Mechanical Properties Of Nickel Research Articles

Nanograin size effects on deformation mechanisms and mechanical properties of nickel: A molecular dynamics study

The grain size refinement of metallic materials to the nanometer scale produces interesting properties compared to the coarse-grained counterparts. Their mechanical behavior, however, cannot be explained by the classical deformation mechanisms. Using molecular dynamics simulations, the present work examines the influence of grain size on the deformation mechanisms and mechanical properties of nanocrystalline nickel. Samples with grain sizes from 3.2 to 24.1 nm were created using the Voronoi tessellation method and simulated in tensile and relaxation tests. The yield and ultimate tensile stresses follow an inverse Hall-Petch relationship for grain sizes below ca. 20 nm. For samples within the conventional Hall-Petch regime, no perfect dislocations were observed. Nonetheless, a few extended dislocations were nucleated from triple junctions, suggesting that the suppression of conventional slip mechanism is not uniquely responsible for the inverse Hall-Petch behavior. For samples respecting the inverse Hall-Petch regime, the high number of triple junctions and grain boundaries allowed grain rotation, grain boundary sliding, and diffusion-like behavior that act as competitive deformation mechanisms. For all samples, the atomic configuration analysis showed that Shockley partial dislocations are nucleated at grain boundaries, crossing the grain before being absorbed in opposite grain boundaries, leaving behind stacking faults. Interestingly, the stress relaxation tests showed that the strain rate sensitivity decreases with grain size for a specific grain size range, whereas for grains below approximately 10 nm, the strain rate sensitivity increases as observed experimentally. Repeated stress relaxation tests were also performed to obtain the effective activation volume parameter. However, the expected linear trend in pertinent plots required to obtain this parameter was not found.

Mechanical Property Comparison of Ni–Cr–Mo Alloys Fabricated via One Conventional and Two New Digital Manufacturing Techniques

This study compared the microstructures and mechanical properties of nickel–chromium–molybdenum (Ni–Cr–Mo) alloys prepared from a single alloy with an identical composition using two new digital processes (selective laser melting (SLM) and soft metal milling (SMM)) and conventional lost-wax casting (LWC). Disc specimens were used to study the microstructures via various analytical methods, while dumbbell-shaped specimens were subjected to tension to determine the mechanical properties (n = 6). The SLM and SMM alloys showed a higher number of large and small pores, respectively, than the LWC alloy. A face-centered cubic (γ)-phased matrix was indexed for all three resultant alloys. The SLM and SMM alloys also showed more homogeneously distributed elements and finer grains (in particular, ultrafine grains in the SLM alloy) when compared to the LWC alloy. Meanwhile, the LWC alloy showed a statistically higher yield strength than the other two alloys (p < 0.001). Notwithstanding, all three resultant Ni–Cr–Mo alloys satisfied the ISO 22674 standard criteria for type 5 materials (yield strength: >500 MPa; percentage elongation: >2%; and elastic modulus: >150 GPa).

Improving the physical and mechanical properties of nickel by adding nano titanium oxide by powder technology

In the current article aims to study the effect of Nano construction on the physical and mechanical properties of nickel, samples were made from samples of nickel-based metal and supported with nano titanium oxide, with volumetric ratios of (0,5,10,15,20) %, where the matrix and the reinforcement were ground using a homemade microwave mill with milling times of (3, 6, 9) hours. After that the required weights were prepared and the powders were pressed at (100 bar) and for a time of one minute only. Then the samples resulting from pressing were thermally treated by means of oven and at 1200°C for a time of two hours, physical tests were carried out that included green density and bulk, true porosity, and mechanical properties are hardness, wear rate. The physical and mechanical tests gave the best results after sintering and at a milling time of 9 hours and reinforcement from (0-20) % where the green density decreased from (7.01-5.20) g/cm3, and the bulk density after sintering decreased from (8.43-7.20) g/cm3, porosity increased from (15.43-8.8)%. The mechanical properties increased the hardness from (99-240) Kg/mm2, while the wear rate decreased from (4.03×10-7-6.59×10-8) g/cm. All these results indicate an improvement in nickel metal with an increase in the Nano composition ratio.

