Effects of tensile stress on electrochemical characteristics and structural morphology of P110SS steels in carbon dioxide-saturated solution

A high-temperature autoclave was used to grow CO2 corrosion-product films on P110SS steel specimens while the surface of the specimens was continuously subjected to tensile stress in a four-point bending jig; the autoclaving times were 6, 18, 36, and 72 h. A scanning electron microscope was used to observe the surface topography of the corrosion-product films formed on the P110SS steels. An X-ray diffraction was used to analyze the phase compositions of the corrosion products. The electrochemical performance of the films was investigated using electrochemical impedance spectroscopy and potentiodynamic polarization curves. The results showed that tensile stress could hinder the formation of corrosion-product films; the integrity and compactness of the films worsened, but the phase compositions of the films did not change. The applied tensile stress resulted in a smaller grain size of the corrosion-product films, and the grain boundaries increased. In addition, owing to the induced tensile stress, the charge transfer resistances decreased, and the corrosion current densities increased for the P110SS steels with corrosion-product films in a 3.5 wt.% NaCl solution saturated with CO2.

Effect of induced ripples on the electronic properties of graphene monolayer: Simulation study

The effect of tensile stress on the electronic properties of pristine graphene mono-sheet was investigated. We applied different stress factors in order to investigate the mechanical and electronic properties of graphene monolayer. As a consequence of the applied tensile stress, different patterns of ripples were created. Whereas, different rippling levels were significantly tuned the electronic properties of the graphene monolayer. For instance, the band gap of graphene monolayer dramatically increased with increasing the tensile stress factor. Moreover, the combined effect of applying tensile stress as well as bending the sheet significantly modified the band gap. However, applying more tensile stress induced a reverse behavior. We highly believe that, controlling local curvatures of graphene monolayer opens up opportunities for strain assisted tuning of local electronic structure such as band gap engineered devices.

High-Frequency Magnetoimpedance (MI) and Stress-MI in Amorphous Microwires with Different Anisotropies

Magnetoimpedance (MI) in Co-based microwires with an amorphous and partially crystalline state was investigated at elevated frequencies (up to several GHz), with particular attention paid to the influence of tensile stress on the MI behavior, which is called stress-MI. Two mechanisms of MI sensitivity related to the DC magnetization re-orientation and AC permeability dispersion were discussed. Remarkable sensitivity of impedance changes with respect to applied tensile stress at GHz frequencies was obtained in partially crystalline wires subjected to current annealing. Increasing the annealing current enhanced the axial easy anisotropy of a magnetoelastic origin, which made it possible to increase the frequency of large stress-MI: for 90mA-annealed wire, the impedance at 2 GHz increased by about 300% when a stress of 450 MPa was applied. Potential applications included sensing elements in stretchable substrates for flexible electronics, wireless sensors, and tunable smart materials. For reliable microwave measurements, an improved SOLT (short-open-load-thru) calibration technique was developed that required specially designed strip cells as wire holders. The method made it possible to precisely measure the impedance characteristics of individual wires, which can be further employed to characterize the microwave scattering at wire inclusions used as composites fillers.

Experimental set up for magnetomechanical measurements with a closed flux path sample

In this article, an experimental procedure is presented to handle magnetic measurements under uniaxial tensile stress reaching the plastic domain. The main advantage of the proposed procedure is that it does not require an additional magnetic core to close the magnetic flux path through the studied sample. The flux flows only in the sample, and no parasitic air gaps are introduced, thus avoiding the use of the H-coil to evaluate the magnetic field, which is often very sensitive and not easy to calibrate. A specimen of nonoriented FeSi (1.3%) sheet (M330-35A) is characterized under uniaxial tensile stress. To validate the proposed procedure, a comparison with the single sheet tester procedure is carried out. The results obtained by the two procedures are in good agreement. Moreover, to illustrate the possibilities offered by the proposed procedure, we confirm some results obtained in the literature. We show that the positive plastic strain leads to a significant degradation of magnetic behavior. An applied tensile stress on a virgin (unstrained) sample leads to a degradation of the magnetic behavior. However, on a pre-strained sample, an applied tensile stress results in reducing the deterioration caused by the plastic strain until a stress value called optimum is attained. Above this threshold, the magnetic behavior re-deteriorates progressively.

