Thermal Stability of YSZ Coatings Deposited by Plasma Spray–Physical Vapor Deposition

Abstract

The plasma spray-physical vapor deposition (PS-PVD) process has received considerable attention due to its non-line of sight deposition ability, high deposition rates, and cost efficiency. Compared with electron beam-physical vapor deposition (EB-PVD), PS-PVD can also prepare thermal barrier coatings (TBCs) with columnar microstructures. In this paper, yttria-stabilized zirconia (YSZ) coatings were fabricated by PS-PVD. Results showed that the as-deposited coating presented a typical columnar structure and was mainly composed of metastable tetragonal (t -ZrO 2 ) phase. With thermal exposure, the initial t phase of YSZ evolved gradually into monoclinic (m-ZrO 2 ) phase. Significant increase in hardness (H) and the Young's modulus (E) of the coating was attributed to the sintering effect of the coating during the thermal exposure, dependent on exposure temperature and time. However, the values of H and E decreased in the coatings thermally treated at 1300-1500 • C for 24 h, which is mainly affected by the formation of m-ZrO 2 phase.

Durability of YSZ coated Ti2AlC in 1300°C high velocity burner rig tests

“…By comparison, the YSZ structure near the cooler grip end (Figure 7B) showed that most porosity was highly aligned along the initial column boundaries. In general, these morphologies mirror those described in a recent study of PS‐PVD YSZ coatings 36 …”

“…Furthermore the 1300°C/500 hours burner sample became primarily cubic with neither tetragonal phase and little monoclinic. Further comparisons are available in the recent PS‐PVD phase stability study that did show transformation to monoclinic 36 …”

“…Coarsening to > 1 μm and uniform dispersal in the hot zone (Figure 7A,C) is compared to the regular arrays of fine as‐coated porosity (~100 nm) remaining at the grip end (Figure 7B,D). A recent PS‐PVD aging study has shown microporosity coarsening, grain growth, and columnar agglomeration over the 1200°C‐1600°C temperature range 36 …”

“…A recent PS-PVD aging study has shown microporosity coarsening, grain growth, and columnar agglomeration over the 1200°C-1600°C temperature range. 36 The Al 2 O 3 scale, identified by EDS, exhibited some fine porosity, Figure 7C,D, which undoubtedly included metallographic pullout as well.…”

Experimental and Modeling Studies of Bond Coat Species Effect on Microstructure Evolution in EB-PVD Thermal Barrier Coatings in Cyclic Thermal Environments

“…The TGO layer acts as a protective layer to retard the thermal and oxidation diffusion. However, the TGO layer may increase the internal stress in TBC systems, which causes potential cracking at the interface between the bond and top coats, eventually leading to spallation or delamination of the top coat [7][8][9][10]. The bond coat in a TBC system is to ensure the 2 of 15 structural integrity and to protect the superalloy substrate from oxidation.…”