Objective
To improve the general availability, decrease costs and increase the quality of intermetallic materials with emphasis on those which exhibit the greatest potential for near-term application.
This would be achieved through the following :
The development of an improved understanding of the structure-chemistry-property-processing-performance relationships of the intermetallic.
The design and development of superior intermetallic materials, such as titanium aluminide (gamma and orthorhombic) alloys for engineered monolithic components,
titanium aluminide alloys as matrices for fibre-reinforced composites, coatings for improved environmental resistance.
The manufacture of titanium aluminide-based components using advanced processing technologies, including near-net-shaping, joining and machining.
The implementation of simultaneous engineering concepts which bring together design, engineering and manufacturing in order to reduce learning-curve costs and accelerate time to market.
The generation of appropriate physical, mechanical and chemical property data to facilitate component design and performance evaluation of the materials in pre-competitive stage.
Current status
Nineteen (19) final project proposals (from Austria, the Czech Republic, Switzerland, France, Germany, Italy, Finland and the United Kingdom) have been accepted by the MC. Estimated total financial resources needed to cover the running period mid-1994 to mid-1997 exceeded 5.5 MECU. In some cases national funding was delayed and materials to initiate research work were not immediately available. As a consequence, certain projects were only initiated in 1995. Nevertheless, all proposals reflect the general goals of the COST Action 513 and cover the following topics with emphasis on the gamma titanium aluminide composition :
Alloy development and structure-property-processing relationships
Ingot metallurgy, powder processing and spray deposition
Micromechanical and microstructural modelling of deformation
Thermomechanical processing and superplastic behaviour
High temperature mechanical properties including creep and fatigue
Tribology and surface engineering
Machinability studies
The research activities and the projects are divided into three Work Packages :
Processing
Alloy Development/Microstructure
Mechanical Properties/modelling
At the Interdisciplinary Research Centre (IRC), a Ti48A12Cr2Nb alloy with 1B addition has been cast as a 100mm diameter ingot and isothermally forged. Some of this material has been distributed to other COST 513 collaborators so that studies can be performed on material from the same source. The material is of special interest because of its fine grain structure. Other alloys with higher alloying additions are being developed but the Ti48A12Cr2Nb will provide generic date which can be used as a baseline for future work.
IRC (Birmingham) is also carrying out work aimed at providing the background to the COST alloy and has reported TTT curves summarising the influence of heat treatment temperatures and cooling rates on the microstructure of this specific alloy. Hence the heat treatment required to give specific structures for this common alloy has been made available to all those working with this material.
The CNRS-Vitry is working on studies of point defects, atomic mobility and creep in model TiAl alloys. It was shown that the atomic mobility decreases with increasing Al content. This work is likely to assist several other COST partners interested in modelling and assessing the creep behaviour of similar alloys.
At the ETH, Zurich, studies on the deformation mechanisms of binary TiA1- alloys and the influence of microstructural and chemical inhomogeneities have been initiated. Future work on the common-base material should extend this knowledge and provide valuable inputs for partners interested in mechanical modelling.
University of Neuchâtel is investigating the influence of stress and strain rate changes on the response under creep conditions for the COST alloy. Twinning has been shown to be very active in tensile tests at 700 C. The dislocations which were dominant were 1/2<110> in all cases in the crept samples and at the low strains possible in tension.
Creep behaviour of Ti-52A1 alloys in the ranges 1010-1150K and 50-300MPa has been investigated at the Institute of Physics of Materials, Zizkova. Based on microstructural studies, it was shown that subgrain controlled creep occurs at strain greater than about 30%. This work will be extended to include examinations of the common-based material.
Bochum will be carrying out work on the COST alloy using double shear tests under creep conditions.
INP (Grenoble) has tested the as-forged pancakes of the COST alloy between 900 and 1100 C to assess their strain rate sensitivity. Values of m between 0.2 and 0.4 were found and it was clear that this material would not deform superplastically.
ETH (Zurich) is also investigating the defects responsible for the deformation of the gamma phase in the as-received samples, in samples heat treated at 1200 C for 4h and at 1380 C for 1h. It has been argued that the lower ductility in the lamellar samples (heat treated at 1380 C) than that in the equiaxed samples (heat treated at 1200 C) was associated with the lack of <101> dislocations. Twinning also observed in the lamellae.
IPM (Brno) has carried out creep tests at 1100K at stresses between 30 and 150MPa in tension and compression. The slope of the curve of the observed minimum strain rate against stress at a strain of 30% in creep was about 5. At this temperature is not possible to define time to 0.5% strain and work will cover lower temperatures in future in order to develop an understanding of the low strain creep behaviour.
Tampere University is attempting to synthesise TiAl alloys using elemental material as feed stock for mechanical alloying. At this stage the biggest problems appear to be associated with contamination from both oxygen and carbon (from the stearic acid). The alloy can be made amorphous after 45h milling, and after HIPping this amorphous powder the material appears to be virtually 100% gamma.
Sulzer Innotec has used plasma spraying with larger particles than normal (200um) in an attempt to produce strip for pack-rolling to foil. Contamination with oxygen could not be avoided even under optimum spraying conditions and values as high as 3,000 ppm were found whereas the target was 1,400ppm. This programme is not ongoing.
At the University of Trento, the tribological characteristics of intermetallic materials are being investigated. Initial work on the dry sliding wear resistance of nickel-based aluminides will be repeated for the COST alloy at room temperature and high temperature.
Contact is being maintained with the Concerted European Action on Structural Intermetallic (CEASI) through joint membership of management committee. More recently through the appointment of M. H. Loretto as Chairman of COST 513 both programmes came under his chairmanship.
Through CEASI a number of proposals for Networks has been put forward, one of which includes TiAI-based intermetallic, and, if set up, this specific network would involve appropriate co-operation with COST 513. Some new Brite-Euram proposals are being discussed which overlap the areas of interest of COST 513 and members of the Management Committee of COST 513 are involved in these.
Programme(s)
Call for proposal
Data not availableFunding Scheme
Data not availableCoordinator
1049 Brussels
Belgium