Abstract
Bulk CoCrFeNiNb0.45 eutectic high entropy alloy (EHEA) with ultrafine-lamellar microstructure shows outstanding thermal stability. The EHEA offers opportunities for the development of thermoelectric materials. In this paper, the thermoelectric properties of a CoCrFeNiNbx (x = 0, 0.25, and 0.45) EHEA system were investigated. The results indicated that the electrical conductivity decreased with a rise in Nb content in the CoCrFeNiNbx alloys, which resulted from the increased eutectic structure and phase interface. Moreover, the thermal conductivity increased with increased Nb content at low temperature (T ≤ 473 K), while thermal conductivity decreased at high temperature (T > 573 K). The CoCrFeNiNb0.45 full eutectic high entropy alloy exhibited the lowest thermal conductivity and higher thermoelectric figure of merit (ZT) at a high temperature (T > 573 K), which shows great promise for the thermoelectric application at high temperature.
Highlights
Thermoelectric (TE) materials, which can realize the conversion between heat and electricity, have received renewed attention in waste heat recoveries and TE refrigeration [1,2,3,4]
We found that ultrafine/regular lamellar eutectic structures can be obtained with a direct solidification method in CoCrFeNiNb0.45 eutectic high entropy alloy (EHEA) [38]
The microstructures of the CoCrFeNiNbx ingots were investigated as shown in Figure 1a–f [38,39]
Summary
Thermoelectric (TE) materials, which can realize the conversion between heat and electricity, have received renewed attention in waste heat recoveries and TE refrigeration [1,2,3,4]. Reducing the size of materials in nano-scale has been demonstrated to be an effective method to improve the thermoelectric performance, several disadvantages exist. Many of these materials are not practical for large-scale application. The sluggish diffusion effect in HEAs results in the crystal growing slowly, promoting the formation of nano-structures [15,16]. The in-situ synthetic EHEAs have several beneficial features relative to the conventional nanostructure thermoelectric materials, such as high thermodynamic stability, low-cost method, low-energy phase boundaries and high symmetry crystal structures.
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