Strain rate effects on the mechanical responses in Mo-alloyed CoCrNi medium entropy alloys

Abstract

In this work, the mechanical responses of the as-recrystallized CoCrNiMox (x = 0 to 0.2) medium entropy alloys (MEAs) across a wide range of strain rate from quasi-static (1 × 10−3 s−1) to dynamic (5 × 103 s−1) were systematically investigated. At 1 × 10−3 s−1, the slightly increased yield strength (YS, ∼133 MPa) of the Mo0.2 alloy compared to the Mo0 alloy is mainly due to Orowan looping of dislocations around the σ precipitates. At 5 × 103 s−1, the Mo0.2 alloy shows a superhigh YS increment (∼880 MPa) compared to the Mo0 alloy, and also a superhigh strain rate sensitivity of ∼0.54 in the dynamic realm. We propose that this strain-rate hardening effect is originated from the local strain rate increase near the hard σ precipitates. After dynamic straining, we evidenced vast deformation products including, the basic twin-twin intersections in the Mo0 alloy, the HCP islands at twin boundaries in the Mo0.1 alloy, and the close-packed nano blocks as well as the amorphous bands in the Mo0.2 alloy. These endows the CoCrNiMox MEA family in particular Mo0.2 high potential to be developed for dynamic load-bearing and energy-absorbing.