Interstitial Alloys Research Articles

THERMODYNAMIC PROPERTY OF ALLOY FCC-AuCuLi AT ZERO PRESSURE

We briefly present the thermodynamic theory of FCC ternary substitutional and interstitial alloy at zero pressure derived by the statistical moment method and apply this theory to alloy AuCuLi. The thermodynamic properties of Au, AuCu and AuLi are specific cases for that of AuCuLi. We compare the thermodynamic properties of alloys AuCuSi and AuCuLi. Our calculated results of thermodynamic quantities for AuCuLi predict and orient experimental results in the future.

EQUILIBRIUM VACANCY CONCENTRATION AND THERMODYNAMIC QUANTITIES OF FCC DEFECTIVE ALLOYS AuCuSi AND PtCuSi UNDER PRESSURE AND TEMPERATURE

We present the analytic expressions of the cohesive energy, the alloy parameters, the equation of state, the mean nearest neighbor distance, the Helmholtz free energy, equilibrium vacancy concentration, and thermodynamic quantities such as the isothermal compressibility, the thermal expansion coefficient, the heat capacities at constant volume and constant pressure for facecentered cubic (FCC) defective ternary substitutional and interstitial alloy ABC derived by the statistical moment method (SMM). The obtained thermodynamic quantities depend on temperature, pressure, the concentration of substitutional atoms, the concentration of interstitial atoms, and equilibrium vacancy concentration. Thermodynamic quantities of FCC defective metal A, FCC defective substitutional alloy AB, and FCC defective interstitial alloy AC are specific cases for thermodynamic quantities of FCC defective ternary substitutional and interstitial alloy ABC. The theoretical results are calculated numerically to alloys AuCuSi and PtCuSi. Our calculated results of thermal expansion coefficient and heat capacities at constant pressure for main metals Au, Pt are in good agreement with experimental data. Our other calculated results for thermodynamic quantities of alloys AuCuSi and PtCuSi at different temperatures, pressure, the concentration of substitutional atoms, and concentrations of interstitial atoms orient and predict new experimental data in the future.

Superconducting interstitial MoReRuCx medium-entropy alloys with a hexagonal structure

We report the results of structural and physical studies on the MoReRuCx medium-entropy alloys (MEAs) with x varying from 0 to 0.20. In the whole x range, a single hexagonal phase is formed. The variation of lattice parameters indicates that carbon atoms are located at the interstitial site for x ≤ 0.10 while occupy both the interstitial and substitutional sites at higher x values, which is corroborated by the x-ray photonelectron spectroscopy (XPS) results. Moreover, the resistivity, magnetic and thermodynamic measurements evidence that these MEAs are bulk fully gapped superconductors. In particular, the transition temperature Tc displays a dome-like dependence on carbon content with a maximum of 9.62 K at x = 0.05, whereas a maximal zero-temperature upper critical field Bc2(0) of 10.5 T is achieved at x = 0.10. For all MEAs, the specific heat data reveal the existence of an inhomogeneous superconducting state, which is discussed in relation to the chemical inhomogeneity and strong atomic disorder. In addition, we show that the key factors that control superconductivity are essentially the same for both MoReRuCx and ReCx, despite their very different Tc values. Our work not only provides the first series of interstitial MEAs with a hexagonal structure, but also demonstrates a feasible way to tune the superconductivity in multicomponent alloys.

Extreme Expansion and Reversible Hydrogen Solubility in h.c.p. Titanium Stabilized by Colossal Interstitial Alloying

Titanium and its alloys are very reactive and have a high affinity to interstitial elements. Titanium is one of the metals that forms very stable borides, carbides, nitrides, oxides, and even hydrides. The solubility of nitrogen and oxygen in the hexagonal crystal structure of (metallic) titanium is very high; on the other end limited quantities of boron, carbon, and hydrogen can be dissolved. In the present contribution, we report on a significant increase in the solid solution limit of hydrogen in hexagonal close-packed (h.c.p.) titanium, where the h.c.p. crystal lattice is stabilized by deliberate interstitial alloying with high quantities of nitrogen or oxygen atoms. The presence of nitrogen/oxygen prevents the hydrogen-induced transformation of the h.c.p. titanium lattice to a face-centered cubic (f.c.c.) titanium lattice that occurs if no oxygen or nitrogen is present. The hydrogen content that can be accommodated at room temperature in h.c.p. titanium is as high as an unprecedented 50 at. pct from about 0 at. pct and causes an anisotropic expansion of the hexagonal lattice. This finding showcases that there could be an unexploited potential for combining large quantities of interstitials in titanium-based lattices.

