Modification of oxide layer in plasma-sprayed thermal barrier coatings

TGO Growth and Crack Propagation in a Thermal Barrier Coating

“…This suggests that the VHT could, to a certain level, suppress the formation of mixed oxides during thermal exposure via developing a thin Al 2 O 3 layer in vacuum at high temperature. This is consistent with previous observations reported by many other researchers ( Ref 6,[11][12][13][14][15][16][17][18]. Similar to the as-sprayed TBC, cracking in the VHT TBC was very limited after up to twenty-five 100-h cycles (Fig.…”

“…Since oxidation of the bond coat has been recognized as the cause for separation of the ceramic layer from the substrate (Ref 2, 3, 7-10), the formation of the detrimental oxides may accelerate crack nucleation during thermal exposure, leading to premature TBC failure. Studies have shown that, when heat treated in low-pressure oxygen conditions, a continuous Al 2 O 3 layer may develop at the ceramic/bond coat interface in both thermally sprayed ( Ref 6,[11][12][13] and electron beam physical vapor deposited (EB-PVD) TBC systems (Ref [14][15][16][17][18]. Therefore, appropriate postspraying heat treatment(s) may suppress the formation of detrimental oxides by developing a TGO composed of a predominantly Al 2 O 3 layer, leading to improved TBC durability.…”

Glass–ceramics as oxidation resistant bond coat in thermal barrier coating system

“…Chen et al showed that heat treatment of the as sprayed TBC in a low pressure oxygen environment promoted the formation of a uniform, thin protective layer of alumina (Al 2 O 3 ) at the bond coat-top coat interface and reduced the formation of some detrimental oxides such as Ni(Cr,Al) 2 O 4 (spinel) and NiO during further thermal exposure in air [5]. Preoxidation surface treatment of the bond coat performed under specific condition decreased the TGO growth rate resulting in improvement in TBC life compared with a conventional TBC system [6].…”

Microstructure and Mechanical Properties of a Glass-ceramic Bond Coated TBC System

“…The decrease in the nanohardness value of the top coat was occurred with increasing the load due to the Indentation Size Effect (ISE). Here, this effect was observed because of the crack formation in the top coat during unloading, which restricted the extent of elastic recovery in the form of shrinkage of the indentation cavity leading to increase in the indentation size (Prescott et al (1992), Chen et al (2006), Singheiser et al (2001)). As a consequence, the nanohardness values of the top coat decreased with the increase in the applied load.…”

“…4c). Chipping, cracking and work hardening reduced the extent of elastic recovery in the form of shrinkage of the indentation cavity leading to an increase in the indentation size and consequently, the nanohardness values of the top coat, bond coat and substrate decreased with increasing the load (Prescott et al (1992), Chen et al (2006), Singheiser et al (2001)). …”