Body-centered Cubic Structure Research Articles

Short-Range Structure of Ti0.63V0.27Fe0.10D1.73 from Neutron Total Scattering and Reverse Monte Carlo Modelling

Ti-V-based body-centered cubic (BCC) alloys have potential for large-scale hydrogen storage if expensive vanadium is substituted with much cheaper Fe-containing ferrovanadium. Use of ferrovanadium reduces the alloys’ hydrogen storage capacity. This is puzzling since the amount of Fe is low and hydrogen atoms are accommodated in interstitial sites which are partly coordinated by Fe in many intermetallic compounds. The present work is aimed at finding a structural explanation for Fe-induced capacity loss in Ti-V alloys. Since such alloys and their hydrides are highly disordered without long-range occupational order of the different metal species, it was necessary to employ a technique which is sensitive to local structure. Neutron total scattering coupled with reverse Monte Carlo modelling was thus employed to elucidate short-range atomic correlations in Ti0.63V0.27Fe0.10D1.73 from the pair distribution function. It was found that Fe atoms form clusters and that the majority of the vacant interstitial sites are within these clusters. These clusters take the same face-centered cubic structure as the Ti-V matrix in the deuteride and thus they are not simply unreacted Fe which has a BCC structure. The presence of Fe clusters is confirmed by transmission electron microscopy. Density functional theory calculations indicate that the clustering is driven by thermodynamics.

Methanol steam reforming microreactor with novel 3D-Printed porous stainless steel support as catalyst support

In order to study the methanol steam reforming performance of the 3D-printed porous support for hydrogen production, three dimensional (3D) printing technology was proposed to fabricate porous stainless steel supports with body-centered cubic structure (BCCS) and face-centered cubic structure (FCCS). Catalyst loading strength of the 3D-printed porous stainless steel supports was studied. Moreover, methanol steam reforming performance of different 3D-printed porous supports for hydrogen production was experimentally investigated by changing reaction parameters. The results show that the 3D-printed porous stainless steel supports with BCCS and FCCS exhibit better catalyst loading strength, and can be used in the microreactor for methanol steam reforming for hydrogen production. Compared with 90 pores per inch (PPI) Fe-based foam support, 3D-printed porous stainless steel supports with FCCS and BCCS show the similar methanol steam reforming performance for hydrogen production in the condition of 6500 mL/(g·h) gas hourly space velocity (GHSV) with 360 °C reaction temperature. This work provides a new idea for the structural design and fabrication of the porous support for methanol steam reforming microreactor for hydrogen production.

Microstructure and mechanical properties of CoCrFeNiMo high-entropy alloy coatings

The CoCrFeNiMo coatings were prepared by laser cladding on 45 steel surface. The microstructure, hardness and wear resistance of CoCrFeNiMo high-entropy alloy were investigated by means of scanning electron microscopy, X-ray diffractometer, hardness tester and wear tester. The effect of laser scanning speed on the microstructure and mechanical properties of the coating was studied. Experimental results show that the coating and matrix combines well, the microstructure of the coatings is mainly composed of equiaxed grains. The phase structure of the coating is mainly composed of face-centered cubic (FCC) structure, body-centered cubic (BCC) structure and Laves phase. There is a slight segregation of Mo element. The CoCrFeNiMo coating has high hardness, the highest surface hardness is 741HV. Fine-grained strengthening, BCC structure and Laves phase provided a guarantee for the excellent wear resistance of the coating. With the increase of scanning speed, the structure is refined, the hardness is improved and the wear resistance is enhanced.

Study on Microstructure and Corrosion Resistance of AlCoCrFeNiTi(x) High-Entropy Alloys

AlCoCrFeNiTi(x) (x=0, 0.4, 0.8, 1.0) high entropy alloys (HEAs) were prepared by vacuum arc melting furnace. The results showed that AlCoCrFeNiTi(x) HEAs transformed from a single body-centered cubic structure (BCC) to two kinds of body-centered cubic structures accompanied by a small amount of Laves phase with the increase of Ti content, and the morphology of alloy structure changed from dendrites to the petal-like equi-axed crystals. In addition, the alloy with the content of 0.4 mol. % Ti has a corrosion potential of -0.335V and a minimum corrosion current density of 7.36×10−7 A/cm2, which indicated that the HEAs with the content of 0.4 mol.% Ti has the best corrosion resistance.

