Manufacturing and characterisations of hafnia-based materials for aerospace applications
Creators: name:  A. JULIAN-JANKOWIAK 
name:   L. AUDOUARD 
name:   J. JUSTIN 
name:   P. BERTRAND 
name:   C. LANGLADE 
name:   M. GARCIA 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: STRUCTURES
MATERIALS
HIGHE TEMPERATURE MATERIALS

description: Today, hydrazine is commonly used pour space propulsion. However, the REACh regulation is threatening the use of this monopropellant, which is considered as substance of very high concern because of its high toxicity and might ban its use in a near future. In this regard, the need for new green propellant has become imperative for Europe to stay in the course of satellite propulsion. Thus, CNES and ONERA began to develop an alternative monopropellant with promising success in terms of energy efficiency and reduced toxicity. However these energetic compounds have the common points to develop harsh conditions which include a high temperature flame ( 2700 K) and very oxidising gases (particularly H2O(g)). From there, CNES, ONERA and ICB-PMDM started research works focused on the development of new combustion chamber materials to answer previous needs. Functionally graded materials (FGM), and especially ceramic/metal FGM demonstrated appropriate behaviour in an ultra-high temperature oxidising environment, associated with good mechanical resistance [1]. These types of materials enable the elimination of sharp interfaces responsible of stress concentration by a gradually evolution of the composition [2]. In our case, FGM is constituted of a refractory metal layer, a gradient layer (ceramic/metal) and a hafnia-based ceramic layer. This work is focused on the development of a 3000 K oxides resistant ceramic layer as Environmental Barrier Coating / Thermal Barrier Coating. In our previous studies, hafnia based samples with different doping strategies in terms of compositions have shown a high potential for their use as the ceramic part of the FGM. In particular, high amounts of additives (33 mol. %) seem to be very promising [3]. To complete these results, hafnia samples with different additives as Lu2O3, Y2O3 and Gd2O3 are sintered using a Field Assisted Sintering Technology (FAST) or natural sintering. The influence of temperature, pressure and dwell-time on the sintering of the samples is studied. After that, the microstructure of the samples is investigated by Scanning Electron Microscopy in terms of grain size, homogeneity, porosity (rate and shape) and composition (by Electron Dispersive Spectroscopy) as those parameters are determinant for further characterisations. Finally, coefficient of thermal expansion (373-1773 K), hardness, toughness, Youngs modulus and mechanical strength are measured for each composition. Thus, the relationship between the microstructure, the process and the properties can be established. Results will be useful to complete our understanding on the influence of the additive on the stabilisation of hafnia and to select the most appropriate composition. [1] B. Saleh et al., 30 Years of functionally graded materials: An overview of manufacturing methods, Applications and Future Challenges , Compos. Part B Eng., vol. 201, p. 108376, nov. 2020, doi: 10.1016/j.compositesb.2020.108376. [2] M. S. EL-Wazery et A. R. EL-Desouky, A review on Functionally Graded Ceramic-Metal Materials , p. 8, 2015. [3] L. Sevin, Developpement de materiaux ultra haute temperature?: optimisation des proprietes thermomecaniques dun composite a gradient de proprietes , These de doctorat, Universite Bourgogne Franche Comte, 2020.