Key Takeaways & Executive Findings
- •• Increasing Al content in AlxCrFe3Ni medium entropy alloys increases BCC phase fraction and decreases FCC phase fraction, enabling microstructural tuning. • The Al0.54CrFe3Ni alloy achieves an exceptional damping capacity (internal friction Q-1 = 0.059), outperforming most FeCr damping alloys. • The unique microstructure of hard BCC matrix surrounded by soft FCC phase hinders vibration wave propagation, enhancing damping. • The Al0.54CrFe3Ni alloy also exhibits high yield strength (811.16 MPa), offering a promising combination of damping and mechanical properties.
Abstract
The phase constitution, microstructure, damping capacity, and mechanical properties of as-cast AlxCrFe3Ni (x=0.5, 0.52, 0.54, and 0.56, respectively) medium entropy alloys were investigated. It is found that the volume fraction of BCC phase increases while that of FCC decreases with increasing the Al content. When the content of Al is 0.54, the alloy is composed of 82.1vol.% BCC matrix and 17.9vol.% FCC phase. Wherein the FCC phase is distributed on the BCC matrix, forming a structure where the hard BCC matrix is surrounded by soft FCC phase. This results in a hindering effect on the propagation process of vibration waves. The damping performance of Al0.54CrFe3Ni alloy, characterized by an internal friction of Q-1 is as high as 0.059, is higher than that of most FeCr damping alloys. The volume fraction of the BCC phase and the peculiar distribution of the FCC phase are identified as the key factors affecting the damping capacity. In addition, the Al0.54CrFe3Ni alloy exhibits a high yield strength of 811.16 MPa.
1. Introduction
High-entropy alloys (HEAs) have become a prominent research hotspot in material science since 2004 [1, 2] due to their superior properties such as high strength and plasticity [3, 4], good corrosion resistance [5], high thermal stability [6], good fatigue properties [7], and excellent radiation resistance [8], which have shown many potential applications in engineering. HEAs typically consist of five or more principal elements with the content of each element ranges from 5at.% to 35at.% and the entropy value greater than 1.5R (R is the gas constant). When the element number is reduced to 3 to 4 and the entropy value is reduced to 1R to 1.5R, the alloys are defined as medium entropy alloys (MEAs), which have also become a research hotspot because of their good comprehensive mechanical properties [9].
The HEAs and MEAs, generally, exhibit phase constitution in the form of face-centered cubic (FCC), body-centered cubic (BCC) or hexagonal close-packed (HCP) solid solutions or a combination thereof, rather than more complex phases [10]. It has been observed that the alloys characterized by a single FCC structure typically exhibit high plasticity albeit with diminished yield strength [11], while the alloys with a single BCC structure exhibit high strength at the expense of plasticity [12]. Leveraging the superior strength of HEAs or MEAs with a BCC phase and the enhanced plasticity of those with an FCC phase offers use inspiration for the development of damping alloys by using hard BCC structure as the matrix and soft FCC structure as the second phase. Furthermore, the inherent ferromagnetic damping effect of the hard BCC phase enhances the overall damping capacity of these alloys.
Traditional Fe-based damping alloys, e.g., Fe-Cr [13-16] and Fe-Al [17-19], are commonly used in industry to address issues related to certain kinds of vibration and noise, in which the Fe-Cr based alloys have been extensively studied and their highest damping capacities evaluated by measuring internal friction (Q-1) at different strain amplitudes are detailed in Table 1. Additionally, Table 1 includes internal friction of various HEAs and MEAs [20-23] that contain key elements such as Fe and Cr. It is observed that the damping capacities of HEAs and MEAs generally surpass those of traditional Fe-Cr based damping alloys. For example, the microstructure of Fe60Mn20Co5Cr15 HEA, synthesized by mechanical alloying and spark plasma sintering [21], mainly consists of BCC and FCC phases. The combined effects of ferromagnetic and dislocation damping within these phases result in a damping value of 0.054. In addition, the Al0.37CrFeNi alloy composed of BCC matrix and FCC second phase prepared using casting method has a damping value of 0.0709 under the combined effects of ferromagnetic damping and interfacial damping [22].
Although the damping properties of HEAs and MEAs containing Fe and Cr are generally higher than those of traditional Fe-Cr damping alloys, their complex preparation methods (e.g., prepared by spark plasma sintering after mechanical alloying) or high raw material costs (e.g., high Ni content) limit their engineering applications. Therefore, it is of great scientific significance to develop HEAs or MEAs with high damping capacity by increasing the content of cheap metal elements (such as Fe) or using simple melting and casting methods. In this work, the molar number
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Ning-ning Geng, Jiang Li, Wei Zhang, Peng Gao, Qing-chun Xiang, Ying-lei Ren, Bo Yu, Ke-qiang Qiu (2025). Effect of Al content on phase evolution, damping capacity, and mechanical properties of AlxCrFe3Ni medium entropy alloys. China Foundry. https://doi.org/10.1007/s41230-025-4146-6
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Frequently Asked Questions
What is the effect of Al content on the phase constitution of AlxCrFe3Ni medium entropy alloys?
Increasing Al content increases the volume fraction of BCC phase and decreases that of FCC phase. At x=0.54, the alloy consists of 82.1vol.% BCC matrix and 17.9vol.% FCC phase.
How does the microstructure of Al0.54CrFe3Ni contribute to its damping capacity?
The hard BCC matrix surrounded by soft FCC phase hinders vibration wave propagation, enhancing damping. The internal friction Q-1 reaches 0.059, higher than most FeCr damping alloys.
What are the mechanical properties of Al0.54CrFe3Ni alloy?
The alloy exhibits a high yield strength of 811.16 MPa, making it suitable for applications requiring both damping and strength.
Why are medium entropy alloys (MEAs) considered promising for damping applications?
MEAs can combine high strength from BCC phases and good plasticity from FCC phases, and their ferromagnetic damping effect enhances overall damping capacity, often surpassing traditional Fe-Cr damping alloys.
What is the significance of using simple melting and casting methods for these alloys?
Simple melting and casting methods reduce production costs and complexity, making these high-performance damping alloys more feasible for engineering applications.
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