Interstitial Solution Research Articles

Wear and Corrosion Behaviour of Supersaturated Surface Layers in the High-Entropy Alloy Systems CrMnFeCoNi and CrFeCoNi

The surface hardening of single-face-centred cubic (fcc)-phase CrMnFeCoNi and the manganese-free CrFeCoNi alloy was conducted using low-temperature nitrocarburisation. The microstructural investigations reveal the successful formation of a homogeneous diffusion layer with a thickness of approximately 16 µm. The interstitial solution of carbon and nitrogen causes an anisotropic lattice expansion. The increase in microhardness is in accordance to the graded concentration profile of the interstitial elements. Wear tests show a significantly enhanced resistance at different loads. The electrochemical tests reveal no deterioration in the corrosion resistance. The absence of precipitates is proven by microstructural investigations. The results prove the applicability of the concept of solution hardening by the formation of supersaturated solutions for the material group of high-entropy alloys. Hence, an increase of entropy with the consideration of lattice interstices provides new development approaches.

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.

Effect of the addition of metakaolin on the carbonation of Portland cement concretes

Abstract Carbonation has been a concern of constructors and researchers because, by lowering the pH of the interstitial solution of the concrete, it can favor the post-deposition and subsequent corrosion of reinforced concrete reinforcement. Among the factors that influence carbonation is the use of pozzolanic materials, such as metakaolin. However, there is no consensus as to the positive or negative contribution of these additions. This work evaluated the influence of metakaolin on the mechanical properties, porosity and in particular on the carbonation of concrete, from the addition of 0%, 5%, 10% and 15% of metakaolin, in relation to the cement mass. From the results, it was observed that the addition of metakaolin, while not significantly influencing the porosity, gave the concrete a greater resistance to axial compression, a decrease in the capillary absorption and delayed the advance of the carbonation front in the concrete.

The effect of sorption of air and hydrogen components on the structural characteristics of superconducting FeTe0.65Se0.35 single crystals

X-ray studies of iron chalcogenide FeTe0.65Se0.35 single crystals were performed after they were exposed in air and hydrogen atmospheres at room and high temperatures, for long periods of time. It is found that impurity components have a significant effect on the structural characteristics of the diffraction pattern for this layered tetragonal superconducting material. It is shown that molecular impurities do not change the matrix symmetry of the tetragonal substitution solutions. However, when hydrogen molecules dissociate close to 200 °C under the thermocatalytic effect of Fe atoms, the tetragonal lattice of the matrix becomes unstable. Symmetry is reduced against the background of an increased concentration of atomic hydrogen and strengthening of the chemical bonds in the crystals. The crystal density sharply increases, and a FeTe0.65Se0.35 + H interstitial solution based on an orthorhombic lattice is formed. It is shown that the structural tetra-ortho phase transition in such solutions occurs near 200 °C.

Laser nitridation on Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy

To give a deep insight into the nitrogen transfer mechanism during laser solid-state surface modification on titanium alloy, laser nitridation was conducted on Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy (TC11) without melting the metal surface. Microstructure characterizations of nitride layer formed under solid state condition were detailedly explored and the formation process of TiN phase was carefully discussed based on the lattice transformation. Results indicate that the nitride layer forming within a few seconds is composed of TiN phase layer and α phase layer with an orientation relationship: (11¯1)TiN // (0001)α, [011]TiN // [211¯0]α. Formation of TiN phase experiences fast solid-state transformation from α phase. Phase transformation from α-Ti lattice to TiN lattice experiences orthorhombic lattice transformation due to the shear deformation caused by rapid interstitial solution of nitrogen. After repeated laser nitridation process upon three times, nitride layer was thickened with an improved hardness of 824 HV. Linearly reciprocating ball-on-plane wear tests indicate that wear resistance of laser nitridation samples could be enhanced by a factor of 13.

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.

