L. Sarholt-Kristensen

Mössbauer and TEM study of martensitic transformations in ion implanted 17/7 stainless steel

It has earlier been shown that implantation of antimony into austenitic stainless steels induces martensitic phase transformations γ (fcc) → α (bcc). In the present work we have investigated which mechanisms are responsible for the transformation. Samples of 11/7 steels were implanted with noble gases (Kr, Ar) or the stainless steel constituent elements (Fe, Ni, Cr). The energies were selected to give ranges ∼ 40 run. The phases present after implantation and the microstructures of the implanted samples were studied by CEMS and TEM respectively. A martensitic (α) phase was found to form after implantation both with Ni, Fe and Cr, in spite of the fact that these elements have opposite tendencies for stabilization of the austenite (γ) phase. The efficiency of martensite formation is therefore mainly related to stress relief associated with secondary radiation damage. This was substantiated from the noble gas implantations, where the highest degree of transformation was observed for fluences where bubble formation occurs. The CEMS analyses show that the transformation efficiency in such cases is nearly 100%. The hyperfine parameters of the implantation induced a phase are similar to those from conventionally induced martensites.

Depth distribution of martensite in xenon-implanted stainless steels

Abstract The amount of stress-induced martensite and its distribution in depth in xenon-implanted austenitic stainless-steel poly- and single crystals have been measured by Rutherford backscattering and channeling analysis, depth-selective conversion-electron Mossbauer spectroscopy, cross-sectional transmission electron microscopy and X-ray diffraction analysis. In low-nickel 17 7 , 304 and 316 commercial stainless steels and in 17:13 single crystals the martensitic transformation starts at the surface and develops towards greater depth with increasing xenon fluence. The implanted layer is nearly completely transformed, and the interface between martensite and austenite is rather sharp and well defined. In high-nickel 310 commercial stainless steel and 19:15 and 19:20 single crystals, on the other hand, only insignificant amounts of martensite are observed.

A contribution to sputtered ejection patterns from collision sequences in atomic cascades: Firm evidence from channeling experiments

Abstract The sputtering of single crystals of radioactive gold by well collimated beams of energetic ions has been investigated in detail, using cylindrical collectors. For 80 keV argon ions incident in and near to channels there is a very sensitive dependence of the height and shape of the spots on angular deviation. This is shown to be a consequence not only of the size and degree of order within anatomic cascade, but also of its position below the bombarded surface, following ion dechannelling. At angles of incidence such that cascades lie at very shallow depths the spots develop an internal structure, which is shown not to be an artefact, but can be due to not fully focused collision sequences, from the cascade. Detailed variations in spot structure and relative intensities for beams incident at and near to axial and {100} planar channels are also described, as are the influences of incoming ion energy.

A note on the optical properties of sputtered gold films

Abstract In a previous paper1 we have reported a spot structure in sputtered ejection patterns from single {100} crystals of gold; a structure which is observed in direct measurements of residual radioactivity on the sputtered fdm. More recently, in investigating sputtering from {110} surfaces,2 we have relied heavily on direct microdensitometry of the patterns, and have encountered difficulties associated with the varying degree of granularity in the films.

Sputtering on copper single crystals

Abstract Copper single crystals have been sputtered at normal incidence in 〈110〉, 〈111〉 and random directions with 100 keV Ar + and 120 keV Cu + ions and the sputtering yields determined by the weight-loss method. The channeled sputtering yields have been measured as a function of fluence and the associated RBS-disorder analyzed by means of 2 MeV He + ions. In Ar-sputtering a reasonable agreement was obtained between experimental yields and the predictions of the transparency theory. By contrast, copper self-sputtering yields deviate rather strongly from expected values, which may be explained by a less crude division of the sputter beam than into a channeled and a non-channeled fraction, the latter being solely responsible for sputtering.

