Innovative diffusion aluminide coating obtained via electroless pure nickel approach: synthesis, characterization and long term oxidation tests

摘要

Materials used in hot components of aero- and land-base gas turbines have to withstand severeoperative conditions and may undergo severe hot corrosion and high temperature oxidationphenomena; for this reason, diffusion aluminide coatings are widely used to protect thesuperalloys-based components against the harsh environment typical of the gas turbine engines. Inthis work is presented an innovative strategy of manufacturing of diffusion coatings by the use ofthe electroless pure plating as carrier for an external nickel layer able to avoid the formation of theinterdiffusion zone between the substrate and the top coat. The first part of the work is focused onthe synthesis strategy for the pure nickel coating; although the chemical deposition of metalliccoatings by autocatalytic reduction of metal ions (electroless plating) has been widely investigatedwith more than 10000 publications, the most studied system involves the co-deposition of the Pinside the metallic coating as collateral products of the redox system (sodium hypophosphite isused as reducting agent). For this reason, a new redox system involving hydrazine as reductingagent, was studied to obtain a pure nickel coating. In the second part of the work, the packcementationwas selected as aluminide coating deposition technique. A long-term oxidation (morethan 1000h) at 1050°C was carried out in order to compare the standard coating with the newmodified coating obtained in this work. The oxidation kinetics was studied by measuring the masschange at different time and the morphological evolution was observed by SEM and EDS analysis.