Interstitial Solid Solution Research Articles

Simulating the mechanisms of serrated flow in interstitial alloys with atomic resolution over diffusive timescales

The Portevin-Le Chatelier (PLC) effect is a phenomenon by which plastic slip in metallic materials becomes unstable, resulting in jerky flow and the onset of inhomogeneous deformation. The PLC effect is thought to be fundamentally caused by the dynamic interplay between dislocations and solute atoms. However, this interplay is almost always inaccessible experimentally due to the extremely fine length and time scales over which it occurs. In this paper, simulations of jerky flow in W-O interstitial solid solutions reveal three dynamic regimes emerging from the simulated strain rate-temperature space: one resembling standard solid solution strengthening, another one mimicking solute cloud formation, and a third one where dislocation/solute coevolution leads to jerky flow as a precursor of dynamic strain aging. The simulations are carried out in a stochastic framework that naturally captures rare events in a rigorous manner, providing atomistic resolution over diffusive time scales using no adjustable parameters.

Elasticity of disordered binary crystals

The properties of crystals consisting of several components can be widely tuned. Often solid solutions are produced, where substitutional or interstitional disorder determines the crystal thermodynamic and mechanical properties. The chemical and structural disorder impedes the study of the elasticity of such solid solutions, since standard procedures like potential expansions cannot be applied. We present a generalization of a density functional–based approach recently developed for one-component crystals to multi-component crystals. It yields expressions for the elastic constants valid in solid solutions with arbitrary amounts of point defects and up to the melting temperature. Further, both acoustic and optical phonon eigenfrequencies can be computed in linear response from the equilibrium particle densities and established classical density functionals. As a proof of principle, dispersion relations are computed for two different binary crystals: A random fcc crystal as an example for a substitutional, and a disordered sodium chloride structure as an example of an interstitial solid solution. In cases where one of the components couples only weakly to the others, the dispersion relations develop characteristic signatures. The acoustic branches become flat in much of the first Brillouin zone, and a crossover between acoustic and optic branches takes place at a wavelength which can far exceed the lattice spacing.

The effect of yttrium on the microwave absorbing properties of Fe78Si13B9 alloy powders

In this study, the effect of rare earth Y on the microwave absorbing properties of the powders was studied, directing against low electromagnetic loss (tanδ) and low dielectric constant of Fe78Si13B9 alloy powders in the frequency band of 0.3–3 GHz. The results showed that when Y content is less than 2 at%, Y solid dissolves in dendrite gap of α-Fe, forming interstitial solid solution. With the increase of Y content, the permeability and dielectric constant of Fe78-xSi13B9Yx alloy powders increase, especially the dielectric loss and magnetic loss increase significantly. Fe76Si13B9Y2 alloy powders have excellent absorbing properties. When the frequency is 0.3 GHz and 1 GHz, the loss tangent value of that is as high as 5.22 and 2.42 respectively, and the minimum interference thickness is reduced to 11.81 mm and 5.20 mm, which is 45% of that of Fe78Si13B9 alloy powders. Fe76Si13B9Y2 alloy powders has excellent electromagnetic loss absorption and interference absorption properties at the same time.

A model for interstitial solid solution strengthening of body centered cubic metals

A model for interstitial solid solution strengthening of body centered cubic metals is proposed and used to analyze strengthening behavior of interstitial solid solutions of body centered cubic metals for which experimental data at near-room temperature are available in the open literature. The proposed model takes into account interstitial solute-dislocation interactions and cross-kink interactions at the core of a/2 [111] screw dislocations. Good agreement between the calculated and experimental yield stress values is found.

Observation of Chemical State for Interstitial Solid Solution of Carbon in Low-carbon Steel by Soft X-ray Absorption Spectroscopy

Observation of Chemical State for Interstitial Solid Solution of Carbon in Low-carbon Steel by Soft X-ray Absorption Spectroscopy

Study on grinding damage of high chromium alloy based on molecular dynamics

The new cast high chromium alloy is the conventional material of the nuclear main pump thrust-bearing with good wear and corrosion resistance. According to the structural characteristics of high chromium alloy, the simulation model and the coupling potential function were constructed to study the grinding damage layer using molecular dynamics method. The simulation results show that the crystal lattice distortion caused by carbon atoms in the formation of interstitial solid solution leads to the occurrence of amorphous structure after full relaxation. The break and recombination of metal bond and non-metal bond between atoms in the alloy result in the occurrence of damaged layer under grinding. And the bond angles between the atoms in the damage layer are less than that in the alloy matrix. The damage layer is mainly composed of atoms in front of the abrasive particle and the atoms of extrusion deformation in the bottom. Moreover, with the increase of grinding depth, the cutting force and the damage layer thickness increase. The study is conducive to understand the damage formation mechanism of high-chromium alloy materials in micro-nano processing, and provides a theoretical reference value for the actual processing.

