Effect Of Second Phase Particles Research Articles

Cold worked Cu-Fe-Cr alloys

The aim of this project was to investigate the properties of copper rich Cu-Fe-Cr alloys for the purpose of developing a new cost effective, high-strength, high-conductivity copper alloy. This paper reports on the influence of cold work. The age hardening response of the Cu-0.7%Cr-2.0%Fe alloy was minimal, but the resistance to softening was superior to that reported for any commercial high-strength, high-conductivity (HSHC) copper alloy with comparable mechanical and electrical properties. For example, an excess of 85% of the original hardness of the 40% cold worked alloy is retained after holding at 700°C for 1 hour, whereas commercial HSHC Cu-Fe-P alloys have been reported to soften significantly after 1 hours exposure at less than 500°C. The Cu-0.7Cr-2.0Fe alloy would therefore be expected to be more suitable for applications with a significant risk of exposure to elevated temperatures. Optical microscope examination of cold worked and aged microstructures confirmed the high resistance to recrystallization for Cu-0.7%Cr-2.0%Fe. The Zener-Smith drag term, predicting the pinning effect of second phase particles on dislocations in cold worked microstructures, was calculated using the precipitate characteristics obtained from TEM, WDS and resistivity measurements. The pinning effect of the precipitate dispersions in the peak-aged condition was determined to be essentially equivalent for the Cu-0.7%Cr-0.3%Fe and Cu-0.7%Cr-2.0%Fe alloys. A lower recrystallisation temperature in the Cu-0.7%Cr-0.3%Fe alloy was therefore attributed to faster coarsening kinetics of the secondary precipitates resulting from a higher Cr concentration in the precipitates at lower iron content.

Refinement and Stability of Grain Structure

The various methods of producing fine-grained alloys are discussed and it is concluded that thermomechanical processing routes are most suitable for the economic production of the large quantities of material required for structural applications. The limits of grain refinement by conventional discontinuous recrystallization are considered, and the production of micron-grained alloys by continuous recrystallization processes during or after large strain deformation is discussed. The stability of highly deformed microstructures against recrystallization is analysed, and the effect of second-phase particles on grain growth is discussed. It is shown that perturbations of the Zener drag during high temperature deformation may lead to dynamic grain growth in two-phase alloys.

Monte Carlo simulation of Zener pinning in two dimensions

The effect of second-phase particles on grain growth was simulated in two dimensions with the help of a Monte Carlo method. A wide range of particle surface fractions was considered, from 10−4 to 10−1. Particle unpinning from grain boundaries was only observed for small volume fractions (f≤2×10−2). The average size of the grains in the pinned microstructure was investigated as a function of f and the fraction φ of particles interacting with the grain boundaries. The normalised stagnant grain size was found to scale with (φf)−1/2. These results are discussed in terms of the available non-random approaches of grain boundary pinning by particles.

A unified theory of recovery, recrystallization and grain growth, based on the stability and growth of cellular microstructures—II. The effect of second-phase particles

A simple theory which analyses discontinuous and continuous recovery, recrystallization and grain growth, and which enables the relationships between the various annealing phenomena to be explored, has been extended to include the effects of a dispersion of second-phase particles. Application to grain growth results in predictions which are consistent with those of more complex theories, and the model is also used to analyse the effect of a dispersion of second-phase particles on recrystallization occurring by either strain induced boundary migration or by particle-stimulated nucleation. An analysis of subgrain growth shows that this may occur discontinuously under conditions in which recrystallization is not possible, thereby suggesting the possibility of a thermomechanical processing route in which complete softening may occur without recrystallization.

Computer simulation of grain growth with second phase particle pinning

The pinning effect of second phase particles on grain growth was simulated by 2-D Monte Carlo simulations. A new variable, the degree of contact between grain boundaries and second phase particles, was introduced to predict the grain size limit in the presence of second phase particles. The modified Zener pinning model containing this new variable can be expressed as: D r = K Rf , where D is the pinned grain size, r is the mean size of second phase particles, K is a constant, f is the area fraction (or the volume fraction in 3-D) of second phase, and R is the degree of contact between grain boundaries and second phase particles. In 2-D Monte Carlo simulations of grain growth the ratio of pinned grain size to second phase particle size was found to be proportional to f −0.5, but also to ( Rf) −1. The degree of contact increased during grain growth and reached a stable value when the grain structure was pinned. The initial location of second phase particles did not have a significant contribution to the pinning of grain boundaries.

