In the last years laser beam cladding was recognised as a high quality coating process. Low thermal influence, high cooling rates, metallic bonding, minimal surface roughness are only some of the positive aspects. On the other hand the process efficiency is very low and the running costs in comparison to PTA or Thermal Spraying are high. Attempts to improve the productivity aim to enhance the efficiency of the beam source itself or to optimize the energy management. This is for example possible through a higher coating speed or through hybrid setups, which allow the use of an additional preheat source (e. g. plasma-assisted laser cladding). Regarding flexibility, defined as the capability of a process to answer in a short time to application requests, the effectiveness of laser cladding can be widely increased through free forming (shaping) of coatings without additional clamping devices. The geometric shape of the coating seam is mainly defined by gravity and surface tension of the melt. An additional force, as for example Lorentz force, can optimize the geometry and improve the process conditions. Wide seams allow for example a low number of overlapping layers when coating large areas and rise the specific area deposition rate. Slim coatings on the contrary are advantageous when generating 3-dimensional structures. The induced force depends from the applied magnetic field and the flow of an electric current. The presented investigations clarify the physical background, the interaction of the magnetic force and the geometric shape of the coating and the possibility to apply them for technical coatings. The application of an external force made it possible to increase the efficiency of the laser cladding process and to gain more interest of the industry.

The paper describes the some differences of laser coating (laser cladding or laser spraying) process in comparison to thermal spraying. Laser coating is a novel coating process, which produces coatings with high density, metallurgical bonding and low heat input to the substrate. Laser coating types and coating properties are reviewed and compared with thermally sprayed coatings. Typical application areas of laser coatings are presented.

In order to broader thermal spraying applications and reduce constraints and time due to conventional surface preparation before thermal spraying, the PROTAL process was developed over the last decade. This process integrates laser ablation, using a Q-switched Nd-YAG laser to prepare the surface simultaneously to the coating build-up during Plasma or HVOF Spraying. The present paper aimed at evaluating the feasibility to use the Protal technology in conjunction with the Twin Wire Arc deposition (Arc spraying) onto the 7075 Aluminum based alloy and to define the optimal Protal process parameters. Coating adhesion, micro-gap at coating-substrate interface and the coating residual stresses are evaluated. The Protal parameters investigated are: the laser energy density onto the substrate and the coating layers, the number of laser passes and the time delay between the laser impact. This study results indicate that it is feasible to use the Protal technology in-situ with the Arc spray process in spite of the challenging overspray and the large plume size of the Arc process. Good adherence and absence of interface micro-gap is obtained with an appropriate range of laser energy density to ablate the substrate. The use of a low energy ablation prior each coating layers reduces coating tensile residual stresses and improves furthermore the bond strength. The elimination of the process ablation dust and overspray dust prior the coating deposition onto the plane substrate was found critical to obtain a good bond strength. This research results from collaboration between the LERMPS in France and National Research Council Canada. Abstract only; no full-text paper available.