Phase stability and elastic properties of Cr–V alloys

Abstract

V is the only element in the periodic table that forms a complete solid solution with Cr and thus is particularly important in alloying strategy to ductilize Cr. This study combines first-principles density functional theory calculations and experiments to investigate the phase stability and elastic properties of Cr-V binary alloys. The cluster expansion study reveals the formation of various ordered compounds at low temperatures that were not previously known. These compounds become unstable due to the configurational entropy of bcc solid solution as the temperature is increased. The elastic constants of ordered and disordered compounds are calculated at both T = 0 K and finite temperatures. The overall trends in elastic properties are in agreement with measurements using the resonant ultrasound spectroscopy method. The calculations predict that addition of V to Cr decreases both the bulk modulus and the shear modulus, and enhances the Poisson's ratio, in agreement with experiments. Decrease in the bulk modulus is correlated to decrease in the valence electron density and increase in the lattice constant. An enhanced Poisson's ratio for bcc Cr-V alloys (compared to pure Cr) is associated with an increased density of states at the Fermi level. Furthermore, the difference charge density in the bonding region in the (110) slip plane is highest for pure Cr and decreases gradually as V is added. The present calculation also predicts a negative Cauchy pressure for pure Cr, and it becomes positive upon alloying with V. The intrinsic ductilizing effect from V may contribute, at least partially, to the experimentally observed ductilizing phenomenon in the literature.

MoNbTaV Medium-Entropy Alloy

“…These issues still need to be resolved [7,22]. In fact, it is well known that most refractory metals lack good ductility at low temperatures [23,24].…”

“…Vanadium has a significantly lower density (6.11 g/cm 3 ) than tungsten (19.25 g/cm 3 ), while the former has a much higher Poisson's ratio (0.365) than the latter (0.28) [7,25]. Poisson's ratio is commonly used to gauge the ductility of metals and alloys, and alloys with higher Poisson's ratio often exhibit higher intrinsic ductility [23,24]. The MoNbTaV alloy is fabricated using arc-melting technique, and its microstructure and mechanical properties at room temperature (RT) were investigated.…”

Ab Initio Study of Binary and Ternary Nb3(X,Y) A15 Intermetallic Phases (X,Y = Al, Ge, Si, Sn)

“…Table 2 gives the results for the independent elastic constants (C ij ) and bulk moduli (B) for all elements and compounds under study. In this Table the and Poisson's ratio (v) [45,46]. The values of the aforementioned properties are listed in Table 3.…”

Modeling the structure and thermodynamics of high-entropy alloys

“…Specifically, we discussed the application of the CPA, 14,41,96,100,101,[113][114][115][116][117][118][119] supercell and SQS methods, 38,40,66,[120][121][122][123] empirical pair-and embedded atom-potentials, [124][125][126][127][128][129][130][131] and the Miedema approximation. 6,56,[58][59][60][61][132][133][134] We explained how these may be combined for direct free energy calculation, 65,85,103,135 incorporated into cluster expansions, 69,70,85,88,109,136 used as the basis for computer simulation, [84][85]…”