocation-oxide interactions induced by the spatial and dimensional random distribution of oxide particles. When the oxide particle size is larger than the critical size to determine the interaction mechanism transformation from cutting to looping, the Orowan mechanism and cutting mechanism would exist simultaneously. Here we propose a modified ODS model for strength and creep rate considering the spatial distribution and size distribution of oxide particles, which is more consistent with the experimental result compared to the classical ODS model. In addition, the contribution of oxide particles to the yield strength and creep strength is evaluated quantitatively for various precipitate sizes and volume fractions. It is believed that this model provides an analytical framework to accurately predict the strength and creep rate of ODS steels.

Improvement of high temperature mechanical properties of Ni-based oxide dispersion strengthened alloys by preferential formation of Y-Ti-O complex oxide

Y2O3 is mainly applied as a dispersoid in Ni-based oxide dispersion strengthened (ODS) alloys. The added Y2O3 reacts with Ti and Al at a temperature above 1150 ℃ to form a complex oxide such as Y-Ti-O or Y-Al-O complex oxide. However, previous studies have shown that Y-Al-O complex oxide has relatively coarser particles than Y-Ti-O complex oxide.In this study, Ti was first added to form Y-Ti-O complex oxide, which has relatively fine particles. Subsequently, Al was added to inhibit the formation of Y-Al-O complex oxide, thus improving the high-temperature mechanical properties of ODS alloys. Ni-based ODS alloy powders with composition Ni-15Cr-xTi-1.1Y2O3 (without aluminum) were mechanically alloyed using a planetary mill. Thereafter, the mechanically alloyed powders were heat treated to form a complex oxide of Y-Ti-O. A second mechanical alloying was performed by adding 4.5 wt% Al to the heat treated powders. The products obtained after the second alloying were sintered by spark plasma sintering. The phase of the sintered specimens were analyzed using X-ray diffraction, their microstructures were analyzed by transmission electron microscopy and the size distribution of oxide particles was confirmed by image analysis. Moreover, the high-temperature mechanical properties of each composition were analyzed using a hot hardness tester.

Crystallographic relationship of YTaO4 particles with matrix in Ta-containing 12Cr ODS steel

The crystallography of monoclinic YTaO4 particles and the atomic structure at the particle/ferrite matrix interface in Ta-containing 12Cr ODS steel have been examined by means of SAD and HRTEM. Three different peaks in size distribution of oxide particles were detected by SANS, with the peak positions at 1.5nm, 9nm, and 100nm in size. The results show that many YTaO4 particles are semi-coherent with the matrix, and the habit plane determined in most cases is {051}O//{011}M. Orientation relationships of (051)O//(1¯1¯0)M, [715¯]O//[1¯11]M; (121)O//(110)M, [2¯10]O//[001]M; (051)O//(011)M, [715¯]O//[01¯1]M and (05¯1)O//(1¯1¯0)M, [3¯15]O//[1¯13]M were found. These orientation relationships provide a very small misorientation between the specific planes of YTaO4 particles and {110} close packed planes of ferrite. Fine particles of around 4nm in size exhibited incoherent relationship with the misfit angle of around 10° with the matrix. Observation on particles ranging from 7 to 50nm in size revealed that the crystallographic relationship is semi-coherent between oxide particles and the matrix.

Effects of Oxygen Concentration on the Size Distribution of Oxide Particles in ODS Steel

ODS steel normally contains an exceptionally high oxygen concentration owing to oxygen adsorption on the metal powder surfaces, as well as to the contamination during mechanical alloying and consolidation. In this study, the effect of oxygen concentration on the size distribution of oxide particles in ODS steel has been investigated. The oxygen concentration in one ODS steel sample was about 7000 ppm (sample A), while that in the other was controlled to be about 2500 ppm (sample B) by a hydrogen reduction process prior to consolidation. Sample A revealed a much smaller mean grain size (~10 μm) than sample B (~25 μm). Two types of oxide particles, fine YTiO4 (< 30 nm) and coarse Cr-O (>100 nm), were mainly found in both samples. The fine YTiO4 particles in sample A showed a larger mean particle size (15 nm) than those (9 nm) in sample B, while their number density was nearly the same. Coarse Cr-O particles in sample A revealed a much higher number density than sample B. It is thus concluded that the size distribution and grain size of ODS steel can be controlled by a control of the excess oxygen concentration.

