Concentration Of Quenched-in Vacancies Research Articles

Effect of Solutioning Conditions on Aging Response in Ti–15V–3Cr–3Sn–3Al

An effect of the solutioning conditions on the aging response (precipitation, age hardening) in a β type titanium alloy, Ti–15V–3Cr–3Sn–3Al, is examined.The aging response is strongly affected by the solutioning conditions and closely related to the concentration of quenched-in vacancies, which is a function of the quenching temperature and the density of vacancy sinks such as β grain boundaries, dislocations, etc. For example, the ω (≤250°C) and the α (300∼350°C) precipitations and the age hardening are greatly accelerated in the specimens in which a large amount of quenched-in vacancies are contained, i.e. the specimens quenched from high temperatures and/or with a small density of vacancy sinks. Furthermore, the α phase precipitates very homogeneously inside the β grains at the aging temperatures between 300 and 500°C. However, the precipitation delays and the denuded zones are sometimes observed in the area in which vacancy sinks exist, e.g. in the vicinity of the β grain boundaries or the isolatedly formed twins, or in the area in which dislocations are introduced due to the weak plastic deformation.In the specimens quenched from lower temperatures in the β region and having a smaller β grain size or a slightly higher density of dislocations, the delay of the aging response is significant and the α phase precipitation is heterogeneous. These phenomena are considered to be caused by a stronger effect of small amount of excessive vacancies, which is due to the relatively high density of the vacancy sinks and the lower quenching temperature, rather than the effect of the β grain boundaries and dislocations as precipitation sites.

Effect of Quenched-in Vacancies on Aged Microstructures in Ti–15V–3Cr–3Sn–3Al

An effect of quenched-in vacancies on the microstructures during aging in a β titanium alloy, Ti-15V-3Cr-3Sn-3Al, is examined using two materials which are considered to have extremely different concentrations of excessive vacancies. In the material which is considered to have high concentration of quenched-in vacancies, the ω (≤250 o C) and the α (≥300 o C) phases precipitate relatively homogeneously in the β matrix regardless of dislocations in an early stage of aging, which indicates that the precipitation sites such as complex clusters of solute atoms and vacancies are formed in the β matrix in an early stage of aging. Meanwhile, in the material which is considered to have a small amount of excessive vacancies, the a phase nucleates on the vacancy sinks such as the β grain boundaries, dislocations, etc

Ti-15V-3Cr-3Sn-3Alの時効組織におよぼす焼入れ凍結空孔の影響

Effect of the quenched-in vacancies on the microstructures during aging in a β titanium alloy, Ti-15V-3Cr-3Sn-3Al, is examined using two materials which are considered to have extremely different concentration of excessive vacancies.In the material which is considered to have high concentration of quenched-in vacancies, ω (≤250°C) and α (≤300°C) phases precipitate relatively homogeneously in β matrix regardless of dislocations in the early stage of aging, which indicates that the precipitation sites such as complex clusters of solute atoms and vacancies are formed in β matrix in the early stage of aging. Meanwhile, in the material which is considered to have little amount of excessive vacancies, α phase nucleates on the vacancy sinks such as β grain boundaries, dislocations, etc.The material which is considered to have low concentration of quenched-in vacancies shows a single maximum peak of the age hardening around 400∼500°C. on the other hand, the material which is considered to have high concentration of quenched-in vacancies shows another peak around 300∼350°C in addition to the peak around 400∼500°C. The temperature range of these two peaks agrees to the temperatures at which two types of α morphologies are formed; one is the equiaxed aggregates morphology composed of small particles formed at 300∼350°C, and the other is the lenticular α morphology formed at (400∼500°C), in which some monolithic α plates are included.

Ti-15V-3Cr-3Sn-3Alの時効特性におよぼす溶体化処理条件の影響

An effect of the solutioning conditions on the aging response (precipitation, age hardening) in a β type titanium alloy, Ti-15V-3Cr-3Sn-3Al, is examined. The aging response is strongly affected by the solutioning conditions and closely related to the concentration of quenched-in vacancies, which is a function of the quenching temperature and the density of vacancy sinks such as β grain boundaries, dislocations, etc. For example, the ω (≤250 o C) and the α (300-350 o C) precipitations and the age hardening are greatly accelerated in the specimens in which a large amount of quenched-in vacancies are contained, i.e. the specimens quenched from high temperatures and/or with a small density of vacancy sinks

Point defects in NiAl near the equiatomic composition

Perturbed γ-γ angular correlation spectroscopy was applied to study the structure and properties of point defects near111In probes in quenched and annealed NiAl samples with five compositions in the range cNi=48–52%. Quadrupole interaction signals are analysed in terms of near-neighbor Ni-vacancy and nextnear-neighbor Ni antisite atom defects. Large mono- and divacancy concentrations were observed in all samples after quenching. For cNi 50%, large quenched-in vacancy concentrations annealed out near 500°C. For cNi=50%, most vacancies annealed out near 500°C, but about 35% of the111In probes retained a trapped monovacancy. This is attributed to a very low value of the formation enthalpy of a vacancy next to the In probe, estimated to be 0.16(2) eV. A lesser annelaing stage detected at 300°C is tentatively attributed to diffusion of Al-vacancies.

