Additive laser deposition of compositionally graded NiCrAlY-YSZ multi-materials on IN625-NiCrAlY substrate

Composites of NiCrAlY-YSZ, with varying volume percentages of YSZ (0%, 15%, 35%, 65% and 100% YSZ), were deposited on a nickel base superalloy IN625 substrate coated with NiCrAlY as a bond coat by the LENS™ additive manufacturing process. The thermal conductivity and coefficient of thermal expansion of the deposits were evaluated. Microstructural and micro-chemical analyses of the composite deposits were carried out using optical microscopy, SEM, EBSD and XRD. The NiAl (β) phase content within the NiCrAlY portion of the higher vol% YSZ deposits was found to be lower, presumably due to the fact that the higher YSZ- containing powder as well as the melt pool have higher laser absorptivity and consequently higher pool temperatures resulting in a greater extent of elemental diffusion. Diffusion of Zr from YSZ to NiCrAlY in the 65%YSZ deposit resulted in the formation of intermetallics of Ni[sbnd]Zr. All composite deposits containing 35% or higher vol% YSZ delaminated from the bond coat immediately on cooling which is attributed to the change in the matrix phase from NiCrAlY(metallic) in lower YSZ deposits to YSZ (ceramic) in higher YSZ deposits. Lastly, compositionally graded thermal barrier coatings with combinations of layer wise increasing %YSZ were deposited, and the influence of the layer characteristics on the thermal cycling life of the coatings was demonstrated.