Damping behavior of AlxCoCrFeNi high-entropy alloys by a dynamic mechanical analyzer

•The Al content is related with structural relaxation and damping capability.•Dynamic modulus is insensitive to the frequency especially for storage modulus.•Several internal-friction peaks are observed in the Al-free or Al-lean alloys.•The damping behavior is proposed to be strongly relied on the level of ordering. For the first time, the damping behavior of high-entropy alloys was studied using the dynamic-mechanical analyzer, over a continuous heating temperature from room temperature to 773K, at a given frequency range from 1 to 16Hz in model alloys AlxCoCrFeNi (x=0, 0.25, 0.5, 0.75, and 1). The experimental results reveal that the Al-rich alloys have a much smaller elastic storage-modulus amplitude over the temperature and thus a larger resistance to structural relaxation, while the Al-free and Al-lean alloys exhibit a much higher loss tangent and thus a much higher damping capability. Overall the elastic storage modulus decreases while the loss tangent increases with increasing the temperature, but little dependence was observed for the frequency. Several visible internal-friction peaks were presented in the face-centered cubic alloys, whose positions and heights are independent of the frequency. The damping capability of these alloys can be comparable to or even overwhelm the conventional Fe–Al alloys. The damping behavior above was proposed to be agreeable with the level of ordering (η) of alloys characterized by two proposed parameters (the relative-entropy effect, Ω, and the atomic-size difference, δ).