K+ Accumulation and Clearance in the Calyx Synaptic Cleft of Type I Mouse Vestibular Hair Cells

Vestibular organs of Amniotes contain two types of sensory cells, named Type I and Type II hair cells. While Type II hair cells are contacted by several small bouton nerve terminals, Type I hair cells receive a giant terminal, called a calyx, which encloses their basolateral membrane almost completely. Both hair cell types release glutamate, which depolarizes the afferent terminal by binding to AMPA post-synaptic receptors. However, there is evidence that non-vesicular signal transmission also occurs at the Type I hair cell-calyx synapse, possibly involving direct depolarization of the calyx by K+ exiting the hair cell. To better investigate this aspect, we performed whole-cell patch-clamp recordings from mouse Type I hair cells or their associated calyx. We found that [K+] in the calyceal synaptic cleft is elevated at rest relative to the interstitial (extracellular) solution and can increase or decrease during hair cell depolarization or repolarization, respectively. The change in [K+] was primarily driven by GK,L, the low-voltage-activated, non-inactivating K+ conductance specifically expressed by Type I hair cells. Simple diffusion of K+ between the cleft and the extracellular compartment appeared substantially restricted by the calyx inner membrane, with the ion channels and active transporters playing a crucial role in regulating intercellular [K+]. Calyx recordings were consistent with K+ leaving the synaptic cleft through postsynaptic voltage-gated K+ channels involving KV1 and KV7 subunits. The above scenario is consistent with direct depolarization and hyperpolarization of the calyx membrane potential by intercellular K+.

Non-adsorbing small molecules as auxiliary dispersants for polycarboxylate superplasticizers

The dispersing ability of polycarboxylate superplasticizers (PCEs) can be ascribed to the electrostatic and steric stabilization of cement suspensions. For this purpose, PCEs need to adsorb on the cement particle surface to become effective at all. In this study, it is demonstrated that at low water to cement ratios ≤ 0.30, even non-ionic molecules like diethylene glycol or 2-methyl-2,4-pentanediol which do not adsorb on cement, but remain dissolved in the interstitial pore solution, can greatly enhance cement dispersion when combined with PCEs such as conventional methacrylate ester based comb co-polymers. Their effect as co-dispersant is particularly pronounced for PCEs possessing a low side chain density and long side chain length. Relative to the co-dispersants it was found that especially non-polar small molecules like neopentyl glycol greatly enhance the paste fluidity. These molecules significantly reduce the surface tension of the pore solution and thus increase the wettability of cement. Based on results from spread flow tests, adsorption measurements and pendant drop tensiometry it is concluded that in cementitious systems formulated at low w/c ratios, non-adsorbing molecules with a molecular weight of ≤ 1000 g/mol induce repulsive depletion forces which prevent cement particles from agglomeration. This way, such small molecules act as auxiliary or co-dispersant when combined with PCEs.

Impact of Technogenic Wastewaters of Kavalerovskii and Dalnegorskii Mining Districts on the Hydrosphere of Primorsky Krai

Continuous development of the mining industry at Primorsky Krai has led to formation of the technogenic mining systems in the Kavalerovskii and Dalnegorskii districts. These systems cause pronounced negative effect on the ecosphere. Discharge of the technogenic wastewaters with metals is potentially high and depends on the ore composition, and mineralization of the circum-ore envelope as well as hypergene and technogenic processes yielding the interstitial solutions, pit, slime, and drainage waters. Consequently, surface and underground waters get polluted by the toxic elements of the sulfide ores such as Cu, Zn, Pb, As, B, Fe, etc., their concentration in the technogenic waters often exceeding the background values and fishery threshold limit values. Sometimes this excess is up to hundreds of thousand times which indicates steady acceleration of hypergene and technogenic processes. Such effect of the mining technogenic systems caused environmental condition of the considered districts to be evaluated as strained and critical.

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.

