J. Delafond

A NEXAFS characterization of ion-beam-assisted carbon-sputtered thin films

Abstract Thin carbon films were deposited by sputtering with various species by means of the technique of dynamic ion mixing (DIM). Transmission electron microscopy experiments reveal that the films are amorphous and contain contaminants, mainly oxygen. Density values are determined by glancing X-ray reflectometry. Friction and wear resistance measurements have been accomplished. Near-edge X-ray absorption fine structure (NEXAFS) experiments are performed at both CK and OK edges. The CK edge NEXAFS data for a film obtained with DIM and an argon-methane mixture filling the sputtering source show a strong peak that is attributed to Cue5f8H and Oue5fbCue5f8OH bonds, while the number of sp 2 -hybridized carbon sites is quite small. More damped features are observed for a film deposited without DIM when an argon-hydrogen mixture is used. However, the number of sp 2 -hybridized carbon sites is then greater. When DIM is used, we observe in the NEXAFS spectrum that the high energy ion irradiation induces hydrogen release. A correlation of the NEXAFS with the wear behaviour is suggested.

Corrosion protection of an AISI 321 stainless steel by SiC coatings

Abstract Silicon carbide coatings were produced by dynamic ion mixing (DIM) at room temperature and at 750 °C by ion beam sputtering of a SiC target and simultaneous bombardment with a 160 keV Ar+ ion beam. The chemical composition of the coatings was determined by Rutherford backscattering and by nuclear reaction analysis. The microstructural state of the coatings was investigated by high resolution transmission electron microscopy whereas their density was determined by X-ray reflectometry. It is found that, for all the deposition temperatures, the DIM treatment promotes the crystallisation of the β-SiC phase. Passivation/corrosion tests performed in 1 N H2SO4 indicate that the corrosion resistance is considerably improved by DIM regardless of the deposition temperature. It is suggested that the interface mixing along with the coating densification is responsible for the protective effect.

Ion-induced phase formation in Ni-Al and Fe-Al thin films: Role of chemical disordering energy on amorphization

Phase formation in the metallic systems Ni/Al and Fe/Al by ion beam mixing is studied at low temperature when chemical diffusion is prevented. Chemical disorder or/and topological disorder are therefore observed. Thermodynamic analysis based on free energy diagrams shows that stored energy in antisite defects in intermetallic compounds plays a determining role. Chemical disorder, by raising the energy of the crystal lattice, induces the transformation towards the amorphous state. The dissimilar results obtained for equiatomic ordered compounds FeAl and NiAl can be easily understood in this regard. Moreover a high mixing energy in the twc phases regions can explain the preferential stability of the topological disordered state.

Structure of TiB2 produced by dynamic ion mixing

Abstract The new technique of dynamic ion mixing is based on the use of a high energy ion beam to homogenize at the atomic scale and to improve the adherence of a growing film on any substrate. TiB 2 films of stoichiometric composition are produced either by co-evaporation or by dynamic ion mixing using 100 keV Ar + ions. The characterization of the films is performed by transmission electron microscopy (TEM) . The results indicate that the ion mixing of the growing film has a crucial importance with regard to the resulting microstructural state. Amorphous TiB 2 films are produced by conventional co-evaporation although crystalline TiB 2 films of hexagonal structure are produced by dynamic ion mixing. The TiB 2 amorphous phase appears to be very stable since crystallization starts only at about 1170 K and complete transformation into the hexagonal crystalline structure is obtained at 1280 K. Relatively thick TiB 2 coatings have been prepared with e = 1 μm and studied by TEM on cross-sectional preparations. The microhardness of crystalline TiB 2 films is about 2800 kgf mm −2 and is in good agreement with the value reported for bulk TiB 2 .

SURFACE CHARACTERISATION AND CORROSION BEHAVIOUR OF SIC-COATED AISI 321 STAINLESS STEEL

Abstract The influence of SiC-coatings on the corrosion properties of AISI 321 austenitic stainless steel (Fe/Cr18/Ni8/Ti) in 1N H 2 SO 4 was studied. SiC-coatings of various thicknesses (100–800 nm) were prepared at room temperature (RT) or at temperatures up to 750°C by ion beam sputtering of a SiC-target. The growing films could be continuously bombarded with a 160 keV Ar + ion beam and the role of this Dynamic Ion Mixing (DIM) on both the structure and corrosion resistance was investigated. The chemical composition of the coatings was determined by Rutherford Backscattering (RBS) using 1.8 MeV α-particles and by Nuclear Reaction Analysis (NRA). Transmission Electron Microscopy (TEM) observations were also performed for the determination of the microstructural state of the samples. The characterisation shows, that for all the deposition temperatures the DIM-treatment promotes the crystallisation of the β-SiC phase. It was also found, that the corrosion resistance of the stainless steel is considerably improved when the coatings are deposited by DIM regardless of the deposition temperature. The possible mechanisms are discussed and it is suggested that the interface mixing along with the coating densification effect are responsible for the improvement of the corrosion resistance.

