Showing papers in "Metal Science Journal in 1971"
TL;DR: In this paper, structural ageing characteristics of aluminium alloys containing 2 and 4 wt.-% lithium are reported and thin-film electron microscopy was used to confirm the ordered L12-typestructure of the δ′ and to study the precipitate size and distribution over a range of ageing temperatures.
Abstract: The structural ageing characteristics of aluminium alloys containing 2 and 4 wt.-% lithium are reported. One transition phase (AI3Li, δ′) occurs in the alloy system and time-temperature-transformation curves have been determined for this phase and the equilibrium precipitate. Strengthening in these alloys is associated with δ′ precipitation, the peak hardness increment occurring in the 2% alloy after ageing for 24 h at 200°C (473K). Thin-film electron microscopy was used to confirm the ordered L12-typestructure of the δ′ and to study the precipitate size and distribution over a range of ageing temperatures. At low temperatures the δ′, which has a spherical morphology, is very fine (∼ 0.01 μm at 100°C, 373K) and resists coarsening. Above 200°C (473 K) coarsening is rapid and the process has been analysed using the Lifshits-Wagner theory. The δ′ interfacial energy was estimated to be ∼ 240 erg/cm2 (0.24 J/m2) and the lattice mismatch 0.18%. At and below 60°C (333K), ageing is accompanied by an incre...
222 citations
TL;DR: In this paper, the shape-memory effect has been studied in a titanium −35 wt.-% niobium alloy and the effect is observed under two different sets of conditions: when the fully martensitic alloy is deformed below Ms, it recovers its original shape when heated above As and if the alloy is artificially depressed by a fine dispersion of ω-phase precipitates, which prevents the martensite forming on cooling through the expected Ms, a strain-induced martensites is formed and on heating above As the deformation is recovered.
Abstract: The shape-memory effect has been studied in a titanium −35 wt.-% niobium alloy. The effect is observed under two different sets of conditions. First, when the fully martensitic alloy is deformed below Ms it recovers its original shape when heated above As Secondly, if the alloy is deformed between Ms and As (with Ms artificially depressed by a fine dispersion of ω-phase precipitates, which prevents the martensite forming on cooling through the expected Ms , a strain-induced martensite is formed and on heating above As the deformation is recovered. When the orthorhombic martensite forms from the cubic β phase, there is an expansion of the unit cell along two axes of the orthorhombic and a contraction along the third. The orientation relationship between the two phases predicts 12 possible variants and on stressing that variant will be formed which results in a relief of the stress, e.g. under a tensile stress those lattice planes with an increased spacing in the orthorhombic phase will tend to lie ...
166 citations
TL;DR: In this article, the diffusional growth of Widmanstatten α rods from ordered β-brass has been studied by means of deep-etching techniques and scanning electron microscopy.
Abstract: The diffusional growth of Widmanstatten α rods from ordered β-brass has been studied by means of deep-etching techniques and scanning electron microscopy. Slow-growing rods have large tip radii. The lengthening rates and tip radii of fast-growing rods are in good accord with a local-equilibrium model in which account is taken of non-ideal thermodynamic behaviour.
47 citations
TL;DR: In this paper, the effect of alumina particles on the creep behavior of powder-compacted copper and copper containing 0.5, 1.0 and 1.5 vol.-%alumina has been investigated in the range where the stressdirected lattice diffusion of vacancies is expected to control.
Abstract: The creep behaviour of powder-compacted copper and copper containing 0.5, 1.0 and 1.5 vol.-%alumina has been investigated in the range where the stress-directed lattice diffusion of vacancies is expected to control. Addition of alumina particles is shown to change the initial flow characteristics from Newtonian, where the creep rate έ is proportional to the applied stress σ, to Bingham type, where έ is proportional to an effective stress σέ. This effective stress is defined by σέ = σ − σ0, where σ0 is a threshold value that increases linearly with volume fraction of alumina and below which no deformation occurs. The proportionality constant between έ and σE is shown to be identical to that between έ and σ and is given by the Nabarro-Herring equation as BΩD/d2 kT, where B is a numerical constant, Ω the atomic volume, D the lattice self-diffusion coefficient, D the grain size, and kT has its usual meaning. Above the threshold stress, creep rate decreases with strain and this curvature is more pronou...