Influence of Alumina Nanofibers Sintered by the Spark Plasma Method on Nickel Mechanical Properties

The article presents the study of alumina nanoparticles’ (nanofibers) concentration effect on the strength properties of pure nickel. The samples were obtained by spark plasma sintering of previously mechanically activated metal powders. The dependence of the grain size and the relative density of compacts on the number of nanofibers was investigated. It was found that with an increase in the concentration of nanofibers, the average size of the matrix particles decreased. The effects of the nanoparticle concentration (0.01–0.1 wt.%) on the elastic modulus and tensile strength were determined for materials at 25 °C, 400 °C, and 750 °C. It was shown that with an increase in the concentration of nanofibers, a 10–40% increase in the elastic modulus and ultimate tensile strength occurred. A comparison of the mechanical properties of nickel in a wide range of temperatures, obtained in this work with materials made by various technologies, is carried out. A description of nanofibers’ mechanisms of influence on the structure and mechanical properties of nickel is given. The possible impact of impurity phases on the properties of nickel is estimated. The tendency of changes in the mechanical properties of nickel, depending on the concentration of nanofibers, is shown.

Influences of Ni content and porosity on mechanical properties of Ni–YSZ composites under solid oxide fuel cell operating conditions

Mechanical properties of nickel and yttria-stabilized zirconia (Ni–YSZ) anodes of solid oxide fuel cells undergo changes not only because of extrinsic conditions but also because of Ni, YSZ and pore proportions. In this study, elastic modulus and fracture behavior of Ni(NiO)–YSZ composites are investigated with changing Ni and pore volume fractions as the main parameters. NiO–YSZ composite stiffness at 800 °C monotonically increases with increasing NiO. However, the reduced form of Ni–YSZ shows drastic changes in elastic modulus and strength around 30 vol% Ni where the deformation behavior and fracture made transition from brittle-like to ductile. Both stiffness and strength show linear decreases with porosity, of which the degree of deterioration at 800 °C was duller than at room temperature. The influences of Ni content and porosity on elasticity are quantified using multiple-linear regression analysis. Pore volume fraction shows large negative effects on elasticity at room temperature in air. However, at 800 °C, Ni volume shows larger negative effects than pore volume under reducing atmospheres.

First Principles Investigation on Thermodynamic Properties and Stacking Fault Energy of Paramagnetic Nickel at High Temperatures

Reliable data on the temperature dependence of thermodynamic properties of alloy phases are very useful for modeling the behavior of high-temperature materials such as nickel-based superalloys. Moreover, for predicting the mechanical properties of such alloys, additional information on the energy of lattice defects (e.g., stacking faults) at high temperatures is highly desirable, but difficult to obtain experimentally. In this study, we use first-principles calculations, in conjunction with a quasi-harmonic Debye model, to evaluate the Helmholtz free energy of paramagnetic nickel as a function of temperature and volume, taking into account the electronic, magnetic, and vibrational contributions. The thermodynamic properties of Ni, such as the equilibrium lattice parameter and elastic moduli, are derived from the free energy in the temperature range from 800 to 1600 K and compared with available experimental data. The derived temperature dependence of the lattice parameter is then used for calculating the energies of intrinsic and extrinsic stacking faults in paramagnetic Ni. The stacking fault energies have been evaluated according to three different methodologies, the axial-next-nearest-neighbor Ising (ANNNI) model, the tilted supercell approach, and the slab supercell approach. The results show that the elastic moduli and stacking fault energies of Ni decrease with increasing temperature. This “softening” effect of temperature on the mechanical properties of nickel is mainly due to thermal expansion, and partly due to magnetic free energy contribution.

Influence of Irradiation on Mechanical Properties of Nickel

The influence of irradiation on mechanical properties of nickel is studied using molecular dynamics (MD) simulation. The single crystal nickel is irradiated with the primary knocked-on atom (PKA) energies of 5 keV, 10 keV, 20 keV, and 30 keV at 300 K, and then the tensile test is performed. The simulation results reveal that the yield strain and yield stress of irradiated nickel decrease with the irradiation energy increasing, while the elastic modulus has no obvious change at various irradiation energies. By analyzing the stress-strain curves and the microstructure evolution, it is found that the effect of irradiation accelerates the damage of the internal structure due to the existence of irradiation defects, and high-energy irradiation leads to the instability of the structure in the process of plastic deformation.

