The continued demand for improved gas turbine engine efficiency stimulates the constant development and application of higher performance materials. The higher the turbine inlet temperature, the higher the efficiency and lower emission of greenhouse effect gases. Hence, the gas turbine engines are affected by a demand to increase their operating temperatures, which is typically limited by the materials used. Ni-base superalloys are commonly used in aircraft engines due to their exceptional combination of high temperature strength, toughness, and great corrosion and oxidation resistance.
High γ’ volume fraction is desirable for high temperature applications. Astroloy with high amount of Al and Ti, which are linked with formation of γ´, Ni3(Al,Ti), is very interesting materials for more efficient engines. However, the vast presence of γ’ precipitates in this material make very difficult the manufacturing process by conventional cast and wrought route. Thus, new routes based on powder such as additive manufacturing (AM) or powder + hot isostatic pressing (HIP) processes are potential choices. Although AM technologies offer benefits from the manufacturing standpoint, the deposited material shows low ductility compromising the containment capacity of the casing. Instead, powder + HIP is more promising technique, in fact, HIP + forging route is the standard manufacturing route for high temperature discs with Ring Rolling as the naturally competitive choice. High temperature powder HIPped materials are less susceptible to being forged in the inherently non isothermal conditions under which Ring Rolling occurs. This together with the higher comparatively raw material costs (powder vs billet) would further challenge the competitiveness of any powder HIP + Forging based solution.
Consequently, Powder HIP without subsequent Forging is a competitive solution for high temperature casing manufacturing route although this technique presents several challenges.
HUC project belongs to the Clean Sky 2 programme and the main objective of HUC has been to develop and validate a powder HIP manufacturing route for Astroloy that has improved the buy to fly ratio through Near Net Shape HIP (NNSHIP). The material developed is suitable to fabricate IPT casings for the very high bypass ratio (VHBR) Ultrafan® engine under development by Rolls Royce, being the IPT casings able to withstand engine relevant conditions guaranteeing its ability to contain. Project had 8 technological objectives:
1: Development and Optimisation of a powder HIP processing route for a high temperature material.
2: Characterisation of mechanical properties to generate a database which supports the component design.
3: Development of experiments and numerical simulations to assess the material´s behaviour under dynamic and ballistic conditions.
4: Characterisation and understanding of mechanical properties with long exposure at high temperatures.
5: Development of low cost tooling for HIPping high temperature superalloy casings.
6: Development and validation of process modelling capabilities.
7: Manufacturing of canning to guarantee the compliance of the finish product with the requirements.
8: Manufacturing of 2 low cost demos and 3 full size IPT casings: 2 for real engine tests and 1 for NDTs.
Once these objectives are reached, HUC will contribute to one of the key societal challenge: smart, green and integrated transport. Moreover, HUC will also contribute to the strengthening of the competitiveness of the European Aircraft and Airlines industry and related SME’s through the development of state-of-the-art technologies.
