Microstructure and mechanical properties of FeCoCrNiMnAlx high-entropy alloys prepared by mechanical alloying and hot-pressed sintering
Introduction
As a new kind of alloy materials, High-entropy alloys (HEAs) have attracted wide attention because of their unique microstructure and properties [[1], [2], [3], [4]]. Among various HEAs, an equiatomic FeCoCrNiMn HEA is considered to be promising [5]. This alloy has excellent ductility and toughness that exceed those of most other materials [[6], [7], [8], [9]]. However, its low strength and hardness have limited its industrial potential [9].
Currently, conventional melting/casting methods are usually used to fabricate this alloy. However, melting/casting easily cause the formation of a microstructure with coarse grains and composition segregation [9]. Fortunately, this alloy has the high Hall-Petch coefficient [9], therefore, different methods can be applied to obtain fine grains and to improve the mechanical properties, including rolling at different temperatures [[10], [11], [12], [13], [14]], high pressure torsion [15] and swaging [16] after arc melting. However, these fabrication routes are uneconomical for industrial manufacturing, and the shape and size of the final products are limited [17]. By contrast, powder metallurgy is a more convenient approach for industrial use. Preparation of HEAs by powder metallurgy usually consists of two processes: mechanical alloying (MA) and sintering. MA has been widely used to prepare the nanocrystalline HEA powders. Combined with the subsequent sintering, the bulk HEAs with ultrafine or nanosized grains can conveniently be obtained [18,19].
In addition, the alloy also was strengthened by the doping of alloying elements, such as Al [20] or C [21,22]. For example, He et al. [20] used the melting/casting method to prepare alloys with the addition of Al. It was found that the crystalline structure of the matrix solid solution phase in the alloys changed from fcc to bcc with the increase of Al concentration. The addition of Al obviously improved the mechanical properties of the alloy.
By combining the powder metallurgy approach and doping with Al, Al-containing FeCoCrNiMn HEAs were prepared by MA and sintering in order to further strengthen the alloy. Pohan et al. [23] and Wang et al. [17] used MA and spark plasma sintering to prepare FeCoCrNiMnAl0.3 and FeCoCrNiMnAl HEAs with ultrafine and nanosized grains, respectively. Al addition induced bcc precipitates in a soft bcc alloy based on FeCoCrNiMn, thus effectively strengthening the alloy. However, systematic studies on the effects of alloying on the phase evolution and strengthening mechanisms of the alloys prepared by powder metallurgy are still rare. Therefore, in this work, we sought to determine the effects of the Al concentration on the microstructure and mechanical properties of FeCoCrNiMn HEA prepared by MA and sintering and to identify the phase formation and strengthening mechanisms.
Section snippets
Experimental
The average grain sizes of Fe, Co, Cr, Ni, Mn and Al metal powders with high purity (≥99.9%) are approximately 45 μm. The FeCoCrNiMnAlx (x represents atomic proportions, that is, x = 0, 0.1, 0.3, 0.5, 0.7 and 1) HEA powders, which are referred to as alloys Al0, Al0.1, Al0.3, Al0.5, Al0.7 and Al1, respectively, were synthesized by MA in a planetary ball mill (QM-QX4L, Changsha Miqi Instrument Equipment Co., Ltd., China).
The MA process was conducted in the stainless steel vials filled with highly
Microstructure
Fig. 1a shows the XRD patterns of the FeCoCrNiMnAlx HEA powders obtained by milling for 45 h. Alloying of the metal powders was achieved after 45 h of milling. When the atomic proportion of Al is less than or equal to 0.5 (i.e., alloys Al0, Al0.1, Al0.3 and Al0.5), the alloys consist of a fcc phase as the matrix and traces of bcc phase. The diffraction peak of the bcc phase is separated from that of the fcc phase, and the diffraction peak intensity gradually increases as the Al concentration
Phase formation mechanism
In conventional steels, the doping with Al easily destabilizes fcc γ-Fe and induces the formation of bcc α-Fe [33]. Similarly, for HEAs, the doping with Al also leads to the transformation from the fcc to bcc [20,34,35]. This occurs because the Al atom has a larger radius than the other alloy elements, such as Fe, Co, Cr and Ni. The solution of Al into the FeCoCrNiMn alloy can increase the lattice strain effect, thus destabilize the fcc structure [20]. Because the bcc structure has a lower
Conclusions
FeCoCrNiMnAlx HEAs were prepared by MA and hot-pressed sintering. The microstructure and mechanical properties of the alloys were characterized, and the phase formation and strengthening mechanisms were investigated. The main conclusions are as follows.
