Jtm Dehosson

Interaction of vacancies with implanted metal atoms in tungsten observed by means of thermal helium desorption spectometry and perturbed angular correlation measurements

Abstract With two techniques the defect complexes are studied when formed after implantation of 5 to 100 keV metal ions into tungsten. Perturbed Angular Correlation (PAC) studies clearly indicate the presence of substitutional impurities in samples implanted with Ag or In. With Thermal Helium Desorption Spectrometry (THDS), however, virtually no substitutional implants (Ag, Cu, Mn, Cr, In) could be seen after implantation due to the nearby vacancies. Migration of vacancies towards the implants during annealing at stage III temperature was observed by means of PAC measurements. At upper stage III vacancy-implant complexes disintegrate, while the substitutional fraction increases. According to THDS, no vacancy-implant complexes are left in the case of 5 keV implantation after annealing to temperatures slightly beyond stage III temperature. In the case of 20 keV implantation a vacancy-type defect is formed which is stable up to 1350 K. The results of both techniques are compared with each other and with mode...

THE ORIENTATION DEPENDENCE OF DISLOCATION SLIP IN NACL SINGLE-CRYSTALS

Abstract Results are presented of investigations into the role of dislocation motion in deforming NaCl single crystals, using the technique of pulsed N.M.R. In particular, the spin-locking pulse sequence is used to measure T 1p, which is the spin-lattice relaxation time in the presence of a resonant r.f. magnetic field. T 1p, depends strongly on the mean free path L which is covered by the dislocations during successive jumps between obstacles in their glide plane. The mean free path is determined in crystals compressed in different directions, in which cases either the {110} or the {100} planes are primarily activated. It is shown that both the mean free path, measured as a function of strain rate and of the applied stress, and the work hardening differ remarkably for the two different primary slip planes. The magnitude of the mean free path is compared with the mean distance between dislocations in the crystal and the activation length of dislocations at obstacles, as obtained from mechanical stress rel...

ATOMISTIC STUDIES OF HELIUM TRAPPING IN METALS

Abstract The various levels of approximations of the following interatomic potentials are discussed: empirical potentials and ab initio potentials based on density functional theory. The discussion is primarily centered on the intrinsic merit of the potential functions considered and the realism of the results obtained using pair-wise interaction functions in the description of He clusters in Ni and Mo.

A STUDY OF SHALLOW AND DEEP DAMAGE IN CU AND AL AFTER SELF-IMPLANTATION

Abstract The damage formed by self-implantation in Cu and Al at two temperatures, where vacancies are considered to be either immobile or mobile, but where interstitials are always highly mobile, is studied before and after annealing, using dechanneling methods. Two different regions of damage are distinguished: a surface region coinciding with the projected range of the implanted self-ions, and a region extending up to 10 times beyond this range. On the basis of differences on the formation of the deep and the shallow damage as a function of implantation temperature and a different behaviour of annealing it is concluded that the two regions contain different types of damage. A mechanism is proposed that explains the observed damage distributions qualitatively. In this model the damage in the surface region of copper is assumed to consist of mainly clusters of vacancies. In the deep region of copper and aluminium it is assumed that the damage consists of clusters or loops formed by interstitials. Due to i...

THE MEAN FREE-PATH OF MOBILE DISLOCATIONS IN DOPED NACL SINGLE-CRYSTALS MEASURED BY NMR BETWEEN ROOM-TEMPERATURE AND 300-DEGREES-C

Abstract The mean free path of mobile dislocations has been measured by determining the spin–lattice relaxation rate of deforming NaCl single crystals as a function of temperature and of the concentration of Ca2+ impurities. The latter may influence the magnitude of the mean free path, but this depends to a large extent on the point-defect configuration. The degree of association and the mobility of the point defects has been studied by measuring the spin–lattice relaxation rate without deforming the samples. On the other hand, the distribution of dislocations also varies with temperature, and this affects the mobility of dislocations too. The work-hardening rate of the crystals is compared with the mean free path as a function of temperature, and it is shown that both quantities have extremes under the influence of competitive mechanisms such as an enhanced thermal activation of dislocations at obstacles, an increasing mobility of point defects and an increasing number of intersections of mobile dislocat...

On the determination of dislocation densities in NaCl single crystals from quadrupolar linewidth measurements

Abstract The N.M.R. quadrupolar linewidth is determined both experimentally and theoretically for dislocations on {110} and {100} slip planes in NaCl single crystals, compressed in different directions. Specifically, the electric field gradients (E3.G.s) around dislocations are calculated using the proportionality between the E.F.G.s and the stress fields around dislocations. The latter are taken from linear anisotropic elasticity theory. The results are compared with measurements on crystals compressed in different directions in which the quadrupolar linewidth is determined as a function of the direction of the external magnetic field. As a result, the dislocation densities and the amount of slip on the different planes are found.

Depth profile and stress measurements on implanted layers

The properties of a metal surface can be enhanced by implantation with noble gas ions. Implantation has its effect on the stress state of the material. In this work, SS304 stainless steel is implanted with Ne+.SS304 bears the property of being easily transformable from the face centered cubic (fee) phase to the body centered cubic (bcc) phase. Before the implantation the SS304 samples were stress free and completely of the fee phase, after the implantation bcc phase material is present and the implanted layer is in a compressive stress state. By using a different approach towards glancing angle X-ray diffraction we were able to measure a depth profile of the bcc material and to measure the stresses in the 0.1 mu m thick implanted layer.

INSITU STUDY OF DEFORMATION-ENHANCED ATOMIC DIFFUSION IN NACL BY NUCLEAR-MAGNETIC-RESONANCE

Abstract Enhancements in atomic diffusion during deformation are investigated by 23Na rotating frame nuclear spin relaxation measurements on pure NaCl single crystals. The enhanced diffusion is shown to arise from deformation-induced excess concentration of vacancies. Evaluation of the data yields the concentration of these vacancies as a function of temperature and strain rate.

HIGHLY PRESSURIZED KR AGGLOMERATES IN SPUTTERED SI FILMS

High resolution electron microscopy experiments are presented for a plasma-sputter-deposited Si film with a high Kr concentration. The amorphous layer deposited shows an oscillating Kr concentration. The Kr resides in very small agglomerates of size < 1 nm. Bending measurements show that the pressure in the Kr agglomerates is very high, 3.9 GPa. Hardness measurements show that this pressure is limited by the fracture stress of the deposited film.

DISLOCATION DYNAMICS IN DOPED NACL SINGLE-CRYSTALS DETERMINED BY PULSED NMR BETWEEN RT AND 300-DEGREES-C

Abstract The mean free path of mobile dislocations is measured by determination of the spin-lattice relaxation rate of deforming NaCl single crystals as a function of temperature and of the concentration of Ca++ impurities. The latter may influence the magnitude of the mean free path but this depends to a large extent on the point defect configuration. The degree of association and the mobility of the point defects is studied by measuring the spin-lattice relaxation rate without deforming the samples. On the other hand the distribution of dislocations varies also with temperature and this affects the mobility of dislocations too. The work-hardening rate of the crystals is compared with the mean free path as a function of temperature and it is shown that both quantities have extremes under the influence of competitive mechanisms such as an enhanced thermal activation of dislocations at obstacles, an increasing mobility of point defects, and increasing number of intersections of mobile dislocations with dis...