F. Maury

A study of irradiated FeCr alloys: deviations from Matthiessen's rule and interstitial migration

FeCr alloys with concentrations ranging from 50 p.p.m. to 3% Cr have been irradiated with electrons of 1.6 MeV at low temperature (30 K) and studied by resistivity measurements. Pre-irradiation measurements show important deviations from Matthiessens rule in the annealed alloys: the resistivity increment per unit concentration of Cr in Fe depends strongly on the solute concentration. It increases from 180 mu Omega cm for a few per cent of chromium up to 400 or 600 mu Omega cm when the chromium concentration is lowered down to 50 p.p.m. This increase is explainable in the two-current model if one considers the dilute alloys with the residual impurities as ternary alloys. The radiation-induced resistivity, measured as 4 K, is also found to depend strongly on the Cr concentration. This can only be explained by assuming that the Frenkel pair specific resistivity, rho F, is an increasing function of the Cr concentration. This variation of rho F in the alloys can be interpreted, in the two-current model, as a deviation from Matthiessens rule in the irradiated alloys considered as ternary alloys. Mixed Fe-Cr interstitials seem to be slightly more mobile than self-interstitials.

Production and mutual annihilation of frenkel pairs in low temperature irradiated zirconium

Abstract 12.5 μ thick zirconium foils were irradiated by monoenergetic electrons in the range 0.5–1.7 MeV at liquid helium temperature. To the measured defect production rate, a theoretical curve was fitted, assuming an atomic displacement probability function P d, (T) and estimating the multiple displacement contribution. The best fit was obtained with: Isochronal and isothermal annealing studies were performed in the recovery stage I (up to 150 °K) and compared with results obtained earlier by Neely. An effect of radiation doping on the behaviour of the different substages has been observed. and a Frenkel pair resistivity of 4 × 10−3 ω cm. The implications of such a multiple displacement function are considered.

Anisotropy of the displacement energy in single crystals of molybdenum

Abstract A “geometrical” model for the threshold cnergy surfaceof a b.c.c. lattice is applied to analyse recent measurements of the resistivity change rates in electron-irradiated monocrystalline molybdenum specimens with the orientations [100], [11O], [111] and [112]. Cross sections computed with this surface were matched to the experimental data using various sets of threshold energies as parameters. The best fit was obtained with Td [100] = (35+2 −2) eV, Td [1101 > 2Td [100], Td [111] = (45 f 3) eV. When corn ared to the experimental damage rates the absolute values for the cross sections yield a Frenkel pair resistivity pio = (13 f 2) pfl cm/at.% F.P. Expressions for the energy necessary to penetrate the potential barriers in the principal crystallographic directions are derived and compared to the id[iik] obtained before, with the interatomic potential as parameter. Taking into account the length of the [111] collision chains and the size of the spontaneous recombination volume, the appropriate poten...

Interstitial migration in irradiated iron and iron-based dilute alloys. II. Interstitial migration and solute transport in FeNi, FeMn and FeCu dilute alloys

For pt.I see ibid., vol.2 no.47, p.9269-90, 1990. Three series of dilute iron alloys, FeNi, FeMn and FeCu, with concentrations ranging from 50 at.ppm to 3 at.%, have been electron-irradiated at low temperature and annealed up to room temperature. The recovery spectra of the radiation-induced resistivity show that mixed-interstitial migration takes place, in the FeNi alloys, at the beginning of stage II (130-150 K, depending on the Ni concentration), thus providing evidence of the formation of stable mixed-interstitial Fe-Ni during self-interstitial migration in stage I. Mixed interstitials are deduced to be formed also in FeMn and FeCu alloys although they are not stable above stage I and are not directly observable. Mixed poly-interstitials migrate below stage III (i.e. below 200 K) in the three alloys studied. Such a migration instead of break-up results in the growth of larger mixed-interstitial clusters and leads to solute clustering and correlated solute bulk depletion. Bulk depletion was indeed observable in the FeCu and, to a lesser extent, in the FeNi dilute alloys through a diminution of the residual resistivity of the samples. In the FeMn concentrated alloys (1 and 3%), the mixed poly-interstitial clustering gives rise in stage II to gamma -precipitation which largely survives the vacancy migration.

Interstitial migration in dilute FeSi and FeAu alloys

Dilute FeSi and FeAu alloys containing 50-400 at. PPM of solute have been electron-irradiated together with pure Fe, first at low temperatures ( approximately 30K) where the induced Frenkel defects are frozen, and then at higher temperatures ( approximately 150K) where the Fe self interstitials migrate freely. The recovery spectra of the radiation-induced resistivity show that both Si and Au impurities do trap migrating Fe interstitials. A rough estimate of the corresponding trapping radii is given. In the case of silicon (a slightly undersized impurity in iron), a mixed interstitial is formed which becomes mobile around 175K before dissociating. In the case of gold (an oversized impurity), detrapping takes place at 160 K, not very far above the self-interstitial free migration. The possible mechanisms for interstitial migration in iron are reviewed and discussed.

