Influence of the superalloy substrate in the synthesis of the Pt-modified aluminide bond coat made by slurry

Surface and Coatings Technology 270 (2015), 102-108, DOI: 10.1016/j.surfcoat.2015.03.015

The influence of the superalloy composition and crystal orientation on the formation of an unconventional thermal barrier coating system (TBC) is reported. A 6 μm-thick Pt layer was first electrodeposited onto a directionally solidified (DS) CM-247LC and a single crystal (SX) PWA-1483 substrate followed by annealing. A water-based slurry containing Al microparticles was then applied and annealed to form simultaneously a ceramic top coat and a diffusion bond coat. Irrespective of the annealing treatment (Pt, slurry), thinner diffused layers were obtained with the SX than with the DS material. Dual PtAl₂ and (Ni,Pt)Al phases formed in both diffused layers but Cr segregation at the coating/substrate interface restricted further ingress of Pt and of Al into the SX superalloy compared to the DS one. This was related to the greater Cr content in the SX than in the DS material and to the absence of grain boundaries in the former. Nevertheless, a ceramic top coat composed of hollow alumina spheres formed over the thermally grown oxide and the diffused layer on both substrates.