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High Entropy Alloys
Published in T.S. Srivatsan, Manoj Gupta, High Entropy Alloys, 2020
Gaurav Kumar Bansal, Avanish Kumar Chandan, Gopi Kishor Mandal, Vikas Chandra Srivastava
The stability of random solid-solution phase in high entropy alloys is mainly attributed to their high configurational entropy [4,45]. In the early studies on high entropy alloys, it was assumed that these alloys behave like an ideal solid solution, in which mixing enthalpies and non-configurational entropies of mixing are expected to be negligible. Under these conditions, the change in Gibbs free energy due to mixing is mainly contributed by the configurational entropy [45,46], as ΔGmix=−TΔSmix=RT∑ciln(ci)
The Statistical Interpretation of Entropy
Published in David R. Gaskell, David E. Laughlin, Introduction to the Thermodynamics of Materials, 2017
In the preceding discussion, the entropy was considered in terms of the number of ways that the energy of identical but distinguishable particles could be distributed. The entropy was seen to be greatest when the occupancy of the energy levels was broadly distributed. The degree of mixed-up-ness corresponded to the spread of the distribution. Entropy can also be considered in terms of the number of ways in which particles themselves can be distributed in space, and this consideration gives rise to the concept of configurational entropy mentioned briefly in Section 4.1.
High-Entropy Alloy-Based Coatings
Published in Sam Zhang, Jyh-Ming Ting, Wan-Yu Wu, Protective Thin Coatings Technology, 2021
Yujie Chen, Paul Munroe, Zonghan Xie, Sam Zhang
High-entropy alloys (HEAs), often referred to as multicomponent alloys, have emerged over the last decade as a new class of metallic materials with excellent physical and mechanical properties (Yeh et al. 2004, Cantor et al. 2004, Zhang et al. 2014b, Zhang et al. 2018a). The original design concept of these novel alloys was proposed to maximize the configurational entropy for the formation of single-phase solid solution by mixing multiple principal alloying elements in relatively high, often equiatomic, concentrations (Gludovatz et al. 2014, Lin et al. 2017). This concept stands in sharp contrast to conventional alloys, in which relatively small amounts of secondary elements are normally added to a primary element, leading to limited number of possible elemental combinations (Figure 6.1). Recently, it has been increasingly realized that maximum entropy, achieved by equiatomic ratios of elements, is not the most essential parameter when designing HEAs with superior properties, enabling the relaxation of the original strict restriction on the equiatomic ratios of HEAs (Otto et al. 2013, Ma et al. 2015, Yang and Zhang 2012). These findings significantly increase compositional space for this kind of novel alloy (Figure 6.1), offering promise to discover exciting new alloys. Many attractive properties have been achieved in HEAs, such as high hardness and strength, excellent corrosion resistance, oxidation resistance, and good high-temperature stability (Miracle and Senkov 2017).
Effects of pressure-temperature protocols on the properties of crystals and ageing effects – an analogy with glasses
Published in Philosophical Magazine, 2022
We consider only atomic or elemental crystals, maintaining that the concepts would be valid for hydrostatically compressed ionic and molecular crystals. Point defects in all crystals are imperfections of the lattice. Their dimensions are of the order of the entities that occupy the lattice sites and their presence distorts the near-neighbor lattice. Random diffusion of atoms through the point defects sites produces different configurations and different local densities. Availability of different configurations adds a configurational part to H, S, V of a crystal and the presence of defects modify the vibrational frequency of neighbouring atoms. Thus the quantity H, S, and V of a crystal contain both the configurational and vibrational parts – the vibrational part modified by the defect-induced spatial disturbance of its neighbours in both the equilibrium state in which structure fluctuations occur on an experiment’s time scale, and in the out-of equilibrium state in which no structure fluctuations occur. For a given material, H, V and S are determined by the structure of a crystal and the number of point defects per mole. The configurational entropy, Sconf, is determined by the entropy of mixing, Smix, of atoms and defects, which is given by the Boltzmann’s equation. When there are no defect-defect interactions, Sconf is equal to Smix. It varies with T and P because neq varies with T and P.
Design of a nickel–cobalt based eutectic high entropy alloy (NiCo)1.7AlCrFe with hierarchical microstructural length scales
Published in Philosophical Magazine, 2023
R.J. Vikram, Khushbu Dash, Shanmukha Kiran Aramanda, Satyam Suwas
The four important parameters that define the theory of alloy design are size difference δ %, mixing enthalpy ΔHmix, the entropy of mixing ΔSmix, and valence electron concentration (VEC). Understanding the possible reciprocation between these critical factors for phase selection is the goal of a HEA. The configurational entropy influences phase stability at higher temperatures [5]. Zhang et al. [17, 18] proposed using atomic size difference and mixing enthalpy ΔHmix as a valuable tool for alloy design. ΔHmix determines whether the atoms want to attract one another to form a single phase or repel each other to phase separate, and it is strongly influenced by the interaction parameters (Ω).
Effect of irradiation on microstructure and hardening of Cr–Fe–Ni–Mn high-entropy alloy and its strengthened version
Published in Philosophical Magazine, 2020
V.N. Voyevodin, S.A. Karpov, G.D. Tolstolutskaya, M.A. Tikhonovsky, A.N. Velikodnyi, I.E. Kopanets, G.N. Tolmachova, A.S. Kalchenko, R.L. Vasilenko, I.V. Kolodiy
Establishing of fusion and GEN IV fission reactors defines new materials challenges in terms of higher operating temperatures, higher neutron exposures, as well as ensuring safe and efficient operation. High-entropy alloys are a new effort in materials science and engineering. These alloys have multiple metallic elements of nearly equimolar compositions and stabilised solid solution phases. The higher configurational entropy leads to reduce the tendency of forming intermetallic phases at high temperatures. It was shown that HEAs have excellent strength and resistance to corrosion, wear, and softening at high temperatures because the diffusion kinetics in HEAs is suggested to be sluggish [1,2].