Pure Nickel Samples Research Articles

Magnetostrictive behavior of pure nickel core: A study on the effects of annealing and magnetization using VSM and optical microscopy techniques

This study investigates the impact of annealing and magnetization on the magnetostrictive behavior of pure nickel, which is used as the core of an ultrasonic transducer. Pure metals are not commonly used as magnetic materials due to their limited magnetic and non-magnetic properties. Analyzing the effects of alloying on different characteristics of pure elements is a complex process. Improving the efficiency of magnetostrictive transducers by enhancing their properties is an area of interest for researchers. Grain size, in particular, is a significant parameter that affects the properties of ferromagnetic materials. This study reveals that exposing pure nickel and magnetized samples to an electro-polishing solution with 10 % oxalic acid for 60 s results in the appearance of grain boundaries. Furthermore, the study finds that the 90° domain wall energy is higher than the 180° domain wall energy, impacting the radial magnetostrictive force more than the longitudinal magnetostrictive force. The results show that annealing reduces the maximum output magnetic hysteresis, while magnetization has little effect. Additionally, annealing significantly reduces the coercive field, increasing the magnetostriction effect. Therefore, annealed nickel is a promising candidate for use as the core of an ultrasonic transducer for removing residual chemicals from fruits and vegetables.

Microstructure and defect evolution in oxygen ion-irradiated pure nickel – Insights from experimental probes and molecular dynamics simulations

Pure nickel samples were irradiated to various doses by 160 MeV oxygen ions and the change in microstructure (domain size, microstrain, dislocation density etc.) were investigated with the help of X-ray diffraction (XRD) data from synchrotron source and Transmission electron microscopy (TEM). The coherent domain size decreased, whereas the microstrain and dislocation density increased in all irradiated samples as compared to the unirradiated one. However, these parameters showed saturation with increasing dose. The analysis reveals that there is an increase in the stacking fault probability with irradiation. TEM study confirmed the presence of stacking fault tetrahedra and dislocation loops in the irradiated samples. Microhardness measurements show an increase in the hardness with irradiation due to formation of defect clusters and dislocations. The effect of irradiation on the microstructure of the pure Ni has been simulated by molecular dynamics using overlapping simulation cascades of PKA generated by oxygen ion.

Feasible evolution process of tensile property dominant effect factor in annealed high purity nickel by a combination of in situ tensile technique and EBSD

Multiple factors, such as crystallographic orientation, twins, dislocation, and grain size, significantly affect the tensile properties of alloys; however, it is difficult to identify the dominant factor from only the initial and final conditions. To mitigate this limitation, a combination of in situ tensile technique and electron backscattering diffraction (EBSD) was used to analyze the dominant factors affecting the tensile properties of pure nickel during the stretching process at different annealing temperatures. This process consists of two parts. The first is the analysis of the dominant factor candidate from the initial alloy condition. The second part is the confirmation step that uses the in-situ EBSD tensile technique via real-time analysis of the microstructural transformation during plastic deformation while measuring the tensile properties. Four pure nickel samples with different initial states and mechanical properties were tested in this study. Using EBSD characterization, the distribution of kernel average misorientation gradually concentrates in the regions of accumulated fine grain as the tensile stress proceeds. The grain size of pure nickel was confirmed to be the most significant factor influencing the tensile properties. Our results reveal a feasible evaluation process for the primary effect factor of the tensile properties of pure nickel owing to grain size.

High pressure suppressing grain boundary migration in a nanograined nickel

Grain boundaries (GBs) of nanograined metals are prone to migrate when subjected to mechanical loading. In this study, nanograined pure nickel samples with an average grain size of about 70 nm were deformed under pressure of 20 GPa and 43 GPa using a diamond anvil cell. It was found that the average grain size decreased slightly after high pressure compression, which meant high pressure suppressed the nanograin boundaries migration. Extensive extended dislocations with large dissociation width (averagely 5-6 nm) as well as Lomer-Cottrell locks were observed in the high pressure deformed nanograined Ni, indicating that partial dislocation activities dominated the plastic deformation, which may facilitate to relax GBs and thus suppress GBs migration. The finding of this study may help to fabricate stable nanocrystalline metals.