Accelerating Cementite Precipitation during the Non-Isothermal Process by Applying Tensile Stress in GCr15 Bearing Steel

In this work, the non-isothermal process of GCr15 bearing steel after quenching and tempering (QT) under different tensile stress (0, 20, 40 MPa) was investigated by kinetic analysis and microstructural observation. The Kissinger method and differential isoconversional method were employed to assess the kinetic parameters of the microstructural evolution during the non-isothermal process with and without applied stress. It is found that the activation energy of retained austenite decomposition slightly increases from 109.4 kJ/mol to 121.5 kJ/mol with the increase of tensile stress. However, the activation energy of cementite precipitation decreases from 179.4 kJ/mol to 94.7 kJ/mol, proving that tensile stress could reduce the energy barrier of cementite precipitation. In addition, the microstructural observation based on scanning and transmission electron microscopy (SEM and TEM) shows that more cementite has formed for the specimens with the applied tensile stress, whereas there is still a large number of ε carbides existing in the specimens without stress. The results of X-ray diffraction (XRD) also verify that carbon in martensite diffuses more and participates in the formation of cementite under the applied tensile stress, which thus are in good agreement with the kinetic analysis. The mechanisms for the differences in cementite precipitation behaviors may lie in the acceleration of carbon atoms migration and the reduction of the nucleation barrier by applying tensile stress.

Disappearance of Martensitic Strengthened-Micro-Texture in Modified 9Cr-1Mo Steel Caused by Stress-Induced Acceleration of Atomic Diffusion at Elevated Temperatures

Modified 9Cr-1Mo steel is a heat-resistant steel developed for a steam generator in a FBR (Fast Breeder Reactor) and it has been applied to various thermal power plants. Recently, it was found that the fatigue limits did not appear up to 108 cycles at temperatures higher than 500oC. The reason for the decrease of the fatigue life was attributed to the change of the initially designed microstructure of the alloy. The initially dispersed fine lath martensitic texture disappeared at temperatures higher than 500°C, when the magnitude of the applied stress exceeded a certain critical value. In order to explicate the dominant factors of the change quantitatively, the change of the microstructure and the strength of the alloy were continuously observed by applying an intermittent fatigue and creep tests at elevated temperatures and EBSD analysis. It was found that there was a critical stress which caused the microstructure change at each test temperature higher than 500°C, and the activation energy of the change was determined as a function of temperature and the applied tensile stress. The dominant factor of the micro structure change was the stress-induced acceleration of the atomic diffusion of the component element of the alloy.

Thermo-Elasto-Plastic Analysis of Pearlitic Transformation Plasticity under Combined Bending-Tensile Loading

In a previous study, we showed the anisotropy of plastic strain due to the pearlitic transformation and proposed a hydrostatic pressure-dependent constitutive equation to describe this phenomenon. In the present study, we assess the validity of this model using a bending-tensile loading system to experimentally and numerically analyze and characterize the pearlitic transformation plasticity. First, the maximum bending deflections due to the austenite-pearlite transformation were measured under different loadings and then transformation-plasticity coefficients were determined. Furthermore, as was done for bending-tensile loading tests, the pearlitic transformation plasticity was simulated using Abaqus Standard under the same austenitization and loading conditions as in experiments, and the calculated results for pearlitic-transformation plastic deformation are compared with the experimental results. The results show that the transformation plastic deflection due to the pearlitic transformation decreases with increasing applied tensile stress. In addition, this behavior can be described by a hydrostatic pressure-dependent model in large-deformation theory.