The aim of this work was to study the modifications induced by 10 ns single or cumulative pulses of a Q-switched Nd:YAG laser emitting in the near-infrared (λ = 1064 nm) on a pure aluminum surface with a laser energy density leading to a regime of interaction below the material ablation. The influence of these laser substrate pre-treatments on the mechanical behavior of an 83 µm thick alumina plasma sprayed coating was observed by evaluating the integrity of the coating/substrate interface with a "laser-ultrasonic method" thanks to a special set up using a probe laser interferometer. An increase in the alumina coating adhesion considering cumulative pulses for a laser energy density of 0.7 J/cm 2 was observed above 100 laser pulses. The highest adhesion was obtained for a laser treatment considering 1000 shots. For a single pulse laser treatment, this increase was found applying an energy density of 1.8 J/cm 2 . These results were correlated with the observation of modifications on topography and morphology of the aluminum surface after laser irradiations using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that the improvement of the adhesion of the plasma-sprayed alumina coatings was correlated to changes of the aluminum oxide morphology.

We have confirmed that in the thermal spraying of practical powder materials, the splat shape changes with increasing substrate temperature to a circular disk shape from a fringe shape with splashing at a critical substrate temperature, Tt. The increase of substrate temperature may accompany a kind of essential change on substrate surface, because the effect is maintained until the substrate is cooled down to room temperature. However, the nature of the substrate surface change due to the heating has not been clearly understood yet. In this study, AISI304 stainless steel was employed as a substrate material, and the substrate was heated in an air atmosphere or laser treated as a pretreatment. Substrate surface topography was analyzed precisely by atomic force microscopy, AFM. We discuss the relationship between surface topography in nano-meter scale and splat morphology. Moreover, in order to evaluate the effect of chemical composition of the substrate surface, gold was coated onto the substrate surface by PVD method after the heat treatment. The effect of adsorbate/condensate on the substrate surface on the flattening behavior of thermal sprayed particles was also verified.

It has been confirmed in the flattening behavior of the thermal sprayed particles that the splat shape on the flat substrate surface changes to a disk type from a splash type at relatively narrow temperature range with increasing the substrate temperature. The temperature increasing actually causes a certain non-reversible change on the substrate surface, because the changing effect is maintained till the substrate is cooled down to the room temperature. We have pointed out that this non-reversible change on substrate surface due to the heating might be the possible domination for the transition phenomenon of the thermal sprayed particles, that is, the essence of the substrate surface change due to the heating is surface roughness in nano-meter range. In this study, several kinds of substrates once heated to some elevated temperature were analyzed precisely by atomic force microscope (AFM) to characterize the change in their surface roughness character. The fundamental static wetting behavior of the substrate surface by a water droplet was investigated for the reference in the present study. The results obtained revealed that the change of the substrate surface topography in nano-meter range affect most effectively the wetting behavior of the droplet or splat on the surface. Hence, the substrate heating may bring about the change in the physical way on the substrate surface and this change induces the transition phenomenon.

In the thermal spraying of powder materials, it has been observed in practice that the splat shape changes to a disk type from a splash type with increases in the substrate temperature. However, the details of the substrate surface change due to the heating has not been fully characterized. In this study, an AISI 304 stainless steel substrate surface heated to 673K was analyzed precisely by atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy. The results obtained revealed that the change of the substrate surface occurred not in the chemical composition but mainly in the surface roughness, especially surface morphology in nano-meter scale. Hence, substrate heating may bring about the change in substrate surface and this change induces the transition phenomenon.

Most of the early applications of thermal spray coatings were focused towards providing a remedy to excessive wear degradation. However, as the introduction of such coatings into wider industrial sections increases there is also exposure to other potential degradation processes - aqueous corrosion is one such process. The complex microstructures in cermet coatings have been shown to translate to complex modes of corrosion attack. In this paper an electrochemical test methodology to probe the local/micro aspects of corrosion initiation and propagation will be described. A new electrochemical cell has been devised in which the corrosion can be followed `live` and in `real time`. The surface is subjected to in-situ imaging by Atomic Force Microscopy (AFM). This paper reports some of the exciting findings which have enabled the sequence of corrosion events in cermet coatings to be defined. The study has revealed that a precursor to coating degradation is the attack of the Co-base matrix. This sets up an environment which can catalyse WC dissolution. The practical and fundamental importance of the results will be discussed.

Most metallic and ceramic splats exhibit temperature-dependent behavior when they strike a metal substrate and assume a shape that suggests temperature-dependent wetting properties. In this study, the authors investigate the relationship between high-temperature oxidation, substrate morphology, and the flattening behavior of free-falling droplets. Substrate surfaces are examined by means of atomic force microscopy, which shows that changes in morphology of just a few nanometers can have an effect on flattening behavior. Paper includes a German-language abstract.

The influence of alumina substrate temperature and phase structure : columnar gamma phase, columnar alpha phase and granular alpha phase on splat formation and crystal growth has been studied by SEM and Atomic Force Microscopy. X Ray Diffraction at low angle has allowed to obtain informations on phase structure of layered splats according to substrate phase structure and coating thickness. Column sizes of splats are correlated to a ID model of splat cooling showing the influence of substrate thermal properties and splat thickness on crystal growth kinetic. Finally, coatings adhesion-cohesion values function of spraying parameters are in good agreement with splat morphology and microstructural evolution.