Effects of SiC particles codeposition and ultrasound agitation on the electrocrystallisation of nickel-based composite coatings

This study analysed the influence of the codeposition of SiC particles with different sizes: 50 nm, 500 nm and 5 μm, and the type of bath agitation (stirring or ultrasonic) on the electrocrystallisation of nickel coatings. The composites matrix microstructure was analysed by means of SEM, EBSD and XRD, to evaluate the grain size, crystal orientation, and internal stresses and was benchmarked against pure nickel samples electrodeposited in equivalent conditions. The codeposition of nano- and microsize particles with an approximate content of 0.8 and 4 vol.%, respectively, caused only a minor grain refinement and did not vary the dominant < 100 > crystal orientation observed in pure Ni. The internal stress was, however, increased by particles codeposition, up to 104 MPa by nanoparticles and 57 MPa by microparticles, compared to the values observed in pure nickel (41 MPa). The higher codeposition rate (11 vol.%) obtained by the addition of submicron-size particles caused a change in the grain growth from columnar to equiaxial, resulting in deposits with a fully random crystal orientation and pronounced grain refinement. The internal stress was also increased by 800% compared to pure nickel. The ultrasound (US) agitation during the deposition caused grain refinement and a selective particle inclusion prompting a decrease in the content of the particles with the larger particles. The deposits produced under US agitation showed an increase in the internal stresses, with double values compared to stirring. The increase in the deposits microhardness, from 280 HV in pure Ni to 560 HV in Ni/SiC submicron-US, was linked to the microstructural changes and particles content.Graphical abstract

Dual-gradient structure leads to optimized combination of high fracture resistance and strength-ductility synergy with minimized final catastrophic failure

Nature-inspired gradients can be implemented in metallic materials to achieve a synergy of strength and ductility. However, due to the small (often microscale) size of the gradient structured samples, their fracture properties have remained relatively unexplored. By fabricating centimeter-sized gradient-structured pure nickel samples using direct-current electroplating technique, we demonstrate that a dual-gradient architecture in pure nickel, comprising grain-size transitions from coarse grains to nano grains and then back to coarse grains (CG→NG→CG), achieves an optimized combination of strength-ductility synergy and exceptional fracture resistance – a crack-initiation toughness exceeding 300 MPa m½ – while minimizing the problem of final unstable catastrophic failure. Significantly, this dual-gradient CG→NG→CG structure can effectively arrest any brittle fracture in the nano grains by inducing a stable rising R-curve with an enhanced crack-growth toughness exceeding 350 MPa m½. We believe that this dual-gradient CG→NG→CG structure provides a promising prototype for designing multi-layer graded structures with exceptional combinations of mechanical properties which can be readily tuned to meet the advanced requirements of safety-critical applications.

How the interface type manipulates the thermomechanical response of nanostructured metals: A case study on nickel

The presence of interfaces with nanoscale spacing significantly enhances the strength of materials, but also the rate controlling processes of plastic flow are subject to change. Due to the confined grain volumes, intragranular dislocation-dislocation interactions, the predominant processes at the micrometer scale, are replaced by emission of dislocations from and their subsequent accommodation at the interfaces. Both processes not only depend on the interfacial spacing, but also on the atomistic structure of the interface. Hence, a thorough understanding how these processes are affected by the interface structure is required to predict and improve the behavior of nanomaterials. The present study attempts to rationalize this effect by investigating the thermomechanical behavior of samples consisting of three different interfaces. Pure nickel samples with predominant fractions of low- and high-angle as well as twin boundaries with a similar average spacing around 150 nm are investigated using high temperature nanoindentation strain rate jump tests. Depending on the interface structure, hardness, strain rate sensitivity and apparent activation volumes evolve distinctively different with testing temperature. While in case of high-angle boundaries for all quantities a pronounced thermal dependence is found, the other two interface types behave almost athermal in the same temperature range. These differences can be rationalized based on the different interfacial diffusivity, affecting the predominant process of interfacial stress relaxation.

