Additive laser deposition of YSZ on Ni base superalloy for thermal barrier application

In the present work, the feasibility of additive laser deposition (ALD) of YSZ on IN625 substrate was studied using two different bond coats (BC) viz. NiCr and NiCrAlY and two different deposition schemes, consisting of direct deposition of YSZ (DI) and compositionally graded (CG) deposition of bond coat-YSZ. These deposits were examined for microstructural features, and their ability to provide thermal barrier to heat flow and to withstand thermal cycling were evaluated. It has been observed that DI and CG NiCr-YSZ coatings survive 240 cycles whereas CG NiCrAlY-YSZ samples survive <5 thermal cycles between 1100 °C and room temperature. The poor thermal cycling resistance of CG NiCrAlY-YSZ coatings is attributed to the formation of a brittle oxide layer at the interface of NiCrAlY and YSZ. Between all four combinations of BC and types of deposition, CG NiCr-YSZ coatings give the maximum temperature drop (350 °C) across the thickness when tested at 1000 °C as hot face temperature and for 600 s duration which, combined with good thermal cycling resistance, makes them potential candidates as thermal barrier coatings (TBCs) applied by additive laser deposition.