THE INFLUENCE OF MARTENSITE STABILISATION ON CHANGES IN DISLOCATION DENSITY IN Cu-Zn-Al ALLOY

From analysis of the amplitude dependence of internal friction for Cu-Zn-Al alloy exhibiting the shape memory effect, the changes taking place in the structure of the martensite during ageing at room temperature were determined. It was ascertained that during stabilisation of the martensite, both the density and mobility of dislocations increase due to the presence in the martensite of a substantial concentration of quenched-in vacancies.

A1-4 mass%Zn合金の2段時効と球状GPゾーンの析出

Effect of pre-aging at 243 K or 273K on subsequent aging at 263 K (two-step aging) in Al-4 mass%Zn alloy was studied by measurements of electrical resistance and small-angle X-ray scattering (SAXS) intensity.When pre-aging time (tApre) was relatively short (<600 s), the final value of the electrical resistivity (ρE) on the aging at 263 K was not affected by the pre-aging. As tApre became longer (>600 s), complicated behavior of ρE was observed according to the change of tApre at 243 K or 273 K.In the case of pre-aging at 273 K the SAXS integrated intensity (q0) of thick specimens after the aging at 263 K decreased gradually from the value of not pre-aged specimens (q0263) with increasing tApre. On the thick specimen pre-aged at 243 K, except when tApre was very long, q0 was, within experimental error, not affected by the pre-aging, regardless of the complicated change of ρE.Concerning thin specimen pre-aged at 243 K, in which annihilation of the vacancies at the surfaces could not be neglected, q0 after aging for long time at 263 K increased to q0263 of the thick specimens, exceeding q0 of the specimen aged at 263 K without pre-aging, as tApre was increased. For very long tApre q0 only reverted partially to a value larger than q0263.The SAXS results have been discussed in terms of reduction in concentration of quenched-in vacancies during the pre-aging and of volume fraction of GP zone.In spite that q0 that was attained on the pre-aging for not so long time at 243 K was fairly smaller than q0263, q0 reduced at the initial stages of subsequent aging at 263 K. It was considered that this reduction would suggest the dissolution of the small GP zones formed at 243 K, even though the solid solution was supersaturated.

A quantitative study of vacancy defects in quenched tungsten by combined field-ion microscopy and electrical resistometry

Abstract A study of quenched, high-purity tungsten has been carried out with a combination of field-ion microscopy (FIM) and electrical resistivity measurements. It is concluded that the quenched-in vacancy defects observed by FIM are monovacan-cies and nearest-neighbour divacancies. From the partitioning during quenching between these two species, a divacancy binding enthalpy H2V b≃0·7eV is deduced. A monovacancy resistivity of 7 × 10−4 Ω cm is obtained from the combined measurements. The quenched-in vacancy concentrations measured directly by FIM are consistent with previous results, if the total vacancy concentration at the melting temperature of tungsten (3695 K) is about 3 × 10−4 and the monovacancy formation enthalpy and entropy are 3·6 eV and 3·2k, respectively. The results are discussed in terms of the atomic-defect mechanisms for self-diffusion in tungsten.

Clustering Process of Vacancies in Quenched Aluminum

Faulted loops and voids in quenched high purity aluminum were observed with an electron microscope and it was investigated how the quenching rate and the aging temperature affect the formation of faulted loops and voids. The clustering process of vacancues durung the quenching and the aging is simulated by using a model which takes into account vacancy clusters containing up to sixteen vacancies for the formation of faulted loops. Comparing the simulated results with the experimental ones, it is confirmed that the density of faulted loops is determined by the concentration of quenched-in vacancies and does not depend on the clustering process during the quenching in the present experimental circumstances. It is conclucled that the cluster composed of around ten vacancies is the origin of faulted loops in the clustering process at room temperature, because the calculated density of them agrees well with the observed one.