Defect evolution in Ni and solid-solution alloys of NiFe and NiFeCoCr under ion irradiation at 16 and 300 K

Single-phase concentrated solid-solution alloys (SP-CSAs) have shown unique chemical complexity at the levels of electrons and atoms, and their defect evolution is expected to be different from conventional dilute alloys. Single crystals of Ni, NiFe and NiFeCoCr are chosen as model systems to understand the chemical complexity on defect formation and damage accumulation in SP-CSAs under ion irradiation. The high-quality crystals were irradiated at 16 and 300 K to different ion fluences, to form irradiated region with little to heavy damages. The ion-induced damage was determined using Rutherford backscattering spectrometry technique along a channeling direction (RBS/C) and the level of lattice damage in irradiated Ni and SP-CSAs was quantified from Monte Carlo (MC) simulations. The results are interpreted using the Multi Step Damage Accumulation model to reveal material damage accumulation kinetics. Key findings of the study are that in case of room temperature irradiations the damage level measured for complex alloys at the highest irradiation fluence of 2 × 1015 cm−2 (∼3 dpa) is significantly higher than that obtained for pure nickel samples and suggest two-step damage accumulation process with a defect transformation taking place at a fluence of about 1.5 × 1015 cm−2. Moreover, structural and damage kinetic differences clearly imply that, with increasing degree of chemical complexity and high solid-solution strengthening effects from Ni to NiFe and to NiFeCoCr, the enhanced lattice stiffness resists to randomization of atomic configurations and inhibits the growth of extended defects.

A methodology for obtaining primary and secondary creep characteristics from indentation experiments, using a recess

A procedure is described for Indentation Creep Plastometery (using a spherical indenter), which is analogous to that developed previously for Indentation Plastometry. As in that case, it is based on iterative numerical simulation of the indentation process, with repeated comparison between an experimental outcome and the corresponding model prediction, systematically varying the values of parameters in a constitutive law until optimal agreement is achieved. The constitutive law used here is the Miller–Norton relationship, which covers both primary and secondary creep regimes (although the transition between them is not well-defined). The experimental outcome is the penetration depth as a function of time, under a constant applied load. An important feature of the procedure is the prior creation of a spherical recess in the sample, having a pre-selected depth and a curvature radius equal to that of the indenter. This allows control over the stress levels created during the indentation creep testing and can be used to ensure that no (time-independent) plastic deformation is stimulated during the test. In the absence of such a recess, this is virtually unavoidable, since the stress levels created during initial contact between a spherical indenter and a flat surface tend to be very high. Such plasticity introduces unwanted complications into creep testing. Confirmation of the viability of the procedure is provided via comparisons between the creep characteristics of pure nickel samples at 750 °C, obtained in this way and via conventional uniaxial tensile testing.

High-pressure strengthening in ultrafine-grained metals

The Hall-Petch relationship, according to which the strength of a metal increases as the grain size decreases, has been reported to break down at a critical grain size of around 10 to 15 nanometres1,2. As the grain size decreases beyond this point, the dominant mechanism of deformation switches from a dislocation-mediated process to grain boundary sliding, leading to material softening. In one previous approach, stabilization of grain boundaries through relaxation and molybdenum segregation was used to prevent this softening effect in nickel-molybdenum alloys with grain sizes below 10 nanometres3. Here we track in situ the yield stress and deformation texturing of pure nickel samples of various average grain sizes using a diamond anvil cell coupled with radial X-ray diffraction. Our high-pressure experiments reveal continuous strengthening in samples with grain sizes from 200 nanometres down to 3 nanometres, with the strengthening enhanced (rather than reduced) at grain sizes smaller than 20 nanometres. We achieve a yield strength of approximately 4.2 gigapascals in our 3-nanometre-grain-size samples, ten times stronger than that of a commercial nickel material. A maximum flow stress of 10.2 gigapascals is obtained in nickel of grain size 3 nanometres for the pressure range studied here. We see similar patterns of compression strengthening in gold and palladium samples down to the smallest grain sizes. Simulations and transmission electron microscopy reveal that the high strength observed in nickel of grain size 3 nanometres is caused by the superposition of strengthening mechanisms: both partial and full dislocation hardening plus suppression of grain boundary plasticity. These insights contribute to the ongoing search for ultrastrong metals via materials engineering.

