This paper deals with coating alternatives to hard chromium plating. Indeed, thermal spraying is already used in industry, but results are not always satisfactory for reasons of porosity and microstructures. In this study, atmospheric plasma spraying (APS) and in situ laser irradiation by diode laser processes were combined to modify the structural characteristics of thick NiCrBSi alloy layers. The microstructure evolution was studied and results show that in situ laser remelting induces the growth of a dendritic structure which strongly decreases the porosity of as-sprayed coatings and increases the adhesion on the substrate. Moreover, no phase transition after laser treatment is observed. At least, a mechanical investigation demonstrates that the combination between the plasma spraying and in situ melting with a diode laser can result in the improvement of mechanical properties. The hybrid process appears to be a possible alternative to hard chromium plating, in order to protect mechanical parts, because of the good mechanical behaviour of NiCrBSi layer. Moreover, the increase of the laser incident power causes an increase of the mean contact pressure, along with coatings hardness.

Pressure to identify alternatives to hard chromium electroplating has increased these few last years, related to environmental requirements, because of the use of hexavalent chromium, a highly toxic substance. The plasma spray technique allows the formation of thick coatings which present moderate adhesion to the substrate and show porosity and formation of oxide interlayers, which impairs to obtain full benefits of the coatings properties. In this sense, a treatment can be necessary to improve the properties of these coatings. In this paper, the effect of an in situ laser melting treatment of NiCrBSi coatings, deposited by plasma spraying was investigated. It is demonstrated by a Life Cycle Assessment (LCA) that this process is clean. Moreover, the corrosion resistance of as-sprayed and in situ remelted layers was evaluated by potentiodynamic polarization curves. The corrosion resistance was increased because of the finer structure and higher densities of the coatings, nevertheless, corrosion mechanisms occurring in all cases are different.

The aim of this study is to propose coatings that could potentially replace hard chromium as a means of corrosion and wear protection. Two NiCrBSi coatings are evaluated, one produced by laser cladding, the other by atmospheric plasma spraying with a post-laser treatment. Although laser-clad NiCrBSi exhibits the best technical properties, the APS coatings were found to be more environmentally justifiable based on the use of life cycle assessment (LCA) software.

Wear resistance of materials in very aggressive environment of different industrial sectors like drilling, mining, cutting, etc, appears to be critical and many efforts have been made to limit the major economic loss that represents a broken or damaged tool. The objective of the CLADIAM project (G5ST-CT-2002-50179) is to develop a cladding technique to coat complex parts based on an innovative cladding material composed of diamond pellets and cast spherical tungsten carbide particles using an automated high power diode laser (HPLD) equipment. The result of these two and a half years of work has led to the finalization of following techniques: A pelletizing alloy that takes into account the constraints of laser cladding, Enrobing of diamond particles to avoid their damage, An industrial technique, technically and economically efficient, of laser cladding that allows the realization of complex shapes. The combination of a new technique of wear and abrasion tests has led to the characterization of the obtained cladding. The results have been compared with the tests on industrial parts in severe and even extreme wear conditions. The development of this new cladding technology has been possible thanks to the use, the characterization and the optimization of specific cladding nozzles associated with the special beam of high power diode laser. The results obtained are very encouraging and open the doors to new claddings that combine the specific advantages of diamond and tungsten carbides for the nature of cladding, but also the fineness of the structure, the improvement of behaviour in wear conditions, the small thermal impact of the parts, some of the well known advantages of laser cladding.

In previous works, laser irradiation was associated to thermal spraying in the so-called MELTPRO process to improve the performance and the durability of TBCs. This study aims at presenting results concerning the thermal behavior of TBC's manufactured according to this process. Two types of severized thermal cycling were implemented: (i) “oxidizing” test: isothermal shocks were performed at different temperatures, ranging from 900°C to 1050°C down to 0°C; (ii) “quite non-oxidizing” test: thermal shocks were implemented from a temperature of 1100°C down to 50°C. Moreover, thermal annealing at 1100°C were performed to compare sintering phenomenon. TBC microstructure and its evolution during heat treating were characterized using image analysis, Knoop micro-indentation and XRD analysis. MELTPRO process was shown to increase twofold the lifetime of TBCs during isothermal shock tests. This is attributed to the fact that the columnar structure and the pore-crack architecture of remelted coatings improve the compliance property and decrease the permeability of TBCs. XRD analyses show that, in the Y-PSZ TBCs, the main phase is the metastable tetragonal (t’) phase both for as-sprayed and MELTPRO processed coatings. Moreover, remelted TBCs show a higher phase stability than as-sprayed TBCs during thermal shock tests: it seems that the remelted coatings have higher phase stability thanks to their pore architecture, which lead to a better compliance in relation to the thermo mechanical stresses, and so to a decrease in the stress variations undergone by the structure during the thermal cycles. During thermal annealing, it seems that MELTPRO processed coatings are less affected by sintering than as-sprayed coatings. Sintering phenomenon primarily concerns inter-lamellar cracks of non remelted areas. Besides, whatever the coating manufacturing process, the main remaining phase is the metastable tetragonal phase whatever the heat treating duration.