Formation of TiB2 coatings at room temperature by dynamic ion mixing

We have deposited crystalline TiB 2 coatings of stoichiometric composition at room temperature by dynamic ion mixing (DIM). The film deposition was obtained by ion beam sputtering of a composite TiB 2 + B target using an intense Ar + ion beam with energy 1.2 keV and the growing films were continuously bombarded with 320 keV Xe 2+ ions. The chemical composition analysis was carried out by means of both Rutherford backscattering spectroscopy (RBS) and X-ray photoelectron spectroscopy (XPS). Complementary information on the microstructural state was deduced from transmission electron microscopy (TEM) observations on cross-sectional samples and by X-ray photoelectron spectroscopy (XPS). Results using both techniques are in complete agreement, indicating that the internal structure of the films corresponds to the hexagonal TiB 2 phase. The XPS analysis shows that an important amount of oxygen is present in the very first surface layers, but after sputter cleaning only TiB 2 was detected. Radiation-induced crystallization and grain growth appear correlated with the displacement damage produced by the high-energy heavy ion bombardment.

X-ray diffraction study of residual stress modification in Cu/W superlattices irradiated by light and heavy ions

Abstract The effect of low temperature ion irradiation on the residual stress state was studied as a function of the ion fluence in Cu/W superlatices prepared by ion beam sputtering. The residual stress tensor in tungsten layers is completely determined from X-ray diffraction data using the “sin2ψ method”. In the as-prepared state, the Cu/W superlattices are strongly strained, and we find in-plane compressive stresses as high as 6.4 GPa in tungsten layers. Relaxation of the stress state is observed after low temperature ion irradiation with increasing dose. This phenomenon is almost complete for doses as low as 0.1–0.2 dpa, and appears related to atomic rearrangement in the elemental layers rather than interfacial mixing. The role of the incident particle mass is also evidenced. Per dpa, heavy ion irradiation (Kr) induces the strain relaxation more quickly than light ions (He).

Relaxation of residual stresses in highly stressed multilayers initiated by ion irradiation

Abstract In situ deformation measurements (static and dynamic) of W/Cu multilayer films were made by employing laser interferometric and piezoelectric transducer techniques to register mechanical waves generated during ion irradiation of multilayers. It is found that the kinetics of relaxation of tensile and compressive stresses initiated by ion irradiation in initially highly stressed microstructures is different. The process of relaxation of compressive stress has a threshold character and takes place when the energy retained in the film is approximately equal to the energy required to produce 10−2–10−1 displacements per target atom.

First stages study of high energy ion beam assisted deposition

Abstract The first stages of growth of gold layers obtained by high energy IBAD have been investigated. Morphological parameters have been calculated from TEM micrographs with the use of image processing. For low Au deposit, assisted deposition leads to a lowering of the cluster density while an opposite result is obtained for higher Au deposit, resulting from an increase of the small clusters part in the double peak size distribution. It is interpreted as the result of a competition between enhanced diffusion and ballistic dissolution effects.

Phase transformation in ion irradiated NiAl and FeAl

Single crystals of NiAl and FeAl B2 type ordered intermetalhc compounds were irradiated at 90 K with xenon ions and the radiation damage studied by in situ Rutherford backscattering and channeling experiments. After a first stage (up to 5 x 1013 Xe cm-−2) where a strong increase in the dechanneling rate of the analyzing ions is obtained, an unexpected reordering effect (i.e. a decrease in the channeling rate) is observed in both alloys. This process is discussed in relation with defect rearrangements or induced crystalline structural phase transformation. Finally for irradiation fluences higher than 2.5 x 1015 Xe CM−2 complete dechanneling occurs, confirming that total amorphization takes place in NiAl, while the disorder level remains at a very low and constant value in FeAl.