Materials Science Forum Vols. 675-677

Abstract: 7075 matrix alloy was fabricated by in-situ reaction liquidus curve casting method, and its as-cast microstructure was analyzed, the wear properties of these composites and matrix alloy were studied under the different conditions. The results show that the wear resistance of TiC/7075 composites is superior to 7075 matrix alloy in the same conditions (with same load or rotating velocity). Because of introduction of particle reinforcements, the wear resistance of the composite is enhanced by 1.5～4 times than that of its matrix. In addition, the wear mass loss of TiC/7075 composites increases almost with increase of load, but decreases with increase of rotating velocity. The wear resistance of the composites increases slightly at low load and high rotating velocity. The SEM analysis of the worn-out surface indicates that the wear mechanism of TiC/7075 composites is mainly abrasive wear.

Abstract: The paper studied the preparation of Al-Sc alloy by molten salt electrolysis. LiF-ScF3-ScCl3 as the electrolyte, Sc2O3 as raw material, liquid Al as cathode and graphite as anode. The process condition of preparating Al-Sc alloy includes the influence of current density, electrolysis time, temperature of electrolysis, Back EMF, content of Sc in alloy and current efficiency.The content of Sc in alloy prepared by this method has reached to the maximum of 3.437%. The components of alloys showed by SEM were uniform, it is applicable for commercial purposes. Preparation of Al-Sc alloys with scandium oxide as raw materials, it not only reduce environment pollution, but also decease the cost of production. It is reported in many documents, preparing aluminum base alloy by the method of molten salt electrolysis[1-3], people could make many alloys such as Al-Ce、Al-La、Al-RE、Al-Ti、Al-Si-Ti in the aluminum cell, also the method to prepare some rare earth alloys such as Al-Sr、Nd-Fe、La-Ni was reported[4,5]. Use the method of electrolysis to produce some aluminum base alloy with high-melting-point , difficult to restore , high-priced element is a good method because it is technological process is brief, economy is rational, the technology is feasible, this viewpoint is broadly approved in the world[6]. It isn’t necessary to use high-priced Sc as raw material in preparing Al-Sc alloy with molten salt electrolysis, it could control the Sc amounts in the alloy through the different current efficiency and electrolysis time, production in this method could be continuous or semi-continuous, so it is easy to be automatic controlled. A new molten salt system is used in this paper, we use molten salt electrolysis to produce Al-Sc alloy, take scandium oxide as raw material, through the study of the effect of the current intensity，electrolysis time and the electrolysis temperature , Back EMF and cell voltage, the final production Al-Sc alloy contains Sc 2~6%.

Abstract: Piezoelectric micromachined ultrasonic transducers (pMUTs) have been investigated as a promising new approach for ultrasound generation and reception. Most of the reported pMUTs employs a unimorph structure of a micromachined piezoelectric thin film on a silicon membrane. In this paper, a dome-shaped model for piezoelectric micromachined ultrasonic transducer (pMUT) was proposed to replace the conventional unimorph structure. A finite element analysis was carried out to study the elecro-mechanical behaviour of the dome-shaped model. The result showed that a considerable improvement of electro-mechanical coupling performance was achieved with the new model.

Abstract: The PZT-based electro-mechanical (E/M) method was utilized to measure the impedance of a 1-D steel beam with cracks introducing and developing. Quantitatively assessment of cracks was made by using damage metrics Root Mean Square Deviation (RMSD) and Covariance (Cov). Changes in the coupled impedance of PZT and the beam (500mm×20mm×6mm) were investigated during the appearance and extension of cracks. With the depth of crack dc increasing from 0.6mm to 1.8mm, the peaks of impedance spectrum shifted to lower frequency in the frequency range of 182 kHz-370 kHz and the amplitude showed a decreasing tendency. Moreover, the initial crack brought more significant changes in impedance than that from the developing of cracks. The relationships between dc and RMSD/Cov were investigated. It was proved that RMSD and Cov were efficient in quantitatively presenting the extension of cracks on the 1-D beam.

