Effects of internal oxide contents on the oxidation and β-phase depletion behaviour in HOVF CoNiCrAlY coatings

Oxidation Behavior of Pre-Strained Polycrystalline Ni3Al-Based Superalloy

“…where a is the activity coefficient and K is the equilibrium constant. During the oxidation process in the (γ + γ ′ ) dendritic region of the original alloy, the Gibbs free energy of the resulting Al 2 O 3 is more negative than NiO [21], indicating that Al has a greater affinity for oxygen than NiO. However, the growth rate of Al 2 O 3 is lower than NiO [37,51], and the stoichiometric amount of NiO is smaller than Al 2 O 3 which means it will not be severely depleted at the reaction front like Al.…”

“…For instance, the outer NiO and inner Al 2 O 3 structures formed during the oxidation process of Ni 3 Al-based superalloys play a crucial role in determining the alloy's antioxidant properties [18]. In addition to applying protective layers to the matrix [19][20][21], the antioxidant properties of the alloys can be enhanced through the processes of heat treatment [8,22,23] and alloying [24,25]. These methods have achieved good results, although it is challenging to achieve further significant improvements in the antioxidant properties of superalloys.…”

Size effects on high temperature oxidation of MCrAlY coatings processed via APS and HVOF depositions

“…1). Intrusive oxidation was reported for different MCrAlY projected coatings, with a sensitivity not clearly associated to a deposition process [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. For instance, several authors reported that HVOF MCrAlY coatings were less prone to intrusive oxidation compared to APS (or even low pressure plasma spraying (LPPS)) [20,23,25].…”

“…However, these projected coatings are much more prone to internal defects such as unmelted particles, pores, internal oxides and/or nitrides, intersplats. Oxygen ingress along these open channels causes oxide intrusions within the coating [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. This oxide intrusion, concomitant to external oxide scale growth, participates in the Al consumption.…”

Effect of Pre-Heat-Treatment on the Oxidation Resistance of MCrAlY Coatings: A Review

“…In the HVOF process, the combustion of fuel gas and oxygen generates a high-speed jet flame that melts and accelerates the MCrAlY powder particles onto the substrate in the air. The intense jetting force leads to rapid particle deformation and quick cooling, resulting in the solidification and formation of a coating [44]. The HVOF MCrAlY bond coat exhibits high oxygen content, low density, and high residual stresses, which could potentially result in negative consequences [45].…”