High Temperature Strengthening Mechanisms in the Alloy Platinum-5% Rhodium DPH

To improve the high temperature properties, platinum can be hardened by solid solution and/or oxide particles. The investigated alloy, dispersion hardened platinum-5% rhodium (Pt-5%Rh DPH), was produced via melting and subsequent annealing of the semi-finished product in order to obtain an oxide particle dispersion. Despite the relatively large oxide particles formed in this process, the creep strength is much higher in comparison to conventional Pt-5%Rh. The aim of this paper is to study the strengthening mechanisms in the alloy Pt-5%Rh DPH by transmission and scanning electron microscopy. The size distribution of oxide particles shows a bimodal distribution, and the average oxide particle diameter is 315 nm for particles larger than 150 nm. For particles between 25 nm and 150 nm the average diameter is 49 nm. The size ranges of oxide particles are not substantially affected by high temperature creep deformation, but particles of &lt;25 nm evolve during high temperature creep. It was found that all particles of different size ranges interact with dislocations and hence contribute to the strengthening of Pt-5%Rh DPH. Dislocation forests are pinned on the surface of oxide particles larger than 150 nm in diameter. Dislocation pile ups form between particles with a size range of about 500 nm. Medium size and small particles of diameters between 50 nm and 10 nm act as obstacles to single dislocations through backside pinning.

Oxide particle size distribution function in combustion of aluminum: Quasi-steady approximation

The size distribution function for oxide particles formed in combustion of aluminum is calculated in a quasi-steady approximation. It is demonstrated that the quasi-steady approximation may be employed for aluminum particles sized 15 to 300 μm. It is observed that the conditions of combustion (temperature, pressure, oxidizer content, and size of aluminum powder particles) have a weak effect on the parameters of distribution function. The results of calculations of the parameters of oxide particles formed as a result of combustion of aluminum powder are compared with the parameters of particles formed after explosion of an explosive containing aluminum powder.

Size distribution of oxides and toughness of steel weld metals

Experiments have been conducted to modify the size distribution of oxide particles in steel weld metals which have predominantly martensitic microstructures. It is found that the toughness improves significantly when the particles are refined, even when the total concentration of oxygen is unchanged in the process.

Alternative chemical-based synthesis routes and characterization of nano-scale particles

Different nano-scale particles have been synthesized by alternative routes: nitrates dehydratation and oxide, or co-formed oxides, reduction by hydrogen. Chemical-based synthesis routes are described and thermodynamics studies and kinetics data are presented to support the feasibility for obtaining single-phase oxides and co-formed two-phase oxides. In addition, the reduction reaction has been applied to successfully produce metal/ceramic nanocomposites. Structural characterization has been carried out by means of X-ray diffraction and, more extensively, transmission electron microscopy operating in conventional diffraction contrast mode (CTEM) and high-resolution mode (HRTEM). Nano-scale size distribution of oxide particles is well demonstrated together with their defect-free structure in the lower range, around 20 nm, size. Structural features related to the synthesized nano-composites are also presented.

Experimental Database Describing Pulse-Triggered Nonlinear Instability in Solid Rocket Motors

Pulse-triggered combustion instability constitutes a considerable problem in the design and operation of solid propellant rocket motors. Results from an experimental study involving 45 full-scale motor e rings are presented to provide guidance in motor design and a database for comparison with existing and future nonlinear theories. The repeatability of pulse-triggered instability along with the effect of variations in propellant formulation, operating pressure, grain cone guration, motor scale, and motor length were evaluated according to the parameters fraction of dc shift and wave strength. The stability rating of a cone guration based on these two different parameters was not always consistent; the fraction of dc shift was judged superior. It was shown that oxidizer particle size distribution and the presence of a stability additive affected pulse-triggered instability. In addition, it was shown that instability tended to increase with pressure, that cylindrical grains tended to be less stable than star grains, that shorter motors tended to be less stable than longer ones, and that smaller motors tended to be less stable than larger ones.

Sorbent Capture of Lead and Barium in a Bench-Scale Incinerator Combusting Simulated Waste Lubricating Oil

The burning of simulated waste lubricating oils containing lead or barium, and the fate of these metals in the presence of sorbents during combustion were investigated in a 13 kW horizontal combustor. An organometallic, lead (II) ethylhexanoate or barium naphthenate, mixed with heptane was burned with air yielding between 15 and 300 ppm. of the metal in the gases. Sorbent (kaolinite or hydrated lime) was introduced upstream of the reaction zone. Samples of lead or barium collected without sorbent injection showed the metals' particle size distributions in the submicron range. A computer code, MAEROS2, was adapted to predict lead oxide particle size distribution for similar combustor conditions and compared with experimental results of Linak er al. (1995). The sorbents were effective in scavenging lead. With kaolinite sorbent, lead concentrations were inversely proportional to particle diameter. Even with sorbent, the barium was found predominantly in the submicron size range suggesting little adsorption.

