Objective
The overall objective of COST 501 is to contribute, through a targeted programme of pre-competitive applied research, to the development of improved materials for advanced components in power-engineering application. The work is focused on topics relating to materials for components that have a critical influence on the enhancement of plant performance and efficiency, on which depends the ability of the European power engineering industry to remain economically competitive in the world market. Discussions with design and development engineers in European industry have helped to define the areas in which the development of materials and components is crucial.
Progress towards this objective has required the extension of the principles of work-sharing to include component development and evaluation, owing to the increased complexity and interdependence of material behaviour and component design. The power engineering systems in which these components are found include : gas turbines (aero and industrial), steam turbines (conventional conditions and high inlet-temperature), diesel engines, FBC, gasification and waste incineration.
The overall objective of the Project, is to maintain and develop the technical base of the European power engineering industry through a programme of applied research in high temperature materials targeted on critical areas of development which will improve the efficiency of plant by raising the operating temperature, increasing the reliability, and by providing a basis for advances in design methodologies.
In each of the technologies key material requirements have been identified which will govern the successful development of the advanced systems that are needed if the competitive position of the European industry is to be maintained. These material requirements are associated with industrial and aerogas turbines, steam power plant, diesel engines, boiler and other heat exchangers used for energy conversion from coal, waste and other nonnuclear sources.
The validity of applying laboratory derived data to corrosion experienced in real plant situations has been assessed. Test specimens exposed in a pilot coal gasification plant have been examined and compared with similar samples exposed in laboratory autoclaves using gaseous atmospheres which model those measured in plant. 4 alloys were studied (ie AISI 310, Alloy 800H, Fecralloy and MA 956).
Sulphide scales had formed on the laboratory coupons, the thickness of which was significantly less for the Fecralloy and MA 956 alloys. This was associated with the formation of a much slower growing chromium sulphide layer compared with the iron and nickel rich sulphide which had grown on the AISI 310 and Alloy 800H. The samples exposed in the gasifier at a similar temperature, however, were covered by oxide scales with evidence of internal sulphide percipitation. The relative behaviour of the alloys was the same as in the laboratory tests. The differences between the types of corrosion product formed in plant compared with the laboratory experiments suggests that perhaps during the startup of the gasifier, higher oxygen levels were present than was predicted by the earlier exposure of a group of reference metals and compounds.
Studies are also continuing in an attempt to elucidate more fully the mechanisms by which cerium ion implantation improves the corrosion resistance of alloys exposed in these coal gasification type atmospheres.
The oxide dispersion strengthened (ODS) alloy MA 760 is considered as an advanced gas turbine blade alloy. Investigations at 1050 C have been completed with a microstructural examination of creep damage. Whereas samples taken transverse to the extrusion direction failed in a classical manner (ie by pore formation in the grain boundaries perpendicular to the stress axis) for samples from the longitudinal direction fast necking, caused by the high stress sensitivity of the creep rate, seems to be an important problem. Final fracture occurs by the accumluation of transverse cracks which, however, are not linked to transverse grain boundaries.
Studies with the heat exchanger material MA 956 have shown a systematic improvement of corrosion resistance to heavily sulphizing gases due to preoxidation. Investigations have therefore been carried out at 600 C to determine the extent to which the scale can withstand mechanical deformation. At low rates of creep strian, 0.5% strain seems to be critical for oxide failure and crack formation which is found to be accompanied by severe external and internal corrosion. Different gas compositions and conditions of thermal and mechanical cycling are also being studied.
Creep and creep rupture investigations are continuing on the intermetallic alloy titanium 5 silicon 3/titanium 3 aluminium at 700 C and 800 C. Although this material has low ductility at temperatures below 600 C, at 700 C about 10% elongation to fracture is found under creep conditions combined with very promising strength properties. At 700 C a stress of 150 MPa is expected to correlate with a lifetime of about 50,000 hours.