42 citations
TL;DR: In this article, the activation energies and volumes of deformation have been evaluated from the effects of changes in strain rate and temperature on the flow stress of single-crystal and polycrystalline NiAl.
Abstract: The activation energies and volumes of deformation have been evaluated from the effects of changes in strain rate and temperature on the flow stress of single-crystal and polycrystalline NiAl. The stress-dependence of these parameters, the appearance of slip-traces, and the agreement with a theoretical analysis are consistent with the rate-controlling mechanism at low temperatures being the nucleation of dislocation/kink pairs over a Peierls-Nabarro barrier. Deformation at high temperatures is complex and several mechanisms, including dislocation climb and cross-slip, appear to be important.
34 citations
TL;DR: In this article, a mixture of magnesium, tough pitch copper, and oxygen-free, high conductivity copper, in which cavities situated on grain boundaries had been introduced by creep, were subsequently annealed in an annealing process.
Abstract: Specimens of magnesium, tough-pitch copper, and oxygen-free, high conductivity copper, in which cavities situated on grain boundaries had been introduced by creep, were subsequently annealed in an ...
31 citations
TL;DR: In this article, a new and rapid computer method for the calculation of phase boundaries in multicomponent systems is described and its application is demonstrated by a determination of the liquid-state miscibility gaps in the ternary system Pb-Cd-Zn and the quaternary system pb-Szn-Sn.
Abstract: A new and rapid computer method for the calculation of phase boundaries in multicomponent systems is described and its application is demonstrated by a determination of the liquid-state miscibility gaps in the ternary system Pb-Cd-Zn and the quaternary system Pb-Cd-Zn-Sn. Provided that the necessary thermodynamic data have been determined or can be calculated, the method is of general application to systems of n components splitting into p (≤ n) phases.
28 citations
TL;DR: In this article, tensile and high-strain fatigue tests have been carried out at elevated temperatures on specimens of oxygen-free, high-conductivity copper and vacuum-cast copper.
Abstract: Tensile and high-strain fatigue tests have been carried out at elevated temperatures on specimens of oxygen-free, high-conductivity copper and vacuum-cast copper. Grain-boundary sliding and grain-boundary migration occur during testing to produce boundaries orientated preferentially at ∼ 45° to the stress axis. In oxygen-free, high-conductivity copper, cracking takes place at triple points as a result of stress concentrations induced by sliding. The cracks increase in length with further fatigue and eventually link together by ductile rupture to cause final failure. With vacuum-cast copper, triplepoint cracking is suppressed owing to the greater mobility of the grain boundaries and failure in tension and fatigue is due to rupture following plastic instability.
24 citations
TL;DR: The surface features and dislocation substructures present in copper single crystals subjected to slow cyclic plastic shear strains of ± 1% are reported and discussed in this article, where it is shown that at no time during the hardening stage are dislocations grouped into a uniform, three-dimensional cell structure; they are arranged in dislocation walls on the glide plane, the plane normal to the primary b and a plane at ∼ 45° to both these.
Abstract: The surface features and dislocation substructures present in copper single crystals subjected to slow cyclic plastic shear strains of ± 1% are reported and discussed. Thin-film electron microscopy has revealed that at no time during the hardening stage are dislocations grouped into a uniform, three-dimensional cell structure; they are arranged in dislocation walls on the glide plane, the plane normal to the primary b, and a plane at ∼ 45° to both these. After cycling at saturation the crystal breaks down into two regions, one exhibiting a misorientated, three-dimensional cell structure and the other showing an intensification of the regular structure generated during the hardening stage. No difference was observed between the dislocation structure at the specimen surface and that in the interior. From optical and scanning electron microscopy studies of the surface it is postulated that slip at saturation occurs preferentially in one of the two regions observed. The marked similarity between the r...
24 citations
TL;DR: A void model for hydrogen diffusion in steel is set up using the simplest assumptions, and the model is then extended to allow for the non-ideal behaviour of hydrogen up to pressures in the region of 1000 atm (l01.33 N/mm2).
Abstract: A void model for hydrogen diffusion in steel is set up using the simplest assumptions. The model is then extended to allow for the non-ideal behaviour of hydrogen up to pressures in the region of 1000 atm (l01.33 N/mm2). The main aim has been-to account for the distinct change in overall activation energy for diffusion with decreasing temperature observed in those cases where the diffusion coefficient is derived by evolution methods, as distinct from permeability data. From a comparison with published results the conclusion is reached that such a model can explain the observed behaviour in non-steady-state diffusion work over a broad temperature range, including the anomalous activation energy usually obtained below ∼ 200°C (473 K).
21 citations
TL;DR: In this paper, the texture measurements and metallographic studies have been made at various strains in material deformed with initial values of strain-rate sensitivity (m) = 0.2, 0.3, and 0.7.
Abstract: Texture measurements and metallographic studies have been made at various strains in material deformed with initial values of strain-rate sensitivity (m) = 0.2, 0.3, and 0.7. Texture becomes more random with increasing strain in both phases, independent of the value of m. Curved. grain boundaries and grain growth are produced by deformation and scratch-offset studies demonstrate that boundary sliding is occurring. The texture measurements are discussed in terms of the sliding process itself and possible associated accommodation mechanisms, both of which lead to grain rotation and a slow reduction in texture with increasing strain.
TL;DR: In this paper, a study of the transformation behavior in low-carbon iron-manganese alloys within the range 2-10% Mn has been made, showing that transformation in alloys containing between 4 and 10% Mn occurs martensitically and produces lath martensite but there was also an upper-bainite mode of transformation that took place in the 4-6% Mn alloy range after slow cooling.
Abstract: A study has been made of the transformation behaviour in low-carbon iron-manganese alloys within the range 2–10% Mn. Transformation in alloys containing between 4 and 10% Mn occurs martensitically and produces lath martensite but there was also an upper-bainite mode of transformation that took place in the 4–6% Mn alloy range after slow cooling.
TL;DR: In this article, the authors used an equation proposed by Margules (S.B. Akad. Wien Math. Naturwiss., Kl.II. Wiss. 1895, 104, 1243), based on a single set of constants.
Abstract: Heats of formation, determined by means of a high-temperature adiabatic calorimeter, are reported for solid Pd-Pt, Au-Pd, and Au-Pd-Pt alloys. The results for these three alloy systems may be described, within the experimental error, by an equation proposed by Margules (S.B. Akad. Wiss. Wien Math. Naturwiss., Kl.II. 1895, 104, 1243), based on a single set of constants. This approach has been adopted to evaluate iso-enthalpy contours for the whole ternary system. Excess partial entropies of palladium in Pd-Pt alloys are presented, calculated from the present heat data using activity data taken from the literature.
TL;DR: In this paper, the Smith-Barnby analysis of the stresses generated at particles along sliding boundaries has been used to confirm the prediction that the fracture-mode transition temperature is increased from ∼ 600 to 800°C.
Abstract: Austenitic stainless steels of base composition Fe-18 Cr-12 Ni have been tested in low-stress-amplitude fatigue in the range 600–8000 C (873–1073K) (0.5–0.62 Tm ). Metallographic evidence, including transmission electron microscopy, illustrates the extent of boundary sliding and subsequent intergranular crack formation that occurs in the solid-solution 18/12 alloy. Pinning the grain boundaries, by M23C6 carbide precipitates, in an 18/12/0.05 C alloy improves the high-temperature fatigue properties by inhibiting both grain-boundary sliding and migration, so that the fracture-mode transition temperature is increased from ∼ 600 to 800°C. Nucleation of the triple-point cracks formed at the carbide/matrix interface at 800°C may be explained by the Smith-Barnby analysis of the stresses generated at particles along sliding boundaries. This analysis gives a value of 820 erg/cm2 (mJ/m2) for the carbide/matrix fracture surface energy. The experimental observations thus confirm the prediction that the fract...
TL;DR: In this article, the effects of varying the stacking-fault energy (SFE) on the microstructure produced during creep for a series of a-brasses have been investigated.