Phase Transition Mechanism and Mechanical Properties of AlCrFe2Ni2 High‐Entropy Alloys with Changes in the Applied Carbon Content

To understand the effect of carbon addition on dual‐phase high‐entropy alloys (HEAs), the mechanism of phase transition and mechanical properties of AlCrFe2Ni2Cx (x = 0, 0.06, 0.12, 0.18, 0.24) are investigated systematically. The results show that carbon addition induced the growth and aggregate of disordered noodle‐like face‐centered cubic (FCC) phases. The volume fraction of the FCC phase increases from 33.2% to 51.2% as the C content increases. The Al and Ni in the alloys are segregated at the phase boundaries. Disappearance of the spinodal decomposition structure compose of a disordered body‐centered cubic (BCC) structure and an ordered BCC structure (B2). The BCC phase transform into a spherical B2 phase with increasing C content. The experimental mechanical properties show that the yield strength of the HEAs is closely related to the volume fraction of BCC phase as the C content increases. The ε phase (Cr, C carbonization) precipitate in an FCC phase when the C content is above 2.0 at%. The hardness of the HEAs increases from 310 to 357 HV as the C content increases. The compressive strength and the fracture strain of the alloy decreases as the C content increases.

Relationship between Microstructure and Properties of Cu-Cr-Ag Alloy.

The microstructure evolution and properties of a Cu–Cr–Ag alloy during continuous extrusion and an aging process were studied by Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). Owing to strong shear deformation that happened during continuous extrusion with working temperatures of 450 to 480 °C, a larger number of fine grains were obtained. Both face-centered cubic (FCC) and body-centered cubic (BCC) precipitates simultaneously existed in the matrix when aged for 450 °C for 2 h, and the Cr phases with BCC structure had an N–W relationship with the matrix. After continuous extrusion, 60% cold deformation, 875 °C × 1 h solid solution treatment, 60% cold deformation, 450 °C × 2 h aging treatment, and 70% cold deformation, the Cu–Cr–Ag alloy acquired excellent comprehensive properties: tensile strength of 494.4 MPa, yield strength of 487.6 MPa, and electrical conductivity of 91.4% IACS.

Construction of an n-body Fe–Cu potential and its application in atomistic modeling of Fe–Cu solid solutions

By means of the embedded-atom method, a Fe–Cu potential has been constructed through a newly mathematic form of cross potential. The newly constructed Fe–Cu potential has demonstrated to be more reliable than the five reported Fe–Cu potentials. Based on the Fe–Cu potential, the mechanical and thermodynamic properties and the structural stability of Fe–Cu solid solutions in the whole composition range are derived by molecular dynamics simulation. It is found that the heat of formation curves of the FexCu100 − x solid solutions with body-centered-cubic (BCC) and face-centered-cubic (FCC) structures intersect at the point of x = 65, implying that FexCu100 − x solid solutions with FCC and BCC structures are thermodynamically stable when 0 ≤ x ≤ 65 and 65 < x ≤ 100, respectively. In addition, the derived lattice constants, structural stability, elastic constants, elastic moduli, heat capacity, and coefficients of thermal expansion of Fe–Cu solid solutions from the new Fe–Cu potential agree well with the data of the experiments, first-principles calculation, and the Miedema model.

Effects of Co and W on the microstructure and wear behavior of NiCrAlMoTiFeNbX equimolar multicomponent-clad layers

In this study, we used the gas tungsten arc welding (GTAW) process for cladding NiCrAlMoTiFeNbCo and NiCrAlMoTiFeNbW multicomponent alloys onto the surface of AISI 1020 low-carbon steel. The microstructures and the sliding wear resistance of the cladding layers were characterized. The experimental results indicated that a multiple-carbide particle composed of (Nb,Ti)C with a TiC-rich core and NbC shell, was synthesized in situ in both multicomponent cladding layers. The eutectic phase of Fe0.875Mo0.125 with the body-centered cubic structure (BCC) was present in the NiCrAlMoTiFeNbCo cladding layer, and the reinforcing phase of Fe2W with the hexagonal-closest-packed (HCP) structure was in the NiCrAlMoTiFeNbCW cladding layer. Wear test results revealed that the wear performance of the multicomponent cladding layers can significantly improve the wear resistance of the AISI 1020 low-carbon steel. The wear resistance of the NiCrAlMoTiFeNbW cladding layer exceeded that of the other cladding layer. The improvement in the wear resistance of the NiCrAlMoTiFeNbW cladding layer was attributable to the high hardness of the cladding layer and the Fe2W reinforcement in the cladding layer. The wear test results confirmed that the cladding layer with higher ratios of hardness to Young's modulus for both the matrix and the strengthening phase exhibited better wear resistance.

