[15] B. Saruhan, K. Fritscher, U. Schulz, Ceram.Eng.Sci.Proc. 2003, 24, 491. [16] B. Saruhan, P. Francois, K. Fritscher, U. Schulz, Surf. Coat.Technol. 2004, 128, 175±183. [17] M. Mineaki, N. Yamaguchi, H. Matsubara, Scripta Ma- ter. 2004, 50, 867. ______________________ DOI: 10.1002/adem.200600059 StructuralEvolutionand MechanicalProperties ModificationofMELTPRO (in Situ Remelted)Processed ThermalBarrierCoatings duringThermalShocks** By Guy Antou,* Ghislain Montavon, Françoise Hlawka, Christian Coddet, and Alain Cornet Thermal Barrier Coatings (TBCs) are widely used in aero- and land-based gas turbines because of their ability to sustain high thermal gradients in the presence of adequate backside cooling. [1±3] A TBC system is hence used to protect the metal- lic components of the turbine hot parts from degradation at high temperatures, erosion, oxidation and corrosion phenom- ena. Four primary constituents, as listed below, comprise the TBC system and enable the above functions: ± the top-coat; i.e., the ceramic TBC, which is commonly manufactured using air plasma spray process and behaves as the thermal insulator; ± the substrate materials, most commonly a superalloy, which sustains the structural loads; ± n aluminum containing bond-coat (BC), usually MCrAlY where M represents Ni, Co or a combination of these two elements, located between the metallic substrate and the ce- ramic. The BC is usually manufactured using plasma spraying or flame spraying and provides oxidation protec- tion to the substrate and behaves as a compliance layer due to the linear coefficient mismatch between the ceramic TBC layer and the substrate; ± a thermally grown oxide (TGO), predominantly a-alumi- na, [4] that grows between the ceramic TBC and the BC dur- ing the initial thermal cycles of the system and plays a rele- vant role in the BC/TBC adhesion. [5±6] Besides corrosion occurring at high temperatures due to sulfur impurities in fuel, the two main damage mechanisms of TBC are: (i) the metal/ceramic thermal linear expansion mismatch during thermal cycling; (ii) the growth of the TGO which induces stresses into the ceramic top coat. This damage induces failure of the TBC system by spallation of the ceramic top coat. For advanced gas turbines, improvements of TBC proper- ties would seek a higher life time, a lower thermal conductiv- ity, a higher thermal stability and a lower surface roughness. These improvements are sought to decrease maintenance fre- quency and/or to increase efficiency by increasing gas tem- peratures at the combustion chamber outlet. One way to improve TBC properties consists in modifying the layer architecture by an alternative manufacturing pro- cess. To reach this goal, plasma spray processing has been combined with laser remelting in this study to alter the pore- crack architecture of the TBC; and hence to modify the TBC COMMUNICATIONS ADVANCED ENGINEERINGMATERIALS 2006, 8,No.7  2006 WILEY-VCHVerlag GmbH& Co. KGaA, Weinheim 657 ± [*] Dr.G.Antou,Dr.F.Hlawky,Prof.A.Cornet Laboratoired'IngØnieriedesSurfacesdeStrasbourg(LISS) InstitutNationaldesSciencesAppliquØesdeStrasbourg (INSA) 24BddelaVictoire,67000Strasbourg,France Prof. C. Coddet Laboratoired'EtudesetdeRecherchessurlesMatØriaux lesProcØdØsetlesSurfaces(LERMPS) UniversitØdeTechnologiedeBelfort-MontbØliard(UTBM) sitedeSØvenans,90010BelfortCedex,France Prof. G. Montavon SciencedesProcØdØsCØramiquesetdesTraitementsdeSurface (SPCTS)±UMR6638 EcoleNationaleSupØrieuredesCØramiquesIndustrielles/ UniversitØdeLimoges 123AveAlbertThomas,87030LimogesCedex E-mail: ghislain.montavon@unilim.fr [**] AuthorsacknowledgethehelpofLydieLahoupe(LERMPS)for sample preparation. LERMPS is a member of the Institut des Traitements de Surface de Franche-ComtØ (ITSFC, Surface TreatmentInstituteofFranche-ComtØ),France. Table 1. Coating structural attributes (see literature [5] for details). structural attributes and physical characteristics as-sprayed insitu remelted (at 1.87 J.mm ±2 ) porosity level [%] 11 ± 0.3 17.2 ± 4.3 non-connectedpores[%] 7 16 connectedpores[%] 4 1 globular pores [%] 5 ± 0.2 13.3 ± 4.3 cracks [%] 6 ± 0.2 3.7 ± 0.2 verticalcracks[%] 30 ± 2 29 ± 1 horizontalcracks[%] 70 ± 2 71 ± 1 apparent thermal conductivity [W.m ±1 .K ±1 ] 1.4 ± 0.1 0.9 ± 0.1 phase tetragonal metastable (T¢)