Abstract: The effects of varying the stacking-fault energy (SFE) on the microstructure produced during creep for a series of a-brasses have been investigated. A dislocationcell structure was observed in all the alloys examined but its intensity of formation decreased with decrease in SFE. The dislocation density within the cells was low for the alloys of high SFE. All the microstructures were very inhomogeneous. Evidence for twinning and short-range ordering during creep was obtained. The minimum creep rate was found to satisfy the relationshipέs = Aγm(σ/E)n exp(−δH/RT)The parameter m was determined as 2.5; n was temperature-dependent, being ∼5 at 673 K and ∼3 at 873 K, and did not show a systematic variation with SFE.
TL;DR: In the absence of a critical concentration of quenched-in vacancies, short-range-order formation only has been detected during ageing below the critical temperature as mentioned in this paper, which can be explained by the formation of embryos of long-range order of the type Ni8Nb in alloys approaching the NisNb composition.
Abstract: The changes in the electrical resistivity of nickel-rich Ni-Nb alloys due to the formation of short-range order exhibit an anomalous dependence on the solute concentration. This anomaly can be explained by the formation of embryos of long-range order of the type Ni8Nb in alloys approaching the NisNb composition and near the critical temperature for long-range order. In the absence of a critical concentration of quenched-in vacancies, short-range-order formation only has been detected during ageing below the critical temperature.
TL;DR: In this article, the authors examined the creep and rupture strength of low-alloy ferritic steels and concluded that there is no evidence that maximum strength accrues from a fully upper bainite structure.
Abstract: The published data on the creep and rupture strength of low-alloy ferritic steels are critically examined and it is concluded that there is no evidence that maximum strength accrues from a fully upper bainite structure. The creep strength, over a range of stress, of samples of one cast of low-alloy Cr-Mo-V steel in various structural conditions has been examined. It is shown that there is no gain in strength (primary creep strain or secondary-creep rate) to be obtained by increasing the bainite content above ∼20% at 11 hbar and 575°C (848 K). At higher stresses, creep strength improves up to ∼60% bainite. The stress-dependence of creep is structure-sensitive and its variation indicates that at itresses <∼11 hbar material containing ∼20–30 % bainite will have a lower secondary-creep rate than fully bainitic structures.
TL;DR: A field-ion microscope study has been made of the early stages of coarsening of gold precipitates in solution-treated, quenched, and aged Fe-12 wt.-% Au, where the hardness of the alloy ranges from...
Abstract: A field-ion microscope study has been made of the early stages of coarsening of gold precipitates in solution-treated, quenched, and aged Fe-12 wt.-% Au, where the hardness of the alloy ranges from...
TL;DR: In this article, a study of the initial stages of spinodal decomposition in a Cu-Ni-Fe alloy of composition close to the center of the miscibility gap is presented.
Abstract: A study has been made of the initial stages of spinodal decomposition in a Cu-Ni-Fe alloy of composition close to the centre of the miscibility gap. During ageing the average wavelength can be accurately determined from a measurement of the sideband spacing along 〈100〉 on the diffraction pattern. The results obtained show that in this alloy decomposition occurs very quickly (e.g. in <10 s ageing at 600°C (873 K)) and the average wavelength follows a coarsening law (∞ t1/3) from the earliest time studied. The initial wavelengths found by extrapolation to zero time are of the order of 35–55 A and vary with degree of undercooling below the spinodal in the manner predicted by theory.
TL;DR: The fatigue and tensile properties of coarse-grained a-titanium containing 0.085 wt.- % oxygen have been determined over the temperature range −196°C (77 K) to 800°C(1073 K) as mentioned in this paper.
Abstract: The fatigue and tensile properties of coarse-grained a-titanium containing 0.085 wt.- % oxygen have been determined over the temperature range −196°C (77 K) to 800°C (1073 K). Metallographic examination of fatigue specimens has shown the following characteristics. In the range −196 to 150°C (77–423 K) fatigue damage was associated with internal {ll2l}-type twins and these acted as preferential crack-propagation paths. In the range 200–500°C (473–773 K) twin formation was not observed and surface-nucleated fatigue cracks propagated transgranularly. Above 600°C (873 K) a transition to inter granular surface-nucleated cracking took place, while above 700°C (973 K) grain-boundary cavitation and crack growth were noted. At ∼ 300°C (573 K) a peak in the fatigue response of α-titanium occurred. This temperature corresponded to that at which dynamic strain-ageing was observed and at which twin/interface and grain-boundary cracking were absent.