Verification and Optimization of Single Phase Solid Solution Rule in High Entropy Alloys

High-entropy alloys (HEAs) with single face-centered cubic (FCC) structures always exhibit excellent ductility, and those with a single body-centered cubic (BCC) structure exhibit high strength. The mixture of FCC and BCC structures contributes to a synergy of strength and ductility. Thus, investigating the formation rules of different structures in HEAs is beneficial for obtaining the desired HEA composition. In this article, several HEAs were designed and prepared to verify the pure single-phase solid-solution rule, i.e., δ 8 for single FCC solid solution and δ 12.47 J mol−1 K−1, while for the other HEAs, the critical values of the rule will be extended.

Molecular dynamics simulation of migration behavior of FCC-BCC atomic terrace-step phase boundary in iron-based alloy

The martensitic transformation between the high-temperature face-centered cubic (FCC) phase and the low-temperature body-centered cubic (BCC) phase in iron-based alloys has been studied for years, which plays a critical role in controlling microstructures and hence properties of the alloys. Generally, the BCC structure martensitic phase forms from the FCC parent phase, involving a collective motions of atoms over a distance less than the interatomic distance in the vicinity of the interphase boundary. Thus the structure of interphase boundary separating the FCC and BCC phases is the key characteristics to quantitatively understanding the mechanism and kinetics of martensitic transformation. Due to the difficulty in observing the atomic motions taking place at a velocity as high as the speed of sound, the experimental investigation on the migration of FCC/BCC interphase boundary during the transformation is as yet limited. Noteworthily, molecular dynamics (MD) simulation has been applied to studying the martensitic transformation, in particular for investigating the mobility of the FCC/BCC interphase boundary in iron. However, in most of the MD studies the atomistically planar interfaces of {111}<sub>FCC</sub> // {110}<sub>BCC</sub> are considered as the initial configuration of the interphase boundary between FCC and BCC phases, which is in contradiction to the high-resolution TEM observations. In fact, the FCC/BCC interphase boundary, which is known as the macroscopic habit plane, is a semi-coherent interface consisting of several steps and terrace planes on an atomic scale. In the present work, the atomic configuration of a terrace-step FCC/BCC interphase boundary of iron is built in terms of the topological model. The MD simulation is conducted to clarify the mechanism of interphase boundary migration in the FCC-to-BCC transformation. The results show that the FCC/BCC boundary migrates along its normal at the expense of FCC phase as a result of the lateral motions of the transformation dislocations. Meanwhile, the interphase boundary maintains the stable terrace-step structure during the transformation. Further examinations reveal that the transformation dislocations move steadily at a velocity as high as (2.8 ± 0.2) × 10<sup>3</sup> m/s, affecting the migration of the interphase boundary with a constant velocity of about (4.4 ± 0.3) × 10<sup>2</sup> m/s. The effective migration velocity of FCC/BCC interface exhibits dynamic properties consistent with the characteristic features commonly observed in a displacive martensitic transformation. Additionally, the motion of transformation dislocations gives rise to the macroscopic shape strain composed of a shear component <inline-formula><tex-math id="M3">\begin{document}$ {\varGamma _{{\rm{yz}}}} = 0.349$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20191903_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20191903_M3.png"/></alternatives></inline-formula> parallel to the boundary and a dilatation <inline-formula><tex-math id="M4">\begin{document}$ {\varGamma _{{\rm{zz}}}} = 0.053$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20191903_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20191903_M4.png"/></alternatives></inline-formula> normal to the boundary in the MD simulation, which is close to the crystallographic calculations by the topological model.