Vacancy concentrations in quenched binary alloys

The effect of solute atoms on quenched-in vacancy concentrations has been studied theoretically using a simple model for vacancy annihilation during quenching. The model has been developed in generalized terms, making the results applicable to a wide variety of experimental conditions. For high quench rates, the quenched-in vacancy concentration is limited by the equilibrium concentration of vacancies at the quench temperature and solute effects are small. For low quench rates, the quenched-in vacancy concentration is determined by vacancy losses during quenching and solute effects can be enormous. Quantitative definition of high and low quench rates depends on vacancy properties, quench temperature, solute concentration and other parameters. The calculated results are in excellent accord with experimental results for pure Au and pure Pt.

Changes of structure and microhardness during the annealing of an aluminium-tin supersaturated solid solution

Abstract Structural and microhardness changes in an A1-0-26 at.-% Sn alloy quenched from the melt and annealed are presented. The experiments show that solid solution of 0-26 at.-% tin in aluminium, as seen in an electron microscope, can be obtained by means of rapid quenching from the liquid state. The kinetics and morphology of structure transformations are discussed in terms of vacancy-solute interactions in which clusters are formed through coagulation of Sn-vacancy couples. Growth of precipitates is explained by the ‘vacancy pumping’ model. The result of the clustering process is a structure containing spheroidal precipitates of β-tin, accommodated without strain in the aluminium matrix with definite crystallographic orientation relationships. The observed high transformation rate is attributed to the influence of an extra concentration of quenched-in vacancies which are assumed to be retained in the alloy bound to tin atoms as a consequence of their known high mutual binding energy.

Longitudinal magnetoresistance of platinum: The influence of lattice vacancies

The longitudinal magnetoresistance of polycrystalline platinum wires has been measured in magnetic fields up to 45 kOe at liquid helium temperatures. The deviations from Kohler's rule found depend on the concentration of quenched-in vacancies, and are interpreted as due to the contribution of single vacancies in platinum to the small angle scattering of electrons. The small-angle scattering may also be responsible for the linear magnetoresistance of platinum in high magnetic fields.

Short-Range Order and the Nucleation of Long-Range Order in Ni-Rich Nickel-Niobium Alloys

AbstractThe 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.

Stacking-Fault Precipitation of Niobium Nitride in Cr–Ni–Nb Austenitic Steels

Precipitation of niobium nitride, particularly in association with stacking faults, has been studied by electron microscopy of carbon extraction replicas prepared from iron-base austenitic alloys containing 18% chromium, 12% nickel, and various levels of niobium and nitrogen. This precipitation occurs during ageing in the range 700–800° C (975–1075 K) after solution-treatment at 1300° C (1575 K). Nucleation takes place primarily at dislocations that are present in the matrix after the solution-treatment. The growth rate of the precipitate and its morphology and distribution are dependent on the rate of quenching. The quenched-in vacancy concentration of the matrix is shown to be an important variable, but the supersaturation of solute atoms and the distribution of dislocations formed during quenching are also significant.

The Zener relaxation and vacancy-controlled atomic mobility in AgZn solid solutions—II The kinetics of vacancy annealing

AgZn alloys containing 24–33 at.% Zn have been down-quenched from temperatures of 200°C or below to aging temperatures of 90°C or above, to produce initial quenched-in vacancy concentrations in the range 5 × 10 −9 − 10 −11 mole fraction. The subsequent decay of the vacancy supersaturation has been determined from analysis of Zener relaxation data obtained by a delayed creep method. In high purity well-annealed specimens, the vacancy decay occurs inhomogeneously and with kinetics that correspond well to the simple migration of vacancies to fixed sinks. In such samples the mean vacancy lifetime is as large as 2 × 10 10 jumps. A small amount of plastic deformation or a less thorough preparatory anneal reduces the lifetime by 2 decades. Vacancy trapping effects due to oxygen and tin were looked for but not found. On the other hand, bismuth at a concentration of 10 −4 was discovered to modify the annealing behavior in a manner indicating strong vacancy trapping. The vacancy-trap binding energy is estimated to be 0.3 eV. It is thought that the traps may consist of bismuth pairs, rather than single bismuth atoms.

Influence of Plastic Deformation on the Clustering of Vacancies in Quenched Gold

Plastic deformtion of quenched gold is found to enhance the formation of stacking fault tetrahedra. The experimental results on the effect of deformation during the two step aging indicate that the enhanced nucleation of tetrahedra is not caused directly by the deformation, such as by the geometrical reaction between glide dislocations, but occurs during aging after deformation. The variation of the influence of deformation with the concentration of quenched-in vacancies denies other possibilities than the enhanced nucleation caused by the localized vacancies produced by jogs on moving dislocations. The mechanism for the appearance of tetrahedra in straight rows along is clarified. The influence of deformation on the formation of vacancy clustered defects is compared between quenched gold and aluminum.

