First report on entire sets of experimentally determined interdiffusion coefficients in quaternary and quinary high-entr
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First report on entire sets of experimentally determined interdiffusion coefficients in quaternary and quinary high-entropy alloys Vivek Verma1, Aparna Tripathi1, Thiruvenkatam Venkateswaran2, Kaustubh N. Kulkarni1,a) 1
Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Uttar Pradesh 208016, India Materials and Mechanical Entity, Vikram Sarabhai Space Centre, Trivandrum, Kerala 695022, India a) Address all correspondence to this author. e-mail: [email protected] 2
Received: 16 September 2019; accepted: 20 November 2019
For the first time in the literature, experimental determination of entire sets of exact interdiffusion coefficients in quaternary and quinary alloy systems is reported. Using the method of body-diagonal diffusion couple, a set of nine quaternary interdiffusion coefficients were evaluated in Fe–Ni–Co–Cr and a set of sixteen quinary interdiffusion coefficients were determined in a Fe–Ni–Co–Cr–Mn system, both at approximately equimolar compositions. Regions of uphill interdiffusion and zero flux planes were observed for nickel and cobalt in quinary couples, indicating the existence of strong diffusional interactions in Fe–Ni–Co–Cr–Mn alloys. The strong diffusional interactions were also manifested in the large magnitudes of cross coefficients in both the systems. The existence of strong diffusional interactions in high-entropy alloys (HEAs) as observed through experimentally determined interdiffusion coefficients in this study establishes beyond doubt the fact that cross interdiffusion coefficients cannot be ignored in HEAs.
Introduction The field of high-entropy alloys (HEAs) has captured tremendous attention from researchers over the past two decades due to their potential applications in a variety of sectors, including aerospace, automobile, biomedical, and energy [1, 2, 3, 4, 5]. Although considerable work has been done on HEAs, focusing mostly on exploring their properties, there have been few experimental studies on exploring their fundamental aspects. The most debated topic in HEAs so far is the existence of sluggish diffusion in these alloys [2, 5, 6]. Earlier reports of sluggish diffusion in HEAs were based on the observation of nano-sized precipitates in as-cast AlxCoCrCuFeNi alloys [7]. These precipitates did not grow or dissolve even after hightemperature annealing, which phenomenon was attributed to the sluggish diffusion in HEAs. Later, in order to understand the diffusion kinetics in HEAs, Tsai et al. [8] performed a series of quasi-binary diffusion couple experiments with Fe–Ni–Co– Cr–Mn alloys. In their work, with the oversimplified assumption of interdiffusion coefficient being equal to intrinsic diffusion coefficient being equal to self-diffusion coefficient, Tsai et al. [8] claimed that the diffusion is sluggish in Fe–Ni–
ª Materials Research Society 2020
Co–Cr–Mn HEAs. Some studies [9, 10] that followed later also suggested the existence of sluggish diffusion in HEAs. However, Some of the recent articles have reported that diffusion does not necessari
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