Exceptional high-strain-rate tensile mechanical properties in a CrCoNi medium-entropy alloy

CrCoNi中熵合金优异的高应变速率拉伸力学性能

Alloys with combined outstanding strength and excellent ductility are highly desirable for many structural applications.However,alloys subjected to deformation at very high strain rates and/or cryogenic temperatures usually suffer from very limited ductility.Here,we demonstrate that a bulk CrCoNi medium-entropy alloy presents exceptional combination of high strength and excellent ductility during deformation at high strain rates over a wide temperature range.Full tensile stress-strain curves at a high strain rate of 2000s^(-1) and temperatures down to 77 K were successfully obtained using an electromagnetic Hopkinson tension bar system attached with a cooling device,revealing high true ultimate tensile strength(σ_(UTS,T))of 1.8 GPa and true strain of~54% at σ_(UTS,T).These outstanding mechanical properties were mainly attributed to profuse deformation twinning.Both high strain rate and cryogenic temperature promoted deformation twinning.Grain refinement caused by deformation twinning,dislocation slip and dynamic recrystallisation added to work hardening and the excellent tensile strain.

拥有优异的力学强度和拉伸塑性对于结构合金是非常重要的.然而,合金在高应变速率或者低温下变形时通常拉伸塑性非常有限.本文展示了块体CrCoNi中熵合金在高应变速率和低温下优异的综合拉伸力学性能.我们使用一种带冷却装置的电磁霍普金森拉杆装置得到了在2000 s^(-1)和77 K下完整的拉伸力学曲线.结果表明合金在1.8 GPa下具有超高的拉伸真应力(σ_(UTS,T)),在σ_(UTS,T)下的拉伸真应变为~54%.该合金优异的力学性能主要归因于大量变形孪晶的启动.高应变速率和低温都促使了孪晶的形成.变形孪晶、滑移、动态再结晶引起的晶粒细化促进了加工硬化,从而增加了拉伸塑性.