Determination of atomic-scale structure and compressive behavior of solidified AlxCrCoFeCuNi high entropy alloys

The atomic configurations play a key role in predicting the solidification process of high-entropy alloys (HEAs). The atomic scale structures of AlxCrCoFeCuNi (x = 0.5, 1.5, 3.0) HEAs that emerge during solidification with a cooling rate of 12 × 109 (K/s) are evaluated using molecular dynamics (MD) simulation. While BCC (body-centered cubic) structure is obtained for Al0.5CrCoFeCuNi and Al1.5CrCoFeCuNi where lattice distortion increases with increasing aluminum fraction from x = 0.5 to x = 1.5, for Al3.0CrCoFeCuNi, an amorphous structure is formed under the same cooling rate. The diffusion coefficient of all the elements at 2200 K and the super-heating temperature of each alloy are evaluated to explain the disordering mechanism due to aluminum addition, which affects both the aluminum mobility and diffusion of the constituent atoms in the HEA. Finally, the compression behavior of all the three HEAs was studied to show the effect of crystalline structure on the stress fluctuation. It was found that phase transformation induced plasticity occurred which led to a secondary hardening of crystalline alloys after ultimate compressive strength (UCS).

Hydrogen storage properties of Nb-based solid solution alloys with a BCC structure

Hydrogen storage properties of Nbx(Ti0.7Cr0.3)1-x (x = 0.3, 0.4, 0.5, 0.6) alloys with a body centered cubic (BCC) structure and the crystal structure of their hydrides were investigated. These alloys absorbed hydrogen up to around 1.8 H/M by forming a di-hydride phase in the absorption process, and desorbed to 0.8 H/M to transform to a mono-hydride phase during the desorption process. These behaviors are similar to those of Ti–Cr–V and Ti–Cr–Mo alloys with the BCC structure. XRD patterns indicated that the alloys transformed to the mono-hydride with a slightly distorted BCC structure (orthorhombic structure), and then to the di-hydride with a CaF2 structure. With increasing Nb content, both the lattice constants for all phases, and the equilibrium pressures for the absorption and desorption processes increased. This indicated that Nbx(Ti0.7Cr0.3)1-x does not follow the well-known relationship of equilibrium pressures decreasing with increasing lattice constants. However, the logarithmic equilibrium pressures had a linear relationship with their estimated bulk modulus.

Designing novel lightweight, high-strength and high-plasticity Tix(AlCrNb)100-x medium-entropy alloys

Due to the demand for reduced energy consumption by transportation vehicles, lighter weight high-entropy alloys (with density comparable to that of commercial Ti alloys around 4.5–5 g/cm3) are attracting more attention in terms of alloy design and application as structural materials. In this study, a nonequiatomic quaternary alloy system, Tix(AlCrNb)100-x, was designed through the calculation of phase diagrams. Simulation results reveal that a single body-centered cubic (BCC) phase can be formed and can be stable at temperatures above 950 °C. Accordingly, a series of Tix(AlCrNb)100-x (x = 45–80) alloys containing a BCC structure were prepared through vacuum arc melting and rapid cooling. The designed alloys can exhibit desirable mechanical properties with high compression yield strength about 1500 MPa, high compression fracture strength about 1800 MPa and high compression plasticity more than 30% at room temperature. Moreover, the Ti65 alloy can demonstrate a tensile strength of 1200 MPa with a tensile elongation of 32%, after a homogenization treatment for 24 h. The specific compression and tensile strength can reach 0.36 and 0.24 GPa cm3/g.

High temperature oxidation study of direct laser deposited AlXCoCrFeNi (X=0.3,0.7) high entropy alloys