X-ray diffraction (XRD) profile analysis of pure ECAP-annealing Nickel samples

X-Ray Diffraction (XRD) profile of pure equal channel angular pressing (ECAP)-annealing nickel samples has been thoroughly investigated for studying the material structures changes that imply to the mechanical behavior. Nickel-based material can be used for several applications such as biomaterial, gear, and some part of the instrument at nuclear facilities, which require high-grade standard material properties. ECAP is one kind of severe plastic deformation (SPD) techniques to obtain excellent mechanical properties without adding another element. However, the ECAP process generates metastable structures due to some mismatch structure and inhomogeneous stress within the material. This problem can usually be resolved by annealing after the ECAP process. In this article, pure Nickel was processed by ECAP at 423 K for two passes. The post-ECAP annealed will be carried out at the temperature range from 298 K until 1373 K. The microhardness test results indicate that the ECAP process increases the microhardness significantly, which remains stable after annealing until 773 K. At higher annealing temperature, the mechanical properties will drop suddenly and reach the microhardness value of pure pre-ECAP Nickel. This behavior could be explained clearly by the XRD data analysis result, which shows similar behavior structure changes. XRD data initially show peak shifting to lower 2θ value, which indicates an expansion to a higher lattice parameter, then at the higher annealing temperature, the diffraction peaks split gradually. This peak splitting could be indexed as pure pre-ECAP Ni peaks, which could be related to the drop of the microhardness value.

A Methodology for Obtaining Primary and Secondary Creep Characteristics from Indentation Experiments, Using a Recess

A procedure is described for Indentation Creep Plastometery (using a spherical indenter), which is analogous to that developed previously for Indentation Plastometry. As in that case, it is based on iterative numerical simulation of the indentation process, with repeated comparison between an experimental outcome and the corresponding model prediction, systematically varying the values of parameters in a constitutive law until optimal agreement is achieved. The constitutive law used here is the Miller-Norton relationship, which covers both primary and secondary creep regimes (although the transition between them is not well-defined). The experimental outcome is the penetration depth as a function of time, under a constant applied load. An important feature of the procedure is the prior creation of a spherical recess in the sample, having a pre-selected depth and a curvature radius equal to that of the indenter. This allows control over the stress levels created during the indentation creep testing and can be used to ensure that no (time-independent) plastic deformation is stimulated during the test. In the absence of such a recess, this is virtually unavoidable, since the stress levels created during initial contact between a spherical indenter and a flat surface tend to be very high. Such plasticity introduces unwanted complications into creep testing. Confirmation of the viability of the procedure is provided via comparisons between the creep characteristics of pure nickel samples at 750˚C, obtained in this way and via conventional uniaxial tensile testing.

Fabrication of Simple Apparatus for Resistivity Measurement in High-Temperature Range 300–620 K

