Ni Specimens Research Articles

Mobile microRNAs (miRNAs) responsive to excess nickel in pumpkin (Cucurbita maxima L.)

Nickel (Ni) is a toxic heavy metal that inhibits plant growth, development, and reproduction. MicroRNAs (miRNA) travel from cell to cell or organ to carry messages to regulate gene expression. The objective of this study is to find mobile miRNAs that are Ni-responsive and are present in pumpkin (Cucurbita maxima L.) phloem sap. For this purpose, pumpkin seedlings were exposed to Ni (100 μM, NiCl2), and root, shoot, and phloem-sap specimens were collected at 0 (control), 24, and 48 hours of the treatment. The stem-loop RT-qPCR and stem-loop semi-quantitative RT-PCR methods were used to determine the abundance of 14 miRNAs in the phloem sap. Compared to the control, the abundance of miR160, miR167, miR393, miR397, and miR398 are suppressed in Ni-treated seedlings. The reduction was verified by grafting experiments, revealing that miR167 and miR393 are Ni-responsive and move/travel from the leaf-to-root direction. Those phloem-residential miRNAs potentially play a role in the Ni-response mechanism. This study can help to understand the early response mechanism of plants against excess Ni and lead to identifying miRNA-mediated long-distance communication of plants.

Revealing the effects of concomitant grain coarsening and refinement on the internal variable evolution and mechanical properties of gradient nanostructured nickel

The outstanding mechanical properties of gradient nanostructured (GNS) metals and alloys such as a superior combination of strength and ductility can be attributed to two important deformation mechanisms: hetero-deformation induced (HDI) strengthening and strain hardening, as well as grain growth. Recent experimental evidence indicates that GNS Ni specimens undergo concomitant grain coarsening and refinement during tensile deformation. Nevertheless, how such grain growth behaviors affect the evolution and distribution of their internal variables such as dislocation density and HDI hardening, and how such effects are manifested in their mechanical properties, are still unknown. Therefore, this work strives to answer these questions by incorporating a modified strain gradient plasticity formulation taking into account the saturation of geometrically necessary dislocations (GND) accumulation due to the dynamic equilibrium between dislocation source formation and deactivation into a crystal plasticity finite element framework, in conjunction with two other models accounting for the evolution of statistically stored dislocations (SSD) and HDI stress, respectively, to explore the effects of grain coarsening and refinement on the internal variable evolution and mechanical properties of GNS Ni specimens with different grain size gradients under deformation. It is revealed that SSD density increases throughout the samples as a result of reduced dynamic recovery in the fine grains induced by grain coarsening as well as enhanced dislocation storage in the coarse grains due to their refinement. In contrast, grain coarsening and refinement leads to a decrease in GND density and HDI stress in the fine grains and an increase in the coarse grains as a result of the corresponding changes in strain gradient intensity. Last but not least, the overall effect of grain growth on the mechanical behaviors of GNS Ni is the outcome of the synergy and competition between its individual effects on the Hall-Petch strengthening, forest dislocation hardening and HDI hardening, respectively, and the different grain size gradients of the GNS Ni specimens give rise to the opposite variations in their mechanical behaviors with respect to grain growth.

Neutron diagnostics using nickel foil activation analysis in the KSTAR

The spatial distribution and the energy spectrum of the neutron yield were investigated with the neutron activation analysis and MCNP simulation was carried out to verify the analysis results and to extend the results to a 3D mapping of the neutron yield distribution in the KSTAR. High purity Ni specimen was selected in the neutron activation analysis. Total neutron yields turned out to be 3.76 × 1012 n/s – 7.56 × 1012 n/s at the outer vessel of the KSTAR, two orders of magnitude lower than those at the inner vessel of the KSTAR, which demonstrates the attenuation of neutron yield while passing through the different structural materials of the reactor. Based on the fully expanded 3D simulation results, 2D cross-sectional distributions of the neutron yield on XY and ZX planes of KSTAR were examined. The results reveal that the neutron yield has its maximum concentration near the center of blanket and decreases with increasing proximity to the vacuum vessel wall.

