Advanced FOrging of an Optimized Turbine casing

Project Information

AFOOT

Grant agreement ID: 620120

Closed project

Start date 1 October 2013

End date 30 April 2016

Funded under

• Specific Programme "Cooperation": Joint Technology Initiatives

Total cost € 596 878,00

EU contribution € 298 438,00

Coordinated by

RTM BREDA SRL
Italy

Final Report Summary - AFOOT (Advanced FOrging of an Optimized Turbine casing)

Executive Summary:
Aero-engine disks and rings made of nickel based alloys such as Inconel 718 alloy are commonly manufactured by a series of several open and/or closed-die forging operations, generally always finishing with one or more closed-die forging steps.
The material flow in the forging operations is very well known. The predominant radial microstructural anisotropy conferred by the forging flow pattern is beneficial for the in-service loading conditions (mainly radial loading) and the final closed-die operation is effective in providing a uniform structure from the point of view of primary, secondary phases and grain size.
Ring-shaped components like those used in the low-pressure turbine stage of aero-engines often undergo an intermediate ring-rolling step propaedeutic to the a closed-die forging step.
In the last 20 years, the material most commonly used for the production of turbine casings have been alloy 718 for lower temperatures and Waspaloy for higher mean service temperatures. In particular alloy 718 is a very versatile Ni-based superalloy: its high corrosion resistance, ductility and strength up to 650ºC and its good weldability has made alloy 718 the material of choice for LP turbine parts and, in particular, low-pressure turbine disks and casings. On the other hand Waspaloy is a significantly stronger superalloy for use up to over 750°C; the main disadvantage of Waspaloy is its hot workability where smallest process variation may cause huge property losses on the finished component.
718Plus® alloy has been developed by ATI Allvac to fill the need for an advanced turbine component alloy that could be processed and welded similarly to the current alloy 718 but that would also be capable of an increase in temperature of about 50°C as compared to 718 closing the gap between this alloy and Waspaloy, that in the past years was the only, but less exploited solution for applications that would require a higher operating temperature (up to 750°C).
718Plus® alloy looks as a very promising material that is claimed to be able to fill a gap currently existing between alloy 718 and Waspaloy, keeping the best features of both competing superalloys. This project has the aim to use this material for the production of an optimised turbine casing and, in the process, to characterize 718Plus® alloy and to validate the alloy’s properties as a consequence of the individuation of the optimal processing and heat treating conditions.
The properties of 718Plus® alloy have been the subject of a comprehensive study by American aeronautics industries and Air Force but the results of such studies are not of public domain. One of the desired outcomes of the present project has therefore been to bring European industries in general, and the topic manager in particular, up to speed with what is already known by their American counterparts. Also, a lot of publications about 718Plus® alloy have been authored or co-authored by researchers of Allvac, the producer of the patented 718Plus® alloy, and an independent evaluation/optimization of the properties of the material has proven to be timely needed.

Project Context and Objectives:
The objective of the AFOOT project was to determine and validate a robust set of forging and heat treatment parameters leading to the forging of a turbine case made from ATI Allvac 718Plus® alloy for a geared turbofan demonstrator as part of the Sustainable and Green Engine (SAGE) platform of Clean Sky This project represents the collaborative effort of an experienced company specialized in forging and ring-rolling of superalloys and a technological research center with great competence in thermo-mechanical processes analysis and modelling.
Development of an advanced predictive simulation modelling tool is a pre-requisite for the success of the project along with a thorough laboratory measurements campaign that will be performed to test the original material as well as the material overaged in conditions similar to those it should work at.
The final outcome of the project will be the production of three fan cases whose design will be agreed upon with the topic manager, one of these cases will be cut up and properly examined in the lab while the other two will be delivered to the Topic Manager.
The main result of the project will not only be the production of such three turbine cases. On top of the mere production of the three turbine cases, we have been working towards
• upgrading the know how about 718Plus® alloy, which is still to be considered as a "new" material,
• completing investigations which are independent from the material supplier while filling the scientific and technical “weak spots” in the state of the art of manufacturing 718Plus® alloy;
• increasing the working experience on 718Plus® alloy and the awareness of its applications;
• introducing 718Plus® alloy properties into a commercial simulation tool with the purpose of avoiding waste of time and of materials as well as reducing costs in selecting hot forming process routes for 718Plus® alloy;
• identifying the most efficient process for a close to shape turbine casing manufacture, allowing European Industry to get even with American Competitors.
• avoiding waste of production time and of costly materials, reducing forging product failures, and reducing costs with the goal to reduce the efforts to get a product that can allow alternative designs of environment-friendly aero-engine components.