A simple and low-cost apparatus has been designed and built to measure the electrical resistivity, (p), of metal and semiconductors in the 300-620-K temperature range. The present design is suitable to do measurement on a rectangular bar sample by using a conventional four-probe dc method. A small heater was made on the sample mounting copper block to achieve the desired temperature. Heat loss from the sample holder was minimized using very low thermal conductive insulator block. This unique design of heater and minimized heat loss from the sample platform provides uniform sample temperature, and also has very good thermal stability during the measurement. The electrical contacts of current leads and potential probes on the sample were made using very thin (42 standard wire gauge) copper wires and high-temperature silver paste. The use of limited components and small heater design makes the present instrument very simple, lightweight, easy to sample mount, small in size, and low cost. To calibrate the instrument, pure nickel sample was used, and two other materials La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (LSMO) and LaCoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (LCO) were also characterized to demonstrate the characterization capability of this setup. p(T) behavior on these samples was found to be in good agreement with the reported data. The metal-insulator transition for LSMO (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MI</sub> = ~358 K) and the insulator-metal transition for LCO (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IM</sub> = ~540 K) were clearly observed and these transition temperatures were also consistent with those reported in the literature.

Effect of Dislocation Density Gradient on Deformation Behavior of Pure Nickel Subjected to Torsion

Gradient hierarchical structures, including grain size gradient, twin density gradient, and texture gradient, are believed to broke up the long-standing dilemma-“strength-ductility trade-off” in materials science. Here we study the effect of dislocation density gradient on deformation behavior of pure nickel subjected to torsion. After applying torsion to cylindrical pure nickel samples, we find that Vickers hardness gradually decreased from surface to centre and the there is no obvious grain size gradient along the radial direction. The compression tests have been conducted on samples with different thickness of gradient layers. The results indicate that the yielding strength of the material can be three-times improved. Especially, the work-hardening rate “up-turn” phenomenon which was usually found in gradient nano-structures is presented in the torsion deformed pure nickel. Finally, the possible reasons and the effect of thickness of gradient structure are carefully discussed.

Catalytic behavior of bimetallic Ni–Fe systems in the decomposition of 1,2-dichloroethane. Effect of iron doping and preparation route

Model bimetallic Ni–Fe catalysts were prepared by coprecipitation from aqueous solutions of nitrates and by mechanical alloying of metal powders. Pure nickel samples subjected to the similar procedures were used as references. The obtained samples were characterized by scanning electron microscopy and X-ray diffraction analysis. Catalytic chemical vapor deposition of 1,2-dichloroethane over the catalysts was studied in a quartz flow reactor equipped with a McBain balance. It was shown that in the case of coprecipitation followed by reduction, Ni–Fe solid solution is formed within the studied range of Fe loading (1–10 wt%). Activation times of 6 min and longer are required to obtain this solid solution by the mechanical alloying method. Despite the known catalytic activity of nickel and iron in hydrocarbon decomposition in accordance with carbide cycle mechanism, iron doping was found to worsen the behavior of nickel in the studied reaction where chlorinated alkane plays a role of substrate to be decomposed. The formation of thermodynamically more stable iron chloride in relation to nickel chloride leads to deactivation of the catalyst and deceleration of the overall process.

Influence of Anneal Time on Σ3 Boundary Segregation in Commercially Pure Nickel

Commercially pure nickel (Ni200) samples were thermo-mechanically processed to drive segregation into Σ3, special grain boundaries. The special grain boundaries were characterized using electron backscatter diffraction, and their segregation behavior at the atomic level was studied using atom probe tomography. Local electrode atom probe analyses showed a lack of segregation at the Σ3 special grain boundary for a specimen annealed at 1000 °C for 30 h except for a slight increase in Si. This specimen was utilized in a previous study by the authors to compare the effects of segregation of type-specific grain boundaries. Local electrode atom probe results showed no segregation at the special grain boundary for a specimen annealed at 1000 °C for 100 h providing preliminary evidence that there is a correlation between increased anneal time and the effectiveness of Σ3 special grain boundaries to inhibit grain boundary segregation.