Impact of interstitial C on phase stability and stacking-fault energy of the CrMnFeCoNi high-entropy alloy

Interstitial alloying in CrMnFeCoNi-based high-entropy alloys is known to modify their mechanical properties. Specifically, strength can be increased due to interstitial solid-solution hardening, while simultaneously affecting ductility. In this paper, first-principles calculations are carried out to analyze the impact of interstitial C atoms on CrMnFeCoNi in the fcc and the hcp phases. Our results show that C solution energies are widely spread and sensitively depend on the specific local environments. Using the computed solution-energy distributions together with statistical mechanics concepts, we determine the impact of C on the phase stability. C atoms are found to stabilize the fcc phase as compared to the hcp phase, indicating that the stacking-fault energy of CrMnFeCoNi increases due to C alloying. Using our extensive set of first-principles computed solution energies, correlations between them and local environments around the C atoms are investigated. This analysis reveals, e.g., that the local valence-electron concentration around a C atom is well correlated with its solution energy.

Description of terminal substitutional solid solutions using the sublattice model

The case of the substitutional solid solutions based on elements possessing several crystallographic sites is discussed. It is concluded that, at least in some cases, especially when the solution domain is large and when strong differences of site occupancies are observed between the different sites, the sublattice model should be used as it is the case for interstitial solid solutions or non-stoichiometric intermetallic compounds. Results of experimental site occupancies are presented and compared with these obtained from the DFT calculations from which the configurational entropy can be calculated. Comparison of the enthalpy and entropy of the solid solutions is made with the available thermodynamic assessments. The β-U phase in U–Pu system is addressed but the most important cases are α-Mn and β-Mn solid solutions in different systems such as Mn–Re, Fe–Mn, Al–Mn and Al–Fe–Mn. These phases are particularly detailed and conclusions are given relative to their thermodynamic modeling emphasizing the need to use the sublattice model.

Laser cladding and in-situ nitriding of martensitic stainless steel coating with striking performance

The nitrogen (N) alloying in traditional bulk martensitic stainless steel (MSS) necessitates high-pressure and high-temperature treatment because of its extremely low solubility. Herein, we report a novel strategy for in-situ nitriding MSS coating with N content up to 0.14 wt% by laser cladding technique without harsh conditions. The resulting coating is composed of martensite, austenite, nano-precipitates M23C6 and M2N, which exhibits striking mechanical properties with tensile strength of 1900 MPa and elongation of 7.3% as well as excellent corrosion resistance, exceptionally superior to the reported laser cladded MSS coatings. This may be ascribed to the combination impacts of grain refinement, nano-precipitation, interstitial solid solution and dislocation strengthening.

A phase-field model for hydride formation in polycrystalline metals: Application to δ-hydride in zirconium alloys

We report a phase-field model for simulating metal hydride formation involving large volume expansion in single- and polycrystals. As an example, we consider δ-hydride formation in α-zirconium (Zr), which involves both displacive crystallographic structural change and hydrogen diffusion process. Thermodynamic Gibbs energy functions are extracted from the available thermodynamic database based on the sublattice model for the interstitial solid solutions. Solute-grain boundary interactions and inhomogeneous elasticity of polycrystals are taken into consideration within the context of diffuse-interface description. The stress-free transformation strains of multiple variants for hcp-Zr (α) to fcc-hydride (δ) transformation are derived based on the well-established orientation relationship between the α and δ phases as well as the corresponding temperature-dependent lattice parameters. In particular, to account for the large volume expansion, we introduced the mixed interfacial coherency concept between those phases—basal planes are coherent and prismatic planes are semi-coherent in computing the strain energy contribution to the thermodynamics. We analyzed the morphological characteristics of hydrides involving multiple structural variants and their interactions with grain boundaries. Moreover, our simulation study allows for the exploration of the possible hydride re-orientation mechanisms when precipitating under applied tensile load, taking into account the variation in the interfacial coherency between hydrides and matrix, their elastic interactions with the applied stress, as well as their morphology-dependent interactions with grain boundaries. The phase-field model presented here is generally applicable to hydride formation in any binary metal–hydrogen systems.

Formation of Nanosized Surface Layers of 03Kh17N12M2 Stainless Steel by Implantation of N+ Ions

Accumulation of nitrogen in nanosized surface layers of 03Kh17N12M2 stainless steel has been detected upon N+ ion implantation up to 14 at % together with metal nitrides, mainly of chromium nitride CrN and interstitial solid solution. It has been demonstrated that N+ ion implantation accompanied by preliminary irradiation by Ar+ and O+ ions decreases maximum nitrogen concentration by at least two times. It is assumed that this is stipulated by segregation to surface layers of iron atoms upon irradiation by Ar+ ions as well as formation of chromium oxide Cr2O3 and chromium hydroxide CrOOH upon irradiation by O+ ions.