Effect of second phase particles on hydrogen embrittlement of iron alloys

The effect of hydrogen on the plasticity and fracture mode of pure iron and iron containing iron oxides, aluminum oxide and cementite particles has been studied. Cathodic hydrogen charging causes the embrittlement of Fe, FeAl 2O 3 and FeC alloys and little or no degradation effect on FeFeO and FeFeOAl 2O 3 materials, despite the high strength of those alloys and high amount of absorbed hydrogen. High hydrogen resistivity of alloys containing iron oxides accounts for the weak iron oxide/iron matrix cohesion established by the internal friction measurements. The effect of hydrogen softening and hydrogen enhanced local plasticity in the resistance of studied alloys to the hydrogen action has been discussed.

The Effects of Second Phase Particles, Dislocation Density and Grain Boundaries on the Electrical Conductivity of Aluminium Alloys

The Effects of Second Phase Particles, Dislocation Density and Grain Boundaries on the Electrical Conductivity of Aluminium Alloys

On Recrystallization in Metal Matrix Composites

The plane strain deformation of model continuous fibre composites such as Cu-W provides a vehicle for the study of the macroscopic effects of second phase particles on the strain distribution in the matrix and its possible effects on subsequent recrystallization behaviour. By using metallographic studies based both on optical gridding methods and low temperature recrystallization, the pattern of flow enforced by the fibres can be quantified and related to the spatial distribution of recrystallization events.

Effect of Second Phase Particles on the Recrystallization Kinetics of a Cu-Cr-Zr Alloy

Effect of Second Phase Particles on the Recrystallization Kinetics of a Cu-Cr-Zr Alloy

Some considerations on the toughness properties of ferritic stainless steels—A brief review

The present paper has attempted to briefly review the factors that influence the toughness properties of ferritic stainless steels. The structure and constitution of ferritic stainless steels were discussed together with the effects of second phase particles on the toughness aspects. Generally the presence of second phases such as carbides, nitrides and oxides, as well as the chromium-rich ferrite, precipitates and sigma-phase, σ, can cause a significant decrease in the toughness of ferritic stainless steels. The influence of structural parameter or microstructural grain size on the toughness considerations, although well documented, are not always clearly understood. This is the result of other varying factors which can obscure the true effects of grain size. Thermomechanical processes, such as cold working, hot working and controlled rolling, can significantly influence toughness properties as a direct result of their effects on grain size and the precipitation of carbides, nitrides and sigma-phase. Finally, the detrimental effects of interstitial elements on the toughness of ferritic stainless steels can be controlled by the addition of stabilising elements, e.g. titanium and niobium.

Study on the foaming of CaO-SiO2-FeO slags: Part II. Dimensional analysis and foaming in iron and steelmaking processes

An empirical equation for the foaming index Σ of a CaO-SiO2-FeO slag was obtained by dimensional analysis. The effect of second-phase particles on slag foaming was well described by calculating the viscosity of the mixture using the modified Einstein equation. The anticipated foaming in basic oxygen furnace (BOF), electric arc furnace (EAF), and bath-smelting processes was estimated using the parameter Σ for various operating conditions and slag compositions. For BOF operations, it is predicted that foaming is most extreme in the middle of the blow, and a stable foam in EAF is achieved with less basic slags with low FeO contents. For bath smelting, foam heights of 5 m are possible, and a higher degree of prereduction prior to smelting will reduce foaming (because of smaller gas evolution) and possibly increase production rates. Running the process at a higher pressure will also reduce foam heights, because the volume of gas generated is less.

Effects of second-phase particles on coarsening of austenite in 0.15 Pct carbon steels

The effects of second-phase particles formed by the addition of vanadium, nitrogen, and aluminum on the austenite grain coarsening behavior of 0.15 pct carbon steels were studied. The oxidation and etching technique has been adopted to reveal the prior austenite grain boundaries. The specimens were austenitized at intervals of 50°C within the range of 900°C to 1150°C under high vacuum (<10−4 torr) for half an hour, toward the end of which they were oxidized for about one minute by introducing oxygen at about 250 mm Hg to reveal the grain boundaries, and then quenched into iced water. The variation of prior austenite grain size with temperature in these steels indicates that vanadium carbonitride, V(C, N), is much more effective in austenite grain refinement than vanadium carbide, VC, at all temperatures. The effect of vanadium carbonitride in austenite grain refinement is more or less the same as that of aluminum nitride. AlN, at temepratures below 1000°C, but this effect of vanadium carbonitride in austenite grain refinement decreases with increasing temperature. Above 1000°C, aluminum nitride is a much better grain refiner than vanadium carbonitride. The presence of the V (C, N) and AlN particles in the same steel causes moderate grain growth of austenite.