Combining the Mie-Lennard-Jones and the Morse Potentials in Studying the Elastic Deformation of Interstitial Alloy AGC with FCC Structure under Pressure

In this study, the mean nearest neighbor distance between two atoms, the Helmholtz free energy and characteristic quantities for elastic deformation such as elastic moduli E, G, K and elastic constants C11, C12, C44 for binary interstitial alloys with FCC structure under pressure are derived with the statistical moment method. The numerical calculations for interstitial alloy AGC were performed by combining the Mie-Lennard-Jones potential and the Morse potential. Our calculated results were compared with other calculations and the experimental data.

Role of interlayer thickness on interdiffusion in Ti/TiN multilayers

In pursuit of a systematized interdiffusion study in Ti|TiN multilayers at low temperature (300 - 973K), x-ray reflectivity measurement aided with soft x-ray absorption and secondary ion mass spectroscopy were employed in the present scope of findings. Despite of TiN interfaced with Ti being a well-known diffusion blocking unit, modulation of individual stacking thickness in nm regime in two set of samples: SET – A : [TiN (10 nm) | Ti (5 nm)]10, SET – B : [TiN (5 nm) | Ti (10 nm)]10, out turns higher interfacial mixing for SET – B samples at elevated temperatures as expected due to lower N repository and eventually lesser Ti-N covalent bonds and higher Ti-Ti metal bonds, leading to plausible lower potential barrier for migration of the diffusion species. In turn, interdiffusion across interfaces promotes two distinct distribution profiles — (i) For SET – A samples, as opposed to discrete multilayer stacks, interdiffusion led to uniformly distributed single volume matrix transformation at 973K, and (ii) For SET – B samples, such transformation is pronounced even at 773K due to faster migration of N and at 973K, surprisingly N diffuses out, with some kind of residual interstitial TiN compound residing in the system.

Highly efficient parallel grand canonical simulations of interstitial-driven diffusion-deformation processes

Absorption of interstitial alloying elements like H, O, C, and N in metals and their continuous relocation and interactions with various microstructural features such as vacancies, dislocations, and grain boundaries have crucial influences on metals’ properties. However, besides limitations in experimental tools in capturing these mechanisms, the inefficiency of numerical tools also inhibits modeling efforts. Here, we present an efficient framework to perform hybrid grand canonical Monte Carlo and molecular dynamics simulations that allow for parallel insertion/deletion of Monte Carlo moves. A new methodology for calculation of the energy difference at trial moves that can be applied to many-body potentials as well as pair ones is a primary feature of our implementation. We study H diffusion in Fe (ferrite phase) and Ni polycrystalline samples to demonstrate the efficiency and scalability of the algorithm and its application. The computational cost of using our framework for half a million atoms is a factor of 250 less than the cost of using existing libraries.

Study on the Melting Temperature, the Jumps of Volume, Enthalpy and Entropy at Melting Point, and the Debye Temperature for the BCC Defective and Perfect Interstitial Alloy WSi under Pressure

The objective of this study is to determine the analytic expressions of the Helmholtz free energy, the equilibrium vacancy concentration, the melting temperature, the jumps of volume, enthalpy the mean nearest neighbor distance and entropy at melting point, the Debye temperature for the BCC defective, the limiting temperature of absolute stability for the crystalline state, and for the perfect binary interstitial alloy. The results obtained from the expressions are combined with the statistical moment method, the limiting condition of the absolute stability at the crystalline state, the Clausius–Clapeyron equation, the Debye model and the Gruneisen equation. Our numerical calculations of obtained theoretical results were carried out for alloy WSi under high temperature and pressure. Our calculated melting curve and relation between the melting temperature and the silicon concentration for WSi are in good agreement with other calculations. Our calculations for the jumps of volume, enthalpy and entropy, and the Debye temperature for WSi predict and orient experimental results in the future.

STUDY ON ELASTIC PROPERTY OF STAINLESS STEEL UNDER PRESSURE

The paper presents analytic expressions of the Helmholtz free energy and characteristic elastic deformation quantities such as the elastic moduli E, K, G and the elastic constants C11, C12, C44 for BCC interstitial and substitutional alloy with four components are determined by the statistical moment method. The obtained elastic quantities depend on temperature, pressure, the concentration of interstitial atoms, and the concentration of substitutional atoms. This is the elastic deformation theory of BCC interstitial and substitutional alloy with four components published for the first time. The elastic deformation theories of BCC metal, BCC binary interstitial alloy, BCC binary substitutional alloy, and BCC ternary interstitial and substitutional alloy are limit cases of the elastic deformation theory of BCC substitutional and interstitial alloy with four components. Our numerical calculations of the obtained theoretical results for metal Fe and alloy FeSi are in good agreement with other calculations and experiments. Other numerical calculations for alloys FeCr, FeNi, FeCrSi, FeNiSi, FeCrNiSi (some atoms Fe are substituted by atoms Cr and some other atoms Fe are substituted by atoms Ni) called stainless steels predict and orient experimental results in the future. Our numerical calculations for alloy FeCrNiSi are published for the first time.