First-principles study on the mechanical properties of interstitial solid solution Aluminum–Boron alloy

The sputtering Al-B alloy film exhibits a unique growth structure and a high strengthening efficiency. In this study, the first-principles method was used to investigate the effect of addition B element on the mechanical properties of Al-B alloys, including the elastic properties, anisotropy, ideal shear strength, generalized stacking fault energy (GSFE), and dislocation core. Results indicate that the solid solution of B slightly decreases the elastic modulus of the alloy and decreases the ideal shear strength. Thus, the anisotropic tendency weakens, GSFE substantially increases, and the Peierls stress and Peierls barrier energy substantially increase. Therefore, the introduce of B has little effect on the intrinsic properties of the alloy, but the interstitial solid solution of B greatly increases the dislocation initiation energy, which limits the initiation and movement of dislocation, and has an important contribution to the strengthening effect.

Co-existence of γ'N phase and γN phase on nitrided austenitic Fe–Cr–Ni alloys- I. experiment

The formation of a metastable and nitrogen-supersaturated f.c.c. interstitial solid solution layer on Fe–Cr–Ni austenitic stainless steel at a moderate temperature around 650–720 K is not entirely understood. In the present work, three groups of austenitic Fe–Cr–Ni alloys, containing systematic variations of chromium, nickel and iron contents were nitrided by plasma-based low-energy ion implantation at 653 K for 4 h and investigated with light-optical microscopy (LOM), electron probe microanalysis (EPMA), (grazing incidence) X-ray diffraction (XRD) and transmission electron microscopy (TEM). Commercial AISI 304L was included for comparison. For the austenitic alloys with a Cr content below 12 wt.%, a duplex layer is observed in the nitrided case where the interface between the top layer, consisting of γ'-Fe4N like ordered γ'N, and the disordered γN (nitrogen enriched austenite) zone underneath is associated with a decrease in N content. For the alloys with a Cr-content over 12 wt.%, a featureless continuous zone is observed with LOM and a gradual decrease in nitrogen content is measured with EPMA. Nevertheless, a similar duplex structure of outer γ'-Fe4N like ordered γ'N and inner γN is confirmed by XRD and TEM for all nitrided alloys, irrespective of the Cr content. The results are discussed in terms of the short-range order (SRO) promoted by the Cr–N interaction and long-range order (LRO) caused by the Fe–N interaction.

Microstructure and mechanical properties of ultra-fine grained MoNbTaTiV refractory high-entropy alloy fabricated by spark plasma sintering

The MoNbTaTiV refractory high-entropy alloy (RHEA) with ultra-fine grains and homogeneous microstructure was successfully fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). The microstructural evolutions, mechanical properties and strengthening mechanisms of the alloys were systematically investigated. The nanocrystalline mechanically alloyed powders with simple body-centered cubic (BCC) phase were obtained after 40 h MA process. Afterward, the powders were sintered using SPS in the temperature range from 1500 °C to 1700 °C. The bulk alloys were consisted of submicron scale BCC matrix and face-centered cubic (FCC) precipitation phases. The bulk alloy sintered at 1600 °C had an average grain size of 0.58 μm and an FCC precipitation phase of 0.18 μm, exhibiting outstanding micro-hardness of 542 HV, compressive yield strength of 2208 MPa, fracture strength of 3238 MPa and acceptable plastic strain of 24.9% at room temperature. The enhanced mechanical properties of the MoNbTaTiV RHEA fabricated by MA and SPS were mainly attributed to the grain boundary strengthening and the interstitial solid solution strengthening. It is expectable that the MA and SPS processes are the promising methods to synthesize ultra-fine grains and homogenous microstructural RHEA with excellent mechanical properties.

Pd–H and Ni–H phase diagrams using cluster variation method and Monte Carlo simulation

ABSTRACTThis work focuses on interstitial solid solutions of hydrogen in the face-centred cubic (fcc) host lattice of palladium and nickel, using a first-principles based approach. Cluster Variation Method (CVM) and Monte Carlo simulation algorithms were especially designed, allowing a coupled use of both techniques, to study hydrogen–vacancy interactions inside an fcc metallic host lattice. First-principles calculations provided the H–Vac interaction energies by structure inversion method. The phase diagrams and thermodynamic properties were computed using only theoretical inputs. The mechanisms leading to the formation of the miscibility gaps observed for both Pd–H and Ni–H systems and the hydrogen ordering on palladium interstitial lattice were reproduced without any empirical term.

