Processing of Sheets and Foils out of Titanium Aluminides
Development of Cost-Effective Processing of Sheets and Foils out of Intermetallic Alloys Based on Gamma-NiAl and O-TiAl2Nb with Improved Superplastic Properties
Tech Area / Field
- MAN-MPS/Manufacturing, Planning, Processing and Control/Manufacturing Technology
8 Project completed
Senior Project Manager
Yakusheva A A
Russian Academy of Sciences / Institute of Metals Superplasticity Problems, Russia, Bashkiria, Ufa
- VNIITF, Russia, Chelyabinsk reg., Snezhinsk
- FormTech Ltd., Germany, Weyhe\nUniversity of Idacho / Institute for Materials and Advanced Processes, USA, ID, Moscow
Project summaryLight alloys based on g-TiAl and O-TiAl2Nb intermetallic alloys (hereafte g- and O alloys) offer mechanical properties, which are not typical for most of conventional structural materials. These are high density-normalized strength and Young’s modulus, which are retained up to high temperatures, good high-temperature strength and creep properties, and good oxidation and burn resistance. In contrast to ceramic materials, g- and O alloys possess certain ductility and fracture toughness. It allows considering these materials as prospective materials for high-temperature structural applications. It seems to be the most promising to use these alloys in aerospace industry. For instance, g- and O alloys may be applied for production of lightweight skin panels of honeycomb core, truss core or integrally stiffened thin sheet and foil configurations etc. For that it is necessary to develop cost-effective hot rolling processes for producing sheet and foil with improved superplastic properties. Material resources which are necessary for developing these processes including isothermal and non-isothermal rolling mills, furnace equipment etc. were produced in the framework of the ISTC project #1153. Besides some new approaches to rolling processes of g- and O alloys were developed too. Thereupon the development of effective experimental-industrial processes for manufacturing of high-quality sheets and foils out of g- and O alloys is the main purpose of the present Project. Analysis of literature data has shown that sheet rolling processes developed by now were extremely expensive because of using expensive consumed materials and expensive rolling mill facility. Furthermore the quality of produced sheets seems to be not satisfactory from the viewpoint of subsequent sheet forming, bonding etc. It is due to relatively coarse-grained microstructure produced in sheet. The stated problems are conditioned by insufficiently developed concepts of sheet rolling of alloys. This leads to using extremely high process temperatures or low sheet rolling speeds. Process of foil rolling out of alloys has not been developed by now.
The present Project offers the new concepts aimed at improvement of ductile properties of sheet (that is necessary for subsequent technological processes) and decreasing its cost. This concepts is basically based on two points: i) preliminary thermomechanical treatment of prematerial before sheet rolling should provide the most homogeneous and fine-grained microstructure, ii) special designed alloy compositions with the most stable and controllable microstructure should be used for sheet rolling process. As was shown by preliminary experiments, such an approach might provide a considerable decrease in the sheet rolling temperature at retention of high rolling speeds that is necessary for decreasing the cost of sheet rolling process and producing more qualitative sheet. Thus designing special alloys and optimization of primary thermomechanical processing are offered in the framework of the present Project. New alloys will be developed on the base of -solidification alloys since these alloys do not undergo peritectic reactions during solidification and have more uniform and controllable microstructure as compared to alloys with higher aluminum content. Primary thermomechanical processing will be developed using generally two stages: hot working in the (+) phase field and hot working in the (2+) phase field. Produced fine-grained preforms will be used for developing sheet rolling process below the eutectoid temperature. Produced sheets in its turn will be used as preforms for subsequent foil rolling. Foil rolling will be fulfilled using isothermal sheet rolling mill. In doing so, temperatures of foil rolling and intermediate annealings (between rolling passes) will be chosen to avoid oxidation of rolled workpiece. Besides quantity of intermediate annealings will be minimized owing to fine-grained microstructure of rolled sheet and isothermal conditions. By this way, a high productivity and quality of foil will be provided. Another way of production of g foils based on ion-plasmous evaporation technique is planned to develop too.
Development of sheet rolling out of O alloys will include the development more effective primary thermomechanical treatment as compared with currently used that will allow decreasing the heating temperature (prior sheet rolling) and sheet rolling without canning up to small thickness of sheet. Rolling of thin sheets and foils is offered to conduct using isothermal rolling mill. It will give a high productivity and improved quality of sheet/foil out of O alloys.
The objective of the Project: Solution of scientific and technical problems relating to the development of the cost-effective “low-temperature” technique of production of semi-finished sheet products out of intermetallic alloys based on g-TiAl and O-TiAl2Nb with improved superplastic properties at 800-1100C.
The following activities will be performed in the course of realization of the submitted Project:
1. Development and upgrading of cost-effective technique of thermomechanical processing of cast g- and O-alloys.
2. Designing the special g alloys which will be the most suitable for thermomechanical processing.
3. Development of technique of producing fine-grained preforms via thermomechanical processing of powder metallurgical g alloys.
4. Development of isothermal sheet rolling methodology and upgrading of the isothermal rolling mill.
5. Development of cost-effective technique of sheet rolling of g and O-alloys.
6. Investigations of microstructure, texture and mechanical properties of the sheets of g and O-alloys. Determination of the optimal superplastic conditions.
7. Experimental investigation of rolling of the foils out of g and O-alloys under isothermal and non-isothermal conditions.
8. Development of the technique of producing the alloy foils via ion-plasmous evaporation.
9. Investigation of superplastic forming and solid state bonding of sheets and foils.
10. Development of non-destructive methods of quality control of ingots, forged pancakes, sheets/foils, and sheet/foil configurations from g- and O alloys.
11. Writing quarterly, annual and final reports. Submitting proposals to industrial implementation of developed techniques and methodology.
Expected Results and their Application
Development of the technique of sheet rolling of g and O-alloys will provide decrease in the cost of g sheet by 5-10 times; decrease in the temperature of superplastic forming of the sheets on 100-250C; increase in the elongation by 2-3 times; decrease in the yield strength during superplastic flow on 30-50%; increase in the coefficient of materials outcome as well as decrease in the materials consumption of tooling and equipment.
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