Corrosion Behaviour of Mg Alloys in Alkaline Solutions and in Alkali-Activated Binders

The reprocessing of spent fuels from UNGG (Uranium Natural Graphite Gas) nuclear reactors in France generates cladding wastes mainly composed of Mg alloys. The management of these wastes involves their immobilization in hydraulic binders with high pH interstitial solutions (12.5<pH<13.7). In the case of magnesium corrosion, the choice of these materials for immobilization and storage is not straightforward due to the characteristic reactivity of these alloys, which is caused by several aspects [1]. First, magnesium corrosion is strongly influenced by the pH and the composition of the electrolyte (the pore solution of hydraulic binder). Furthermore, the electrochemical potential of Mg places this metal as an anode with respect to several materials [2] (e.g. residual graphite materials initially present in the fuel assemblies or steel from the container), which can create galvanic couplings and accelerate corrosion. Previous work has found low corrosion rates of Mg-Zr alloys and low H2 releases produced when Mg is immobilized in a Na-geopolymer mortar in the presence of fluorides (magnesium corrosion inhibitor) [3]. Similarly, there was a low release of H2 from corrosion during the galvanic coupling between Mg-Mn and graphite, as well as the formation of thinner corrosion product layers when Mg-Mn is immobilized in an alkali-activated slag mortar [4]. These results have contributed to the choice of these two materials as the most appropriates for embedding these wastes. Nevertheless, the electrochemical mechanisms responsible for this weaker corrosion, compared to conventional cementitious matrices, must be identified in these two reference scenari. The purpose of this work is to investigate the corrosion processes that occur once the Mg alloys are embedded in their immobilization matrices. The goal is to understand the phenomena that lead to low corrosion rates in these materials, in the case of general and galvanic corrosions. From these guidelines, a study of the cementitious matrices (porosity, resistivity and gas diffusion) and its interstitial solutions (pH, ionic species and conductivity) was carried out in order to identify the main parameters that can limit the corrosion rate of magnesium. The corrosion behavior of Mg alloys against these conditions has been tested in model solutions and in each cementitious binders using electrochemical techniques (OCP, ZRA, EIS and polarization curves), gravimetry and surface characterization (XRD, SEM/EDS and FIB/STEM). Both matrices are relevant for the storage of Mg wastes and have a thermodynamically favorable pH for magnesium passivation due to the precipitation of Brucite (Mg(OH)2) on its surface. The high resistivity of the alkali-activated slag and the possible consumption of O2 by the sulphides of the pore solution are favorable aspects to reduce galvanic corrosion rate. In the case of the Na-geopolymer/NaF, the oxygen concentration can also limit the rates of galvanic corrosion, since, during storage, oxygen access could be restrained. However, the presence of corrosion inhibitors (silicates and fluorides) is mainly responsible for the reduction of Mg corrosion, because of a protective film formed at the MgZr/Na-geopolymer interface. This corrosion rate may vary with the concentration of fluoride available in solution and is probably related to the nature of the corrosion product formed on the magnesium surface. General and galvanic corrosion in the Na-geopolymer/NaF mortar were quantified by gravimetric measurements and in both cases the nature of the corrosion products was characterized by scanning electron microscopy (SEM/EDS), X-ray diffraction (XRD) and FIB/STEM (Focused Ion Beam/Scanning Transmission Electron Microscope). The results revealed the stratification of the corrosion products found at the Mg-Zr/Na-geopolymer interface and were in good agreement with the experiments performed in the model alkaline solution. Magnesium corrosion in the Na-geopolymer/NaF mortar is rather limited by the chemistry of the interstitial solution. [1] K. W. Guo , “A Review of Magnesium/Magnesium Alloys Corrosion and its Protection”, Recent Patents on Corrosion Science, vol. 2, pp. 13-21, 2010. [2] G. L. Song and A. Atrens, “Corrosion Mechanisms of Magnesium Alloys”, Adv. Eng. Mater., vol. 1, no. 1, pp. 11–33, 1999. [3] D. Chartier, B. Muzeau, L. Stefan, J. Sanchez-Canet and C. Monguillon, “Magnesium alloys and graphite wastes encapsulated in cementitious materials: Reduction of galvanic corrosion using alkali hydroxide activated blast furnace slag”, Journal of Hazardous Materials, vol. 326, pp. 197-210, 2017. [4] D. Lambertin, F. Frizon and F. Bart, “Mg-Zr alloy behaviour in basic solutions and immobilization in Portland cement and Na-geopolymer with sodium fluoride inhibitor”, Surface and Coating Technology, vol. 206, pp. 4567-4573, 2012.