Influence of rolling temperature on the structural evolution and residual stress generation of nanocrystalline Nickel during nano-rolling process

Although the rolling process is significant on developing the preferred crystallographic orientation in the metallic sheets, its implementation at the nanoscale is uncertain. However, it is believed that the nano-rolling process can be realized with progressive scientific and technological advancement in material processing. Presently, we have modeled the rolling process of nanocrystalline Ni specimen using molecular dynamics simulations and investigated the underlying deformation mechanism along with the orientation evolution. Moreover, we have also analyzed the effect of temperature on the residual stress generation and the grain rotations. This atomistic model takes both shear and compressive forces into consideration, which makes it efficient in representing the actual deformation process. It is found that the compressive stress accumulation majorly occurs at grain boundary whereas tensile stresses are accumulated at triple junctions. At elevated temperatures, the stresses during the deformation are diminished and gets dispersed due to the thermal vibrations caused by the high temperature deformation. Through this study, we have evidently shown the orientation change, grain refinement, and formation of sub-grain boundaries during the rolling process. In addition, we have also characterized the specimens with virtual diffraction analysis, which has shown the preferred orientations to be (002) and (111) after rolling through the first and second set of rollers respectively.

An Anomaly in Creep Property Dependence on Grain Size for Ultrafine Grain Nanocrystalline Nickel at Higher Creep Temperature

In this present study, molecular dynamics simulation of creep for ultrafine grain NC Ni specimens with different grain sizes have been carried out under a constant 1 GPa applied load for various creep temperatures to study the dependence of grain growth on creep temperature and grain size during creep process and its influence on creep properties. It is observed that the extent of grain growth in ultrafine grain NC Ni during creep deformation process is more if creep in creep temperature is higher. A noteworthy anomaly, that is NC Ni with smaller grain exhibits better creep property compared to NC Ni with larger grain, is observed in case of higher creep temperatures (i.e. around or greater than 1400K).

Self-Calibrated Absolute Thickness Measurement of Opaque Specimen Based on Differential White Light Interferometry

In this article, we present a self-calibrated absolute thickness measurement method for opaque specimens based on fiber-optic white light interferometry. A new type of self-reference probe, which is composed of a fiber ferrule, an integrated beam splitter, and a gradient index lens, is presented. In our setup, two probes of this kind are fixed facing each other, and the distance between them can be measured. Then we insert a specimen between the probes and measure the distance between the specimen surfaces and probes on both sides. This way, a self-calibrated measurement of specimen thickness can be realized without the traditional calibration process using a standard thickness sample. Thus, the uncertainty component introduced by the standard thickness sample can be eliminated. The performance of the proposed method is evaluated by measuring standard thickness samples calibrated by the National Institute of Metrology of China, and the results show a good agreement with the nominal values. Also, we analyzed several key uncertainty components, as well as the reliability of our method. The calculated extended measurement uncertainty (k = 2) is 0.06 μm for Cr specimen with a nominal thickness of 10.56, and 0.08 μm for Ni specimen with a nominal thickness of 31.46 μm.

Effect of Chemical Additives in the Plating Bath on Surface Corrosion Resistance of Ni(P)

In this work, the effect of the chemical additives (surfactant, stabilizer) on the corrosion resistance of the Ni(P) layer was investigated. The average O content at the depth of 1 nm of the tested Ni(P) specimens was used as the indication of the corrosion degree for the tested Ni(P) specimen. The average O content at the depth of 1 nm of the tested Ni(P) specimens prepared with thiourea is 27.74 at.%, which is larger than the average O content (14.43 at.%) at the depth of 1 nm of the corrosion-tested Ni(P) layer. It can be concluded that the corrosion resistance of the Ni(P) layer would be greatly reduced two times with adding thiourea in the Ni(P) plating bath. The effect of the solder mask was also investigated on the corrosion resistance of the Ni(P) layer. We found that S impurities leaching from the solder mask might be co-deposited into Ni(P), and decrease the corrosion resistance of the Ni(P) layer. Yet, its influence is relatively lower than the effect of thiourea on the corrosion resistance of the Ni(P) layer. With adding CTAB, as a surfactant, in the Ni(P) plating bath, the average P content in the Ni(P) layer increases. The high P content further improves the corrosion resistance of the Ni(P) layer. Moreover, the positive effect of adding CTAB in the plating solution on the corrosion resistance of the Ni(P) layer would suppress the negative effect of the thiourea additive and solder mask in the plating solution. The main innovation finding of the work is that we found that adding CTAB in the Ni(P) plating solution can reduce the co-deposition of S impurities, from thiourea in the Ni(P) plating bath and the solder mask, in the Ni(P) layer. Consequently, the corrosion resistance of the Ni(P) layer can be further improved.

