Thin (0.1–1 μm) MoSx (x = 1.2) films were deposited onto 440C steel by ion beam sputtering of an MoS2 target with (or without) high-energy (160 keV) Ar+ ion beam assistance. The coatings were analyses for microstructure by transmission electron microscopy and grazing incidence X-ray diffraction and their tribological performance was evaluated using a pin-on-disc machine operating under argon environment. The sputter-deposited MoSx films were amorphous with short-range order in the form of layered clusters parallel to the substrate, whereas the high-energy ion-beam-assisted deposition (high-energy IBAD) films were partially crystallized with no preferential orientation of the layered structure with respect to the surface. In all cases, the initial friction coefficient was low (less than 0.05) but the wear-life (number of revolutions to reach a friction coefficient of 0.2) was much better for the sputter-deposited films (30 000 revolutions for a thickness of 0.5 μm) than for the high-energy IBAD coatings (a few revolutions for a thickness of 0.5 μm). Diffusion processes enhanced by the defects created during the high-energy ion bombardment of the deposit can explain the disappearance of the preferential parallel-to-the-surface orientation of the layered microstructure and, as a consequence, the poor performance of the high-energy IBAD coatings.

In previous work it has been shown that the N+ implanted NiTi alloy surface consists of crystalline TiN precipitates embedded in an amorphous structure. This surface modification considerably reduces the friction coefficient and dramatically increases wear resistance. A coating of this type on stainless steel has been prepared using a high-energy ion beam assisted deposition (IBAD) technique. TEM, SIMS and XPS analyses show that sputtering of an Ni49Ti51 target with 1.5 keV N+ ions leads to an amorphous N153Yi47 film with a high content of nitrogen and containing small TiN precipitates (5 nm). When the growing film is simultaneously bombarded with a 160 keV Ar+ beam the precipitates are bigger (10 nm) and the coating-substrate interface is mixed over a thickness of 200 nm. The wear resistance of these coatings deposited on stainless steel 304L is excellent: this is explained in terms of the amorphous structure, fine precipitates created during ion-beam assisted deposition and the diffuse interface.

Ni+ implantation-induced amorphization of NixTi1−x (0.3 ⩽ x ⩽ 0.7) alloys, vs. the temperature, is studied by transmission electron microscopy. Two conflicting processes are shown to occur: ballistic disordering competes with a close pair recombination process (with a low activation energy of approximately 0.03 eV) in the cascades at low temperatures, and with an irradiation-enhanced interstitial mobility (activation energy approximately 0.6 eV) at higher temperatures (beyond 250 K). Nitride precipitation has been observed in N+-implanted Ni50Ti50 alloys. These precipitates, embedded in the amorphous layer, are oriented at low temperature (77 K) and high temperature (473 K) and disoriented around room temperature (293 and 373 K). It is suggested that this orientation occurs when the first epitaxial precipitates nucleate in the crystalline substrate before the amorphization.

Implantation of nickel ions into pure aluminium is found to produce either amorphization or precipitation of a cubic phase not predicted by the AlNi phase diagram. Under low ion current (I ⩽ 1 μAcm−2) and for fluences between 8 × 1016Ni+cm−2 and 2 × 1017Ni+cm−2 an amorphous phase forms. Under high current (I ∼ 20 μAcm−2) and for the same fluences a new face-centred cubic (f.c.c.) Al85Ni15 precipitate phase is formed in epitaxy with a supersaturated Al95Ni5 solid solution. The epitaxial relationship between the precipitates p and the solid solution matrix m is (001)p|(001)m planes, and [040]pz.sfnc; [240]m directions in the planes. The large lattice misfit between the precipitates and the matrix is accommodated by twinning and a tetragonal distortion of the precipitates.

In order to explain the improved tribological properties obtained on NiTi alloys after N+ implantation, complementary surface sensitive techniques (TEM, SIMS and XPS) are used to characterize an initially martensitic NiTi alloy. When the nitrogen ions are implanted at 293 K, the affected zone is fully amorphous with embedded fine disoriented TiNx (x ≈ 0.8) precipitates. At 473 K the implanted region consists of an amorphized layer and an underneath crystalline austenitic layer both containing TiNχ precipitates. These precipitates are in epitaxy with the austenitic matrix. After implantations at 573 K and above, the implanted zone is fully austenitic with epitaxial TiNx precipitates. Post implantation annealings under 823 K do not sensibly affect the implanted element distribution but favor the evolution of TiNχ precipitates towards the stoichiometric compound TiN. Beyond 823 K the amorphous layer crystallizes.