High entropy alloys (HEAs) are being explored as prospective substitutes for high temperature structural components. These HEAs are typically fabricated using conventional techniques like arc melting, mechanical alloying etc., but these routes exhibit a wide range of limitations. Direct laser deposition (DLD) process (an additive manufacturing technique) generates complex products from metal powder by selectively melting alloy powder in successive layers. The present study shows the development of HEAs namely Al0.3CoCrFeNi, Al0.7CoCrFeNi possessing crystal structures face-centered cubic (FCC) and FCC plus body-centered cubic (BCC) respectively using direct laser deposition (DLD) technique. HEA plates of the above-mentioned alloys were fabricated using DLD technique. In the present work, microstructures, mechanical (mainly hardness) and cyclic oxidation behaviors at 1100 ̊Cof developed HEAs have been investigated. Microstructural studies revealed FCC and FCC + BCC structures respectively, for Al0.3CoCrFeNi and Al0.7CoCrFeNi alloys with corresponding hardness of 170HV and 380HV. Cyclic oxidation studies were performed on the HEAs at a temperature of 1100 ̊°C for 200 h. Both the HEAs displayed quasi parabolic oxide growth after an initial sharp growth slope. Over the studied oxidation period, the mass gain for HEA Al0.3CoCrFeNi was greater than for Al0.7CoCrFeNi. Each oxidized HEAs forms an external Cr2O3 scale with Al2O3 subscale formed beneath, but the thickness and continuity of oxide layers vary according to Al content. Increased Al content enhanced the oxidation resistance of the HEA.

Thermodynamic properties of interstitial alloy FeC with BCC structure under pressure

The analytic expressions for the thermodynamic quantities such as the mean nearest neighbor distance, the free energy, the isothermal compressibility, the thermal expansion coefficient, the heat capacities at constant volume and at constant pressure of binary interstitial alloy with body-centered cubic (BCC) structure and the small concentration are derived by the statistical moment method. The theoretical results are applied to the interstitial FeC alloy in the interval of temperature from 50 to 1000K and in the interval of interstitial atom concentration from 0 to 5%. In special cases, we obtain the thermodynamic quantities of the main Fe metal. Our calculated results for the thermal expansion coefficient and the heat capacity under constant pressure of main metal Fe are in good agreement with experiments.

High-Throughput Nanomechanical Screening of Phase-Specific and Temperature-Dependent Hardness in AlxFeCrNiMn High-Entropy Alloys

Development of structural materials for service under extreme conditions is slowed by the lack of high-throughput test protocols. Here, a method that integrates high-throughput nanoindentation mapping with precise temperature control under a vacuum atmosphere is demonstrated. High-entropy alloys (HEAs) may possess the strength and stability required of high-temperature structural materials in next-generation nuclear applications. These alloys, including the compositional variation AlxFeCrNiMn (x = 0, 0.3, 1) presented in this work, have distinct microstructural morphologies, and nanoindentation mapping reveals the mechanical behavior of the distinct phases as a function of temperature up to 400°C. FeCrNiMn (Al = 0) consists of a face-centered cubic (FCC) matrix with body-centered cubic (BCC) precipitates and exhibits significant softening in both phases at elevated temperature. In contrast, both the FCC phase and FCC–BCC phases present in Al0.3FeCrNiMn show approximately 90% retention of the room temperature hardness at 400°C, and AlFeCrNiMn with BCC and B2 structures shows a similar 85% retention of hardness.

Effects of Al addition on structural evolution and mechanical properties of the CrCoNi medium-entropy alloy

In this study, we synthesized a series of (CoCrNi)100-xAlx (x = 0–30 at.%) medium-entropy alloys (MEAs), investigated alloying effects of Al element on microstructure and mechanical properties of CrCoNi MEA, then analyzed the strengthen mechanism caused by Al element. Microstructural evolutions were evaluated by means of X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The microstructures of (CoCrNi)100-xAlx MEAs evolved from single face-centered cubic (FCC) (x < 12 at.%), to duplex FCC plus body-centered cubic (BCC) (12 ≤ x < 22 at.%), then to double BCC (x ≥ 22 at.%) structures with Al content increase. When Al content increase to 16 at.%, BCC phase decomposed into plate-like intervened structure with ordered and disordered BCC phases (B2 and A2 structure) by spinodal decomposition mechanism. When Al content higher than 22 at.%, spinodal structure evolve from plate-like intervened structure to spherical particles dispersed in matrix structure. The hardness of Alx alloys increased from HV170 to the maximum of HV700 and the compressive yield strength rose form 204 MPa–1792 MPa. The solid-solution strengthening of Al element and formation of hard BCC phase were the two main factors contributing to the strengthening effect in this alloy system. Experimental results showed that the duplex FCC plus BCC structure can significant enhanced the strength-ductility synergy of CrCoNi MEA. It is especially noted that Al19 alloy which consist of 40% volume fraction FCC and 60% volume fraction BCC exhibits the most attractive properties accompany with compromise compressive yield strength, fracture strength and facture strain of 1226 MPa, 2542 MPa and 21.97%, respectively, and the corresponding hardness of 494 HV.

