Role of Ti on Phase Evolution, Oxidation and Nitridation of Co–30Ni–10Al–8Cr–5Mo–2Nb–(0, 2 & 4) Ti Cobalt Base Superalloys at Elevated Temperature

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 52; no. 11; pp. 5004 - 5015
• Main Authors: Roy, Apurba, Singh, Mahander Pratap, Das, Saurabh Mohan, Makineni, Surendra Kumar, Chattopadhyay, Kamanio
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-11-2021; Springer Nature B.V
• Subjects: Alloys; Aluminum oxide; Characterization and Evaluation of Materials; Chemistry and Materials Science; Chromium; Cobalt aluminate; Cobalt base alloys; High temperature; Materials Science; Metallic Materials; Microstructural analysis; Molybdenum; Nanotechnology; Original Research Article; Oxidation; Phase stability; Reaction kinetics; Structural Materials; Superalloys; Surfaces and Interfaces; Thin Films; Titanium
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-021-06445-9

Titanium is an important alloying addition to
γ
/
γ
′ cobalt-based superalloys that enhances the high temperature microstructural stability and make the alloys lighter. In this work, we probe the role of Ti composition on the phase stability and oxidation behavior of Co–30Ni–10Al–8Cr–5Mo–2Nb superalloys. With Ti addition, the
γ
′-solvus temperature is enhanced and the
γ
′-precipitate shape changes from spherical to rounded cuboids. Addition of 4 at. pct Ti to the alloy promotes topologically-close-packed (TCP) phase formation that are rich in Co, Cr, and Mo. During oxidation at 900 °C, Ti was found to facilitate the early formation of passivating oxide layers (spinel CoCr
2
O
4
/CoAl
2
O
4
) on the exposed surfaces, however, it was not effective in reducing the oxidation-induced mass gain. Microstructural analysis reveals that Ti delays the Al
2
O
3
layer formation eventually leading to faster oxidation kinetics. Additionally, we also found formation of (Ti,Nb)N in the
γ
′ denuded zones near the alloy-oxide interface.