Abstract: In this paper, the exact solutions of PZT coupled electric impedance and structure mechanical impedance were derived with the investigation of the dynamic interaction between the PZT and the host structure. In the frequency range of 0.1-120 kHz, numerical simulation of the PZT coupled electric impedance was performed using MATLAB code. Experimental investigations were conducted with a PZT excitation and electric impedance measurement system developed by our laboratory in the frequency ranges of 30-55 kHz and 80-100 kHz. The profile and resonant frequencies of predicted and measured impedance frequency spectra were in close agreement and the largest deviation is 0.402%.

Abstract: A Ti-50at%Pt alloy synthesized using the spark plasma sintering (SPS) technique has been characterized for phases’ identification. TiPt alloys have potential use as high temperature shape memory alloys(HTSMAs). Test specimens were prepared at SPS temperature of 1300°C. Sintering pressure and time were varied. The microstructural features of the specimens were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electron microscope used was equipped with an EDS detector, that, together with the XRD, were used for both the identification and analyses of the phases in the starting materials and the sintered alloys. High temperature XRD (800 -1300°C) as well as ambient temperature XRD analyses were done on the starting mechanically alloyed powders. All the samples tested at elevated temperatures were subsequently tested at room temperature after cooling. XRD analyses of the sintered samples were all done at room temperature. Analyses of the XRD results revealed new distinct phases from a temperature of 1000°C. A comparison of the room temperature XRD results for alloy powders and that of the sintered alloys was made. The following phases have been identified and studied TiPt B2, TiPt B19, Pt3Ti, Ti3Pt and Pt5Ti3. SPS pressure and sintering time did not show much effect on the phases detected. The alloy composition was found to be very inhomogeneous.

Abstract: The paper presents a new design concept for evaluating the mechanical strength of unidirectional composite material with shape memory alloy (SMA) fiber in the presence of matrix crack. NiTi SMA fiber with both ends knotted is used to actively control the composite strength instead of straight fiber for purpose of better ensuring stress transfer from the matrix to the fiber. Experiment is conducted to verify the effectiveness of this new design concept.

Abstract: According to micromechanics, consider the porous shape memory alloy (SMA) as a composite-sphere model. Isolate a constant thickness spherical shell which is composed of SMA, and is traction free on its inner surface and subjected to the uniform hydrostatic pressure and the deviatoric stress on its external surface. Then, a constitutive model for porous SMA considering hydrostatic stress is proposed by elasticity solution. The stress distribution of the spherical shell was calculated. Corresponding to different applied stresses, the spherical shell is divided into different regions of pure austenite, pure martenite, and austenite/martensite mixture under isothermal circumstances. The martensite volume fraction is then obtained. The predicted results have been compared with the obtained experimental data by Zhao and Sia Nemat-Nasser. It shows that the modeling results are in good agreement with the experiments and the initial phase transition point for porous SMA is lower than the dense SMA.

Abstract: In this paper, radial impact responses of TiNi phase transformation cylindrical shell were experimentally studied on two-directional constraint. The nominal load-displacement curve was gained by advanced SHPB; meanwhile, the deformation process of the cylindrical shell was recorded by the high speed camera (30000 fps). The effect of stress wave on the whole structure during load process was as follows: the load-displacement curve fluctuated fiercely and rose gradually in the beginning period, whose frequency was basically the same as that of the stress wave propagation in the Striker 2; After that, the load-displacement curve tended to flat, the shell structure became to be ellipse as the compression increases, and the whole unload process slowed down. Finally, the surface strain was obtained by processing the shell deformation image, and the dynamic effect of the material phase transition and phase transition hinge on the cylindrical shell was examined.

Abstract: The <110> grain oriented alloy was grown by zone melting directional solidification technique. The strain-stress curves of Tb0.3Dy0.7Fe2 <110> oriented alloy in different magnetic fields have been measured and the magnetic field dependence of Young’s modulus under different compressive stress has been confirmed. It is found that Young’s modulus gradually decreases with increasing the magnetic fields when the compressive stress is in the range of 15-25 MPa and changes a little in the range of 40-50 MPa. The experimental result indicates that the magnetic field has a marked effect on the Young’s modulus of the Tb0.3Dy0.7Fe2 <110> oriented alloy at a low compressive stress and its change should be considered during the design of magnetostrictive devices.