Plastic Deformation Of Nickel Research Articles

Theoretical Analysis of the Distortion Tensors During the Formation Of 90° <110> Reorientation Nanobands in the Course of Plastic Deformation of Nickel on Bridgman Anvils

Based on the results of electron microscopy examinations, a theoretical study of the distortion tensors of strain localization nanobands with a 90° reorientation of the crystal lattice is performed. The analysis is carried out in the direct-plus-reverse model of FCC→BCC→FCC martensitic transformations in an approximation of the linear theory of small strains. Using the atomic model of martensitic transformations based on a system of cooperative thermal fluctuations of planes in the BCC lattice, the distortion tensors of the contraction and shear deformation modes are estimated and so is their contribution to the total distortion of the reversible martensitic transformation.

Systematical analysis on the grain orientation evolution of pure nickel under plastic deformation by using in-situ EBSD

A combination of an in-situ tensile technique and electron backscattering diffraction (EBSD) was used to investigate the changes in microstructure and texture during plastic deformation of nickel with a high cubic texture. Surprisingly, unlike most data in the literature, it was found that the grains in nickel with a high cubic texture tended to align rather than scatter under a large force; thus, a large tensile stress causes enhancement of the cubic texture. The in-situ tensile tests are allowable to observe the entire process in real-time, while the EBSD results are helpful to separate texture changes at individual-grain resolution and to uncover the regular progression. It was found that, except for tiny grains and twins, most of the recrystallized grains tended towards the <001> pole. The only difference was that grains with a soft orientation effortlessly joined in the activation of the slip system, with the movement of dislocations playing a significant role in these grains. Conversely, the hard-orientation grains maintained the coordination of plastic deformation by means of rotation. Our results validate the in-situ tensile technique combined with EBSD as a systematic research method applied to the study of texture transformation for pure nickel.

Теоретический анализ тензоров дисторсии при формировании нанополос 90° &lt;110&gt; переориентации в процессе пластической деформации никеля на наковальнях Бриджмена

Теоретический анализ тензоров дисторсии при формировании нанополос 90° &lt;110&gt; переориентации в процессе пластической деформации никеля на наковальнях Бриджмена

Research of Stress Field Distribution in FCC-Single Crystal Samples in Compression

.Theoretical distribution of a stress field in a sample in the form of a rectangular parallelepiped in compression for an isotropic material was calculated using the method of finite elements. Calculations showed that the highest stress is observed at the top and front edges of a sample. There are areas of the tension stress on vertical edges in the area of sample tops. Shift anisotropy was determined by imposing of the distributed tension field in a sample on FCC crystal of a certain crystallographic orientation.Change of shift symmetry in single crystals for different crystallographic orientations of a compression axis was considered. It was established that a shift fragmentation in the parallel octahedral planes in the conditions of plastic deformation determines the process of low-symmetric shift deformation and maintenance of higher single crystal pseudo-symmetry. Connection of the obtained results and test data on heterogeneity of plastic deformation of nickel and aluminum single crystals is discussed.

Mechanical Aspects of Plastic Deformation of Nickel Based Superalloy

Variations of a true stress vs. true strain illustrate behaviour of materials during plastic deformation. Stress-strain relationship is generally evaluated by a torsion, compression and tensile tests. Results of these tests provide crucial information pertaining to the stress values which are necessary to run deformation process at specified temperature and cooling rate. Uniaxial compression tests at temperatures below the γ solvus were conducted on nickel based superalloy CMSX-4, to study the effect of temperature and strain rate on its flow stress. On the basis of received flow stress values activation energy of a high-temperature deformation process was estimated. Mathematical dependences (σpl -T i σpl - ἐ) and compression data were used to determine material constants. These constants allow to derive a formula that describes the relationship between strain rate, deformation temperature and true stress.