TL;DR: In this paper, an analytical treatment of the precipitation kinetics of inert-gas bubbles in solids is presented, with emphasis upon the behaviour of the variance of the distribution of bubble radii.
Abstract: An analytical treatment is presented of the precipitation kinetics of inert-gas bubbles in solids, with emphasis upon the behaviour of the variance of the distribution of bubble radii. Using a modified van der Waals equation of state, it is shown that the variance decreases as precipitation proceeds, its square root varying approximately linearly with the reciprocal of the mean bubble radius. Results of the analysis are in good accord with published data describing the growth of small bubbles in UO2.
TL;DR: In this paper, electrical-resistance measurements of the alpha (α) → sigma (σ) phase transformation in body-centred cubic iron-vanadium alloys containing tantalum, tungsten, manganese, rhenium, and zirconium suggest that the degree of long-range order present in a phase before the transformation is a controlling factor in the reaction kinetics.
Abstract: Electrical-resistance measurements of the alpha (α) → sigma (σ) phase transformation in body-centred cubic iron-vanadium alloys containing tantalum, tungsten, manganese, rhenium, and zirconium suggest that the degree of long-range order present in the a phase before the transformation is a controlling factor in the reaction kinetics. The influence of ternary alloying elements on the transformation is probably dependent on the manner in which they affect the longrange order. Twinning has been observed in the bcc iron-vanadium phase which shows long-range order.
TL;DR: In this article, an ultrasonic method was used to identify crack initiation in polycrystal1ine 1100 and high-purity single-crystal aluminium samples were anodized to give oxide thicknesses between 200 and 1500 A, then subjected to low-cycle fatigue in highhumidity and vacuum environments.
Abstract: Polycrystal1ine 1100 and high-purity single-crystal aluminium samples were anodized to give oxide thicknesses between 200 and 1500 A, then subjected to low-cycle fatigue in high-humidity and vacuum environments. An ultrasonic method was used to identify crack initiation. Fatigue in a vacuum produces oxide cracks that are wider and fewer in number and results in an increase in fatigue life. Although the mode of fracture of both oxide and matrix is strongly dependent upon oxide thickness, it was found that neither the cycles to crack initiation nor the total fatigue lives were dependent upon oxide thickness.
TL;DR: In this article, the anomalous resistivity increase in Ni-Ni-Cr solid solutions was investigated and the temperature coefficient decreased with rise in Ni content. But the effect of Ni content on the resistivity of Ni-Cr alloys was not investigated.
Abstract: The resistivity of Fe-Ni-Cr solid solutions increases and the temperature coefficient decreases with rise in nickel content. This explains the peculiarity observed in γ′-forming stainless steels of a resistance increase on ageing that is greater when measured at the ageing temperature than at a low temperature. A range of steels with varying Ni content and Ti/Al ratio has been examined and the anomalous resistivity increase calculated. This is shown to be independent of temperature within the accuracy of the experiments and to decrease slowly with increase in γ′ size, but some effect remains at particle sizes of 25–30 nm dia. Cold work lowers the resistivity of Fe-Ni-Cr alloys with high Ni content and a rapid increase occurs on annealing at 500°C (773 K). A similar effect is observed in the high-nickel γ′ - forming alloys and is thought to be due to short-range order in the matrix.
TL;DR: In this article, the influence of atmospheres of differing oxidizing potential (up to 1 × 10−3 atm (101 N/m2) pressure of oxygen) on the tensile creep of high-purity iron has been studied in the range 1050-1100°C (1323-1373 K).
Abstract: The influence of atmospheres of differing oxidizing potential (up to 1 × 10−3 atm (101 N/m2) pressure of oxygen) on the tensile creep of high-purity iron has been studied in the range 1050–1100°C (1323–1373 K). The creep rate at 1096°C (1369 K) increased and the time to failure decreased with increasing oxygen pressure in continuously oxidizing conditions. Preoxidation at 1081° C (1354 K), before creep testing in non-oxidizing conditions, increased the extent of substrate cavitation, which promoted a higher creep rate and reduced time to failure. A greater number of metal surface cracks occurred in oxidizing atmospheres compared with inert conditions. Crack growth and crack linking took place between grain-boundary oxides and substrate cavities.