Atomistic simulation study of the helium effects on the deformation behavior in nickel bicrystals

Experimental and theoretical studies have shown that helium impurities in nickel tend to precipitate into nano-sized bubbles. The formation of helium bubbles has been found to have detrimental effects on the mechanical properties of nickel and its alloys. However, the mechanisms that lead to the observed helium-induced embrittlement are still unclear. In the present work, we perform molecular dynamics simulations to study helium effects on the deformation behavior of nickel systems. The role of symmetric tilt grain boundary (STGB) structures in nickel is investigated for various helium concentration levels. The deformation behavior is investigated in relation to the STGB properties, the helium distribution, and the evolution of lattice defects in the nickel matrix. In pure nickel bicrystals, it is found that the tensile strength and failure strain depend on the misorientation angle and the GB energy, with the lowest-energy STGB exhibiting the highest strength. In bicrystals with helium, we observe that the emission of dislocation loops nucleated at helium clusters significantly reduces the strength. The mechanical properties were found to be dependent on the GB misorientation angle, with the GB energy having no significant effect. Reduction of the material strength, with the presence of helium, was found to be associated with heterogeneous nucleation of dislocation loops at helium bubbles, which was not limited to GB region.

Impact of Interlayer Dwell Time on Microstructure and Mechanical Properties of Nickel and Titanium Alloys

Path planning in additive manufacturing (AM) processes has an impact on the thermal histories experienced at discrete locations in simple and complex AM structures. One component of path planning in directed energy deposition is the time required for the laser or heat source to return to a given location to add another layer of material. As structures become larger and more complex, the length of this interlayer dwell time can significantly impact the resulting thermal histories. The impact of varying dwell times between 0 and 40 seconds on the microstructural and mechanical properties of Inconel® 625 and Ti-6Al-4V builds has been characterized. Even though these materials display different microstructures and solid-state phase transformations, the addition of an interlayer dwell generally led to a finer microstructure in both materials that impacted the resulting mechanical properties. With the addition of interlayer dwell times up to 40 seconds in the Inconel® 625 builds, finer secondary dendrite arm spacing values, produced by changes in the thermal history, correspond to increased yield and tensile strengths. These mechanical properties did not appear to change significantly, however, for dwell times greater than 20 seconds in the Inconel® 625 builds, indicating that longer dwell times have a minimal impact. The addition of interlayer dwell times in Ti-6Al-4V builds resulted in a slight decrease in the measured alpha lath widths and a much more noticeable decrease in the width of prior beta grains. In addition, the yield and tensile values continued to increase, nearly reaching the values observed in the rolled plate substrate material with dwell times up to 40 seconds.

Growth mechanism of intermetallic compound and mechanical properties of nickel (Ni) nanoparticle doped low melting temperature tin–bismuth (Sn–Bi) solder

This paper investigates the effects of Ni nanoparticles on the formation of intermetallic compound (IMC) layers and mechanical properties of low melting temperature Sn–58Bi (wt%) based solders on copper (Cu) substrate. At the initial reaction for the plain Sn–Bi solder/Cu substrate system, an island-shaped Cu6Sn5 IMC layer was found to adhere at the substrate surface. A very thin Cu3Sn IMC layer was also observed between the Cu6Sn5 IMC layer and Cu substrate as the reaction time increased. However, in the composite solders doped with Ni nanoparticles, a scallop-shaped ternary (Cu, Ni)–Sn IMC layer appeared at the interface without Cu3Sn IMC layer. In the solder ball region, the Bi phase with bright contrast was homogeneously distributed in the β-Sn matrix. After adding the Ni nanoparticles, an additional very fine Sn–Ni IMC particle was found to have been distributed in the β-Sn matrix. The IMC layer thicknesses were increased with the reaction time and temperature. However, the IMC growth behavior of composite solder was slower than that of the plain solder system. Furthermore, the mechanical properties of the composite solder exhibited higher values than that of the plain Sn–Bi solder due to the strengthening effect of fine Sn–Ni IMC particles.