Plastic deformation of nickel under high hydrostatic pressure

Samples of nickel were deformed in torsion under very high hydrostatic pressures (up to 8 GPa) up to strains being much larger than those reached under normal pressure conditions. The obtained stress–strain curves were fitted by the model of Zehetbauer and Kohout which has been developed from the work hardening model of Zehetbauer designed for conventional large strain deformation. The configuration parameters of dislocations were determined from strain dependent dislocation densities which were measured by Multiple Whole X-ray Bragg Peak Profile Analysis (MXPA). Using actual materials and physical constants of Ni, the obtained values of fitting parameters could be related to realistic numbers of physical quantities hidden in those. The main part of the deformation stress increase observed with increasing hydrostatic pressure can be ascribed to the increase of dislocation density which arises from the restriction of diffusion controlled annihilation mechanisms. This restriction is related to the pressure-induced decrease of diffusion, i.e. to the increase of vacancy migration enthalpy which is due to the shrinking of interatomic spacing when the hydrostatic pressure is enhanced. However, the calculated concentrations of deformation induced vacancies for pressures 5 GPa and beyond are unacceptably high. Data from measurements of microhardness and MXPA after unloading show that beyond a pressure of 4 GPa both the strength and the dislocation density is not being increased anymore which suggests the onset of spontaneous vacancy and dislocation annihilation due to the high overall concentration of vacancies reached. This failure of the model is not surprising since it has not considered so far any limits in the vacancy concentration.

Effect of Joining Compressive Stress on Solid State Bonding of Graphite to Nickel

Graphite was bonded to nickel in a vacuum using an RF-induction furnace with temperature, keeping time and joining compressive stress as variables. The bending strength of graphite/nickel joints, the changes of microstructure and hardness of nickel near the interface were investigated. Thermal stress induced in the joints was estimated by means of finite element analysis. On the basis of these results, the influences of joining compressive stress on bonding were examined. Joining compressive stress and joining temperature are important factors for close contact and strong bonding between the joining surfaces of graphite and nickel. At a high joining temperature, nickel is plastically deformed even under low joining compressive stress so that full contact and strong bonding are accomplished. At a low joining temperature, strong bonding was not achieved when joining compressive stress is low, because plastic deformation of nickel is restrained. The plastic deformation of nickel plays an important role in enabling good contact and strong bonding. The strength of the joints increased with joining compressive stress. The plastic deformation of nickel near the joining interface increases with the joining compressive stress so that graphite is elastically deformed during annealing. Therefore, compressive stress is retained on the graphite surface near the joining interface. Thermal tensile stress induced on the graphite surface after cooling is relaxed by this compressive stress.

黒鉛とニッケルの固相接合に及ぼす接合圧縮応力の影響

Graphite was bonded to nickel in a vacuum using an RF-induction furnace by changing conditions of temperature, keeping time and joining compressive stress. The bending strength of graphite/nickel joints and the changes of microstructure and hardness near the joining interface of nickel were investigated. Thermal stress induced in the joints was estimated by means of finite element analysis. On the basis of these results, the influences of joining compressive stress on bonding were examined.Joining compressive stress and temperature are important factors for close contact and strong bonding between joining surfaces of graphite and nickel. At high temperature, nickel is plastically deformed even under low joining compressive stress so that full contact and strong bonding are accomplished, while at low temperature, no strong bonding are attained when joining compressive stress is lower, because plastic deformation of nickel is restrained. Plastic deformation of nickel plays an important role in full contact and strong bonding.The strength of the joints increased as joining compressive stress increases, because of the following reasons: The plastic deformation of nickel near the joining interface increases with joining compressive stress so that graphite is elastically deformed in radial direction during annealing. Therefore, longitudinal compressive stress is induced on the graphite surface near the joining interface. Thermal tensile stress induced on the graphite surface after cooling is relaxed by this compressive stress.

