Role of internal oxidation on the failure of air plasma sprayed thermal barrier coatings with a double-layered bond coat

Abstract

Failure of air plasma sprayed (APS) thermal barrier coatings (TBCs) with a double-layered bond coat was investigated. The bond coat consists of a dense layer near the substrate side and a porous layer on the surface. Both were made of NiCoCrAlY alloy and deposited using high velocity oxygen-fuel technique. After thermal cycling, a large amount of internal oxides formed (up to 45% in volume fraction), introducing a significant volume expansion both in in-plane and perpendicular direction in the bond coat. However, the presence of the ceramic top coat can suppress the bond coat in-plane swelling thus lowering the internal oxidation rate.Compared with the fully dense bond coat, the interface roughness of the porous bond coat increases significantly when internal oxidation occurs. There is a strong correlation between the internal oxidation and the interface roughness. In addition, both the beneficial and detrimental effects of internal oxidation on TBC failure were discussed. It is proposed that a fully dense bond coat with a proper surface roughness should have a longer thermal cycling

Investigation on the performance of air plasma sprayed thermal barrier coating with Lu/Hf-doped NiAl bond coat

“…The area fraction of the internal oxide within the bond coat was quantified by image analysis using ImageJ software [27]. All the images were taken on the cross-sections in BSE mode, and at least six randomly selected areas (~135×300 m 2 ) were analyzed for each sample.…”

“…For plasma sprayed metallic bond coats exposed to high temperature, internal oxidation is an inevitable phenomenon, which may influence the durability of TBC systems [27,30,35]. As shown in Fig.…”

“…4 presents the internal oxidation behavior of the NiAl bond coat and the area fractions of the internal oxide for all the samples as a function of cycle number. For measurement, the TGO layer at the bond coat/top coat interface was not taken into account, and for simplicity, the "internal oxide fraction" refers to area fraction of the dark contrast areas including the oxide and possible pores within the bond coat [27,30]. Initially, all the bond coats included a certain amount of oxide and pores (6~8 %) due to in-flight oxidation during plasma spraying.…”

Assessment of the performance of Y2SiO5-YSZ/YSZ double-layered thermal barrier coatings

“…Yttria-stabilized zirconia (7-8 wt. %, YSZ) is the state of art material for the thermal barrier coatings (TBCs) application due to its low thermal conductivity and exceptional mechanical properties [1][2][3][4]. As the engine temperature increases, the YSZ encounters the following issues: (i) tetragonal to monoclinic phase transformation (t-m) occurs at high temperature (e.g., >1200 °C) and lead to catastrophic failure of TBCs [5][6]; (ii) molten silicate attack becomes increasingly important which could degrade the strain tolerance of the coating and subsequently cause coating spallation [7].…”

The oxidation performance of plasma-sprayed NiAl bond coat: Effect of Hf addition in bond coat and substrate

“…[11] used cold spraying followed by a annealing process to fabricate NiAl coating. As a versatile and economic method, air plasma spraying (APS) has been widely applied to deposit bond coats (e.g., MCrAlY) in the hot sections of industrial gas turbines [12][13][14]. However, compared with MCrAlY, deposition of NiAl by APS is more challenging and used less often [15][16][17].…”