TL;DR: In this paper, an approximate analysis of the state of plastic deformation in a ductile matrix containing second-phase particles, before and at the point of incipient internal necking between the particles, is used to estimate the matrix/particle bond strength necessary to prevent decohesion.
Abstract: An approximate analysis of the state of plastic deformation in a ductile matrix containing second-phase particles, before and at the point of incipient internal necking between the particles, is used to estimate the matrix/particle bond strength necessary to prevent decohesion. The analysis is carried out for the cases where no decohesion has occurred and where decohesion has taken place at the ends of the particles but not at the sides. The results suggest that if internal necking between strong second-phase particles is to be prevented or delayed, the matrix/particle bond strength must exceed a quantity which is a function of both the current matrix yield stress and the transverse stress component acting in the matrix.
TL;DR: In this paper, an Al-Cu-Mg alloy has been fatigued in various environments at high (20 kHz) and low (96 Hz) frequency and a frequency effect was observed and discussed in relation to the influence of environment and the inhibition of the nucleation and early crack-growth mechanisms at high frequency.
Abstract: An Al-Cu-Mg alloy has been fatigued in various environments at high (20 kHz) and low (96 Hz) frequency. A frequency effect was observed and is discussed in relation to the influence of environment and the inhibition of the nucleation and early crack-growth mechanisms at high frequency. Metallographic and fracto graphic examination of the high- and low- frequency specimens revealed similar fatigue features, except that at high frequency the ripple spacing tended to be smaller, persistent slip-bands were more localized and, in certain environments, multiple cracking occurred.
TL;DR: In this article, tensile tests have been carried out on four low-alloy ferritic steels at temperatures up to 700°C (973 K) and showed large elongations, large reductions in area, and transgranular fractures over the whole temperature range.
Abstract: Tensile tests have been carried out on four low-alloy ferritic steels at temperatures up to 700°C (973 K). The elongations of three high-purity steels increased rapidly at temperatures above 500°C (773 K), whereas the reductions in area decreased sharply in the same temperature range. This was dependent on the change of fracture mode from transgranular to intergranular. Comparative tests on a commercial material showed large elongations, large reductions in area, and transgranular fractures over the whole temperature range. These property differences have been related to the various carbides present in the structures. Metallographic evidence confirmed that large elongation values imply good crack-nucleation-resistance and that low values of reduction in area imply poor crack-propagation-resistance.
TL;DR: In this paper, a fracture mechanism based on the cracking of brittle silicate inclusions and the existence of groups of grains with the same orientation is proposed to estimate the yield-stress anisotropy of both materials.
Abstract: A study of the low-temperature mechanical properties of two 3¼% silicon iron sheets with different crystallographic textures but alike in all other respects has been carried out. It has been shown that the yield-stress anisotropy of both materials may be quantitatively estimated by a calculation of polycrystalline orientation factors, taking into account simultaneous slip on five independent slip systems. The anisotropy of the cleavage-fracture stresses has been related to the cleavage-plane distributions in the samples. A fracture mechanism taking into account this anisotropy and based on the cracking of brittle silicate inclusions and the existence of groups of grains with the same orientation is proposed.
TL;DR: In this article, the miscibility gap in the Cr-Mo system is calculated using the free energies derived from calorimetric and vapour-pressure data, and the liquidus and solidus curves for the Mg-Cd system were calculated in a similar way.
Abstract: Some numerical problems associated with the calculation of phase diagrams from thermochemical data are discussed. Two simple cases are considered. The miscibility gap in the Cr-Mo system is calculated using the free energies derived from calorimetric and vapour-pressure data. The liquidus and solidus curves for the Mg-Cd system were calculated in a similar way. These did not agree very well with the directly determined curves and a method is described for refining the estimated solidus curve using the measured liquidus curve. For both systems it is shown that unless care is taken in representing the thermochemical data spurious features appear in the phase diagram.