Three-dimensional characterization of grain boundaries in pure nickel by serial sectioningviamechanical polishing

Five macroscopic boundary parameters can be extracted from three-dimensional orientation maps. Serial sectioning, which includes consecutive steps of material removal, and electron backscatter diffraction (EBSD) measurement were employed to extract a stack of two-dimensional sections of a pure nickel sample. The EBSD patterns were collected from large millimetre scale areas and mechanical polishing was applied to prepare the sections. The three-dimensional microstructure was then reconstructed from these sections. A new alignment algorithm based on the minimization of misorientation between two adjacent sections has been developed to accurately align the sections. Differently from the conventional alignment methods, the new algorithm corrects not only the translational misalignment but also rotational and plane parallelity misalignments. The aligned three-dimensional microstructure exhibits smooth grain boundary planes and continuous orientation gradients inside the grains as experimental scatter induced by misalignment was largely removed. Grain boundaries were reconstructed from the aligned three-dimensional map, and the distribution of boundaries in the domain of five macroscopic boundary parameters was computed using kernel density estimation. Methods for estimating the reliability of the distributions are demonstrated. This distribution is compared with the distributions obtained previously for other face-centered cubic materials, including a different pure nickel sample.

Grain boundary character distribution derived from three-dimensional microstructure reconstruction

Manual serial sectioning which includes consecutive steps of sample preparation and Electron Back Scattering Diffraction (EBSD) measurement was employed to extract the twodimensional (2D) sections of a pure nickel sample and to reconstruct the three-dimensional (3D) microstructure. A general alignment algorithm based on the minimization of misorientation between two adjacent sections has been developed to accurately align the sections. By employing this alignment algorithm, any in-plane (translational) and rotational misalignment as well as the planparallelity can be corrected. Surface triangulation technique was used to reconstruct the grain boundary surfaces. The Grain Boundary Character Distribution (GBCD) was derived from reconstructed grain boundaries. The results show that a smoother grain boundary plane can be obtained after precise translational and rotational alignment and correction of planparallelity.The relative grain boundary energy was computed as a function of the five grain boundary parameters based on equilibrium at triple lines. The results show that the grain boundary planes carrying a Σ3 type misorientation are dominantly parallel to the {111} crystal plane, which indicates the presence of coherent twin boundaries. It was observed that coherent Σ3 type boundaries exhibit the minimum relative grain boundary energy, which is approximately 57% smaller than the average of all Σ3 boundaries, including also incoherent twin boundaries.

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiCNP Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites (Ni–SiCNP), with a SiCNP content ranged from 1 to 3.5 wt%, were prepared using mechanical alloying and spark plasma sintering. In addition, unreinforced pure nickel samples were also prepared for comparative purposes. To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–SiCNP composites transmission electron microscopy (TEM) was used, while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests. TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample, whereas, for the Ni–SiCNP composites, the presence of nano-dispersed SiCNP and twinning crystals was observed. These homogeneously distributed SiCNP were found located either within the matrix, between twins or on grain boundaries. For the Ni–SiCNP composites, coerced coarsening of the SiCNP assembly occurred with increasing SiCNP content. Furthermore, the grain sizes of the Ni–SiCNP composites were much finer than that of the unreinforced pure nickel, which was considered to be due to the composite ball milling process. In all cases, the Ni–SiCNP composites showed higher strengths and hardness values than the unreinforced pure nickel, likely due to a combination of dispersion strengthening (Orowan effects) and particle strengthening (Hall–Petch effects). For the Ni–SiCNP composites, the strength increased initially and then decreased as a function of SiCNP content, whereas their elongation percentages decreased linearly. Compared to all materials tested, the Ni–SiCNP composite containing 1.5% SiC was found more superior considering both their strength and plastic properties.

Small-angle neutron scattering investigation of the substructure of nickel irradiated with fast neutrons

The method of small-angle neutron scattering has been used to investigate the samples of pure nickel before and after irradiation with fast neutron fluences of Φ = 1018, 1019, and 1020 cm−2 (E n ≥ 0.1 MeV). It has been found that the substructure of the samples consists of vacancy clusters with two characteristic sizes of 2.5–4 and ∼7 nm. The sizes of precipitates weakly depend on fast neutron fluence. The magnitude of their density is on the order of 1022 and 1019 m−3, respectively, and increases by three to ten times as the fluence grows.