Project Results:
The activities of the project have been divided in 5 work packages:
WP1: Project management – It stood alone and lasted through the entire project.
WP2: Collection of available information and definition of a detailed project plan - This work package run along the full duration of the project but it did not represent a continuous activity: there was a strong effort concentrated in the first three months of the project and then other activities were performed regularly during the following months. Within the first three months of the project the material properties of a 718Plus® alloy billet were collected and a hot processing map for the material was compiled and used, along with the information collected in the initial literature search, to prepare a draft manufacturing instruction sheet that was later updated with WP3 results, in order to use it for the turbine casing production.
WP3: Optimization of the forging process - This work package was the pivotal one in this project and it included activities that took place along the full duration of the project. The final goal of WP3 was the production of 3 prototypes of the turbine casing according to the specifications of the Topic Manager. In the first part of the project, three trial rings that would mimic the behaviour of the full-scale casing were produced and thoroughly analysed. Later, a first casing was produced and used as a cut-up to characterize its properties from both mechanical and metallurgical point of view and finally, after the previous phase had valeted the forging and rolling and heat treatment schedule, two casings were produced and delivered to the Topic Manager.
WP4: Testing of specimens – all the testing activities, both on the trial rings and on the cut-up full-scale casing were part of this work package.
WP5: Results reporting - The final report was created as a summary of all activities and systematically and thoroughly highlighted all the conditions and all the procedures that were used to obtain the results. The report detailed and motivated the choices made in the procedure for the fabrication of 718Plus® alloy turbine casing and specified the quality level of the final product through the results of the tests on the sacrificial cut-up. The final report provides guidelines for the design of the forging process to be applied to a 718Plus® alloy turbine casing.

Results

a) Timeline & main milestones

The project started in October 2013 and was successfully completed in April 2016 with the delivery of two casings to the Topic Manager.

The following milestones were achieved:
• Turbine casing specification prepared – April 2015
• Optimized forging and heat treatment procedure for manufacturing of turbine casing in place – October 2015
• Two turbine casings delivered to the Topic Manager – April 2016

b) Environmental benefits

Within the operational framework of further improving the technologies of the advanced geared turbofan demonstrator in the SAGE platform, the aim of this project has been to determine the optimal forging and heat treatment parameters for the turbine casing manufacture in ATI Allvac 718Plus® alloy, so that stable service conditions are guaranteed. Indeed, the results of this project represent the necessary guideline in the designing of a dedicated turbine case by complex forging. To date, 718Plus® alloy is the right compromise between the necessity of having a material with a workability and weldability comparable to 718 alloy, which maintains excellent strength and stress rupture properties at higher temperatures (700°C) and has a reduced costs if compared to other superalloys like Waspaloy and René 41. The optimized forging and heat treatment process developed during this project by means of the combination of an advanced predictive simulation modelling tool together and of a laboratory measurements campaign, has led to the achievement of a microstructure and material properties conformant with the requirements for design and serial production.
The optimization of the processing of 718Plus® alloy will lead to the application of this high performance material in the turbine manufacture and to the enhancement of the overall efficiency of the module, since the turbine will be able to work at higher temperatures and less cooling air will be needed.

Potential Impact:
A full report will has been delivered to the Topic Manager at the end of the project and it clearly highlights all the results obtained and gives evidence of the advantages and limitations of the material and of the existing manufacture procedure of Alloy 718Plus® alloy turbine case.
The know-how dissemination inside the consortium during the project lifetime and afterwards has been and will be guaranteed and a fertile environment for future collaboration of the partners in this field has been created and maintained.
In coordination with the Topic Manager: currently it is envisaged that some selected results of the present project might be presented in public conferences in the area of high temperature structural materials (in particular, the TMS series on “Super alloy 718 and Derivatives”) and published in internationally recognized Journals included in the SCI list. Tentative journals where the results might be submitted are: Materials Science and Engineering, Journal of Materials Processing and Technology, Aerospace Science and Technology, International Journal of Materials and Product Technology, etc.