Extreme hardening of titanium with colossal interstitial contents of nitrogen and oxygen

Homogenous thin foils of titanium with nitrogen and oxygen in interstitial solid solution were characterized with X-ray diffraction, light optical microscopy and electron backscatter diffraction. Samples covering the broad solubility ranges of O and N were synthesized. The mechanical properties were assessed using nanoindentation and related to the interstitial content, h.c.p. lattice expansion and grain orientation. Effects of surface pile-up and sink-in during nanoindentation were adequately accounted for, yielding hardness and indentation modulus values for nearly the full range of concentrations, finding consistency with theoretical expressions and very limited literature values. The hardening/strengthening achieved by colossal interstitial alloying of O and N correlates with the change in c/a ratio of the h.c.p. Ti lattice as caused by interstitial occupancy.

Impact of N on the Stacking Fault Energy and Phase Stability of FCC CrMnFeCoNi: An Ab Initio Study

Interstitial alloying has become an important pillar in tuning and improving the materials properties of high-entropy alloys, e.g., enabling interstitial solid-solution hardening and for tuning the stacking fault energies. In this work we performed ab initio calculations to evaluate the impact of interstitial alloying with nitrogen on the fcc–hcp phase stability for the prototypical CrMnFeCoNi alloy. The N solution energies are broadly distributed and reveal a clear correlation with the local environments. We show that N addition stabilizes the fcc phase of CrMnFeCoNi and increases the stacking fault energy.

Realization of interstitial boron ordering and optimal near-surface electronic structure in Pd-B alloy electrocatalysts

The fundamental understanding and precise tuning of interatomic s,p-d orbital hybridization are critical to the design of interstitial alloy catalysts containing light constituent atoms. Here, we present a joint theoretical and experimental study that reveals the importance of distribution, concentration and ordering of interstitial boron atoms in Pd-B alloy’s near-surface electronic structure and catalytic performance. Our theoretical results demonstrate that the sub-surface location of interstitial boron atoms with a Pd:B atomic ratio of 2:1 is necessary to ensure an appropriate degree of interatomic s,p-d orbital hybridization, and thereby an optimal surface electronic structure for the hydrogen evolution reaction (HER). We experimentally achieve this with highly-crystalline intermetallic Pd2B. Due to its optimal electronic structure and ordered arrangement of interstitial boron atoms, the intermetallic Pd2B exhibits Pt-like catalytic activity for HER and has excellent catalytic stability for over seven days.

Study on the diffusion of interstitial atom in interstitial alloy AuSi with FCC structureStudy on the diffusion of interstitial atom in interstitial alloy AuSi with FCC structure

The paper derives analytic expressions of the diffusion coefficient depending on strain and pressure for the interstitial alloy AB with FCC structure by the statistical moment method based on previous studies for metals and semiconductors. Theoretical results are applied to alloy AuSi. Our numerical results satisfy the Arrhenius law

Ammonia production using iron nitride and water as hydrogen source under mild temperature and pressure

Ammonia generation was studied in the reaction between water and nitrogen-containing iron at 323 K and atmospheric pressure. Similar to metallic Fe, the interstitial compound Fe3N reduced water through Fe oxidation to produce hydrogen gas, while the N combined with atomic hydrogen to produce ammonia as a byproduct. The addition of carbon dioxide to this system accelerated the reaction with concomitant consumption of carbon dioxide. The promoted ammonia production upon addition of carbon dioxide can be attributed to the generation of atomic hydrogen from the redox reaction of carbonic acid and Fe, as well as removal of used Fe from the reaction system through the formation of a soluble carbonato complex. When carbonate was added to the reaction system, the production rates of ammonia and hydrogen increased further. The results here confirmed that ammonia can be synthesized from iron nitride under mild conditions by utilizing carbon dioxide.

