Effects of Al addition on the microstructure and mechanical property of AlxCoCrFeNi high-entropy alloys
Highlights
► AlxCoCrFeNi alloys can possess FCC, BCC or mixed structure, depending on Al content. ► Low Al content alloys with <11 at.% addition form a single FCC solid solution. ► The increase of Al content enhances formation of BCC phase which hardens the alloy. ► All BCC phase have a nano-scale two-phase structure formed by spinodal decomposition.
Introduction
The conventional strategy for developing alloys is to select one or two elements as main component for primary properties and other minor elements as alloying addition for modifying microstructure and properties [1], [2]. This traditional alloy concept has led to most of traditional alloys which are composed of single principal metal element, such as Al-, Cu-, Mg-, Ni-, Fe-(steel), Ti-, and Sn-based alloys. However, this conventional approach also restricts the number of alloys that can be studied and utilized. In view of this limitation, a novel alloy approach coined as high-entropy alloys (HEAs) was proposed by Yeh [3], [4], [5] to broaden the alloy field. A HEA was originally defined as an alloy composed of at least five principal metallic elements, each ranging from 5 to 35 at.% [5]. In the past decade, many high-entropy alloy systems composed of five to nine metal elements e.g., AlxCoCrCuFeNi [6], [7], [8], [9], [10], AlxCoCrFeNiTi [11], TixCoCrCuFeNi [12], CoCrMnNiFe [13], CuNiAlCoCrFeTiMo [14], [15], AlCoCrCuFeNiSi [16], AlxTiVCrMnFeCoNiCu [17], MoNbTaW, MoNbTaVW [18], [19], and AlxCrCuFeNi [20] have been studied and characterized for their microstructures and properties.
Traditional metallurgical theory suggests that multiple alloying elements will lead to the formation of many intermetallic compounds which not only cause brittleness but also become difficult to analyze [21]. However, high-entropy alloys tend to enhance the formation of simple solid solution structures (FCC, BCC or mixed) [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [22] rather than many complex phases due to high mixing entropy effect [3], [4], [5]. It is this effect to make HEAs abundant of possible opportunities to have promising properties such as high elevated-temperature strength [7], [18], [19], [23], and excellent wear [7], [8], [23], [24], corrosion [25], [26] and oxidation resistance [21].
Recently, a five-component HEA system of AlxCoCrFeNi alloy [27], [28], [29], [30] modified by excluding Cu element from AlxCoCrCuFeNi alloy system was synthesized and characterized for its microstructures, mechanical properties, work-hardening and age-hardening behavior. However, the relationship between microstructures and mechanical properties was less mentioned and explained. To understand the effects of Al addition in the AlxCoCrFeNi alloy system (x value in molar ratio, from 0 to 2.0), the crystal structure, casting microstructure and mechanical property of fourteen alloys were investigated using X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Vickers hardness tester. The resultant microstructures and mechanical properties due to the variation of Al content are discussed, which provides essentials of this HEA system for further research and applications.
Section snippets
Experimental procedure
The HEA ingots with nominal composition of AlxCoCrFeNi (0 ≤ x ≤ 2.0) were prepared using vacuum arc remelting method. The purity of the raw elemental metals is above 99.9%. Approximately 200 g raw materials were melted in a water-cooled copper mold under an ultrahigh-purity argon (Ar) atmosphere to prevent oxidation after purging with argon three times. The ingots were re-melted at least 5 times to improve chemical homogeneity. The dimension of solidified ingots was about 45 × 45 × 10 mm. The
Crystal structure and Vickers hardness
Fig. 1(a) and (b) show the X-ray diffraction profiles of as-cast ingots with different aluminum contents. Two cubic crystal structures, face-centered cubic (FCC) and body-centered cubic (BCC), are found. Low aluminum content alloys (Al0–Al0.4) form a single FCC crystal structure. A minor (110)B reflection of BCC structure nearby (111)F reflection starts to appear in the Al0.5 alloy, as indicated by arrows in Fig. 1(a). Then, the relative intensity of the (110)B reflection peak increases with Al
Conclusions
The crystal structure, microstructure and mechanical property of as-cast AlxCoCrFeNi high-entropy alloy have been investigated on fourteen alloys with finely divided Al contents. Low Al content alloys form an FCC structure and continuous increase of Al content induces the formation of BCC phase which further spinodally decompose into modulated spinodal structure. The range of x value for FCC plus BCC mixture is from near 0.5 (11.0 at.%Al) to 0.9 (18.4 at.%Al). The solidified microstructure
Acknowledgment
The authors gratefully acknowledge the financial support for this research by the ITRI South and the Ministry of Economic Affairs of Taiwan under Grant No.7327HB3110.
References (42)
- et al.
Adhesive wear behavior of AlxCoCrCuFeNi high-entropy alloys as a function of aluminum content
Wear
(2006) - et al.
On the elemental effect of AlCoCrCuFeNi high-entropy alloy system
Mater Lett
(2007) - et al.
Nanocrystalline CoCrFeNiCuAl high-entropy solid solution synthesized by mechanical alloying
J Alloys Comp
(2009) - et al.
Microstructure and mechanical properties of CoCrFeNiTiAlx high-entropy alloys
Mater Sci Eng A
(2009) - et al.
Novel microstructure of multicomponent CoCrCuFeNiTix alloys
Intermetallics
(2007) - et al.
Microstructural development in equiatomic multicomponent alloys
Mater Sci Eng A
(2004) - et al.
Alloying behavior of binary to octonary alloys based on Cu–Ni–Al–Co–Cr–Fe–Ti–Mo during mechanical alloying
J Alloys Comp
(2009) - et al.
Competition between elements during mechanical alloying in an octonary multi-principal-element alloy system
J Alloys Comp
(2009) - et al.
Anomalous decrease in X-ray diffraction intensities of Cu–Ni–Al–Co–Cr–Fe–Si alloy systems with multi-principal elements
Mater Chem Phys
(2007) - et al.
Microstructural and compressive properties of multicomponent Alx(TiVCrMnFeCoNiCu)100−x high-entropy alloys
Mater Sci Eng A
(2007)
Refractory high-entropy alloys
Intermetallics
Mechanical properties of Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 refractory high entropy alloys
Intermetallics
Microstructure and electrochemical properties of high entropy alloys – a comparison with type-304 stainless steel
Corros Sci
Corrosion behavior of FeCoNiCrCux high-entropy alloys in 3.5% sodium chloride solution
Mater Chem Phys
Microstructure and compressive properties of AlCrFeCoNi high entropy alloy
Mater Sci Eng
Microstructure and mechanical property of as-cast, -homogenized, and –deformed AlxCoCrFeNi (0 ≤ x ≤ 2) high-entropy alloys
J Alloys Comp
Age hardening of the Al0.3CoCrFeNiC0.1 high entropy alloy
J Alloys Comp
Microstructure and tensile behaviors of FCC Al0.3CoCrFeNi high entropy alloy
J Alloys Comp
Spinodal decomposition – phase diagram representation and occurrence
Effect of precipitates on damping capacity and mechanical properties of Ti–6Al–4V alloy
Mater Sci Eng A
The effect of compressive deformation of austenite on the Widmanstätten ferrite transformation in Fe–Mn–Si–C steel
Mater Sci Eng A
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