Investigation of reorganization of a nanocrystalline grain boundary network during biaxial creep deformation of nanocrystalline Ni using molecular dynamics simulation.

In this paper, simulated biaxial creep deformation behaviour for nanocrystalline (NC) nickel (Ni) has been performed at various applied load (i.e. 1GPa, 1.4GPa, 2GPa, 2.5GPa and 3GPa) for a particular temperature (i.e. 1210K) using molecular dynamics (MD) simulation to investigate underlying deformation mechanism based on the structural evolution during biaxial creep process. Primary, secondary and tertiary stages of creep are observed to be exhibited significantly only at 3GPa applied stress. While, only primary and secondary stages of creep are exhibited at 1GPa applied stress. Atomic structural evaluation, dislocation density, shear strains, atomic trajectory, inverse pole figures and grain orientation with texture distribution have been carried out to evaluate structural evolution. Stress exponent (m) for NC Ni is analysed for a particular creep temperature (i.e. 1210K) and obtained m value is 1.30. According to shear strains counter plot, accumulation of higher shear strains are observed at grain boundary (GB) during biaxial creep deformation. It is found that dislocation density during biaxial creep is increased with the progress of creep process. Grain rotation and texture evaluation during biaxial creep process are studied using grain tracking algorithm (GTA). Grain rotation in ultrafine-grained NC Ni specimen during biaxial creep deformation is happened and exhibits almost distinct distribution, which is occurred due to the atomic shuffling within the GBs. Grain growth of ultrafine grained NC Ni is observed during biaxial creep deformation which is caused by mechanical stress.

Molecular dynamics simulation based investigation of strain induced crystallization of nickel metallic glass

Molecular dynamics simulation based study of amorphous to crystalline transformation under compressive loading at different temperatures (10 K, 100 K and 300 K) has been performed using embedded atom method potential for nano-size Ni specimen. Intermediate BCC and HCP phases are found to be formed during the transformation from amorphous to FCC structure. The extent of transformation to FCC structure in the final specimen is found to be comparatively more during deformation process at 100 K temperature when compared to 10 K and 300 K temperatures for applied compressive load.

Cold Sintering of Ni–Ag Nanocomposite Particles Produced by Electric Explosion of Wires

77 Ni–23 Ag nanocomposite powder as well as nanopowders of Ni and Ag were produced by electric explosion of wires, and compacted specimens were made with the help of a cold sintering method at a high pressure. It is shown that electric explosion results in formation of mainly janus-nanoparticles of immiscible Ni and Ag metals with retention of nanostructure in consolidated bulk specimens. Microstructure and mechanical properties of cold sintered specimens prepared from as prepared and heat treated in hydrogen flow have been studied. It is ascertained that treatment of 70% dense compacts in hydrogen flow results in higher density and higher ductility of cold sintered specimens. Density of cold sintered at 3 GPa pressure 77 Ni–23 Ag and Ni specimens was reached about 95% from theoretical value whereas the density of Ag specimens is close to 100% of that. High strength was obtained under three-point bending tests and in compression tests.

Effect of amorphization-mediated plasticity on the hydrogen-void interaction in ideal lattices under hydrostatic tension

A thermodynamic model is derived to study the void nucleation in ideal lattices under hydrostatic tension loading and predicts that the plasticity has to be initiated before homogeneous nucleation of voids. Molecular dynamics simulations are performed to evaluate the mechanical behavior of Ni specimens with and without hydrogen charged. The results show that in both cases dislocations are generated before the nucleation of voids, and the insertion of hydrogen atoms does not alter the void nucleation significantly. The fact that the mechanical property is not sensitive on hydrogen is attributed to the formation of an amorphous shell around the voids.

