Microstructural investigations of EBPVD thermal barrier coatings

This paper deals with the morphology, constitutive phases and fine microstructures of some EBPVD processed yttria partially stabilized zirconia thermal barrier coatings. This study has been performed by X-ray diffraction and scanning and transmission electron microscopy. It was shown that the coatings studied were constituted of a single metastable tetragonal t' phase, as expected if one refers to the well-known non equilibrium paths in the zirconia-yttria phase diagram, and not of a cubic solid-solution, as it is claimed in several papers in the literature. It was also shown that this tetragonality is not easily evidenced by X-ray diffraction because the t' grains exhibit a particular crystallographical texture (c axis generally parallel to the substrate/coating interface). The relationship between the coating tetragonality, its particular texture and its ability to resist crack propagation is discussed. It is suggested that the former could significantly contribute to the well-known toughness of EBPVD coatings, leading to increased resistance to thermomechanical fatigue

Correlation between the wear behaviour and the mechanical properties of several surface treatments

Surface mechanical strength of chromium base (electrolytic and plasma sprayed) coatings is studied for friction and wear applications in nuclear environment. Indentation, scratch, and wear testing results are compared. In particular intrinsic coating brittleness is investigated as a mechanism responsible for impact wear. Electrolytic, hard chromium plate has a wear resistance well below that of the spray coated specimens studied. Acoustic emission level and brittle damage features are shown to be correlated

Study of the oxide layer formed on potential SOFC interconnect materials in dry and humid air

In the last years a greater importance has been given to several chromia-forming stainless steels as interconnects for solid oxide fuel cells (SOFC). These steels were selected due to a lower price and a good electrical conductivity without limiting the lifetime of the stack. The interconnect materials have to present a good behaviour not only in dry but also in humid air, which is the anode side atmosphere of the fuel cell. In this context, studies were performed on different chromia-forming alloys using high temperature X-ray diffraction (XRD) in dry and humid air, to evaluate in-situ the growth of the oxide scale (Fig.1). Afterwards, a microscopic analysis by field emission-scanning microscopy (FE-SEM) was done to verify the composition and structure of the oxide scale (Fig.2,3). Impedance measurements of the oxidized samples were carried out during temperature cycles in order to determine the electrical conductivity and activation energy of the oxide layer. The pape r will show the results obtained by oxidation at 800°C of two potential interconnect materials having a similar composition, Crofer 22 APU and ZMG 232 (Tab.1), which form principally chromia (Cr2O3) and the Cr-Mn spinel (MnCr2C4). A time evolution of the oxide formation and growth observed in the XRD analysis will also be presented (Fig.1). In addition, to corroborate this first approximation to the oxidation behaviour, the microscopy study of the surface and a transversal cut of the oxide scale will also be presented (Fig. 2,3)

Microstructural investigation of plasma sprayed yttria partially stabilized zircona TBC (in relation with thermomechanical resistance and high temperature oxidation mechanisms)

Tire de : 37th ASME Congress on 4Gas Turbine and Aeroengine', Koln (Germany), June 1-4, 1992SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1992 n.73 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

T.E.M. investigations of high toughness non-equilibrium phases in the ZrO_2- Y_2O_3 system

Tire de : Scipta metallurgica et materialia, vol. 25, pp. 1815-1820, 1991 (Pergamon Press, USA)SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1991 n.184 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Alumina scale growth at zirconia/MCrAY interface : a microstructural study

Tire de Microscopy of oxydation, march 26-28, 1990SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1990 n.51 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Alumina scale growth at zirconia/MCrAY interface : a microstructural study

Tire de Microscopy of oxydation, march 26-28, 1990SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1990 n.51 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Thermal barrier coatings : microstructural investigation after annealing

Publie dans : 'Material science and engineering structural materials : properties, microstructure and processing', A121, 1989, p. 475-482SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1990 n.62 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc