Effects of Y, GdCu, and Al Addition on the Thermoelectric Behavior of CoCrFeNi High Entropy Alloys

Abstract

Thermoelectric (TE) materials can interconvert waste heat into electricity, which will become alternative energy sources in the future. The high-entropy alloys (HEAs) as a new class of materials are well-known for some excellent properties, such as high friction toughness, excellent fatigue resistance, and corrosion resistance. Here, we present a series of HEAs to be potential candidates for the thermoelectric materials. The thermoelectric properties of Y x CoCrFeNi, Gd x CoCrFeNiCu, and annealed Al 0.3 CoCrFeNi were investigated. The effects of grain size and formation of the second phase on thermoelectric properties were revealed. In HEAs, we can reduce the thermal conductivity by controlling the phonon scattering due to the considerable complexity of the alloys. The Y, Gd-doped HEAs are competitive candidate thermoelectric materials for energy conversion in the future.The thermoelectric-power generation or refrigeration device made of thermoelectric material has the advantages of being noise free, zero emission and pollution free, lacking vibration, small volume, etc. It has been applied in deep space exploration and refrigeration, and has great potential in waste heat power generation [20,21].Conventional thermoelectric materials currently in use include Bi 2 Te 3 based, PbTe based and SiGe based, etc. Bi 2 Te 3 is currently the most commercially successful thermoelectric material near room temperature. It is widely used in the field of the thermoelectric refrigeration, and is also the thermoelectric material with the highest power generation efficiency at low temperature [22]. Although Bi 2 Te 3 has been commercialized, its performance can be further improved by doping, composition adjustment, etc. PbTe is the medium temperature thermoelectric material that has been studied for the longest time and PbTe-based materials have been successfully used in the NASA aerospace missions many times since 1960. In recent years, PbTe-based thermoelectric materials have made great progress. The application temperature range of the Si-Ge alloy is more than 1000 K. It has been successfully applied to some deep space detectors. For example, in the radioisotope temperature difference battery of the Cassini Saturn detector, the thermoelectric conversion device is prepared by the Si-Ge alloy. However, the reserves of Te and Ge elements are scarce and very costly; Pb is toxic, pollutes the environment, and endangers people's health. Therefore, the development of environmentally friendly, new low-cost thermoelectric materials is particularly urgent.HEAs are always being studied for their mechanical properties. Maybe many new and unexpected properties remain for us to explore. In the search for TE materials, the performance of this kind of material is estimated by the dimensionless figure of merit, defined as ZT = S 2 Tσ/k [23], where S is the Seebeck coefficient, T is the absolute temperature, σ is the electrical conductivity, and k = k e + k l is the total thermal conductivity, where k e and k l are the electronic and lattice co...

High entropy alloy CrFeNiCoCu sputter deposited films: Structure, electrical properties, and oxidation

“…It is interesting to compare the structure reported here with that of the same HEA prepared by different methods. It has often been reported 6,15,20,26,49,50 that material casted from the melt may have inhomogeneities in composition and/or be a mixture of two fcc structures, both with a high concentration of the elements. For example Wang et al 51 reported two fcc structures for CrFeCoNiCu alloys made by a casting facility attached to an arc melter.…”

Multiobjective Optimization and Machine Learning Algorithms for Forecasting the 3E Performance of a Concentrated Photovoltaic-Thermoelectric System

“…The transport properties have an interdependency relationship with different forms of materials as shown in Figure 2 [63,64]. Generally, an insulator material may have high Seebeck coefficient and very low electrical and thermal conductivities.…”

Nanostructured high-entropy materials

“…Electrons scattering in highentropy systems can be exacerbated because of high lattice distortion, which has been used to reduce electronic thermal conductivity in thermoelectric materials. As specific tests on electrical properties of HEAs are seldom conducted [91,100,101,102], electrical conductivity is often a property measured to characterize the thermoelectrical performance of materials [86,87,89,103]. The synthesis routes and compositions of NC HEAs can significantly affect their electrical properties.…”

“…As the optimization of thermoelectric performance of HEAs requires a systematic approach rather than programmable high-throughput evaluation, similar nanostructures have been shown to exhibit completely opposing phenomena. For example, adding Gd to the CoCrFeNi system facilitates the formation of nanoscale Laves phases, leading to a decrease in all of its thermoelectric parameters (electrical conductivity, thermal conductivity, and Seebeck coefficient) and having a reduced figure of merit, ZT [89]. In the NC-Ti 2 NiCoSnSb system (grain size ;12 nm), a secondary phase of TiC is obtained after long ball-milling times, facilitating more Ni 3 Sn 4 formation and leading to higher electrical and thermal conductivities, but undermining the thermoelectric performance [103].…”

“…nanoscale structures in an HEA matrix, such as precipitates and secondary phases, indeed affect the functional performance significantly. Among all HEAs, most studies have focused on Al xCoCrFeNi [76,86,87,88,89,90,91]. Such HEAs show considerable property variations that can be obtained through both a drive for phase transformation (from FCC to BCC) caused by different Al compositional ratios and nanostructure evolution resulting from its synthesis route.…”