Sputtering on cobalt with noble gas ions

Single crystals of cobalt have been bombarded with 80 keV Ar+ ions and with 80 keV and 200 keV Xe+ ions in the 〈0001〉 direction of the hcp phase and the 〈111〉 direction of the fcc phase. The sputtering yield has been measured as function of target temperature (20°C–500°C), showing a reduction in sputtering yield for 80 keV Ar+ ions and 200 keV Xe+ ions, when the crystal structure changes from hcp to fcc. In contrast to this, bombardment with 80 keV Xe+ ions results in an increase in sputtering yield as the phase transition is passed. Sputtering yields for 〈111〉 nickel are in agreement with the sputtering yields for fcc cobalt indicating normal behaviour of the fcc cobalt phase. The higher sputtering yield of 〈0001〉 cobalt for certain combinations of ion mass and energy may then be ascribed to disorder induced partly by martensitic phase transformation, partly by radiation damage.

Sputtering yield measurements on single crystal cobalt

Abstract Single crystals of cobalt have been bombarded with 80 keV Ar + ions in the 〈0001〉 direction of the h.c.p. structure and in the 〈111〉 direction of the f.c.c. structure. The sputtering yields, measured by the weight loss method, depend on the crystal structure, and damage introduced by the ion bombardment is shown to play a significant role in the explanation of the measured sputtering yields.

Temperature and fluence effects in lead-implanted cobalt single crystals

Abstract The channelled sputtering yields of the h.c.p. and f.c.c. phases of cobalt depend on the crystal structure and the radiation-induced damage. Earlier irradiations of cobalt with argon ions channelled in the 〈0001〉 hcp direction give sputtering yields higher than expected in the temperature range 100–350°C. This effect was attributed to a combination of radiation-induced damage and a possible implantation-induced h . c . p . → f . c . c . phase transition. Sputtering yields for cobalt single crystals irradiated with 150 keV Pb + ions along the 〈0001〉 direction of the h.c.p. phase and the 〈111〉 direction of the f.c.c. phase have been measured using the weight loss method. The radiation damage and the amount of lead retained in the implanted surface have been investigated by “in situ” Rutherford backscattering-channelling analysis. Measured partial sputtering yields of lead of approximately 1 atom ion −1 indicate preferential sputtering of lead atoms.

The effect of boron implantation on the corrosion behaviour, microhardness and contact resistance of copper and silver surfaces

In order to investigate the influence of boron implantation on the corrosion resistance of electrical contacts, a number of pure copper, pure silver and copper edge connector samples have been implanted with boron (40 keV) to fluences of 5 × 1020 and 2 × 1021 m′2. Atmospheric corrosion tests of the implanted species were conducted using the following exposures: H2S (12.5 ppm, 4 days), SO2 (25 ppm, 21 days), salt-fog (5% NaCl, 1 day), moist air (93% RH, 56 days), and hot/dry air (70°C, 56 days). The boron implantations lead to a significant reduction in the sulphidation rate of copper and silver. The corrosive film formed during exposure in H2S and SO2 atmospheres is confined to pitted regions on the implanted areas, while a thick and relatively uniform film formation is observed on the unimplanted samples. The corrosion resistance of copper and silver in salt-fog atmosphere is somewhat improved by boron implantation, whilst the results from exposures to moist air or hot/dry air are inconclusive. The improved corrosion behaviour is accompanied by an increase in the contact resistance and in the microhardness of the implanted samples.

Extended solubility and martensitic hcp nickel formation in antimony implanted nickel

Radiation damage microstructure and associated disorder have been investigated in antimony implanted nickel crystals using combined RBS and TEM analyses. In crystals implanted at and below room temperature with 80 keV Sb+ ions to a fluence of 5 × 1020 m−2, the retained antimony concentration in the implantation zone is approaching 10–15 at.%, with nearly all the antimony located substitutionally. The associated disorder as seen in the RBS analysis is insignificant. Annealing up to 600°C has little influence on the antimony distribution, whilst the dechanneling level is reduced. TEM and diffraction analysis of room temperature implanted samples show that the radiation damage consists of dense distributions of dislocation clusters and tangles, superimposed on a rather homogeneous background of new phase particles, identified as hcp nickel. The particles have a size 0.1–0.2 μm and an orientation relationship to the fcc matrix given by (0001)hcp || (111)fcc and [2110]hcp ||; [011]fcc, which is well known from martensitic transformations. The high substitutional antimony concentration at and below room temperature, which exceeds the solubility limit, indicates that its formation is thermally diffusionless and rather an effect of radiation enhanced solubility. The diffusionless nature of the microstructure is also indicated from the presence of martensitic hcp nickel, believed to form due to relief of radiation induced internal stress.