Development of investment casting process of nickel superalloys with enhanced weldability.

Project Information

HiperTURB

Grant agreement ID: 755561

DOI

10.3030/755561

Project closed

EC signature date 15 May 2017

Start date 1 June 2017

End date 30 November 2020

Funded under

• SOCIETAL CHALLENGES - Smart, Green And Integrated Transport

Total cost

€ 802 728,75

EU contribution

€ 699 356,25

Coordinated by

FUNDACION AZTERLAN
Spain

Periodic Reporting for period 2 - HiperTURB (Development of investment casting process of nickel superalloys with enhanced weldability.)

Reporting period: 2018-12-01 to 2020-11-30

Summary of the context and overall objectives of the project

H2020 Europe´s research and innovation program has identified as one key societal challenge the smart green and integrated transport. In this context the Clean Sky programme aims at developing and demonstrating competitive and environmentally friendly technology for the aeronautic sector The Clean Sky2 ENGINES Integrated Technology Demonstrators (ITD) will demonstrate developed technologies at a whole engine level. Therefore, a set of new engine components have to be developed and manufactured, one of them is a Turbine Rear Frame (TRF).
The demands on reliability of this part are very high due to the combination of high thermal (around 700ºC) and structural loads. The main material characteristics to be considered are creep, mechanical properties at room and high temperature and weldability. During the engine lifetime cracking is major concern and TRF´s have to be inspected over time, overhauled, tested and repaired and this supposes not only a problem of enhanced costs, but also presents a mayor safety issue. Nowadays the alloys commonly used for the manufacturing of these parts are weldable nickel base superalloys.
It should be also noted that the TRF components and maintenance cost are an important issue as frames represent 16.3% of the total engine weight and around 15% of its total cost [1]. Furthermore, engine maintenance accounts for 35-40% of the total aircraft maintenance costs, (see section 2). Material replacements due to parts wear out represent about 60-70% of this percentage
In the HiperTURB project it is envisioned to improve weldability of a number of commercially available superalloys. This will be achieved by tailoring the solidification structure acting on the local cooling rate in the part (simulations tool, chillers, directional solidification etc.), performing inoculation and minor chemistry modifications, adapting the thermal processing and developing the welding process for the new alloys. Alloy and heat treatment development will be aided by microstructure simulation tools.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Main results that have been obtained can be summarized as follows in the casting area:
-Improvement in mechanical properties (stress to rupture tests in low silicon alloys compared with high silicon ones)
-Effect of cooling rate in Laves phases after the HIP heat treatment
-Higher silicon content generates on heating and on cooling worst Gleeble properties than standard Si content and lower silicon content
-Inoculation rendering in grain refinement in pilot plant development

Linked with welding;
-LMD repairing process generating no cracks in repaired areas
-Alloy B with less trend to cracking in Varestraint test
-Generation of cracks in HAZ due to mushroom shape of welded area in comparison with bowl like shape generating no cracks
-Bead on plate tests is more relevant to detect cracks generation than Varestraint tests

In terms of results for exploitation following advances have been adressed.
-High temperature mechanical properties improvement with the reduction of silicon content
-Pre-HIP heat treatment as an alternative for laves phases reduction
-Automated TCL measuring process based on thermography and automated vision analysis
-Alloy B resulting in advantageous weldability properties
-Repairing ssytematic with no cracks generation
-Inoculation as an alternative for grain refainement
-Technical procedure to avoid cracks in welding casting components

DIssemination has been performed with the participantion in 3 congresses and the publication of 3 papers two of them (the most recent ones of green open access). Another paper linked with the project will be published during 2021

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The ambition of this project is to improve the weldability and castability of high temperature capable superalloys by a novel manufacturing process. This novel process consist of a combination of innovative chemistry adjustments, tailored casting solidification and specific heat treatments to control grain size, phase formation, segregation and residual stresses.
In general the main industrial impacts of project results are related to:
i) The costs reduction in manufacturing process to be obtained by the reduction of rework needed in the casting and assembly welding process. HiperTURB expects to down by 10 % for TRF by the reduction of rework needed in the casting and assembly welding process, which impacts directly in aero engine OEMs and Tier1 profits (the total cost of poor quality in aircraft engines / engine parts is estimated between 5.4 and 6.3 % of sales ).Welds with no cracks have been reported in this project by correct component investment casting manufacturing, preprocesing and welding conditions. No cracks means no reworks and this target is achievable by the final user once developments will be adopted.
ii) The in-flight overhauling and repairing TRF cost reduction as far as nowadays only a 30% of the expected in life performance time is achieved. Aircraft Monitor’s 2011 report establishes that material replacement is the most significant item in engine maintenance. Typically, it can account for 60% - 70% of the engine’s direct maintenance cost . It is caused simply because parts wear out and have to be either replaced or repaired. A 20% engine maintenances cost reduction is expected, nowadays engine maintenance costs represents the 35% of the total aircraft’s maintenance cost (see Figure 2.5). This number is based on the development of robust and reliable TIG and laser based repairing techniques. The combined effect of stress to rupture increase in IN718 low silicon alloy variant together with the reduction of cracks which are prone to failure modes in service, makes this objective realistic.
iii) The fuel consumption reduction due the possibility of performing more lightweight designs of TRF enabled by the use of higher perfomance Ni superalloys at around 700ºC and by the improvement of structural welds quality in castings. This has a big impact in operational costs of airlines. Linked with mechanical properties and weldability improvemente can be considered as an achievable result, once improvements have been adpted by final users.

Environmental impact:
1) Reduction of 30% of spare parts consumption rendering in around 30% less residues generation and natural resources savings due to the 20% increase in stress to rupture and no cracks achievement after welding. Even if it is less relevant, there is also a reduction of the amount of rework needed in the assembly welding process, and an expected weight reduction of the TRF component after the new achieved properties.
2) Reducing gaseous effluents and noise emissions (around 3%) in service thanks to future UHPE technology use in aircrafts. It affects the environmental impact of aircrafts during operation.

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