The bulk alloys consist of the matrix fcc or fcc + bcc solid solution phase(s) and a small quantity of M23C6 + M7C3 carbides and Al2O3 phases. The single fcc solid solution phase was formed in alloys Al0 and Al0.1. With the increase of the Al
Acknowledgements
The research was supported by the Major Industry-academy Cooperation Project of Fujian Province (Grant No. 2014H6005).
References (43)
- et al.
Microstructures and properties of high-entropy alloys
Prog. Mater. Sci.
(2014) - et al.
An assessment on the future development of high-entropy alloys: summary from a recent workshop
Intermetallics
(2015) - et al.
Microstructural development in equiatomic multicomponent alloys
Mater. Sci. Eng. A
(2004) - et al.
Recovery, recrystallization, grain growth and phase stability of a family of FCC-structured multi-component equiatomic solid solution alloys
Intermetallics
(2014) - et al.
Tensile properties of high- and medium-entropy alloys
Intermetallics
(2013) - et al.
The influence of temperature and microstructure on the tensile properties of a CoCrFeMnNi high-entropy alloy
Acta Mater.
(2013) - et al.
High temperature deformation behavior and dynamic recrystallization in CoCrFeNiMn high entropy alloy
Mater. Sci. Eng. A
(2015) - et al.
Microstructural evolution of a CoCrFeMnNi high-entropy alloy after swaging and annealing
J. Alloys Compd.
(2015) - et al.
Microstructural evolution after thermomechanical processing in an equiatomic, single-phase CoCrFeMnNi high-entropy alloy with special focus on twin boundaries
Intermetallics
(2014) - et al.
Microstructure and texture evolution during annealing of equiatomic CoCrFeMnNi high-entropy alloys
J. Alloys Compd.
(2014)
Mechanical properties, microstructure and thermal stability of a nanocrystalline CoCrFeMnNi high-entropy alloy after severe plastic deformation
Acta Mater.
Microstructural evolution of a CoCrFeMnNi high-entropy alloy after swaging and annealing
J. Alloys Compd.
Mechanical alloying and spark plasma sintering of CoCrFeNiMnAl high-entropy alloy
Adv. Powder Technol.
Alloying behavior and novel properties of CoCrFeNiMn high-entropy alloy fabricated by mechanical alloying and spark plasma sintering
Intermetallics
Structure and properties of ultrafine-grained CoCrFeMnNi high-entropy alloys produced by mechanical alloying and spark plasma sintering
J. Alloys Compd.
Effects of Al addition on structural evolution and tensile properties of the FeCoNiCrMn high-entropy alloy system
Acta Mater.
Nano-twin mediated plasticity in carbon-containing FeNiCoCrMn high entropy alloys
J. Alloys Compd.
Effect of thermomechanical processing on microstructure and mechanical properties of the carbon-containing CoCrFeNiMn high entropy alloy
J. Alloys Compd.
Microstructure and mechanical properties of mechanically alloyed and spark plasma sintered Al0.3CoCrFeMnNi high entropy alloy
Mater. Chem. Phys.
Synthesis of in-situ NiAl-Al2O3nanocomposite by reactive milling and subsequent heat treatment
Intermetallics
CoCrFeMnNi high entropy alloy matrix nanocomposite with addition of Al2O3
Intermetallics
Cited by (55)
Effects of Fe content on microstructure and properties of ferrous medium-entropy alloys prepared using powder metallurgy
2023, Materials Today CommunicationsInternal nitridation during creep of IN617 superalloy
2022, Corrosion ScienceStudy on strengthening mechanism and high temperature mechanical properties of TiC-Fe-HEA cemented carbide
2022, Materials Today CommunicationsDamping capacity and mechanical properties of Fe<inf>3</inf>Cr<inf>2</inf>NiCuAl<inf>x</inf> medium entropy alloys by tuning phase constituents
2022, Journal of Alloys and CompoundsCitation Excerpt :The results show that the increase of the Al atomic ratio in the alloys facilitates to the formation of BCC structural phase. This was shown by many other literatures [33,34], e.g., the phase constituents of FeCrNi2CuAlx (x = 0.2, 0.4, 0.6, 0.8, 1.0, 1.2) HEAs [35] are tunable by the Al addition. Fig. 3 shows the EBSD images of the Fe3Cr2NiCuAlx alloys.