J. Hirvonen

Self‐diffusion in silicon as probed by the ( p,γ) resonance broadening method

The self‐diffusion preexponential factor D0=8.0 cm2/s and activation energy Q=4.1 eV for intrinsic silicon have been determined with the (u2009p,γ) resonance broadening method in the temperature region 900–1100 °C, in a first application of this method to self‐diffusion measurements. Its suitability was tested by extending the self‐diffusion measurements to lower temperatures than those performed with other methods.

Annealing behavior of implanted nitrogen in AISI 316 stainless steel

The behavior of implanted nitrogen during post‐implantation annealing has been studied at 400, 450, and 500u2009°C by depth profiling of 15N‐implanted samples using the nuclear resonance broadening method. During the initial states of the annealing the nitrogen depth profiles behaved as if all the nitrogen would be able to diffuse, i.e., to be in solution, whereas for the longer annealing times the concentration of migrated nitrogen in the unimplanted region reached equilibrium with the implanted layer. The diffusion coefficients were determined as well as the equilibrium concentrations at the temperatures involved. The published values of the diffusion coefficients were extended to temperatures more than 500°u2009C lower than before.

Effect of temperature on the transfer film formation in sliding contact of PTFE with stainless steel

Abstract The transfer of polytetrafluoroethylene (PTFE) to AISI 316 stainless steel during the first ten unidirectional traverses at room temperature, 100 °C and 200 °C was investigated. The amount of transferred PTFE was determined by detecting fluorine on the counterface utilizing the resonance of the nuclear reaction 19F(p,αγ)16O at a proton energy of 340 keV. The transfer of PTFE was observed to increase with increasing temperature and pin load, the deposition rate being the highest in all cases during the first traverse. During subsequent traverses, the transfer of PTFE still occurred and a constant deposition rate at a given temperature and nominal pressure was observed. The temperature dependence of the amount of deposited PTFE was modelled using the concept of a temperature enhancement factor, which was found to be independent of the number of traverses and was a function of temperature only. This indicates that bulk PTFE rather than the interface properties were affected by the increased temperature.

Wear and hardness of diamondlike coatings prepared by ion beam deposition

The wear rate of 10‐μm‐thick 12C coatings prepared by mass separated ion beam deposition has been measured to be 60 times lower than WC+Co hard metal and 10 times lower than the conventional hard coating material TiN. The hardness of the 12C coatings was measured to be at least the same as that of the natural diamonds.

Characterization and unlubricated sliding of ion-beam-deposited hydrogen-free diamond-like carbon films

Abstract Diamond-like carbon films with a thickness of 0.5 μm were deposited onto silicon and WC-Co cemented carbide substrates using mass-analyzed 12 C beams at an energy of 500 eV. The microstructure of these films was amorphous as determined with transmission electron microscopy. The Auger electron and Raman spectra were identical with those observed on hydrogenated amorphous carbon films although the hydrogen concentration of the films was below the detection limit (about 0.5 at.%) for forward recoil spectroscopy. The unlubricated sliding properties of these films on WC-Co cemented carbide were examined using hardened steel or Si 3 N 4 as the counterparts. In both cases, low friction and wear were found in circumstances where untreated WC-Co substrate suffered from significant damage. In the case of the Si 3 N 4 pin rubbed against the diamond-like film a very low friction coefficient of 0.06 and altered morphology of the wear scar on the diamond-like film were observed. In contrast, in the case of hardened steel on the diamond-like film the thin deposition was found on the steel surface, indicating material transfer between sliding surfaces which resulted in a friction coefficient of 0.14. In both cases the diamond-like film remarkably reduced the wear of the counterface.

Annealing behavior of nitrogen‐implanted proton‐irradiated molybdenum

The irradiation effect of 0.45‐MeV protons on the solubility and diffusivity of interstitial impurities has been studied by annealing nitrogen‐implanted molybdenum samples in the temperature region 600–800u2009°C. The nondestructive (p,γ) resonance‐broadening method was applied as a probe for the nitrogen. Even for the low proton irradiation doses, a remarkable increase in solubility and a decrease in diffusivity were observed.

Dezincification of boron implanted brass

Abstract Dezincification tests, transmission electron microscopy and γ-yields of the reactions 10B(p, αγ) 7Be, 10B(α, pγ) 13C and 11B(p, γ) 12C obtained by using a 2.5 MV Van de Graaff accelerator were employed in corrosion, structure and composition analyses in improving the dezincification resistance of brass with additions of boron. The macrosegregation analyses revealed that the poor dezincification resistant as-cast brasses, which have large additions of boron, also have a large accumulation of boron near the centerline, whereas boron implantation with 5 at. % maximum boron concentration is able for a short time to give such effectively improved dezincification resistance, which in the case of low boron alloyed brasses has been attributed to the trapping of vacancies with boron atoms.

A simple method for distinguishing between deformation and wear of modified surfaces

Abstract The measurement of surface topography alone is often insufficient for determining the amount of material removed during a wear and friction experiment because of the simultaneous deformation of the surface. We demonstrate a simple, quick, and non-destructive method for distinguishing between the two processes based on monitoring the characteristic X-ray emission while scanning an electron beam across the wear track. This technique is readily combined with the usual analysis using scanning electron microscopy of the surface. Results may be used to explain the improved wear and friction properties sometimes extending beyond the depth of a modified surface layer.

Range and damage distributions of low energy 4He ions in α-Fe and Mo

A new method, which is based on nitrogen trapping with He atoms, has been used for the measurement of 4 He range and damage distributions for 5–60 keV 4 He in α -Fe and for 10–100 keV 4 He in Mo. The computer simulation program COSIPO was used to calculate the distributions. The experimental and calculated modal ranges are in excellent agreement. The comparison of the measured and calculated distributions yields information on the electronic stopping power of 4 He. The effect of polycrystallinity is found to be noticeable.

Coating of pellet pressing tool with 12C by ion beam deposition

Abstract The pressing tools, used in the preparation of the samples needed for example for such nuclear elemental analysis methods as PIXE, PIGE and RBS, have been coated with a diamond-type 12 C-layer by ion beam deposition. Using carbon-coated pressing tools prepared in this way contamination of the sample surfaces during the pill pressing operation is avoided.