Development of a large size FCC high-entropy alloy with excellent mechanical properties

A large size 10 kg Fe40Mn40Co10Cr10 high-entropy alloy (HEA) with 3.3 at. % C-doped was prepared by electromagnetic levitation melting. The hot deformation behavior of the as-cast ingot was investigated to guide the hot forging process. Annealing was further conducted on the as-forged samples to obtain more optimized mechanical properties. The as-forged HEA had yield strength (YS) of 792 MPa, ultimate tensile strength of 1055 MPa and a satisfactory fracture elongation (EL) of 22.6%. The YS of the HEA annealed at 1050 °C increased from 393 MPa to 512 MPa and EL from 26.5% to 55.3% in comparison with the as-cast HEA. It is suggested that the enhanced yield strength of the as annealed HEA was attributed to carbon interstitial solid solution strengthening, grain refining and precipitation of tiny carbides, and the improvement of ductility was due to the elimination of cast defects and twinning-induced plasticity. This work paved the way for the application of HEA as high performance structure materials.

Ultrafine nanocrystalline microstructure in Mg[sbnd]B alloy for ultrahigh hardness and good ductility

Mg alloys are remarkably light but lack the strength offered by other structural materials. They can be traditionally strengthened by introducing hard reinforcements, but such method usually compromises ductility (toughness). An ingenious structural design could provide a way of retaining lightness while adding hardness of Mg. Here, we focus on B as light-weight dopant and develop new MgB alloy with small B content addition of 6.6 at.% using non-equilibrium magnetron sputtering technology. The special nanostructure with ultrafine Mg(B) interstitial solid solution grains (mean diameter: ~5 nm) embedded into narrow amorphous shell (~2 nm thick) is highlighted. The resulting binary alloy has substantially improved hardness from 2.6 ± 0.2 to 8.5 ± 0.4 GPa and elasticity modulus from 89.9 ± 4.7 to 150.3 ± 6.3 GPa, without much compromising the good ductility of pure Mg, as a consequence of the synergistic actions from almost-dislocation-free refined grains and narrow amorphous matrix. This newly simple approach can overcome the long-standing challenge of trade-off between hardness and toughness, and can offer a widely applicable route to high-performance light-metal materials for both structural and nonstructural applications.

Isothermal section of the Ho–Cu–Sn ternary system at 670 K

The interaction of the components in the Ho-Cu-Sn ternary system was investigated at 670 K over the whole concentration range using X-ray diffraction and EPM analyses. Four ternary compounds were formed in the Ho–Cu–Sn system at 670 K: HoCuSn (LiGaGe type, space group P63mc), Ho3Cu4Sn4 (Gd3Cu4Ge4-type, space group Immm), HoCu5Sn (CeCu5Au-type, space group Pnma), and Ho1.9Cu9.2Sn2.8 (Dy1.9Cu9.2Sn2.8-type, space group P63/mmc). The formation of the interstitial solid solution based on HoSn2 (ZrSi2-type) binary compound up to 5 at. % Cu was found.

Formation of Metallic and Carbide Phases via Codecomposition of [NiEn3]WO4 and Lithium Hydride in the Range 410–1060°C

The formation of metallic and carbide phases during the thermal decomposition of a mixture of the coordination compound [NiEn3]WO4 (En = ethylenediamine) and LiH in a He atmosphere has been studied by X-ray diffraction. The results demonstrate that heat treatment of the mixture at 410°C for 10 min leads to the formation of a Ni(Cx) interstitial solid solution based on the HCP Ni lattice and a W1 –xNix substitutional solid solution based on the BCC W lattice. Starting at 510°C, a Ni1 –xWx solid solution based on the FCC Ni lattice is also formed. The double carbide Ni2W4Cx appears at 660°C, and Ni6W6Cx forms at 860°C. Under similar conditions (700°C, He), the thermal decomposition of a mixture of NiWO4 and LiH leads to the formation of W and an FCC Ni1 –xWx (x ~ 0.12) solid solution.

Lu-V-{Ge, Sn} ternary systems


 The isothermal sections of the phase diagrams of the Lu–V–Ge and Lu-V-Sn ternary systems were constructed at 870 K over the whole concentration range using X-ray diffraction and EPM analyses. In the Lu-V-Ge system a formation of the substitutional solid solution Lu5Ge3-xVx based on the Lu5Ge3binary compound (Mn5Si3 structure type) was found up to 6 at. % V. Insertion of the V atoms in the structure of the LuGe2 binary germanide (ZrSi2structure type, up to 5 aт. % V) results in the formation of the LuV0,15Ge2 ternary phase (CeNiSi2 structure type, space group Cmcm, a=0.40210(4),b=1.5661(1), c=0.38876(3) nm), which corresponds to the limit composition of the interstitial solid solution LuVxGe2. The interaction between the elements in the Lu-V-Sn system results in the formation of one ternary compound LuV6Sn6 (SmMn6Sn6-type, space group P6/mmm, a=0.5503(2), c=0.9171(4) nm) at investigated temperature.