Papers by Author: Marie Helene Berger

Abstract: Basically, thermal spray and laser processing can be considered as half brothers since they show many common features due to the use of a (more or less) high-energy source for both. Their combination can therefore be very fruitful and prominent to achieve coatings, which results in their most recent and advanced applications. In the materials processing development story, the laser will thus have moved from cutting to coating. This keynote presentation focuses on the recently-developed coupling of laser processing to cold spray). In this dual process, a cold spray gun is combined to a laser head in a single device, e.g. on a robot. Series of coating experiments using various laser irradiation conditions, primarily pulse frequency, were carried out for Al-based and Ni-based alloys. Laser pre-treatment of the substrate just prior to cold spray, was shown to be beneficial for adhesion of cold-sprayed coatings. Adhesion improvement was exhibited and studied from LASATesting (LASAT for “LAser Shock Adhesion Test”). Incidentally, through LASAT also, the role of lasers in the development of thermally-sprayed coatings can be considered as major. Results are discussed in the light of a TEM (Transmission Electron Microscope) study of the coating-substrate interface with and without laser pre-treatment.

Abstract: The mechanical properties of directionally solidified two-phase eutectics can be superior to that of either constituent alone due to the strong constraining effects of the interlocking microstructure. The present work focuses on the failure mechanisms that occur in Al2O3-Al2TiO5 composites fabricated by directional solidification. Two compositions rich in alumina have been considered. The constituents were the same in both materials, primary Al2O3 dendrites surrounded by a TiO2-containing phase, with different morphological and size characteristics. The dendrites in the material containing the smallest amount of Al2O3 were short and highly interpenetrated by the secondary phase whereas those of the material with the highest Al2O3 content were long and much less interpenetrated. The mechanical behaviour in bending was determined by these microstructural differences because the load bearing phase in these directionally solidified materials in the system Al2O3-Al2TiO5 are the Al2O3 dendrites.