The influence of hot pressing conditions on mechanical properties of nickel aluminide/alumina composite

The influence of hot pressing conditions on mechanical properties of nickel aluminide/alumina composite has been investigated in the present paper. In particular, effect of the process parameters, viz. compacting pressure, sintering temperature and sintering time on the evolution of density, elastic constants and tensile strength properties of the intermetallic-ceramic composite has been studied. Elastic constants, the Young's modulus and Poisson's ratio, have been evaluated using an ultrasonic testing method, and the tensile strength has been determined by a Brazilian-type splitting test. Microscopic observations of microstructure evolution complemented the experimental procedure. Experimental results have been confronted with theoretical models showing a good agreement between the data compared.

Hydrogen and helium in nickel and 12Kh18N10T steel

A brief review of data for the influence of helium on the hydrogen sorption and mechanical properties of nickel and 12Kh18N10T steel is presented. When in the metallic matrix, helium considerably deteriorates the ductility of these metals. It is shown that 3He present in 12Kh18N10T steel generates high-energy hydrogen traps.

Size Effects and Structure-Sensitivity of Properties in Electrodeposited Nanomaterials

An analysis of grain-size dependent structure-sensitivity of various physical and mechanical properties of nickel is presented, covering the crystal size range from 10 nm to 10 μm. It is shown that the well established general trends regarding defect-sensitivity observed for conventional polycrystalline materials also apply to porosity-free nanomaterials with grain sizes less than 100 nm produced by the electrodeposition process.

Intrinsic Effects due to the Reduction of Thickness on the Mechanical Behavior of Nickel Polycrystals

Uniaxial tensile tests were performed on high-purity nickel polycrystals with thicknesses (t) ranging from 12.5 to 3200 μm. The grain size (d) of each sample was set to a value close to 100 μm in order to avoid grain size effects. Experimental results highlight the intrinsic effect of the thickness on the mechanical properties of nickel. For plastic strains higher than 0.01, a strong softening of the flow stress is clearly observed when the t/d ratio decreases from four to one. This critical range is independent of the plastic strain. Transmission electron microscopy (TEM) investigations of dislocation structures were carried out in core and surface regions of samples plastically strained in the second hardening stage. It is shown that the mean dislocation cell diameter obtains values two or three times higher near free surfaces than in core areas for specimens with t/d ratios lying at a range of 1 to 4. This observation can be interpreted in terms of an increase in the mean free path of mobile dislocations in the second hardening stage. The transition between polycrystal and single-crystal behavior for nickel with constant grain size and various thicknesses is, therefore, an intrinsic effect related to progressively stronger surface softening effects.

Microstructure evolution and mechanical properties of nickel based honeycomb sandwich

A nickel based superalloy honeycomb sandwich was manufactured by high temperature brazing. The microstructure evolution and the out of plate mechanical properties were investigated for honeycomb sandwiches aged at 1000°C in the present paper. The maximum tensile stress was 28·5 MPa and the compressive yield strength was 29·6 MPa for the original specimens. These parameters decreased to 22·9 and 20·5 MPa for specimens aged for 2 h, to 18·2 and 12·2 MPa for specimens aged for 5 h and to 20·2 and 14·3 MPa for specimens aged for 10 h respectively. With increasing aging time the tensile elongation decreased, the intermetallic compounds and the eutectic structure in the brazing region disappeared, and the solid solution approaching the matrix gradually increased.

