Yi-chun Zhou

Wavelet analysis of acoustic emission signals from thermal barrier coatings

The wavelet transform is applied to the analysis of acoustic emission signals collected during tensile test of the ZrO2-8% Y2O3 (YSZ) thermal barrier coatings (TBCs). The acoustic emission signals are de-noised using the Daubechies discrete wavelets, and then decomposed into different wavelet levels using the programs developed by the authors. Each level is examined for its specific frequency range. The ratio of energy in different levels to the total energy gives information on the failure modes (coating micro-failures and substrate micro-failures) associated with TBCs system.

Dependence of crystalline, ferroelectric and fracture toughness on annealing in Pb(Zr0.52Ti0.48)O3 thin films deposited by metal organic decomposition

Crystalline, electric and fracture properties of Pb(Zr0.52Ti0.48)O3 (PZT) thin films are strongly affected by annealing temperatures in rapid treatment annealing (RTA) of metal organic decomposition (MOD). X-ray diffraction (XRD), RT66A standard ferroelectric analyzer and Vickers indentation method were used to investigate the crystalline, ferroelectric and mechanical properties, respectively. PZT thin film with complete perovskite structure and best ferroelectric property can be obtained at 750 °C, however the fracture toughness was weaker than the thin films annealed at 600 °C and 650 °C. With the increase of annealing temperature from 600 °C to 750 °C, the remanent polarization and coercive field increased in the ranges 13.8~25.2 (µC/cm2) and 7.2~8.3 (kV/cm) respectively, while the fracture toughness of PZT thin films decreased from 0.49 MPam1/2 to 0.47 MPam1/2.

Determination of damage parameter in particle reinforced metal matrix composite by ultrasonic method

Ultrasonic technique is well known as a powerful tool for characterization of materials. It is typically used to determine the elastic constants of material but rarely to measure the damage parameter of materials [1, 2]. Particle reinforced metal matrix composites (PMMC) are excellent candidates for structural components in the aerospace and automotive industries due to their highly specific modulus, strength, and thermal stability [3]. It is necessary to study the properties of PMMC subjected to the combined loads of thermal and mechanical loads [4]. The damage and failure of SiC particle reinforced metal matrix composite have been studied induced by laser thermal shock and mechanical load [5]. It is found that when the combined loads of applied mechanical load σmax and laser energy density, EJ, were low, i.e., σmax and EJ were lower than the thresholds, there were no damage phenomena observed in the specimen. However, when the combined loads (σmax, EJ) became higher than the thresholds, damage phenomena were observed at the notch-tip of specimen by using scanning electron microscopy (SEM). It was observed that microscopic feature of damage was the voids in the matrix and interfacial debonding. Once the combined loads (σmax, EJ) were up to the high thresholds, the micro-cracks formed in the notched region would grow into macroscopic cracks. The fracture of the reinforcement particle was the dominant damage mechanism for macro-crack propagation. The reinforcements were broken by cracks perpendicular to the loading axis, and the fraction of broken reinforcements increased near the crack tip zone. It is very interesting that although the particles were broken near the macro-crack tip region, there was no damage in the matrix and at the particle/matrix interfaces. In this letter, the damage parameters of PMMC induced by laser thermal shock and mechanical load were quantitatively measured by ultrasonic technique. In order to study quantitatively the damage level, the damage parameter ω is defined as follows [6, 7],

Ferroelectric properties of dysprosium-doped Bi4Ti3O12 thin films crystallized in various atmospheres

Abstract Dysprosium-doped Bi 4 Ti 3 O 12 (Bi 3.4 Dy 0.6 Ti 3 O 12 BDT) ferroelectric thin films were deposited on Pt(111)/Ti/SiO 2 /Si(111) substrates by chemical solution deposition (CSD) and crystallized in nitrogen, air and oxygen atmospheres, respectively. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to identify the crystal structure, the surface and cross-section morphology of the deposited ferroelectric films. The results show that the crystallization atmosphere has significant effect on determining the crystallization and ferroelectric properties of the BDT films. The film crystallized in nitrogen at a relatively low temperature of 650 °C, exhibits excellent crystallinity and ferroelctricity with a remanent polarization of 2 P r = 24.9 μC/cm 2 and a coercive field of 144.5 kV/cm. While the films annealed in air and oxygen at 650 °C do not show good crystallinity and ferroelectricity until they are annealed at 700 °C. The structure evolution and ferroelectric properties of BDT thin films annealed under different temperatures (600–750 °C) were also investigated. The crystallinity of the BDT films is improved and the average grain size increases when the annealing temperature increases from 600 °C to 750 °C at an interval of 50 °C. However, the polarization of the filas is not monotonous function of the annealing temperature.