Experimental Studies on Al2O3 Inclusion Removal from Steel Melts Using Ceramic Filters.

Filtration tests were made on Al-deoxidized iron melts in a 50 kg vacuum induction melting and casting unit using commercial foam, multi-hole and loop filters. Samples from the solidified metal were prepared for chemical analysis and quantitative metallography. Al2O3 inclusions were produced by the addition of pure Al to the oxidized metal. Filtration efficiencies based on the content of chemically analysed total oxygen or oxide particle size distribution were evaluated. Filtration of pure iron melts using ceramic foam filters reaches efficiencies up to 90%. A minimum of total ixygen content around 20 to 30 ppm is attained independent from the initial oxygen content of the melt. The lowest levels are achieved when 25 ppi foam filters are applied. Filtration tests using 100 cpsi multi-hole filters for pure iron reveal filtration efficiencies of 80% and total removal of inclusions larger than 20 μm in diameter. Filtration efficiencies of 72 to 84% for pure iron were obtained using ceramic loop filters of different string diameters. From the evaluation of volume flow capacities and filter resistances it was evident that casting time is prolonged up to the threefold as compared to casting tests without integrated filters. Filtration of steel melts using ceramic foam, multi-hole or loop filters is an effective tool. High separation efficiencies are achieved, but filtration capacities of the porous filter media are limited in view of large steel volumes.

Propellant properties conducive to electrostatic discharge ignition

Abstract A mechanism for electrostatic discharge (ESD) ignition of composite rocket propellants was developed based on review of recent literature on spark-induced ignition of gaseous fuel/air mixtures, dispersions of liquid fuel droplets in air, and solid energetic materials. Ignition implies substantial amounts of available propellant are consumed subsequently. The role of mechanical properties in facilitating ignition by maintaining subsurface hot spot pressure developed by the discharge and products of reaction was identified. Other analysis demonstrated additional thermophysical, thermochemical, chemical kinetics, and electrical propellant properties important to ESD sensitivity. Properties which facilitate ignition (e.g., low activation energy for ignition delay) and high propellant burn rate (e.g., small median diameter of oxidizer particle size distribution) favor combustion of the energetic material after a discharge, as do those which inhibit heat losses (small propellant thermal diffusivity) an...

Plasticity of oxide dispersion strengthened ferritic alloys

Two 13%Cr oxide dispersion strengthened (ODS) ferritic alloys, DT and DY, exhibiting different oxide particle size distribution and a χ phase precipitation were studied. Their tensile properties have been tested from 20 to 700 o C. Experimental observations during room temperature tensile tests performed in a scanning electronic microscope have shown that the main damage mechanism consists in microcraking of the χ phase precipitates on grain boundaries. These alloys are high tensile and creep resistant between 500 and 700 o C. Their strongly stress-sensitive creep behaviour can be described by usual creep laws and incorporating a threshold stress below which the creep rate is negligible

Microstructural phase stability of Cu-base alloys under 300 keV Cu + ion irradiation

Stability of particles of a second phase in Cu-base alloys under irradiation with 300 keV Cu + ions has been investigated. The irradiation were carried out in the temperature range of 293 to 803 K at displacement rates of 2.3 × 10 −5 and 2.3 × 10 −2 dpa/s. The irradiation dose was between 0.01 and 30 dpa. Transmission electron microscopy was used to study the microstructure. In the present paper we report the results obtained on Cu-Cr-Zi-Si and Cu-A125 alloys. The precipitates of the hardening phase in the Cu-Cr-Zi-Si alloy are unstable under the irradiation. Their disappearance at room temperature is much more effective than at 803 K. Irradiation of the Cu-A125 caused significant changes in the oxide particle size distribution. Particles smaller than 10 nm in diameter dissolved rapidly, whereas the big ones fragmented into smaller particles.

Effect of temperature on the rheological behavior of hydroxyl terminated polybutadiene propellant slurry

AbstractHydroxyl terminated polybutadine (HTPB) based composite solid propellants have gained prominence in advanced missiles and launch vehicles including the Space Shuttle's Inertial Upper Stage (IUS) motor (1). To achieve a blow‐hole free well performing casting, the knowledge of the processability characteristics and rheological behavior of the propellant slurry are of vital interest. In our earlier communication (2) we had discussed the effect of compositional aspects, namely solid loading, oxidizer particle size distribution, and aluminum content on the rheology of HTPB propellant. For an optimized solid loading with corresponding oxidizer particle size distribution and aluminium content, the effect of temperature on the processability and the pot life are studied and reported in this paper. This study establishes the fact that the HTPB slurry shows a complex rheological behavior having thixotropy and yield stress. The thixotropic index and yield stress show minimum values at an optimum temperature. This optimum temperature shifts to lower values as time elapses. Activation energies have been calculated for the cure reaction based on yield stress and viscosity. It is observed that the activation energy values reach asymptotic levels after about three hours of curative addition.