Work has concentrated on a 2.25 chromium 1 molybdenum steel with the test pieces being removed from a 70 mm wall steam pipe. Multiaxial creep tests have carried out under axial tension, internal pressure or combined loading conditions on tubular components at 550 and 600 C. By using uniaxial creep data, predictions of the strain development under multiaxial stresses could be deduced from the previously developed continuum damage mechanics based model. Creep crack growth measurements on the same alloy have continued using the potential drop method. Tests have been completed on both longitudinally and circumferentially notched tubular components stressed through tensile and/or internal pressure loading. In the analysis of the data, a limit load analysis is applied in order to derive the C* integral as the creep crack develops, thereby enabling a successful juxtaposition of the data determined directly on components with that obtained conventionally from compact tension specimens.
The parallel study on creep crack growth data in ferritic steels for hydrogen service has advanced on 2 fronts. Firstly, the basic creep crack growth data in air has been provided from miniature compact tension specimens and a special rig has been designed and is under construction for testing identical specimens in a 200 bar hydrogen environment. Secondly, baseline tests have been carried out on components containing internal defects under internal pressure. The potential drop technique has been adapted for this situation which will facilitate experiments where defects are exposed to high pressure hydrogen environments under conditions close to those observed in petrochemical plant.
The study of oxide dispersion strengthened materials for high temperature heat exchanger applications has suffered due to difficulties in sealing tubes for internal pressure testing. 3 potential joining methods are being examined in this respect, namely electron beam welding, diffusion bonding and explosive welding. This aspect is not only critical for the testing programme but also for the high temperature heat exchangers constructed with this advanced material.
The fatigue behaviour of the oxide dispersion strengthened (ODS) alloy MA 760 was investigated at 1050 C to generate a database and to analyze the damage accumulation and failure mechanisms under isothermal low cycle fatigue (LCF) and thermomechanical fatigue conditions.
Development has continued of the computer vision system for the in situ monitoring of the initiation and growth of microcracks on the surface of samples while being mechanically tested. The disks used for storage of the acquired images were upgraded to 200 Mbyte capacity, corresponding to 700 images. Since 1 scan represents 30 images, the storage capacity of a disk is enough for 23 scans, allowing 1 complete mechanical test to be monitored in a fully automated mode without any intervention by the operator. Software improvements were also made to the system.
The system is being used in the investigation of the thermomechanical fatigue behaviour of bare and coated single crystal nickel based alloys for aero-gas turbine applications. An evaluation has therefore been made of its potential for detecting and measuring microcracks by comparing its accuracy with that achieved by the traditional replica method and direct optical observations. The comparison was made at the level of resolution used for the scan mode. The computer vision system turned out to be most accurate technique for monitoring microcracks.
A universal testing machine programmed for the uniaxial cyclic testing of alloys and ceramics at high temperature under carburation oxidationsulphidation (COS) type corrosive environments has been equipped with an environmental chamber and with the necessary control and safety instrumentation. A new activity aimed at modelling the lifetime and the constitutive behaviour of single crystal nickel based alloys has also been launched. Work in the preliminary phases has focussed on micromechanics and macromeachanics modelling.
Current status
The second phase of COST 501 was substantially completed by the end of 1993. The final reports of all the Work Packages have been approved by the MC. The results of the joint effort as well as of the excellent individual programmes in the Work Packages are well demonstrated by the contributions to Liège Conference : "Materials for Advanced Power Engineering", October 1994. A really important feature in the evolution of the collaborative approach has been the development of demonstration prototype components in advanced materials. As a result, European technical capability has been greatly enhanced, the adoption of new and improved materials has been accelerated, and the overall costs of technical innovation have been reduced through work-sharing. When account is taken of the different design approaches in the various companies, each with its own set of commercial considerations, the establishment and execution of the joint research programme on a pre-competitive basis represents a considerable achievement. The co-operative work has been continued with the extension of the Action to a third round.