Experimental Determination of Diffusion and Formation Energies of Thermal Vacancies in Germanium

Intrinsic germanium semiconductor specimens with various dislocation densities were quenched from high temperatures to introduce vacancies, after purification by the surface oxidation technique. The contamination due to copper atoms diffused into these specimens was below 1×10 13 atoms/c.c.. Annealing curves of exponential decay type were observed for specimens with dislocation densities ( n D ∼5×10 3 ∼10 5 ). The activation energy for diffusion and diffusion are found to be: 1.2∼1.3 eV and D V ( T )=2×exp (-1.2 eV/ k T )cm 2 /sec.. After annealing of quenched-in vacancies, copper atoms were introduced into the specimens by diffusion procedures. By the analysis of precipitating manner of supersaturated copper atoms thus introduced, the formation energy of a vacancy is found to be 1.9 eV. Considering the number of quenched-in vacancies obtained by the quenching experiments, the concentration of quenched-in vacancies is concluded to be: N V ( T )=1.85×10 23 exp (-1.9 eV/ k T )/c.c..

Al-Zn合金の低温時効におよぼすCr, Mn, Zrの影響

Experiments have been carried out to investigate the influence of addition of Cr (0.01∼0.2 at%), Mn (0.01∼0.3 at%) and Zr (0.01∼0.2 at%) to Al-2.5 at% (6.0 wt%) Zn alloy upon the pre-precipitation or clustering phenomenon.The results are as follows:(1) The rate of clustering of Zn atoms is reduced by the addition of Cr, Mn and Zr, but general features of pre-precipitation in these ternary alloys are not different from those in Al-2.5 at%Zn binary alloy since these third elements in the above-mentioned range do not interact with Zn atoms.(2) The decrement in the rate of clustering of Zn atoms increases in the order of Mn<Cr<Zr, particularly by the addition of Mn 0.2∼0.3 at%, Cr 0.1∼0.2 at% and Zr 0.03∼0.2 at% which is characterized by the existence of the second phases.(3) This effect can be more reasonably explained in terms of the increase in boundary area by grain refining and in dislocation density by remaining of dislocations introduced by plastic deformation which could act as sinks to cause the decrease in the concentration of quenched-in vacancies, rather than the binding energy between an atom of the third elements and a vacancy which is greater than that between a Zn atom and a vacancy.

LOW-TEMPERATURE NEUTRON IRRADIATION DAMAGE IN ALUMINUM AND GOLD

Fast-neutron irradiation damage at 1.74 °K and its recovery to 100 °K have been investigated in Al and Au by means of residual electrical resistivity measurements. The effects of impurities, quenched-in vacancies, and dislocations were studied. It was found that the damage rate of Al was unchanged by impurity concentrations of less than 0.5 at. % and quenched-in vacancy concentrations of less than 0.002 at. %. Dislocation concentrations of ~2 × 1010/cm2 in Al and ~1011/cm2 in Au increased their damage rates by 35%and 50% respectively. Small amounts of impurity (~0.02 at. %) in Au increased its damage rate by 15% and suppressed the enhancement caused by deformation. The stage I recovery of Al and Au was only slightly increased by extra dislocations, but was increased considerably by quenched-in vacancies. An impurity concentration of ~0.5 at. % suppressed the stage I recovery of Al, but not that of Au. The results are interpreted in terms of channeling in Al and collision chains in Au.

Quenched-in vacancies and quenching strains in gold

The contraction in length of quenched gold specimens was observed during annealing at room temperature and was interpreted in terms of vacancies. The concentration of quenched-in vacancies can be given by C = ΔV T V α = ( A α ) exp ( −E F kT Q ) , where ΔV T V is the total fractional-volume change deduced from the length measurement, α the fractional volume of a vacancy, E F the formation energy and T Q the temperature from which the quench was made. Experimentally, the values of A and E F vary with the specimen radius r as A = A 0 exp (− ar 2) and E F = E F 0 − br 2, where A 0 = 1.39 and E F 0 = 0.98 eV for the ideal case of r = 0 with the quenching rate infinitely large and no quenching strain. Using the experimental value of A 0 and the published data for the pre-exponential coefficient, A α , the volume of a vacancy, α, is derived to be 0.43 or 0.56, depending upon the resistivity increase per 1 at.% vacancies is taken as 1.4 or 1.8 μΩ cm, respectively. Ascribing the total contraction observed to the disappearance of excess vacancies, the concentration of vacancies caused by quenching strains was calculated; it was found to be quite large for thicker specimens. The energy for the motion of vacancies was also found to decrease with increasing specimen radius as E M = E M 0 − mr 2, where E M 0 = 0.83 eV. Variation of the vacancy half-life time for a given annealing temperature but with different quenching temperatures and specimen sizes was also observed.