Effect of Additives on Microstructure and Mechanical Properties of Nickel Plate/Mask Fabricated by Electroforming Process

We fabricated a Ni plate by the electroforming process and evaluated the effects of the addition of brighteners to the electrolyte on its microstructure and mechanical properties. It was found that the microstructure and mechanical properties varied considerably with the different combinations of brighteners added (i.e., the addition of class-I, class-II, or both class-I and class-II brighteners). The grain size and degree of crystallization of the Ni plate decreased when the class-I or class-II brightener was added, while the degree of crystallization decreased even further and the degree of preferred (002) orientation decreased when both the class-I and class-II brighteners were added. These results are thought to be due to the “inhibited process,” which was accelerated by the presence of both additives. In addition, the hardness, yield strength, and wear properties increased when the brighteners were added. The highest mechanical properties (a hardness of , yield strength of , and friction coefficient of 0.66) were obtained when both the class-I and class-II brighteners were added, which is probably due to the fine grain, poor degree of crystallization, and smooth surface.

Effect of pulse frequency on the morphology and nanoindentation property of electroplated nickel films

This paper reports the effect of pulse current with different frequencies on the morphology and mechanical properties of nickel (Ni) films deposited by electroplating. The pulse frequency varies from 0 (DC) to 500 Hz while the duty cycle (Ton/Toff) is 1 during electroplating. The average roughness and deposition rate of Ni films decrease with the increasing frequency. The smoothest Ni surface with average roughness of 16.5 nm is achieved at the frequency of 500 Hz while the deposition rate reaches a nearly stable rate of 0.04 μm/min. The surface concentration of ions does not vary with time at a sufficiently high frequency with a long off time for ion to diffuse onto the surface. It will result in much more nuclei formed on the surface of cathode at a limited growth rate to get small grains for smooth morphology. The nanohardness of Ni film initially decreases rapidly from 3.9 to 1.18 GPa at 0 to 10 Hz, respectively, then increases to about 4.87 GPa in the range of 100–200 Hz, and decreases slowly to 4.0 GPa at 500 Hz. The stiffness of Ni films electroplated by pulse current at 100–200 Hz is higher than that by dc electroplating. The compromised Ni film with smooth morphology, good hardness and proper deposition rate is obtained at frequency of 100–200 Hz under the current density of 3 Adm−2.

Excellent Mechanical Properties of Nickel Processed by High Pressure Technique

It was shown that nickel processed by equal channel angular pressing (ECAP) followed by cold rolling and annealing presents quite unique mechanical properties. This permits to produce in a controlled way nickel samples with high mechanical strength and ductility. Mechanical properties ranged from ultimate tensile stress (UTS) of 1270 MPa, with elongation to rupture of about 6%, to UTS of 900 MPa, and elongation to rupture up to 12%. The high strength properties of the material result from the additive strengthening contributions of grain boundaries in ultra fine grains and dislocation substructures. The grain boundaries and, in particular, degree of their nonequilibrium state influence primarily ductility and strength of the material. The material was deformed with the formation of shear bands of diameter much larger than the grain size, and it seems that its ductility is connected with a deformation mechanism involving collective relative displacement of grain groups, with extensive grain boundary sliding. The produced high strength Ni with good ductility has a potential for practical applications, particularly, for micro-electromechanical systems (MEMS).

