W.Y. Chu

Giant magnetoelectric effect in Ni–lead zirconium titanate cylindrical structure

The magnetoelectric (ME) coupling of a bilayered Ni–lead zirconate titanate composite structure synthesized by electrodeposition was studied in this paper. The ME voltage coefficient was measured in the range of 1–120kHz as the bias field is parallel to the axial. The results indicate that an electromechanical resonance appears at 59.9kHz. The bilayered cylindrical ME composite exhibits a special field dependence of ME coefficient. Either for the resonant state or the nonresonant state, above 1kOe, the ME voltage coefficient increased linearly with the strengthening of bias field, up to 30V∕cmOe at 8kOe.

In situtem observations of nucleation and bluntness of nanocracks in thin crystals of 310 stainless steel

Nucleation and bluntness of nanocracks were studied through in situ tensile tests for thin crystals of 310 stainless steel by transmission electron microscopy (TEM). A dislocation free zone (DFZ) could form after the dislocation emission had just ceased. The DFZ is an elastic zone so that the local stress near the crack tip in the DFZ is possibly up to the cohesive strength, because of which a nanocrack could initiate in the DFZ or at the crack tip. The nanocrack in the DFZ or at the crack tip would blunt into a void or a notch through the increment and movement of dislocations in the plastic zone even when keeping constant displacement. If constant displacement was kept for a long time, nanovoids could initiate in the DFZ through diffusion and enrichment of supersaturation vacancies. The connection of the nanovoids would result in the initiation of nanocracks.

Ni–PZT–Ni trilayered magnetoelectric composites synthesized by electro-deposition

We reported the high strength of magnetoelectric (ME) coupling of trilayered composites prepared by electro-deposition. The ME coupling of Ni–lead zirconate titanate–Ni trilayered structure was measured in the range of 1–120 kHz. The trilayered composites exhibit high ME voltage coefficient because of good interfacial bonding between piezoelectric and magnetostrictive layers. The peak value of the ME voltage coefficient can be up to 33 V cm−1 Oe−1 at the electromechanical resonance frequency. This magnetoelectric effect shows promise for application in transducers for magnetoelectric energy conversion.

In situ SEM study of formation and growth of shear bands and microcracks in bulk metallic glasses

Abstract Formation and growth of shear bands and microcracks in bulk metallic glasses of Zr 57 Cu 15.4 Ni 12.6 Al 10 Nb 5 and Zr 41.2 Cu 12.5 Ni 10 Ti 13.8 Be 22.5 have been investigated through in situ tensile tests in scanning electron microscope using a single-edge notched specimen. Atom force microscope was used to study the three-dimension pattern of fine shear bands. The results show that besides shear stress, normal stress plays also an important role in forming and growing of shear bands, which appear first during loading. Mode II shear microcrack will initiate and propagate first in the shear planes along shear bands. The mode II cracks will open and become a shallow I+II complex crack because there is a component of normal stress. As soon as the complex crack (or cracks) becomes a mode I crack penetrating the thickness through propagating from the surface (or surfaces) toward the centre, the specimen will fracture immediately.

The effect of anodic polarization on the ambient creep of brass

The effect of anodic and cathodic polarizations on the ambient creep of brass in 3.5% NaCl and CH3COOH + CH3COONa solutions has been investigated. The results showed that the creep rate in both solutions increased linearly with the increase of the anodic current density and was approximately inversely proportional to the square of the radius of the specimen. The de/dt in 3.5% NaCl solution was much higher than that in the CH3COOH + CH3COONa solution at the same anodic current density. The creep rate resulting from dislocation climb induced by vacancy supersaturation during the anodic polarization has been calculated as follows: dϵdt = Kβir2 where K = 8παMϱDsΔtΔr/C0dFZ ln (R/b), and β is a constant related to the degree of de-alloying. The experimental data support the proposed mechanism. Cathodic polarization could also increase the ambient creep of brass by a mechanism related to hydrogen-facilitated local plastic deformation.

Magnetoelectric effect in a Ni–PZT–Ni cylindrical layered composite synthesized by electro-deposition

Magnetoelectric (ME) coupling of a cylindrical trilayered composite was studied in this paper. A Ni?lead zirconate titanate (PZT)-Ni trilayered cylindrical composite was synthesized by electro-deposition. The maximum ME voltage coefficient of the cylindrical ME composite is 35?V?cm?1?Oe?1, about three times higher than that of the plate trilayered composite with the same raw materials and magnetostrictive?piezoelectric phase thickness ratio. The high ME voltage coefficient of the cylindrical composite is due to the self-bound effect of the circle. Moreover, the resulting complex condition can induce a double peak in the field dependence of the ME coefficient.

The correspondence between susceptibility to SCC of brass and corrosion-induced tensile stress with various pH values

Abstract Corrosion-induced stress and susceptibility to stress corrosion cracking (SCC) of brass in an ammonia solution with various pH values have been studied. pH value dependence of corrosion-induced stress measured by two different methods showed a good agreement, and was correspondent to that of susceptibility to SCC. When pH⩾8, with increasing pH value, the corrosion-induced tensile stress had a maximum value and hardly changed; at the same time, the susceptibility to SCC exhibited a maximal value and a slight change. However, when pH⩽6, with decreasing pH value, both the corrosion-induced tensile stress and the susceptibility to SCC reduced rapidly. So, the SCC of brass in an ammonia solution was in close relationship with the corrosion-induced stress.

Humidity effects on (001) BaTiO3 single crystal surface water adsorption

Water adsorption on (001) BaTiO3 single crystal surface under varying relative humidity conditions was studied by ab initio calculations and scanning probe microscopy utilizing different operation modes. At 95% relative humidity water droplets nucleated only on c domains, preferential adsorption location for water dipoles. BaTiO3 (001) surface long 65% relative humidity exposure lead to no contrast between a and c domains observed by electrostatic force microscopy. Ab initio calculations confirm that water molecules prefer to adsorb on c domains due to their higher surface energy.

In-Situ Transmission Electron Microscopic Observation of Corrosion-Enhanced Dislocation Emission and Crack Initiation of Stress Corrosion

Abstract A constant deflection device designed for use within a transmission electron microscope (TEM) was used to study the change in dislocation configuration ahead of a crack tip during stress corrosion cracking (SCC) of brass in water, Ti-24% Al-11% Nb alloy in methanol (CH3OH), and the initiation of SCC. In-situ tensile tests in the TEM also were carried out to assess deformation without the influence of environment. Results showed that corrosion during SCC enhanced dislocation emission, multiplication, and motion as well as produced a dislocation-free zone (DFZ). Nanocracks of SCC initiated in the DFZ or from the crack tip when the corrosion-enhanced dislocation emission and motion reached a certain condition. The action of the corrosion process prompted nanocrack propagation into a cleavage or intergranular microcrack rather than blunting into a void as seen during experiments in the TEM.

Stress Corrosion Cracking Caused by Passive Film-Induced Tensile Stress

Abstract α-Ti foil with a protective layer formed on one side was deflected as a result of corrosion in a methanol (CH3OH) solution containing 0.6 mol/L potassium chloride (KCl) because of tensile ...