Investigation of mechanical properties, formability, and anisotropy of dual phase Mg–7Li–1Zn

In this article, the mechanical properties, microstructure, forming limit diagram (FLD) and anisotropy of dual phase Mg-7Li–1Zn alloy have been evaluated by a uniaxial tensile test at three directions, scanning electron microscopy (SEM), optical microscopy (OM) and hemispherical punch test at ambient temperature. The optical microscopy images showed that the microstructure of as-cast LZ71 alloy possesses a dual phase microstructure such as β-Li matrix with body-centered cubic (BCC) structure and a partitioned α-Mg phase with hexagonal closest packed (HCP) structure in lath shape. After rolling process, the α-Mg phase has been elongated and arranged in the rolling direction and anisotropy at different directions increased, but after full annealing, microstructure arranged more uniform and changed from elongated to the uniform structure which this is the factor that reflects the reduction of anisotropy. FLD shows the limiting surface strains that sheet metal can endure before the start of localized necking and fracture at different deformation modes in tension-tension and tension-compression loading paths. The FLD of Mg–7Li–1Zn showed that this material has desirable formability due to the BCC structure with high slip system in the ambient temperature. Also, the results of the tensile test matched with the obtained FLD. Results of SEM revealed many dimples and some flat and cleavage planes. They showed the combination of ductile and brittle fracture, but the ductile fracture is the dominant fracture mechanisms for Mg–7Li–1Zn. In summary, in the dual phase, Mg–Li alloys via controlling the weight percent of lithium and other alloying elements can be achieved the desired mechanical properties and used for various applications.

Dissimilar metals deposition by directed energy based on powder-fed laser additive manufacturing

In this research, powder-fed laser additive manufacturing based on directed energy deposition (DED) technology is utilized for 3D printing/fabrication of dissimilar alloy walls. Three-dimensional fabrication of metallic layers (A410-L stainless steel, A316-L stainless steel, and zirconium) with different crystallographic structures such as body-centered cubic (BCC), face-centered cubic (FCC), and hexagonal close-packed (HCP) are studied. Solidification cracking of the HCP metal structure inhibits the manufacturing of a sound dissimilar wall during direct deposition of zirconium on stainless steel. Different techniques are employed to eliminate cracking during the deposition of such dissimilar walls. First, a functionally graded transition layer is employed to gradually transition from a BCC or FCC layer to a zirconium layer. However, several longitudinal and horizontal cracks are observed in the functionally graded structure, deteriorating the overall integrity of the wall. Subsequently, inter-layers are applied to reduce the metallurgical differences between the BCC, FCC, and HCP metal structures. These inter-layers are designed to suppress the formation of brittle intermetallic compounds and decrease the level of thermal stress leading to cracking. Several metallic powders including nickel, titanium, vanadium, and copper are tested and analyzed as inter-layer materials during layer by layer fabrication of the dissimilar wall. Cross-sectional examinations are performed for each case, in order to study the feasibility of fabricating a sound dissimilar wall without deleterious phases. Embrittlement and presence of nickel-rich intermetallics within the Zr matrix restricts the successful fabrication of a dissimilar alloy wall through the formation of vertical cold cracks. Samples with titanium and vanadium inter-layers demonstrate horizontal hot solidification cracking at the stainless steel interface, which is attributed to the large solidification temperature range. Nonetheless, best results are attained with the copper inter-layer due to its high compatibility with both of the stainless steel and Zr metals.

Study on the Melting of the Defective Interstitial Alloys TaSi and WSi with BCC Structure

The statistical moment method is used to study the melting of defective interstitial AB alloys, where A is the main element and B is an interstitial atom, with a body-centered-cubic (BCC) structure. The melting temperature of the AB alloy with defects is obtained from the temperature of absolute stability for the crystalline state and the equilibrium vacancy concentration. Numerical calculations are performed for the interstitial alloys TaSi and WSi. Our calculated results are in good agreement with other calculations.