Precipitation behavior and its effects on tensile properties of FeCoNiCr high-entropy alloys. (December 2016)

• Record Type: Journal Article
• Authors: He, J.Y.; Wang, H.; Wu, Y.; Liu, X.J.; Mao, H.H.; Nieh, T.G.; Lu, Z.P.
• Is Part Of: Intermetallics. Volume 79(2016:Dec.)
• Page Start: 41
• Page End: 52
• Publication Date: 2016-12
• Subjects: High-entropy alloys -- Precipitation hardening -- Strengthening mechanisms -- Tensile behavior -- Thermodynamic stability; Intermetallic compounds -- Metallography -- Periodicals; Metallic glasses -- Periodicals; Composés intermétalliques -- Métallographie -- Périodiques; 669.94
• DOI: 10.1016/j.intermet.2016.09.005
• Languages: English
• ISSNs: 0966-9795

Abstract

Abstract: In this work, we present a systematic study on the precipitation behavior and mechanical properties of a FeCoNiCr-based high-entropy alloy alloyed with dilute amounts of Ti and Al, (FeCoNiCr)100-x-y Tix Aly (where x = 1–3, y = 4–9 at.%). It was found that, upon aging, nano-sized L12 -Ni3 (Ti, Al) particles are formed within grains, whilst L21 -(Ni, Co)2 TiAl Heusler particles are formed mainly along grain boundaries. The relative thermal stability of the two phases were studied at different aging temperatures (700–900 °C) with various durations of time (up to 48 h) and the results were directly compared with Thermo-calc calculations. Tensile tests were also conducted on alloys aged under different conditions. The measured properties, including strength and ductility, were correlated with the microstructure of aged (FeCoNiCr)100-x-y Tix Aly alloys, with particular attention on the distribution and morphology of the two kinds of precipitate. Whereas both phases could contribute to the strengthening of the alloys via either Orowan bowing or particle shearing mechanism, the brittle (Ni, Co)2 TiAl Heusler phase was found to mainly affect the tensile plasticity. A simple composite model was proposed to describe the plastic strain of alloys. Based on observed microstructure and its corresponding mechanical performance, the alloy with the composition of (FeCoNiCr)94 Ti2 Al4, when aged between 700 and 800 °C, gives the best balanced strength/ductility properties. Highlights: Precipitation behavior and tensile property of a HEA doped with Ti & Al was studied. Effects of alloying and aging on phase competition was investigated. Effects of alloying and aging on the structure-property relation were revealed. Contribution of different strengthening mechanisms was examined. The underlying reason for ductility loss was discussed.