Sidney Siegel

Sidney Siegel, a solid-state physicist who became a respected pioneer in nuclear reactor development, died of cancer on 15 March 2001 at his home in Pacific Palisades, California. He also was one of the first scientists to study the effect of radiation on solids.Born in New York City on 10 January 1912, Siegel began his career as a physicist in the 1930s at Columbia University. At that time, solid-state physics was just emerging as a specific branch of physics. He earned his bachelor’s degree in physics at Columbia in 1932. As a graduate student under S. L. Quimby, Siegel was one of the first to experimentally investigate the relationship between magnetic and mechanical properties of nickel. This investigation was aimed at testing some consequences of Werner Heisenberg’s 1932 theory of ferromagnetism. Siegel received his PhD in physics in 1936; his thesis was on the relationship between the magnetic and mechanical properties of nickel. During World War II, working as a research engineer with the Westing-house Electric Corp in Pittsburgh, Pennsylvania, Siegel helped develop an influence exploder for electric torpedoes and an airborne radar system. After the war, in 1946, Westinghouse sent Siegel to participate at what is now Oak Ridge National Laboratory in the design of a pilot-scale, gas-cooled reactor for civilian power—the Daniels power pile. The reactor was designed with graphite as a moderator. Eugene Wigner, then director of ORNL, had predicted that graphite in a reactor would swell and otherwise deteriorate under the intense bombardment of fast neutrons. Siegel, with his background in solid-state physics, was one of the earliest pioneers in the study of this so-called Wigner effect.While at ORNL, Siegel attended the Oak Ridge School of Reactor Technology. Many of the alumni of this school became prominent figures in the unfolding American development of power reactors. Among the students was (then) Captain H. G. Rickover.In 1949, Siegel returned to the newly organized Bettis Field reactor laboratory, which was operated by Westinghouse for Rickover’s Naval Reactor Branch of the Atomic Energy Commission. At the time, two naval reactors were being worked on: a sodium-cooled intermediate neutron reactor (SIR) at General Electric and a pressurized water thermal neutron reactor—originally called submarine thermal reactor (STR) and, later, pressurized water reactor (PWR)—at Westinghouse. Although prototypes of both reactors were built, the US Navy adopted the Westinghouse STR rather than the GE SIR.Siegel played an important role in these earliest days of naval reactors, when many combinations of coolant and moderator were proposed and some were actually built. He assembled and then headed a group of capable young physicists and engineers to conduct the critical experiments on the core of the STR and to analyze the reactor’s solid-state aspects. But of the perhaps 10 different combinations of coolant and moderator, only the PWR (and its relative, the boiling water reactor) survived, mainly because it was based on the extensive and expensive effort of Rickover’s Nuclear Navy.Siegel, like several other leaders of reactor development, chafed at Rickover’s imperious scrutiny. In 1950, he left Westinghouse to become the associate director of the newly founded nuclear program of Atomics International, a division of North American Aviation Inc.The main job of Atomics International at the time was to design and build a 500-kilowatt (electrical) graphite-moderated, molten-sodium-cooled reactor. Siegel was project engineer for this very successful reactor experiment. This experiment was followed by a much larger sodium-cooled reactor sponsored by the Consumer Public Power District of Nebraska. However, that reactor developed serious leaks in the stainless steel cans that enclosed each graphite module.Because Atomics International had so much experience with sodium as a coolant, the company became heavily involved in the sodium-cooled fast breeder project, which was the main line of advanced reactor developments in the US. The primary focus of the breeder programs was the so-called Clinch River Fast Breeder, which was to be built in Oak Ridge but was abandoned. Siegel, at the time, served as the main technical spokesman for the Atomics International version of fast breeders.In 1973, Siegel returned to ORNL as associate lab director and coordinator for the NSF-sponsored program on energy and the environment. He retained this post until 1975, when he retired to California.Siegel served as both vice president (1965) and president (1966) of the American Nuclear Society. He also practiced his extraordinary talents as an art photographer and creator of exquisite large wood sculptures.I knew Siegel well and was one of his great admirers. Beyond his capabilities as a solid-state physicist and a technical administrator, he was widely learned and able to convey his thoughts in unusually lucid prose. He represented the best of the nuclear pioneers: He was thoughtful, knowledgeable, and articulate. Many of his colleagues shall miss him, as shall I.Sidney SiegelPPT|High resolution© 2002 American Institute of Physics.

Growth mechanisms of oxide scales on ODS alloys in the temperature range 1000–1100°C

AbstractAfter a short overview of the production, microstructure and mechanical properties of nickel‐ and iron‐based Oxide Dispersion Strengthened (ODS) alloys, the oxidation properties of this class of materials is extensively discussed. The excellent oxidation resistance of ODS alloys is illustrated by comparing their behaviour with conventional chromia and alumina forming wrought alloys of the same base composition.ODS alloys exhibit improved scale adherence, decreased oxide growth rates, enhanced selective oxidation and decreased oxide grain size compared to corresponding non‐ODS alloys. It is shown, that these experimental observations can be explained by a change in oxide growth mechanism. The presence of the oxide dispersion reduces cation diffusion in the scale, causing the oxides on the ODS alloys to grow mainly by oxygen grain boundary transport. As oxide grain size increases with time, the oxide growth kinetics obey a sub‐parabolic time dependence especially in the case of the alumina forming iron‐based ODS alloy.