The main objective of the project was the improvmenet of the reliablility of components containing ceramic materials, with emphasis. A methodology was established for qualification, based on morphological and chemical analysis for the interface and simulation of the life cycle.
For testing, the emphasis was placed on adhesion mechanisms. Thin coating on Nimonic80A was studied. The external layer was silicon carbide, the definition of the need of a bonding layer was part of the research programme. Thermal barrier coating was also investigated; the substrate was a super alloy with operating temperature higher than 1300K, the external layer was zirconia, the bonding layer was NiCoCrALY. Laminated SiSiC assembly was studied.
Various tests were used to study the systems: adhesion, fractive mechanics (pull, crack propagation, bending, fatigue), creep tests, thermal shock, adhesive and erosive wear, hot corrosion.
Plasma spray deposition equipment has been installed, with the possibility of spraying in vacuum or under controlled atmosphere, and of cooling by means of liquid argon spraying. Investigations are proceeding into an application in turbines for gas power stations and turbines for aircraft engines.
Basic ideas about silicon carbide chemical vapour deposition growth have been extended to other applications, inparticular for cutting tools and for heat exchangers.
Methods have been developed for assessing the reliability of ceramic ceramic and metal ceramic joints.
A joining technique for silicon silicon carbide sheets has been optimized using silicon as a binder material, polishing the surfaces to be joined, and joining them at 1680 K for 1500 s at a pressure of 2-5 MPa in a vacuum better than 1E-3 Pa. The reliability of the laminate has been tested yielding information on failure modes, failure stress and Weibull modulus, and fatigue behaviour.
Studies on metal ceramic interfaces have resulted in the definition of a suitable alloy, a suitable composition of the bonding layer, an optimized plasma spray procedure, the temperature of the substrate during the deposition of the zirconia thermal barrier and the composition of this partially stabilized zirconia with the contribution of ceria.
THE MAIN OBJECTIVES OF THIS PROJECT CONCERN THE RELIABILITY OPTIMIZATION OF CERAMIC-METAL INTERFACES RELEVANT TO THE COATING TECHNOLOGY OF SUPERALLOYS AS THERMAL BARRIER AND-OR WEAR AND CORROSION PROTECTIVE COATINGS AND CERAMIC-CERAMIC INTERFACES RELEVANT TO THE JOINING OF STRUCTURES IN COMPLEX SHAPE FORMING.
APPLICATIONS ARE FORESEEN WHERE THE SYSTEM PERFORMANCE REQUIRES RESISTANCE TO LONG TERM THERMOMECHANICAL STRESSES AND-OR AGGRESSIVE HIGH TEMPERATURE ENVIRONMENTS (I.E. GAS TURBINE, HEAT ENGINES, COAL GASIFIERS) AND HIGH TEMPERATURE STRESSES (I.E. CERAMIC HEAT EXCHANGERS).
FOR CERAMIC COATINGS OR SUPERALLOYS THESE OBJECTIVES SHOULD BE ACHIEVED BY:1. A DEEPER UNDERSTANDING OF THE ADHESION PHENOMENA OCCURING BETWEEN THE COATING AND THE SUBSTRATE METAL BY EVALUATING MOLECULAR SEGREGATION, INTERDIFFUSION AND CHEMICAL COMPOUND FORMATION.
2. THE STUDY OF THE INFLUENCE OR THE DEPOSITION PROCESS VARIABLES, (THIS WILL ENABLE THE TAYLORING OF THE INTERCOMPATIBILITY LAYER COMPONENTS BETWEEN THE SUBSTRATE AND THE TOP COATING).
3. SETTING AND TESTING A FRACTURE MECHANICS MODEL TO PROVIDE A RELIABLE PREDICTIVE FRAMEWORK TO ASSESS THE SYSTEM PERFORMANCES AS A FUNCTION OF THE MICROSTRUCTURAL CHARACTERISTICS.
Funding SchemeCSC - Cost-sharing contracts
79108 Freiburg (In Breisgau)