Evaluation of grain growth criteria in particle-containing materials

The present work consists of a critical evaluation of the theoretical approaches describing the grain growth inhibiting effect of second phase particles in a material. The combination of the most realistic relations giving the driving force for grain growth and the pinning force of the particles, results in a satisfactory estimation of the limiting grain size, as a function of the structure parameters (homogeneity, particle size and volume fraction). Some special particle configurations require a refinement of the general model, e.g. in the case of a specific particle shape or when the precipitates are not homogeneously sized or dispersed. The validity of the general and adjusted grain growth criterion is shown in β-Cu-based shape memory alloys with a particle forming addition.

Auger Electron Analysis of Oxides Grown on a Dilute Zirconium/Nickel Alloy

ABSTRACTAuger electron analysis of oxides grown at 573 K in dried oxygen on the matrix and on precipitates in a 0.5 wt% Ni in zirconium alloy, is part of a larger program to study the effect of second phase particles on the oxidation and hydriding behaviour of Zircaloy-2. The alloy consisted of a zirconium matrix containing randomly distributed Zr2Ni precipitates of up to 10 μM in diameter. Oxidation simultaneously proceeded about the whole periphery of the precipitate and after approximately 50 days exposure was completely oxidized and of nearly uniform composition. The chemical structure of the oxides grown on the matrix and on the free and internal surfaces of the precipitate were determined as a function of depth in the oxide film.

Internal friction caused by sliding on grain boundaries with second phase particles—Cu-Fe and Cu-SiO 2

Following a theoretical study on the retardation effect of second phase particles on grain boundary sliding [ Acta metall. 31, 275 (1983) we have conducted internal friction experiments in Cu-Fe and Cu-SiO 2. The relaxation peaks produced by the grain boundary sliding are reduced by the α-Fe or SiO 2 particles on the boundary, when the usual polycrystalline specimens are tested. The relaxation time is also shortened. The dependence of the relaxation time and strength on the grain size and the particle size and spacing compares satisfactorily with that predicted by the theory. Internal friction peaks of relaxation character, originating from the particle-blocked boundary sliding, exist when the bamboo structured specimens have the particles on the boundary. The relaxation parameters of the internal friction for the bamboo structured specimens are also accounted for by the theory.

Grain coarsening in FeNiCr alloys and the influence of second phase particles

The effects of second phase particles, e.g. M 23C 6, MC and M(C, N) carbides on the grain growth phenomenon of FeNiCr alloys have been determined. Various theoretical models on grain coarsening have been compared. The grain size at all stages of grain coarsening was dependent on the undissolved carbide particle size ( r), the volume fraction ( f), and the nature of the carbides. The nature of M 23C 6 carbides varied, since Fe, Ni and Mo entered the M 23C 6 unit cell; and complex carbides such as (Cr 15Fe 4Ni 2Mo 2)C 6 were formed. Gladman's equation was verified for predicting the observed grain size values to a significant degree, and other models were less successful.

フェライト鉄の低温引張性質におよぼす第2相粒子の影響

フェライト鉄の低温引張性質におよぼす第2相粒子の影響

Grain-Size Control in Steels

An account has been given of the methods of grain-size control in steels. The importance of particle pinning in inhibiting grain coarsening has been described and some consideration given to the solubities and coarsening characteristics of the particles themselves. Grain-size control by hot working has also been considered, where the recrystallization characteristics of the austenite are important in connection. with the grain size of the ferrite-transformation product. The effects of second-phase particles on the recrystallization of cold-worked carbon steels have also been considered. The importance of the integrated nucleation rate on the final grain size has been demonstrated, independent of whether the ferrite grains are formed by transformation or by recrystallization.The mechanism of secondary recrystallization has been described, and it is suggested that this process can be caused by the presence of critically dispersed second-phase particles.

Some observations of grain boundary sliding in the presence of second phase particles

Some effects of second phase particles on grain boundary sliding have been observed in shear tests of bicrystal specimens. The majority of the test specimens were produced from an Al-0.05 % Fe alloy which yielded specimens containing second phase particles at the grain boundary only. Some specimens of pure Al and Al-4 % Cu were tested for comparison purposes. Sliding was observed to take place sharply at the grain boundary particles in the absence of grain boundary migration, but the ratio of sliding to crystal shear deformation was markedly reduced by the presence of grain boundary particles. Some evidence indicating a yield stress for the onset of sliding was obtained and the magnitude of this stress was related qualitatively to the density of grain boundary particle coverage. The mechanism through which the particles exerted their influence on sliding is also discussed.

Cleavage fracture in mild steel

Brittle fracture of steel structures has been a matter of considerable concern to both engineers and metallurgists for many years, it now being generally recognized that the cleavage mode of failure occupies a central position with respect to the problem. The paper reviews experimental evidence pertaining to the cleavage process in mild steel, particular attention being given to very recent work on the effect of second phase particles. A physical model of the process is thereby constructed, and in so doing, previous theories are critically examined and extended or modified where appropriate.