Stage IE recovery of electron‐irradiated pure silver and of its dilute alloys with cadmium and indium

Irradiations of silver specimens with electrons in the energy range 0.4–1.7 MeV were performed at liquid‐helium temperatures. A subthreshold phenomenon has been observed which is taking over below ∼750 keV. After separation of this effect, we have studied the annealing spectra of pure silver and of AgCd (25 and 50 ppm Cd) and AgIn (15 and 50 ppm In) diluted alloys following irradiation with different doses of 1.7‐MeV electrons and after irradiation doping. The stage IE recovery has been analyzed in terms of the chemical reaction rate theory. The corresponding rate equations have been solved numerically yielding the following values for the capture radii of a silver self‐interstitial atom by a Cd and an In impurity: rCdAg=0.15rv, rInAg= (0.05–0.10) rv, where rv is its annihilation radius at a vacancy. The best fit was obtained with a value of Em=88 meV for the migration energy of a self‐interstitial.

Interstitial mobility in FeNi, FeCo and FeMn dilute alloys

The trapping of radiation-induced self-interstitials by solute atoms in iron dilute alloys has been investigated by means of resistivity measurements. The present paper deals with the three systems FeNi, FeCo and FeMn. Specimens containing 50 to 400 at. p.p.m. of solute has been electron irradiated together with pure iron. The production and the recovery of the radiation-induced defects have been studied throughout stage I and stage II (up to 200K). The experimental results are interpreted as follows. The three solutes Ni, Co and Mn act as traps for the iron self-interstitial during its free migration in stage IE around 130K. A mixed interstitial is formed with these three solutes, which migrate just above stage IE (Fe-Ni) or in IE temperature range (Fe-Co, Fe-Mn), by the same mechanism as the self-interstitial in IE, thus resulting in solute long-range diffusion below stage III (vacancy migration). The present results are compared with previous ones from the literature.

Interstitial trapping during stage IE recovery of electron‐irradiated pure aluminum and its dilute alloys with Ag and Mg

Recent experimental data on the influence of additional vacancies and Frenkel pairs upon the stage IE recovery of electron‐irradiated Al and Al‐15 ppm Ag and newly obtained results on the dilute alloy system Al‐ (5–65) ppm Mg are analyzed in terms of the chemical reaction rate theory. The corresponding rate equations are solved numerically yielding the following quantitative results: the capture radius of a vacancy for an Al self‐interstitial, rAlv=2.1a0; the capture radii of an Mg and of an Ag atom, respectively, rMg=0.33rv, rAg=0.6rv; the electrical resistivity of a unit concentration of vacancies, ρv=2.0×10−4 Ω cm/unit concentration. The best fit has been obtained with a value of Em=112 meV for the migration energy of la self‐interstitial and a frequency factor of 3×1014 sec−1.

Interstitial trapping by Ni, Ag, in impurities in electron irradiated copper

Abstract Samples of copper, pure and alloyed with very small amounts of Ni, Ag, In impurities have been submitted to isochronal recovery between 10K and 60K after low temperature electron irradiation. The capture radii of the self interstitial atoms by the impurities are found: R Ni ∽ 0, R Ag = 1, R In = 1.5 in units of rv, the average vacancy capture radius for migrating self-interstitials.

INTERSTITIAL MIGRATION IN IRRADIATED IRON AND IRON-BASED DILUTE ALLOYS. I,INTERSTITIAL TRAPPING AND DETRAPPING IN FEMO, FEV AND FETI DILUTE ALLOYS

Three series of dilute iron alloys, with oversized solutes, FeTi, FeV and FeMo, in the concentration range 50 at.ppm to 3 at.%, have been electron-irradiated at low temperature together with the metal. A strong dependence of the solute and defect resistivities on the solute concentration is observed, which is analysed in terms of the two-current model. The specimens have then been annealed throughout stage I (self-interstitial migration) and stage II up to stage III (vacancy migration), with their resistivity measured. In these alloys, the mobile Fe self-interstitials, which are not annihilated at vacancies, are observed to get trapped at solute atoms in stage I and released from traps in stage II. Detrapping occurs in stage I at a temperature, TII, depending on the solute. Trapping is the weakest for V (TII approximately=140 K) and the strongest for Ti (TII approximately=180 K). At very low concentration (50 and 100 at.ppm), the solute trapping efficiency is lost at the beginning of stage III (200 K) for all these solutes. In the most concentrated FeMo alloys, an important fraction of the radiation-induced resistivity is retained at 200 K, due to multiple trapping (trapping of iron interstitials by more than one Mo atom).