Microstructure stability and hardening determination through heat treatment of sintered Co γ/γ′ based alloys

ABSTRACT

Aiming to improve γ′ volume fraction through alloying elements and heat treatments, the influence of the combined effect of 2 Ti and 2 Ta addition (at%) to a nominal Co–12Al–10W at.% Co-based superalloy, and the heat treatments parameters have been investigated. The Co-based alloys were manufactured by PM using mechanical alloying for powder processing, and a field-assisted sintering technique to consolidate the material. The specific study of solution temperatures and ageing times to promote the γ/γ′ dual-phase was carried out through a complete microstructural analysis and micro and nano hardness measurements. The composition of the γ (fcc)-matrix and γ′ (L12)-precipitates, the nanoscale properties including γ′ volume fraction and γ/γ′ misfit were measured as a function of increasing solution and ageing time. In the end, Ti and Ta addition to the Co–12A–10W alloy increases γ’ volume fraction and thermal stability for long ageing time detecting slow coarsening.

KEYWORDS:

• Co-based superalloys
• solution
• heat treatment
• volume fraction
• field-assisted sintering techniques

Acknowledgements

Authors would like to acknowledge funding from the Madrid region under the program S2018/NMT-4381-MAT4.0-CM and the UC3M grants for researcher mobility in a foreign research centre in 2016. Prof David Dunand and Prof David Seidman are kindly thanked for co-advising during the research stay at Northwestern University. This work was supported via award 70NANB14H012 from the US Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Comunidad de Madrid [grant number S2013/MIT-2775].

Notes on contributors

Rafael Casas

Rafael Casas received his PhD in Materials Engineering, Group of Powder Technology (GTP), from Universidad Carlos III of Madrid (UC3M) in 2018, specialising in superalloys by powder metallurgy techniques. He is a postdoctoral research fellow in the school of mechanical engineering at Dublin City University (DCU) and the Materials Processing Development area in the SFI Research Centre for Advanced Manufacturing (I-form). He is working on Laser surface modification and 3D metal printing in Prof. Brabazon’s Research Group.

Francisco Galvez

Francisco Galvez is a full professor of the Escuela de Ingenieros de Caminos, Canales y Puertos at Universidad Politecnica of Madrid (UPM) and director of the Materials Science Department. His research topics comprise the study of materials under dynamic loading, impact behaviour and numerical analysis.

Mónica Campos

Monica Campos is graduated in Physics at Univ. Complutense Madrid in 1995 and as Materials Engineering at Univ. Politécnica Madrid in 1998. She received the PhD in Industrial Technologies at Univ. Carlos III de Madrid in 2002. At present, she is a full Professor and develops her research and teaching activities in the Department of Materials Science and Engineering and Chemical Engineering of Universidad Carlos III de Madrid as Associate Professor from 2008. She is member of the research group of Powder Technology (GTP). Her research is currently involved in the processing and microstructural design of several alloys’ families, from sintered low alloyed steels, master alloys, iron base-ODS alloys and Co and Ni-based alloys for high T. Besides, is working on additive manufacturing, from powder preparation to final components. Responsible for R&D projects, including co-operations with other international institutions, industrial companies, and research centres. Former Deputy Vice-President for University Admission at University Carlos III de Madrid, the present Vice-President of Students and Equality.