Hot workability and microstructure control in Co20Cr15W10Ni cobalt-based superalloy

• Published in: Journal of alloys and compounds 2016-08, Vol.676, p.527-541
• Main Authors: Anil Kumar, V., Gupta, R.K., Narayana Murty, S.V.S., Prasad, Akula Durga
• Format: Article
• Language: English
• Subjects: Cobalt-based superalloy; Constitutive equation; EBSD; Hot-workability; Microstructure; Processing map
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2016.03.186

Hot isothermal compression tests were conducted on Cobalt-based superalloy Co20Cr15W10Ni using a thermo-mechanical simulator to study the hot workability and microstructure evolution over a wide range of temperatures and strain rates. Strain hardening was observed at lower strain rates and flow softening at higher strain rates. Microscopy revealed presence of deformation bands at a temperature of 1323 K and a strain rate of 10 s−1; whereas at temperatures above 1423 K, fine recrystallized grains were observed at all strain rates. Dynamic recrystallization (DRX) initiates at 1373 K. At 1473 K, sudden increase in the recrystallized grain size (DDRX) is noticed, indicating grain growth. Processing maps have been developed to delineate the regions of stable and unstable metal flow during high temperature deformation. Using Ziegler's continuum principles and processing maps, regions of stable metal flow was observed in the temperature range of 1323–1500 K and strain rate range of 0.1–1 s−1. Activation energy (Qavg) for the alloy was found to be 421 kJ mol−1. As Zener Holloman parameter (Z) increases, DDRX decreases indicating higher nucleation, restricted grain growth, when deformation resistance is high. Constitutive equation and relation between ‘Z’ and DDRX for the alloy has been established. [Display omitted] •Hot working behavior of Co20Cr15W10Ni alloy studied over wide range of T andε˙.•DRX is dominant softening mechanism in stable regime of hot working of this alloy.•Suggested hot working regime for the alloy is T: 1323–1500 K andε˙: 0.1–1 s−1.•Constitutive equation established for the alloy to estimate σasaf(ε˙,T).•Relation between ‘DDRX’ and ‘Z’ for the alloy has been established.