Analysis of the co-deposition of CrAlYTa particles with nickel by an electrolytic–electroless route: The influence of solution and hydrodynamic parameters

MCrAlY coatings are good candidates for abradable seals used in compressors of aircraft and industrial gas turbines to decrease clearance between the stator casing and rotor blade tips and hence to increase turbine efficiency and decrease fuel consumption. Such coatings were produced using an electroless like co-deposition route. In this process, a CrAlYTa powder is embedded at the surface of a material during the deposit of a nickel matrix according two simultaneous reactions: an electrolytic one and an electroless one. Hydrodynamic (position of the sample in the bath, stirring rate) and solution (current density, concentrations of the reducer and of the nickel complex) parameters were systematically investigated in order to calculate the mean weight powder fraction αW and the total deposition rate rd. It was found that the hydrodynamic parameters influence only αW and that the current density influences rd. There is also a competition between the electroless reaction (mainly at the particle surface) and the electrolytic one (at the surface of the sample). Prior to the entrapment, the powder particles must be coated by an electroless nickel deposit to obtain a high powder fraction embedded in the coating.