Phase Evolution and Thermal Stability of Low-Density MgAlSiCrFe High-Entropy Alloy Processed Through Mechanical Alloying
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ORIGINAL ARTICLE
Phase Evolution and Thermal Stability of Low-Density MgAlSiCrFe High-Entropy Alloy Processed Through Mechanical Alloying Nandini Singh1 • Yagnesh Shadangi1 • Nilay Krishna Mukhopadhyay1
Received: 30 January 2020 / Accepted: 8 July 2020 The Indian Institute of Metals - IIM 2020
Abstract An equiatomic MgAlSiCrFe high-entropy alloy was synthesized by mechanical alloying. The alloying behavior, phase evolution, phase composition and thermal stability of as-milled nanostructured powders of HEA were ascertained through X-ray diffraction and transmission electron microscopy, scanning electron microscopy and differential scanning calorimetry (DSC), respectively. The milling of elemental powders for 60 h led to the formation of HEA with a major BCC phase having lattice parameter of 0.2887 ± 0.005 nm very close to that of the a-Fe and a minor fraction of undissolved Si. The nanocrystalline HEA powder formed during milling has crystallite size of 19 ± 0.8 nm. The STEM–EDS mapping of these milled powders confirms the homogenous elemental distribution after 60 h of mechanical alloying. The DSC thermogram of 60 h milled HEA powder shows the thermal stability of milled powder up to * 400 C. The exothermic heating events observed in the DSC thermogram correspond to phase transformation of MgAlSiCrFe HEA powder, and it may be correlated with the phases observed through the ex situ XRD of HEA powders annealed at different temperatures up to 700 C. After annealing the 60 h milled powder, various phases along with parent BCC phase have evolved, i.e., B2 type Al–Fe phase, FCC phases (Al–Mg solid solution), Cr5Si3, Mg2Si, Al13Fe4. Further, the experimental findings were correlated with various thermodynamic parameters for understanding the phase evolution and stability.
& Nandini Singh [email protected] 1
Department of Metallurgical Engineering, Indian Institute of Technology (BHU), Varanasi, Uttar Pradesh 221005, India
Keywords Low-density HEA Mechanical alloying Phase evolution Thermal stability
1 Introduction The upsurge in the demand for materials with high strength-to-weight ratio has led to design and development of many new classes of materials. The conventionally used alloys for engineering applications are mostly based on a single element with minor addition of other elements to enhance its mechanical and functional properties [1]. In the last three decades, considerable efforts were made by researchers toward development of high-strength materials. This led to the discovery of quasicrystals [2], bulk metallic glasses [3] and high-entropy alloys [4, 5]. Among the various new classes of materials developed, the high-entropy alloys (HEAs) are a relatively new category of alloys based on highly concentrated multicomponent elements. High-entropy alloys are defined as multicomponent alloys with five or more elements having a concentration between 5 and 35 at.% [6–10]. They can form a solid solution, intermetallics or bulk metallic glasses depending on composition and processing routes se
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