Computation of deformation-induced textures in electrodeposited nickel coating

The deformation-induced textures in electrodeposited nickel coating were numerically studied. The finite element method (FEM) for polycrystalline was developed based on Taylor model. Then the deformation-induced textures in electrodeposited nickel coating with initial random and lamellar texture were simulated under tensile load. It is found that the initial textures significantly influence the deformation-induced textures. For nickel coating with the initial random textures, when the tensile strain is about 40%, there are some lamellar textures. For nickel coating with the initial lamellar textures, the lamellar texture is more intensity with the increase of the tensile strain. With the increase of the tensile strain in the coating, there are more pronounced element distortion and a more inhomogeneous deformation. Due to the different crystal orientations, the grain-scale roughness is observed. With increasing tensile strain in the coating, the surface grain-scale roughness increases on the free surface. The surface roughness of the coating with initial random texture is lower than that with the initial lamellar texture.

Elastic-plastic solution to stamping thin strip on elastic foundation

An analytical method was proposed to solve the mechanical problems of stamping a thin strip on an elastic foundation. The thin strip was divided into four parts according to its deformation and contact with the punch and the elastic foundation, especially an elastic-plastic part was considered in the deflection of the thin strip. Analytical solutions were derived individually for each part and two models were established with the help of elastic and plastic large deflection theories. Compatibility conditions between the neighboring parts of the thin strip constructed the non-linear equation group. Solutions were carried out by programming with a software. The deformation shape, the membrane force, and the moment and shear force of the deformed thin strip were obtained. The results of the two models were compared. The study shows that the method is effective.

Characterization of ultra-thin Y2O3 films as insulator of MFISFET structure

Abstract The possibility of ultra-thin Y2O3 (yttrium sesquioxide) films as insulator of metal ferroelectric insulator semiconductor (MFIS) structure was investigated. The ultra-thin Y2O3 films with thickness of 10–40 nm were fabricated on p-type Si (100) substrates by molecular beam epitaxy(MBE) in vacuum and subsequently submitted to rapid thermal processing (RTP) in air ambient at 700, 800 and 900 °C for 30 min, respectively. The films were characterized by X-ray diffractometry and Raman spectroscopy. High frequency capacitance—voltage (C—V) characteristics and current—voltage (I—V) characteristics of the Y2O3/Si structure were analyzed. A Raman peak of the Y2O3 thin films was observed at 378 cm−1. From the C—V data, these films exhibit dielectric constants ranging from 13 to 17.28, the hysteresis width (ΔVFB) ranging from 0.07 to 0.22 V and the density of trapped charges ranging from 1.65×1011 to 4.01×1011 cm−2. A leakage current of 4.75×10−8−9.0×10−6 A/cm2 at 1.5 MV/cm was observed. The results show that the Y2O3 buffer layers are suitable for non-volatile MFIS structure field-effect-transistors (FETs) memory application.

ELECTRICAL PROPERTIES OF METAL-FERROELECTRIC-INSULATOR-SEMICONDUCTOR CAPACITORS USING Pt/(Bi3.15Nd0.85)(Ti3−x V x )O12/ Y2O3/Si STRUCTURE

ABSTRACT The metal-ferroelectric-insulator-semiconductor capacitors, fabricated using Pt/(Bi3.15Nd0.85)(Ti3−x V x )O12/Y2O3/Si(100) structure, accommodate a Y2O3 thin film (20 nm) deposited on p-type Si(100) as an insulating layer, and a Nd3+/V5+-cosubstituted bismuth titanate, (Bi3.15Nd0.85)(Ti3−x V x )O12 film prepared by chemical solution deposition as a ferroelectric layer. The capacitors exhibit large clockwise capacitance–voltage memory windows of 2.0, 2.2 and 2.4 V, and low leakage current densities of 7.3 × 10−9, 6.1 × 10−9 and 5.5 × 10−9 A/cm2 at an applied voltage of 6 V for different vanadium contents of 0.09, 0.06 and 0.03, respectively. They are also characterized by good data retention, keeping the high and low capacitance values biased in hysteresis loops distinguishable for a period of over 14.6 days.

A novel design of 0.25μm2.5 V 2T-2C sensing scheme for FeRAM

A novel design of 0.25 μm 2.5V 2T-2C sensing scheme for FeRAM is proposed. The proposed scheme converts the voltage signals between the two bit lines to current signals and compares them using the current-sensing amplifier to realize magnify the read-out signals of 2T-2C FeRAM. The simulation of PSPICE shows that the new sensing scheme is more suitable for low voltage supply applications and the sensing speed is improved.