The influence of boron and nitrogen ion implantation on wear behaviour and processes of 304 austenitic stainless steel is studied in this paper. It is shown that the best decrease in wear rate is obtained after B+ implantation for a lower fluence than after N+ implantation. Direct transmission electron microscopy (TEM) examination of wear tracks does not reveal the austenitic stabilization effect of boron. Grazing incidence X-ray diffraction and TEM studies of the implanted layer show α′bcc martensite formation without boride precipitates. Thus, it is assumed that the improvement in wear resistance of B+-implanted 304 steel is not due to a chemical effect of boron or precipitates formation, but to α′ martensite formation and eventually to dislocation interactions with the dispersion of boron atoms.

Transmission electron microscopy (TEM) including intensity analysis of electron diffraction patterns and conversion electron Mössbauer spectroscopy (CEMS) are associated to determinate the microstructure of the equiatomic Ni-Ti alloy amorphized under ion implantation at 300 K as well as that obtained after post-implantation annealing during the amorphous to crystal (A/C) transition. In the first part, radial distribution functions are deduced from the analysis of microdensitometer traces performed through diffraction patterns. It appears that the distribution of distances between first and second neighbours is broader in ion implanted Ni-Ti 50 at.% than in amorphous vapor deposited Ni-Ti 44 at.%; for these two compositions, the first neighbour coordination number is found to be 10 and 12, respectively. The second part is devoted to the implantation of 57Fe+ into Ni-Ti 50 at.% which allows a CEMS study of both the initial amorphous and the (A/C) transition in the 300–900 K range. Special attention is paid to the following phenomena: short-range order, structural relaxation, crystallization and diffusion of 57Fe; the temperature range of each one has been carefully determined.

The effect of ion implantation on friction and wear of NiTi alloys is presented. Surface amorphization is obtained in all cases for doses greater than 1015 ions cm−2, but wear resistance is dependent on the dose and the implanted ion. It is shown that amorphization is a necessary but not sufficient condition for wear resistance improvement; surface or subsurface reenforcement seems necessary.

Two types of ion beam surface modifications have been performed. 1.(i) Superficial amorphization has been induced in an industrial NiTi shape memory alloy by direct ion implantation. A remarkable increase in the wear resistance and exceptional reduction in the friction coefficient has been observed for an implantation of 3 × 1017 N+ cm-2.2.(ii) An FeAl coating 1 μm thick on steel has been obtained by iron and aluminium evaporation simultaneously with argon ion irradiation. This coating significantly improves the tribological behaviour of this steel and presents an exceptional adherence to the substrate, which is not so if the coating is performed without ion assistance.

Etude de la resistance a l'usure et du frottement a sec dans des alliages a effet de memoire de forme NiTi, implantes par des ions N + . Formation d'une couche amorphe parce bombardement dont l'epaisseur depend de la fluence des ions. Influence de la microstructure (alliage austenitique au martensitique) sur la resistance a l'usure

Synthese d'alliages Ni-Ti non cristallins par trempe de vapeur dans la gamme de concentration 25-70 at.% Ni. Variation de la distance entre premiers voisins en fonction de la concentration, fonction de distribution radiale et observations en microscopie electronique en transmission

Amorphous Ti-Ni alloys may be prepared by a variety of techniques, including: liquid quenching, ion implantation, electron irradiation, and vapor synthesis. Each of these techniques involves fundamentally different atomic processes with concomitant different effective quench rates. Since quench rates affect the degree of structural order, it is conceivable that a variety of metastable configurational states may thus result. Radial distribution functions (RDF’s) from diffraction experiments are a generally accessible probe for statistical characterization of amorphous alloys, and hence, a useful tool to compare amorphous structures. However, not all of the amorphization methods are capable of producing sufficient quantities of material required for x-ray or neutron scattering. Therefore, the purpose of this paper is to report the preliminary results from a comparative structural investigation of Ti-Ni alloys by x-ray and electron diffraction.

Transmission electron microscopy (TEM) and conversion electron Mössbauer spectroscopy (CEMS) are used to characterize the amorphous layer obtained by ion implantation in the Ti-50% Ni alloy, well known for its “two-way shape memory” effect. Presented in this paper is the influence of: 1.(i) the initial structure (martensite, austenite, Ti4Ni2O particles),2.(ii) the ion type (Ni+, Si+, 57Fe+),3.(iii) a post implantation annealing, on the microstructure of the implanted layer.

Conversion electron Mössbauer spectroscopy shows it is possible to induce a magnetic splitting caused by atomic disorder by implantation of Al ions into Fe-Al 40 at %.However a paramagnetic component remains, which decreases with increasing fluence.On montre, par la spectrométrie Mössbauer d'électrons de conversion, qu'il est possible de créer un éclatement magnétique, lié à une mise en désordre atomique, par implantation d'ions Al dans l'alliage Fe-Al 40% at. Toutefois, sur le spectre, il demeure une composante paramagnétique qui diminue lorsque la dose implantée augmente.