Interstitial effects on the incipient plasticity and dislocation behavior of a metastable high-entropy alloy: Nanoindentation experiments and statistical modeling

Owing to the partial dislocation assisted twinning and/or displacive transformation upon stress loading, metastable high-entropy alloys (HEAs) and their interstitial variants have shown excellent strength-plasticity synergy. However, the fundamental mechanisms of the dislocation nucleation and the onset of plasticity in these emerging materials remain unclear. The present study is to provide quantitative insights into the dislocation nucleation in the metastable HEAs and reveal the corresponding effects of interstitial alloying elements through combined instrumented nanoindentation experiments and statistical physical modeling. The results indicate that dislocation nucleation in a representative metastable non-equiatomic FeMnCoCr HEA is triggered by the thermally activated displacement of single principal atom, suggesting a dominant homogeneous mode of dislocation nucleation according to a continuum mechanical description for neonatal dislocation loop energy. Also, minor heterogeneous nucleation via monovacancy-atom exchange is possible according to a quantitative analysis for the potential effects of pre-existing defects. The activation volume necessary for dislocation nucleation in the metastable HEA is increased upon dissolving 0.5 at.% C plus 1.0 at.% N into the face-centered cubic structure. Statistical modeling and experimental nanoindentation results suggest that interstitial C and N atoms are prone to facilitate the nucleation rate of Shockley partials under intense shears. Yet, the significant drag effect by interstitial atoms can trap those neonatal mobile partials and reduce their mean free path before exhaustion. Thus, the width of stacking faults (SFs) formed by slip of such partials is severely constrained, which hinders the generation of SFs on multiple atomic layers and further inhibits the displacive phase transformation during deformation of the C-N co-doped metastable HEAs.

Effect of carbon content, deformation and annealing on the structure and properties of interstitial TRIP high-entropy alloys

In this work, the effect of carbon content on the structure and mechanical properties of Fe(50-x)Mn30Co10Cr10Cx (x=0; 0.5; 1.0 at.%) interstitial high entropy alloys was studied. In the as-cast condition, the alloys were composed of the face centred cubic (fcc) and hexagonal close packed (hcp) phases; the amount of the hcp phase decreased from 46% to 20% as the carbon concentration increased from 0 to 1 at.%. The carbon content had a limited effect on the strength of the alloys, yet the ductility was enhanced significantly as the result of interstitial alloying. Furthermore, Fe49Mn30Co10Cr10C1 alloy was cold rolled to a reduction of 56% reduction and annealed at 700-900°C for 1 hour. After cold working, the alloy has attained almost fully the hcp structure. Annealing resulted in (i) transformation of the deformation-induced hcp phase into fcc; (ii) development of recovery and recrystallization; (iii) precipitation of Cr-rich M23C6 carbides. The cold-rolled alloy was very strong but brittle; annealing resulted in softening and increase of the ductility. The relationships between the chemical composition, structure and mechanical properties of the alloys are briefly discussed.

Interstitial carbon in bcc HfNbTiVZr high-entropy alloy from first principles

The remarkable mechanical properties of high-entropy alloys can be further improved by interstitial alloying. In this work we employ density functional theory calculations to study the solution ene ...

Microstructure and mechanical behavior of laser aided additive manufactured low carbon interstitial Fe49.5Mn30Co10Cr10C0.5 multicomponent alloy

Laser aided additive manufacturing (LAAM) was used to fabricate bulk Fe49.5Mn30Co10Cr10C0.5 interstitial multicomponent alloy using pre-alloyed powder. The room temperature yield strength (σy), ultimate tensile strength (σUTS) and elongation (εUTS) were 645 MPa, 917 MPa and 27.0 % respectively. The as-built sample consisted of equiaxed and dendritic cellular structures formed by elemental segregation. These cellular structures together with oxide particle inclusions were deemed to strengthen the material. The other contributing components include dislocation strengthening, friction stress and grain boundary strengthening. The high εUTS was attributed to dislocation motion and activation of both twinning and transformation-induced plasticity (TWIP and TRIP). Tensile tests performed at −40 °C and −130 °C demonstrated superior tensile strength of 1041 MPa and 1267 MPa respectively. However, almost no twinning was observed in the fractured sample tested at −40 °C and −130 °C. Instead, higher fraction of strain-induced hexagonal close-packed (HCP) ε phase transformation of 21.2 % were observed for fractured sample tested at −40 °C, compared with 6.3 % in fractured room temperature sample.

Frontiers in atomistic simulations of high entropy alloys

The field of atomistic simulations of multicomponent materials and high entropy alloys is progressing rapidly, with challenging problems stimulating new creative solutions. In this Perspective, we present three topics that emerged very recently and that we anticipate will determine the future direction of research of high entropy alloys: the usage of machine-learning potentials for very accurate thermodynamics, the exploration of short-range order and its impact on macroscopic properties, and the more extensive exploitation of interstitial alloying and high entropy alloy surfaces for new technological applications. For each of these topics, we briefly summarize the key achievements, point out the aspects that still need to be addressed, and discuss possible future improvements and promising directions.

Editorial: Biographical Memoirs, Volume 69

Editorial: Biographical Memoirs, Volume 69