Oxide layer phase structure of MCrAIY coatings

Abstract

During operation, stationary blades and vanes of gas turbines are subjected to high thermal and mechanical stresses and severe oxidation. This situation can only be controlled by a composite approach in which the base material provides the necessary mechanical properties and coatings provide protection against oxidation, corrosion and, in the case of thermal barrier coatings, a part of the heat flux. For a better understanding of the oxidation processes on standalone MCrAIY overlays as well as MCr AIY used as a bond coat, in situ X-ray diffraction measurements of the formation and composition of the oxide scale at high temperatures are presented. The phase changes during oxide scale formation are discussed. Data are presented for MCrAlY coatings with 12%AI and 3%Re at three different temperatures versus time. At 950, 1000, and 1050°C a three phase oxide layer of Cr203‘ A1203, and NiCr2O4 was detectable. Rhenium could not be found in the oxide layer at any of the three temperatures.

High temperature oxidation of HFPD thermal-sprayed MCrAlY coatings

“…4) according to the analysis carried out using the electron microprobe, the dark-contrast inner layer, which has a uniform thickness is alumina and the lighter-contrast exterior layer, which was intermittently present and also has a more irregular morphology, is the corresponding mixed spinel-type oxide (NiAl 2 O 4 and CoAl 2 O 4 , respectively). Similar results were obtained by other authors when characterizing the oxidation behaviour of low pressure plasma-sprayed MCrAlY coatings [8][9][10]. The presence of alumina and mixed spinel-type oxides was also revealed from the diffraction pattern of the surface of these samples, as can be seen in Fig.…”

The influence of pyrolysing Al2O3 precursor on the high temperature properties of the YSZ-Al2O3 composite coating

“…After TGO formation, the inward diffusion of O 2 could be blocked and the growth rate is decreased. These results indicate that the continuous TGO layer formation had a protective role and act as a diffusion barrier against the diffusion of oxygen [29].…”

Modeling the Influence of Reactive Elements on the Work of Adhesion between Oxides and Metal Alloys

“…Delamination is enhanced by the presence of impurities such as sulfur in the coating alloy and also by the environment in which the turbine is operated. The addition of reactive elements to the bond coat has been found to dramatically improve the adhesion of the TGO to the bond coat 14,26–35 . This reactive element effect is attributed to a number of mechanisms, including the direct promotion of chemical bonding between the oxide and the bond coat alloy.…”

“…The addition of reactive elements to the bond coat has been found to dramatically improve the adhesion of the TGO to the bond coat. 14,[26][27][28][29][30][31][32][33][34][35] This reactive element effect is attributed to a number of mechanisms, including the direct promotion of chemical bonding between the oxide and the bond coat alloy. Other mechanisms include impurity scavenging, in particular, scavenging of sulfur, 36 reduction of cation diffusion from the bond coat to the oxide, and enhanced nucleation of a-Al 2 O 3 .…”