Effect of Ni content on stainless steel fabricated by laser melting deposition

The novel stainless steel + x wt.% Ni (x = 0, 3.05, 6.10, 9.15) specimens were successfully fabricated by laser melting deposition, aiming at investigating the influence of Ni content on stainless steel structure and property. The effects of Ni content on phase compositions, microstructure, microhardness, wear and electrochemical corrosion resistance of as-deposited stainless steel were studied systematically using XRD, OM, SEM, microhardness tester, friction-wear tester and potentiodynamic polarization measurement, respectively. Experimental results showed that with the increase of Ni content, the constituent phase of the as-deposited specimen changed from ferrite phase (specimen for x = 0) to austenite phase (specimen for x = 9.15). The microstructure growth followed the principle of dendrite growth. However, the dominant microstructure varied from equiaxed dendrite to columnar dendrite with increasing Ni content. Phase transition from ferrite phase to austenite phase with the addition of Ni content resulted in the decrease of microhardness value from 643HV to 289HV. Meanwhile, the wear resistance of as-deposited specimens decreased gradually with the increasing of Ni content, which might be attributed to the fact that the wear resistance is proportional to microhardness according to Archard's law. It was noted that corrosion resistance of as-deposited stainless steel was extremely improved with the increase of Ni content. The higher Ni content specimen (specimen for x = 9.15) exhibited the best corrosion resistance among the tested specimens based on corrosion rate, which was one order of magnitude lower than that of the lower Ni content specimens (specimens for x = 0, 3.05).

Evaluation of welding performance of 20 kHz and 40 kHz ultrasonic metal welding

In this study, ultrasonic horns are designed by using vibration equations, vibration modal analysis and harmonic response analysis in order to compare welding performance when ultrasonic welding is performed at resonance frequencies of 20 kHz and 40 kHz. For the weldability evaluation of the manufactured horn for 20 kHz and 40 kHz, welding strength between Ni specimens with a thickness of 0.1 mm using tensile test are compared and analyzed. The lengths of horns with resonance frequencies of 20kHz and 40kHz were calculated as 130mm and 68mm respectively. As a result of vibration modal analysis, the optimum longitudinal vibration modes of 19,584Hz and 39,794Hz are obtained in 10th mode, and the frequency response of the two horns are 19,600 Hz and 39,800 Hz respectively. As the welding conditions are changed to welding pressure 2 bar, 3 bar and 4 bar, vibration amplitude of horn 60%, 80% and 100%, tensile strengths of welded specimens are observed. The welding strength was smaller at 40 kHz than at 20 kHz even at the same amplitude. This is because diffusion action of Ni in the weld interface is facilitated at 20 kHz than at 40 kHz.

Healing mechanism of nanocrack in nanocrystalline metals during creep process

Molecular dynamics (MD) simulation has been performed to demonstrate the fate of cracks present inside ultrafine-grained (grain size ~ 7 nm) nanocrystalline Ni specimen during creep deformation process. It is observed that internal nanocracks are healed within a few pico-seconds of initial part of creep process even if the constant applied load on the specimen is tensile in nature and acting normal to crack surface in the outward direction. This kind of crack-healing phenomenon can be accounted by the facts such as stress-driven grain boundary migration, grain boundary diffusion and amorphization of specimen as per results obtained from this MD simulation. This MD study also reveals that the presence of nanocrack inside ultrafine-grained NC Ni in fact slightly improves creep properties and such enhancement of the creep properties is intensified as the size of internal crack increases.

A Short Review of High-Temperature Wetting and Complexion Transitions with a Critical Assessment of Their Influence on Liquid Metal Embrittlement and Corrosion

The basic concepts and new developments in the general areas of grain boundary segregation (adsorption), wetting, and complexion (interfacial phase-like) transitions are briefly reviewed. Subsequently, recent studies in several relevant areas are discussed. At the atomic level, the formation of bilayers in Ni-Bi and Cu-Bi have been observed and found to be the root cause for liquid metal embrittlement (LME). At the microstructural level, the presence of minor impurities or co-alloying elements can significantly enhance the intergranular penetration and liquid metal corrosion (LMC). Furthermore, triple-grain-line wetting by a liquid metal can occur at high temperatures, which may significantly affect corrosion resistance (for LMC), as well as LME. Somewhat surprisingly, Bi vapors can penetrate along the triple-grain lines in S-doped Ni specimens to form open channels, which can be considered as an unusual case of triple-line wetting by a vapor phase. A coherent theme of this review and critical assessment ...