Approval for an extension of COST 501 to a third round of research activities, to be carried out during the three year period 1993-95, was granted by the Committee of Senior Officials in April 1992. This decision led to the definition of five new Work Packages, the research work being focused on high priority topics relating to materials in components with a critical influence on plant performance to enable higher efficiency and lower emission levels to be attained. In some fields where there has been activity during Phase II, new top-priority requirements have been identified and new goals defined. In addition, a number of entirely new activities will be initiated in response to the long-term strategic need of the industry. The Work Packages are :
WP 11 : Advanced Steam Cycles
WP 12 : High Temperature Tribology Coatings
WP 13 : Clean Combustion Technology
WP 14 : Advanced Gas Turbine Blading
WP 15 : Advanced Coating Technology for Gas Turbine Engines
All 13 countries active during Round II continued to participate. They have been joined by Czech Republic, Iceland and Hungary. The situation required a request for a Technical Extension of the Third Round. At the CSO meeting of May 1995, the extension up to the end of 1997 was agreed by the senior officials.
The status of the Work Packages is :
WP11 : The major activities for boiler components concern manufacture, testing and investigations of E911, developed in COST 501-II, compared with the Japanese material P92. Long term results of mechanical tests, more than 20,000h, have shown satisfactory strength for E911. Extrapolation to 100,000h leads to rupture strength of 120 MPa at 600 C, a value which should be realistic. For forged and cast components for steam turbines, materials tested exhibited 50,000h proof duration. Additional weld metals, joints and new experimental tests for application temperature of 620 C are now under investigation. The key micro-structure features of these new steels and the long-term stability mechanisms are under evaluation to help in designing new 9 to 12% chromium steels.
WP12 : MCrAlY and low friction coatings of liners and valves in diesel engines have been developed and are under successful operational tests in marine diesels. The co-ordinated work ends in 1996.
WP13 : In a very high temperature heat exchanger, ODS-tubes have been tested for 100h successfully by British Gas. Different COST 501 materials are tested in pilot plants in a co-operative work by different partners. Substantial work has been done in the field of waste incineration to understand corrosion mechanisms and performances of various materials.
WP14 : Four batches of GTiAl alloys have been produced and tested in creep, low cycle fatigue, high cycle fatigue, fracture mechanics and oxidation environments. The density corrected creep strength of TiAl appears similar to that of the Ni-base alloy IN738. About 400 single-crystal test bars of SC-alloy tests. The casting experiments of internally cooled blades are still not satisfying the acceptance criteria.
WP15 : The work of all subgroups has been in progress since October 1995. The subgroups are :
oxidation and corrosion resistant coatings
thermal barrier coatings
advanced repair techniques.
In 1995-1996 the MC established seven short term scientific missions to improve the co-operative work.
Contracts
PECO contracts were signed with :
Institute of Physical Metallurgy, Czech Academy of Sciences (two contracts)
Research Institute of Vitkovice, Ostrava (CZ)
Skoda-concern Central Research Institute, Pilsen (Plzen,CZ)
Institute for Mechanical Technology and Materials Science at Technical University of Budapest (HU). GMSX-4, oriented in <001>, <011> and <111> direction, have been produced and tested in creep, LCF, and TMF
The Commission has placed one study contract concerning "Assessment of Steam Oxidation and Fireside Corrosion of 9-12% Cr steels". The Final Report has been prepared and circulated to the members of the MC for the decision on eventual publication as a monograph.
Two further contracts were proposed by the MC and are under discussion in the European Commission.
Work planned
The MC started with the preparation of the next Liège Conference "Materials for Advanced Power Engineering 1998". There is also an on-going discussion on how to preserve the co-operative work and what the requirements of power engineering in the next century will be.
Programme(s)
Call for proposal
Data not availableFunding Scheme
Data not availableCoordinator
1049 Brussels
Belgium