L.J. Qiao

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.

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 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.

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 ...

Correlation between passive film-induced stress and stress corrosion cracking of α-Ti in a methanol solution at various potentials

Abstract The flow stress of a specimen of α-Ti before unloading is different with the yield stress of the same specimen after unloading and forming a passive film through immersing in a methanol solution at various constant potentials. The difference is the passive film-induced stress. The film-induced stress and susceptibility to stress corrosion cracking (SCC) in the methanol solution at various potentials were measured. At the stable open-circuit potential and under anodic polarization, both film-induced tensile stress σ p and susceptibility to SCC had a maximum value. The film-induced stress and SCC susceptibility, however, decreased steeply with a decrease in potential under cathodic polarization. When the potential V ≤−280 mV SCE , the film-induced stress became compressive; correspondingly, susceptibility to SCC was zero. Therefore, the variation of film-induced stress with potential was consistent with that of susceptibility to SCC. A large film-induced tensile stress is the necessary condition for SCC of α-Ti in the methanol solution. The symbol and amount of the film-induced stress were related to the compositions of the passive film, which have been analyzed using the X-ray photoelectron spectrum (XPS).

Failure modes after exhaustion of dislocation glide ability in thin crystals

The changes of microstructures after the exhaustion of dislocation glide ability but before cracking, as well as microcrack initiation by them, were studied in detail byin-situ transmission electron microscopy (TEM) for pure copper, aluminum and iron. Thinning occurred in the thicker regions through dislocation gliding in the three metals. After that, {111} 〈112〉 twinning or tensile cracking took place in thinned zones in fcc metals. In the case of twinning, new microcracks were initiated along another {111} plane by the high stress concentration near the growing tip of the twin, while in iron (bcc), many nanocracks were initiated in the thinned areas just ahead of the crack front, resulting in misorientation microstructure from which microcracks or microvoids were developed.

Correspondence between hydrogen enhancing dezincification layer-induced stress and susceptibility to SCC of brass

Dezincification layer formed during corrosion or stress corrosion cracking (SCC) of brass in the ammonia solution could induce an additive stress. The effect of hydrogen on the dezincification layer-induced stress and the susceptibility to SCC were studied. The dezincification layer-induced stress was measured using the deflection method and the flow stress differential method. The susceptibility to SCC was measured using a slow strain rate test. Results showed that both the dezincification layer-induced stress and the susceptibility to SCC increased with increasing hydrogen concentration, and the hydrogen concentration dependence of the susceptibility to SCC was in a good agreement with that of the dezincification layer-induced stress. Hydrogen in brass facilitates the selective dissolution of Zn in the ammonia solution, and then enhances the dezincification layer-induced stress.

Delayed fracture of lead zirconate titanate ferroelectric ceramics under sustained electric field

In this letter, we report on delayed fracture of lead zirconate titanate ceramics with a Zr/Ti ratio of 52/48(PZT-5) ferroelectric ceramics in silicon oil under sustained electric field, and that in silicon oil or moist atmosphere under sustained mechanical load. The experimental results show that sustained electric fields may cause delayed fracture of PZT-5 ceramics and there is a threshold field for the delayed fracture. The threshold electric field is less than one third of the critical electric field to cause instant fracture and is also half of the coercive field of the PZT-5 ceramics.