OBTAINING OF NICKEL AND COBALT COATING ALLOYS BY DIFFUSION SATURATION WITH DYSPROSIUM IN LiCl–KCl–DyCl3 MELT

A gravimetric method was used to study the influence of process temperature (Т) and duration (τ) on the specific mass variation of nickel and cobalt specimens during their currentless diffusion saturation with dysprosium in a liquated eutectic mixture of lithium and potassium chlorides with dysprosium chloride added (5 wt.%). The experimental results allowed to calculate the mathematical dependences Р(τ) for nickel specimens in the temperature range of Т = 773÷973 К at τ = 1÷8 h, and for cobalt specimens in the temperature range of Т = 873÷973 К at τ = 1÷7 h. Their analysis showed that the solid-state diffusion is the rate-controlling step of currentless dysprosium transfer to Ni and Co specimens. The composition of coating alloys was studied using the X-ray fluorescence spectrometer, X-ray microanalyzer, and scanning microscope. It was found that under experimental conditions, the coating forming on the nickel substrate surface consists of one structural zone, but when substrate material is cobalt, the coating consists of two structural zones. This is consistent with available literature data on the alloying of similar bimetallic systems.

Multiscale modeling of crack initiation and propagation at the nanoscale

Fracture occurs on multiple interacting length scales; atoms separate on the atomic scale while plasticity develops on the microscale. A dynamic multiscale approach (CADD: coupled atomistics and discrete dislocations) is employed to investigate an edge-cracked specimen of single-crystal nickel, Ni, (brittle failure) and aluminum, Al, (ductile failure) subjected to mode-I loading. The dynamic model couples continuum finite elements to a fully atomistic region, with key advantages such as the ability to accommodate discrete dislocations in the continuum region and an algorithm for automatically detecting dislocations as they move from the atomistic region to the continuum region and then correctly “converting” the atomistic dislocations into discrete dislocations, or vice-versa. An ad hoc computational technique is also applied to dissipate localized waves formed during crack advance in the atomistic zone, whereby an embedded damping zone at the atomistic/continuum interface effectively eliminates the spurious reflection of high-frequency phonons, while allowing low-frequency phonons to pass into the continuum region.The simulations accurately capture the essential physics of the crack propagation in a Ni specimen at different temperatures, including the formation of nano-voids and the sudden acceleration of the crack tip to a velocity close to the material Rayleigh wave speed. The nanoscale brittle fracture happens through the crack growth in the form of nano-void nucleation, growth and coalescence ahead of the crack tip, and as such resembles fracture at the microscale. When the crack tip behaves in a ductile manner, the crack does not advance rapidly after the pre-opening process but is blunted by dislocation generation from its tip. The effect of temperature on crack speed is found to be perceptible in both ductile and brittle specimens.

Response to “Comment on ‘Microstructure and Properties of Electrochemically Deposited Ni-Fe/Si3N4 Nanocomposites from a DMF Bath’[J. Electrochem. Soc., 162, D87 (2015)

