International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 09 Issue: 05 | May 2022
p-ISSN: 2395-0072
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Critical Investigation of Influence of Al/Cr Ratio on the Properties of High Entropy Alloys Murtaza Maajid1, Abhishek Thakur2 1M.Tech
Scholar, Universal Institute of Engineering & Technology, Lalru Professor, Universal Institute of Engineering & Technology, Lalru --------------------------------------------------------------------------***----------------------------------------------------------------------Abstract: Due to the obvious high concentration of each superior elements, HEAs have unusual physical, chemical, 2Assitant
mechanical, and electrochemical characteristics. HEAs also have a unique structure. In order to improve the qualities even further, certain trace amounts of elements (at. percent 5 percent) are also included. In the current investigation, the synthesis and characterisation of high-entropy alloys based on AlCoCrFeMnNi will be the primary focuses. In this study, the influence of the Al/Cr ratio on the phase formation and corrosion behavior was investigated. By refining the grains, the addition of Co has an effect on both the microstructure and the corrosion. In addition, the ratio of aluminum to chrome has an effect on the microstructure as well as the behavior of corrosion. The synthesis of AlCoCrFeMnNi HEAs utilizing melting and casting as the process was the first step in this research project. The samples that were synthetically produced were analyzed using x-ray diffraction and optical microscopy respectively. Keywords: High entropy alloys (HEAs), X-ray diffraction; Optical Microscopy, Corrosion behavior 1. Introduction: Among all components of the alloy, aluminium shows the largest impact on the structure and properties; hence, the amount of information regarding AlxCoCrFeNi alloy. As the aluminium content of the AlxCoCrFeNi alloy increases, the fcc phase turns into the bcc phase [1,2]. For x in the molar ratio, the structure changes as follows: fcc occurs when x 0.4, a mixed fcc and bcc phase appears between 0.5 x 0.9, a single bcc phase is present when x 0.9 [3]. Through spinodal decomposition, the bcc phase consists of disordered bcc (A2) and ordered bcc (B2) [4]. Guo et al. indicate that the stability of the bcc or fcc in HEAs are associated with the concentration of valence electrons [5]. The change from fcc to bcc by increasing the Al content is also considered to occur due to lattice distortion. The alloys form a structure with lower atomic-packing efficiency, which is bcc due to the larger Al atomic size than the other major components [6]. Ogura et al. [7] explained the effect of Al content content on the phase transition. For this purpose, he used first principles electronic structure calculations. They claimed that the transformation from fcc to bcc with increasing Al content is mainly because of the high energy gain of the DO3 structure with Al addition. They observed that with increasing Al content, the total energy difference between fcc and bcc decreases. They pointed out that Cr and Fe stabilize the bcc structure, and Ni and Co are fcc stabilizers. Other studies also indicate that there is significant elemental segregation in the dendritic and interdendritic regions in the AlxCrCoFeNi alloy. The dendritic regions are enriched in NiAl, while the interdendritic regions show an increased FeCr content [8]. For as-cast alloys, the microstructure also changes with the change in Al content [9]. The solidified microstructure changes from a columnar cellular when x in the molar ratio is up to 0.3 to a columnar dendritic structure when 0.4 x 0.6, then to equiaxed non-dendritic grain when 0.7 x 0.8, next to equiaxed dendritic grains when 0.9 x 1.5 and finally to non-equiaxed dendritic structures when 1.8 x 2.0 [57]. The Al content also affects other properties of the alloy. Increasing the aluminium content in the AlxCoCrFeNi alloy increases its strength while decreasing its plasticity [10]. All HEAs showed significantly higher wear resistance than AISI 304 at temperatures above 300 ◦C and Inconel 718 at temperatures greater than 800 oC. The study showed a positive effect of increasing Al content in AlxCoCrFeNi alloy on wear properties. The AlxCoCrFeNi alloy with a low aluminium content shows weak magnetic properties, while a high content makes the alloy ferromagnetic. This is due to the change in the crystal structure of the alloy from the fcc phase to the bcc phase [11]. Studies indicate that as the Al content in AlxCoCrFeNi alloy increases, the corrosion resistance decreases due to the porosity and inferior nature of the Al protection oxide film in these alloys [12].
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