Electrical resistivity and surface elastic wave velocity exhibited the highest anisotropic behaviors for the thickest films and the lowest pressure.
The tilt angle of the columnar microstructure and fanning of their cross-section were tuned as a function of the pressure and film thickness. The A15 β phase exhibiting a poor crystallinity was favored at high pressure and for the thinner films, whereas the bcc α phase prevailed at low pressure and for the thicker ones.
NIOH CRACK RESOULTION SERIES
A second series was produced with a constant thickness of 400 nm, whereas the pressure was gradually changed from 2.5 × 10−3 to 15 × 10−3 mbar. A first series of films was obtained at a constant pressure of 4.0 × 10−3 mbar with the films’ thickness increasing from 50 to 1000 nm. Tungsten films were prepared by DC magnetron sputtering using glancing angle deposition with a constant deposition angle α = 80°. This result reveals that NiCo2O4 is a prominent electrode material for supercapacitor application. The NCO-W, NCO-WE and NCO-WD electrodes showed specific capacitance values of 271, 553 and 140 F/g respectively at the current density of 0.5 mA/cm² and excellent capacitance retention of 90%, 91% and 80% after 2000 cycles for NCO-W, NCO-WE and NCO-WD samples respectively. The Electrochemical performance of these NiCo2O4 thin films were studied using cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy techniques. The NCO-WE favored the formation of uniformly distributed leaf-like nanostructure whereas NCO-WD showed randomly oriented nanoplates all over the surface area. NCO-W exhibited the spikes of Crossandra infundibuliformis like nanostructures. The morphologies of NiCo2O4 thin films modify substantially with change in a solvent. The films have been named as NCO-W for DDW, NCO-WE for DDW: Ethanol (1:1) solvent and NCO-WD for DDW: N, N dimethylformamide (1:1) solvent. We used different solvent composition as Double Distilled Water (DDW), DDW:Ethanol (1:1) and DDW: N, N dimethylformamide (1:1). The consequences of different compositions of solvents on morphological and electrochemical properties have been studied systematically. The present investigation deals with controlled synthesis of nanostructured NiCo2O4 thin films directly on stainless steel substrates by facile and economical chemical bath deposition technique, without adding a surfactant or a binder. The predicted rates are shown to be in good agreement with available experimental data. The time taken to reach this critical stress for oxide failure has been calculated, from which dwell crack growth rates are computationally derived. However, mechanical equilibrium requirements induce tensile stresses at the tip of the oxide wedge, where failure of the oxide is predicted. Stability conditions for oxide formation are investigated and is associated with the prediction of compressive stresses within the oxide layer just ahead of the crack tip, which become progressively negative as the oxide wedge develops.
It is shown that a unimodal dispersion leads to reduced oxide growth rates (parabolic behaviour) when compared to a bimodal one. Simulations indicate that the presence of a fine γ’ size distribution has a strong influence on the predicted ow stress of the material and consequently on the relaxation in the vicinity of the crack-tip/oxide wedge.
Comparison of predicted compositional fields across the matrix/oxide interface are compared with experiments and shown to be in good agreement.
The resulting set of constitutive and mass transport equations have been implemented within a finite element scheme. A multicomponent mass transport formulation is used to simulate the formation/evolution of an oxide wedge ahead of the crack tip, where stress-assisted vacancy diffusion is assumed to operate. The viscoplastic model explicitly accounts for multimodal γ’ particle size distributions. A dislocation-based viscoplastic constitutive description for high temperature deformation is used to simulate the stress state evolution in the vicinity of a crack at elevated temperature. In particular, this study investigates the influence of an externally applied load and variations in the γ’ dispersion on the grain boundary oxide growth kinetics. A theoretical treatment on the oxide-controlled dwell fatigue crack growth of a γ’ strengthened nickel-based superalloys is presented.
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