The paper was focused on electrodeposition of Ni-Fe/Si3N4 nanocomposites from a DMF bath and study of microstructure and some of its physical properties. The comments of Bakonyi in context of resistivity that it is unphysical is not agreeable because the authors (Tripathi et al.) never claimed the values as absolute rather it has been already written as apparent values, which are relative only. We agree that the bulk value of the resistivity of a metal refers to that of a well-annealed, high purity state and defect free. Attention is drawn to the fact that the quoted 1 Ni specimens after annealing turned microcrystalline for which they (Laubitz et al.) measured the room temperature resistivity while in our case the resistivity values are reported for nanocrystalline deposits. Further, the grain boundary contribution of electrical resistivity may be non-negligible and the resistivity should be higher than the bulk. However, the observed lower values of resistivity are not unlikely in case of nanocrystalline deposits unlike 2–5 and it is most probable due to possible hopping mechanism which may be applicable for the size of crystallites observed in our case. The comments of the reviewer on our earlier publication 6 are based on conjecture because in 1989 whatever TEM was available, almost defect free deposits were reported with best resolution and with possible higher magnification, which the reviewer considered as an inference. The present results obtained on advanced model of TEM again arrive at the same conclusion. It is agreed that embedding the non-metallic Si3N4 particles in the metallic matrix causes an increase of the resistivity of the nanocomposite formed, and the same was observed by the authors. We (Tripathi et al.) measured the apparent electrical resistivity of nano-Ni of the order of 10 –9 cm while that for the Ni-Fe/Si3N4 nanocomposites it has the order of 10 –8 cm. It is to be noted that the nanocompos

Enhanced plasticity and superplasticity of ultrafine-grained nickel

Although superplasticity has intensively been studied for half century, few observations have been reported for pure metals due to fast grain growth at temperatures required for superplasticity. With developing of nanocrystalline materials, there was a hope that superplasticity could be obtained in a number of pure metals. Indeed, low temperature superplasticity in pure nickel was reported in pioneering work in 1999, later superplastic feature of nanonickel was attributed to sulfur presence in grain boundaries. Recently, it was concluded that superplasticity it is not related to the presence of sulfur at grain boundaries or a liquid phase at grain boundaries. Thereby, the phenomenon of superplasticity in pure metals is still far away for our understanding and it requires future work. This report is devoted to reassessment of superplastic behavior of nano-nickel and it provides new results on enhanced plasticity of pure nickel processed by HPT consolidation of rapid quenched ribbons. Bulk ultrafine-grained nickel was successfully processed by RT consolidation of rapid quenched ribbons using high-pressure torsion. RQ nickel possesses equiaxed grain structure with mean grain size of 1−2 μm showing well defined grain boundaries. Upon HPT consolidation mean grain size of ~0.2 μm and high dislocation density have been achieved. However, consolidated Ni specimens show enhanced plasticity >140% at testing temperature of 450°C and strain rate of 10-3 s-1. No superplastic regime has been attained for given testing conditions.

Experimental Investigation and Thermodynamic Modeling of the Ni-Rich Part of the Ni-N Phase Diagram

The N uptake of thin Ni foils was monitored by use of nitriding experiments performed in NH3-H2 gas atmospheres as function of the atmosphere’s composition between 673 K and 873 K (400 °C and 600 °C). With increasing nitriding potential $$ r_{\text{N}} = {{p_{{{\text{NH}}_{3} }} } \mathord{\left/ {\vphantom {{p_{{{\text{NH}}_{3} }} } {p_{{{\text{H}}_{2} }}^{3/2} }}} \right. \kern-0pt} {p_{{{\text{H}}_{2} }}^{3/2} }} $$ (with $$ p_{{{\text{NH}}_{3} }} $$ and $$ p_{{{\text{H}}_{2} }}^{{}} $$ being the partial pressures of the ammonia and hydrogen in the nitriding atmosphere at the Ni specimen’s surface) first an increasing uptake of N by the terminal Ni[N] solid solution was observed up to about 1 at. pct N. Upon surpassing a threshold nitriding potential, the Ni3N compound was formed. A thermodynamic interpretation of the observed data is only possible by taking into account the (small) degree of decomposition of the NH3 at the surface of the specimens, to arrive at the effective values of r N genuinely acting at the surface of the specimen. The data obtained were used to determine model descriptions for (i) the Gibbs energy of dissolution of N into Ni[N] (at infinite dilution), which was modeled as an ideal interstitial solid solution, and (ii) the Gibbs energy of formation of Ni3N (in equilibrium with Ni[N]). The thermodynamic model descriptions of Ni[N] and Ni3N, associated with these Gibbs energies, were used to calculate the Ni-rich part of the phase diagram Ni-N. A comparison of the values of the Gibbs energy of dissolution of N in various 3d-metal based terminal solid solutions reveals a considerable decrease of the stability of such solutions with increasing atomic number.