High-temperature creep of nickel under conditions of grain-boundary diffusion of impurities from the surface

Comparative investigations of the effect of diffusion streams of copper atoms (a weakly segregating impurity) and silver atoms (a strongly segregating impurity) from the surface in the high-temperature plastic deformation of nickel have been carried out. It has been established that in the high-temperature plastic deformation of nickel, when there are diffusion streams of copper and silver from the surface, there is a reduction in the creep resistance of nickel due to an increase in the contribution of grain-boundary slip to the overall deformation. Two stages, characterized by different values of the rate sensitivity factor m, are observed on the curve of the stress against the rate of deformation over a certain temperature range for each impurity. In the region of deformation rates of $$\dot \varepsilon< 2.5 \cdot 10^{ - 6} $$ sec−1, m≊0.2, and for $$\dot \varepsilon > 2.5 \cdot 10^{ - 6} $$ sec−1, m becomes less than 0.05.

The kinetics of nickel passivation in sulfuric acid, and the effects of plastic deformation on the kinetics of various electrochemical reactions on nickel

The kinetics of passivation in sulfuric acid of undeformed nickel have been measured by the rotating cyclinder technique at various IR-drop-compensated applied potentials. The passivation efficiency as a function of passivation time has been measured by the rotating ring-disc technique. These results are compared with those obtained on continuously scratched, rotating cylindrical electrodes at passivating potentials, supplemented by measurements at active anodic, and cathodic potentials. It is found that plastic deformation of nickel much enhances the cathodic reduction of hydrogen ion and the anodic dissolution of nickel, but impedes the passivation of nickel and reduces the passivation efficiency. Furthermore, the deformation-produced surface features responsible for these differences have a limited duration controlled by surface diffusion in the cathodic range, and by surface diffusion and preferential dissolution in the anodic range.

The effect of hydrogen on the solid solution strengthening and softening of nickel

The effects of hydrogen on the plastic deformation of nickel and nickel-carbon alloys were studied using plastic deformation techniques over a wide range of strain rates at about 300 K. The emphasis of the study was on the behavior at very low strains and low strain rates. Hydrogen was introduced as a solute element by quenching from a gaseous H 2 atmosphere or by testing in a gaseous H 2 atmosphere. The behavior of a number of different purities of nickel with hydrogen additions was examined. The most significant impurity element seemed to be C and this element was varied over a wide composition range by annealing in different atmospheres. Both solution softening and solution strengthening was observed depending on the amount of H in solution relative to the amount of C in solution. The nature of this solution softening effect is discussed.

Effect of plastic deformation and quenching on the absolute thermal emf of nickel

The effect of the degree and rate of plastic deformation of nickel on the change of its absolute thermal emf was studied. The dynamic effect of the change of thermal emf was established, the dynamic coefficient being 1.22–1.25. Plastic deformation of quenched nickel reduced its absolute thermal emf, on the basis of which conclusions are drawn about the contributions, different in sign, of holes and dislocations to the change of the absolute thermal emf of nickel. The kinetics were studied of the recovery of the thermal emf induced in nickel by plastic deformation, and the existence was established of two stages of recovery, differing in nature and with different activation energies, 0.1 and 0.3 eV.

Stable Strain-Induced Magnetic Remanence in Nickel, Cobalt, and Magnetite

Three magnetic materials have been deformed at room temperature, and stability aspects of their magnetomechanical behaviour examined. Plastic deformation of nickel and cobalt, and elastic deformation of magnetite, give a strain induced moment. The remanence is larger and much more relatively stable than isothermal remanent magnetization (IRM) from the field applied during deformation. It is also more stable than an IRM with an equal magnitude, and can have a significantly different microscopic coercivity spectrum. The results are consistent with a model for magnetomechanical effects based on the response to changes in the physical structure.

Recent advances in magnetic analysis

Some recent developments in the examination of materials with the aid of the magnetization curve are described. The well-known method of estimating internal stresses by means of magnetic measurements has recently been much refined so that a quantitatively correct estimate of the internal stresses arising from plastic deformation of nickel and even iron can be made. In special cases even inhomogeneous stresses can be magnetically estimated and the approach to saturation is related to the dislocation density. A fair amount of information about non-magnetic inclusions and precipitates in a magnetic material can be derived from a critical assessment of its coercivity. On the other hand, the measurement of torque curves and of rotational hysteresis allows a comprehensive analysis of the shape, size and density of magnetic precipitates. Finally, the use of magnetic viscosity measurements for structure studies is mentioned.