Key Engineering Materials Vols. 434-435

Abstract: A functionally gradient piezoelectric actuator based on PbNi1/3Nb2/3O3-PbZrO3-PbTiO3 (PNN-PZ-PT) system was prepared. The cantilevered actuator consists of a high piezoelectric & low dielectric layer, a low piezoelectric & high dielectric layer and a thin middle diffusion layer. Frequency dependences of impedance were measured from 100Hz to 3MHz. The resonance modes were characterized. A number of low frequency modes were observed and identified as bending resonance. The dimension dependence of resonance frequency of bending resonance was investigated. The results of the measurement were compared with calculated values. There is a good agreement between the determined resonance frequencies and calculated values.

Abstract: One of the fabrication methods for functionally graded materials (FGMs) is a centrifugal method, which is an application of the centrifugal casting technique. In the method, a centrifugal force applied to a homogeneous molten composite assists the formation of the desired gradation. The compositional gradient is then achieved primarily by the difference in the centrifugal force produced by the difference in density between the molten metal and solid particles. The centrifugal method has the advantage that it is possible to fabricate large size products with low cost. However, disadvantage of the centrifugal method is the difficult for the gradual distribution of small particles. In this study, we proposed a novel fabrication method, centrifugal mixed-powder method, by which we can obtain FGMs containing nano-particle. On first of this processing, powder mixture of functional nano-particle and matrix material is inserted into rotating mold. After that, matrix ingot is melted in crucible and then the melt is poured into the rotating mold with powder mixture. At that time, powder of matrix material is melted by matrix melt poured from crucible. Finally, an FGM ring with functional nano-particles distributed on its surface is obtained. Using this processing method, Al-based FGMs containing TiO2 nano-particles or SiC particles on its surface were fabricated.

Abstract: To enable sintering net-shape capabilities, a novel procedure for the fabrication of net-shape functionally graded composites by electrophoretic deposition and sintering are developed. The initial shape of the green specimen produced by electrophoretic deposition is designed in such a way so that the required final shape is achieved after sintering-imposed distortions. The shaped components can be metals, ceramics, polymers, and their combination as long as the material is in the form of powders. Through adjustment of an externally applied electric field and the shielding of electrical filed, the particles in the slurry are selectively deposited onto the porous mold which defines the desired geometry. By changing the slurries’ composition, the deposited component’s composition can be precisely tailored.

Abstract: Site-selectively array of single walled carbon nanotubes (SWCNTs) is one of the key points for the fabrication and application of nanodevices. This research is focused on developing a technology to assemble site-selective high density SWCNTs on flexible substrate. Patterned SWCNTs were assembled on flexible poly (ethylene terephthalate) (PET) substrate via inducing directed charge (DC) field. In this process, the modification of hydrophilic or hydrophobic substrate surface is accomplished by selective ultraviolet (UV) irradiation, and which is very important to the self-assemble behavior and accurately site-selective location of SWCNTs. This method, a composition of “Top-Down” approach and “Bottom-Up” approach, is expected to give a way for the fabrication of nanodeivces and nanosystems.

Abstract: The joining of high temperature structural ceramics to other materials is an important process commercially and technologically. Due to the existence of physical and economic limitations for the manufacture of large parts, joining is essential. Functional gradient materials (FGMs) are designed to exhibit a desirable gradient in a property, due ether to a gradient in composition, or microstructure, or both. In this paper, Si3N4-Al2O3 functional gradient joining material was prepared by hot press sintering of multilayered FGMs with 20 layers of thickness 400um each using β-Sialon as transient interlayer. The structure and properties of the materials were analyzed by the means of scan electron microscopy(SEM), X-ray diffraction(XRD) and micro-sclerometer. The components of the materials have gradient distribution and successional. The microhardness is gradient changing with the change of micro-structure. The interface between layers is tightly coupling and has no stress convergence. The test of thermal shock and fatigue cracks of FGM between 1300 °C and 900 °C show good properties of thermal stress relaxing and resistance for high temperature.

Abstract: The MoSi2 nanocrystal was prepared by mechanical alloying (MA) large particle-sized starting powders, in which the milling time is much longer than usual MA time. It was found that the Mo-Si powder mixture mixed at stoichiometry proportion forms α-MoSi2 and β-MoSi2 in the MDR mode rather than pure α-MoSi2 in the SHS mode. The grain size of MoSi2, calculated using Scherrer′s formula, is 18nm when milled for 96h, and decreases to 12nm when further milling to 144 h. This is because that the milling balls provide enough energy to refine most of the rough crystal grain. The average grain size increased to 15nm when milled for 192 h, which indicates that further expand time could not refine the crystal grain while cause the growth of a part of the crystal grain. The particle size of MoSi2 is about 0.5μm when milled for 96 h and the agglomerating phenomenon is severe. The particle size of MoSi2 decreases to 0.4μm and releases the agglomerating phenomenon with the milling time for 144 h.

Abstract: A cylindrical standing wave ultrasonic motor using cantilever type bending transducer is proposed in this paper. There are four cantilevers outside the cylinder, and four PZT ceramics are set on each end surface of cantilevers. The bending mode of cylinder is excited by the bending vibration of transducers. Thus, a linear simple harmonic motion is achieved at the particle on the tooth. The working principle of proposed motor is analyzed. The cylinder and transducer are designed with FEM. The bending vibration modals of transducer and cylinder are degenerated. The transient analysis is developed to gain the vibration characteristics of stator, and the results indicate the proposed motor has potential good output characteristics. The results of this paper verify the theoretical feasibility and provide instructions for the development of proposed motor.

Abstract: A double driving feet linear ultrasonic motor using longitudinal vibration transducer is proposed in this paper. The stator of proposed motor contains a horizontal transducer and two vertical transducers. The horizontal transducer includes two exponential shape horns located at the leading ends, and each vertical transducer contains one exponential shape horn. The horns intersected at the tip ends where located the driving feet. The horizontal and vertical vibrations of driving feet are generated by the longitudinal vibrations of horizontal and vertical transducers, respectively. Longitudinal vibrations are superimposed in the stator and generated elliptical motions at the driving feet. The two vibration modals of stator are gained with FEM, and the resonant frequencies of two vibration modals are degenerated by adjusting the structural parameters. Transient analysis of piezoelectric coupling states the good and strong elliptical motions of driving feet, and verifies the theoretical feasibility of proposed motor.

Abstract: The influence of input power on the spayed powder and final coating was quantified for particular case of water-stabilized plasma spray torch (WSP®) and ceramic coating formed from titanium dioxide (TiO2). All other spray setup parameters were fixed during the experiment with electric supply power as the only variable factor. In-flight particles were characterized by Doppler particle velocimetry, microstructure of the coatings was observed by microscopic techniques and computer image analysis and phase composition was studied by X-ray diffraction. Various mechanical properties were measured – microhardness, surface roughness and wear resistance in a slurry. The results indicate that the higher power means better coating quality – its microstructure and mechanical performance. This substantial difference has the same trend for both power supplies utilized for the testing.

Abstract: Silicon nitride ceramics with MgSiN2 as additives were sintered by hot pressing at 1600° ~ 1750 °C for 1-12 h under uniaxial pressure of 20 MPa. The specimens were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and photothermal deflection spectroscopy. After sintered at 1750°C for 1 h, the thermal conductivity of the material was 90 W·m-1·K-1. The thermal conductivity could remarkably increase to 120 W·m-1·K-1 by prolonging the dwell time from 1 h to 12 h. The present work demonstrated that MgSiN2 additives were effective to improve the thermal conductivity of β-Si3N4 ceramic.