Designing solid solution hardening to retain uniform ductility while quadrupling yield strength

Single-phase metals can be strengthened via cold work, grain refinement, or solid solution hardening. But the yield strength elevation normally comes at the expense of ductility, i.e., a conspicuous decrease of the uniform elongation in uniaxial tension. This strength-ductility trade-off is often a result of inadequate strain hardening rate that can no longer keep up with the elevated flow stress to prevent plastic instability. Here we alleviate this dilemma by designing oxygen interstitial solution hardening in body-centered-cubic niobium: the strain hardening rate is exceptionally high, such that most of the uniform tensile ductility of Nb can be retained despite of quadrupled yield strength. The oxygen solutes impose random force field on moving dislocation line, promoting the formation of cross-kinks that dynamically accumulate vacancy-oxygen complexes. These obstacles enhance the trapping/multiplication of screw dislocations as well as cross-slip, all promoting strain hardening and strain de-localization. This approach utilizes only a low concentration of interstitial solutes to achieve effective strengthening and strain hardening simultaneously, and is an inexpensive and scalable route amenable to the processing of bulk samples.

Catalytic synthesis of segmented carbon filaments via decomposition of chlorinated hydrocarbons on Ni-Pt alloys

Abstract A series of micro-disperse Ni1-xPtx alloys with the sponge-like structure was prepared by a simultaneous precipitation method with subsequent sintering of the sediment in H2 atmosphere at 800 °C. The formation of single-phase solid solution Ni1-xPtx was confirmed by powder XRD analysis for entire range of Pt concentrations (1.3–75.9 wt.%). The synthesized samples were studied in a process of catalytic decomposition of C2H4Cl2 at 600 °C. In situ kinetic studies of the carbon deposition process were carried out in a flow gravimetric setup equipped with McBain balances. Interaction of Ni-Pt alloys with reaction mixture is characterized by an induction period (18–32 min) followed by rapid disintegration of the bulk alloys with intensive growth of carbon fibers. The stage of the induction period was explored in detail by means of XRD and SEM techniques. According to XRD data, the interaction of Ni-Pt alloys with C2H4Cl2 vapors is accompanied by formation of Ni1-xPtxCδ interstitial solution due to entry of carbon into the crystal lattice of the alloy. The effect of Pt addition on catalytic activity of Ni in CCVD process was also studied. It was found that the yield of carbon product depends extremely on Pt concentration with a maximum at CPt =4.3 wt.% (26 g/gNi for 120 min). The impact of Pt concentration upon morphology and structural features of the produced carbon fibers was investigated by SEM and TEM techniques.

Microstructures and mechanical properties of FeCoCrNi high entropy alloy/WC reinforcing particles composite coatings prepared by laser cladding and plasma cladding

FeCoCrNi HEA coatings with 20% mass fraction of WC reinforcing particles were prepared by two different cladding methods, laser cladding (LC) and plasma cladding (PC). The microstructure of HEA matrix and WC particles of LC and PC coatings were discussed respectively. For HEA matrix, dendritic morphology was observed in both coatings. For WC particles, a few granular (Cr,W)2C carbides around WC particles in LC coatings, and a large number of crystal and fishbone Fe3W3C carbides around WC particles in PC coatings. Mechanical properties as hardness and wear resistance of the two kinds of coatings were also investigated. The interstitial solution strengthening effect of C element is stronger in PC coating, and the hardness of HEA matrix in LC coatings is twice that of in PC coating, which shows a strong retention force on WC particles. The friction coefficient of LC coating is lower and stable, with the volume wear rate of 0.7 × 10−5 mm−3/N·m, showing high wear resistance. PC coatings have poor wear resistance due to decarbonization and oxidation of WC particles and reduction of retention force of HEA matrix, with the volume wear rate of 8.29 × 10−5 mm−3/N·m. The wear mechanism of both coatings were also discussed.

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.