Development and Production of Base Bleed Grain for 155 mm Rounds

The continued development and production of a base bleed grain described here is based on initial development performed by the Swedish National Defence Research Institute. The baseline composite propellant which has been used previously for base bleed grains for smaller caliber gun ammunition, was modified with the primary goal of meeting more rigid requirements for mechanical properties. Other goals included improving the aging properties, especially in exposure to humid air, and reducing health hazards in production. The means used besides conventional tailoring by optimizing curative ratio and oxidizer particle size distribution, were introducing a new bonding agent, a new antioxidant, and introducing fiber reinforcement of the propellant. Selected results from the development activities are presented. Special test methods and equipment for evaluating effects of specific influences on base bleed systems of high linear acceleration and rotation rate, are described. The RAUFOSS production process for base bleed grains for 155 mm rounds is briefly described.

Effect of oxidizer particle size distribution on efficiency of combustion catalysts

Effect of oxidizer particle size distribution on efficiency of combustion catalysts

The intenral oxidation of CuSi alloys

The internal oxidation of Cu-Si alloys has been investigated with particular attention to the kinetics of formation of the precipitated oxide. Experiments were performed on copper alloys containing 0.067 5, 0.15 1 and 0.27 0 wt.% Si at 928, 998 and 1073°K. Measurements included diffusion coefficients of oxygen in copper and number, size and size distribution of oxide particles for various penetration depths of the oxidation front. The results were analyzed on the basis of previously formulated mechanisms for internal oxidation and the Becker-Döring nucleation theory and, on this basis, estimates of supersaturation at the instant of nucleation and of the surface energy between the copper matrix and the precipitated SiO 2 phase were made.

A Model of Composite Propellant Combustion Including Surface Heterogeneity and Heat Generation

The surface heterogeneity of a composite propellant is incorporated in a model of the propellant combustion process. This process is pictured as the sum of fuel pyrolysis, oxidizer decomposition, heterogeneous chemical reaction between the fuel and decomposed oxidizer in small fissures surrounding individual oxidizer particles, and gas phase combustion of all final decomposition products. Expressions for the burning rate and the rate of heat generation at the propellant surface and in the gas phase flame are formulated, explicitly including the oxidizer particle size distribution. Expressions for the mean, one-dimensional, propellant surface and flame temperatures are derived assuming planar regions of heat generation. A collected set of implicit, algebraic equations is solved numerically for the propellant burning rate, surface (and flame) temperatures for a variety of physical parameters. The burning rate is found to depend strongly on the oxidizer particle ignition delay at low pressures, and upon the position of the external flame at high pressures. The effect of the heterogeneous reaction on the burning rate is strongest at intermediate pressures. The results agree quite well with experimental data on the effect of pressure and oxidizer particle size on composite propellant burning rates, surface temperatures, and surface structure.

Emittance of condensed oxides in solid propellant combustion products

The spectral radiance of hydrogen-oxygen-water-alumina and RP-1-oxygen-magnesia rocket flames was recorded and the magnitude of continuum emission measured. This measurement, with knowledge of the flame geometry and the oxide particle-size distribution, mass fraction, and concentration, was converted into a quantity of radiation from each particle and a spectral hemispherical emittance calculated. The near-infrared emittance of liquid alumina particles 1 to 10 microns in diameter varied from about 10 −2 to 10 −1 as the temperature increased from the melting point to 2900°K. The emittance of solid magnesia particles of a similar size range at 0.59 microns wavelength was found to average 0.4 over a range of temperatures. Mie theory calculations were made for both the magnesia and the alumina. Using best available low temperature optical properties of magnesia, the emissivity was calculated and found to be about 3 orders of amgnitude below the experimental measurements. Calculations were also made for solid-phase alumina particles based upon available temperature-dependent optical properties valid up to the melting point of alumina. These calculations showed that solid alumina particles of the same size as the experimental particles had an average nearinfrared spectral emittance varying from about 10 −5 to 10 −4 as the alumina temperature changed from 1800°K to the melting point, 2320°K. Thus, these experiments indicate that a discontinuous jump in emittance of alumina occurs as the phase changes from solid to liquid. In addition to description of the experiments and results, some possible physical effects associated with radiant emission from condensed phase particles are discussed.