Key Engineering Materials Vols. 353-358

Abstract: As silicon ICs continue to scale down, several reliability issues have emerged. Electromigration- the transportation of metallic atoms by the electron wind- has been recognized as one of the key damage mechanisms in metallic interconnects. It is known that there is a threshold current density of electromigration damage in via-connected lines. The evaluation of the threshold current density is a matter of the great interest from the viewpoint of IC reliability. In this study, Al polycrystalline lines with two-dimensional shape, i.e. angled lines are experimentally treated for the evaluation. Comparing the experimental result with that of straight-shaped line, the effect of line-shape on the threshold current density of electromigration damage is discussed.

Abstract: This paper studies the crack propagation at Sn37Pb-copper interface in push-pull low cycle fatigue. Bonded specimens of Sn37Pb and copper having notch holes with different distances from the interface were fatigued at 313K and the crack propagation paths were observed. Cracks propagated at the interface when the notch hole was near the interface but propagated in the solder when the notch hole was away from the interface. The propagation rate of the interfacial crack was faster than that of non-interface crack. The crack path and crack propagation rate of the two types of cracks were discussed in relation to J integral range calculated by finite element method.

Abstract: ZnO is an n-type semiconductor having a hexagonal wurzite structure. ZnO exhibits good piezoelectric and optical properties, and might be a good candidate for an electroluminescence device like an UV laser diode. Then, these devices are very small, their films are very thin and they are prepared in the limited size and shape, so they are unsuitable for the extensive mechanical testing. In this present work, ZnO thin films are prepared on the glass, GaAs(100), Si(100) and Si(111) substrates at various temperatures by the pulsed laser deposition (PLD) method. ZnO thin films were evaluated by X-ray diffraction (XRD) and mechanical properties such as hardness and elastic modulus were measured through the nano-indenter.

Abstract: This study is to present a numerical investigation on fragmentation and perforation of concrete slab by hard projectile using discrete particle approaches. Discrete Element Method (DEM) and Discontinuous Deformation Analysis (DDA), the two representative discrete particle approaches, are employed to simulate a normal perforation of concrete slab by a hard ogival-nose shaped projectile, and the phenomena of spalling, plugging and scabbing are reproduced.

Abstract: In this paper, the fractal characterization of the sealing surface topography of metallic gaskets was studied. The influence of the compressive stress on the fractal parameters was also investigated. It’s found that the sealing surface of metallic gaskets is fractal, and its topography can be characterized by the fractal dimension and the scale coefficient. The leakage model of metallic gaskets was established. The research results indicate that the larger the fractal dimension is, and the less the scale coefficient and the non-contact area are, the better the sealing performance of metallic gaskets is.

Abstract: Al-Ti-C grain refiners have been prepared by combining self-propagating high-temperature synthesis (SHS) technique and melting-casting method. Effects of Al powder size and C/Ti ratio on the microstructures and grain-refining efficiency of Al-Ti-C grain refiners were studied by OM, XRD, SEM and EDS. The results show that when Al powder size is fine, and C/Ti ratio is 1: 8, SHS reaction among the mixed powders can easily carry on in the melt. As a result, the prepared grain refiner consists of blocky Al3Ti and fine TiC particles distributed in Al matrix, and exhibits excellent grain refining performance on commercially pure Al.

Abstract: The cooling medium choice is restricted due to no detailed regulations for temperature control as the specimen with gaseous cooling medium in the API, ASTM and the standards or specifications of China. The analysis and calculating are made to the physical process of the cooling. The preservation hold time are provided for DWTT specimen at different temperature in the gaseous cooling medium. It provide primary sustaining base to control the cooling process of gaseous cooling medium. The essential point of the precise means of temperature testing is brought forward at the same time.

Abstract: While the fact that abrasion leads to change of surface topography is taken into consideration, the influence of spring pressure both on leakage rate and on friction characteristic of contacting mechanical seals are investigated by fractal theory. Several GY-70 type mechanical seals are tested. Both theoretic analysis and test results indicate that the friction will be more serious because lubrication medium between two end faces reduces as spring pressure increases, though the increase of the spring pressure may not be enough to change the face friction state of mechanical seal. There is an optimum spring pressure for mechanical seal operation. Under different operating conditions, identical type mechanical seals may possess different spring pressure. Appropriate selection of spring pressure is key to the mechanical seal operation under the best condition.

Abstract: The twin shear strength criterion has been proposed to consider the intermediate principal stress effect on the rock mass strength. The unified rock mass strength criterion could consider the intermediate principal stress effect on the rock mass strength. The unified rock mass elasto-plastic material model is implemented in ABAQUS user interface. As a case for study, the stability analysis of Dongjusi railway tunnel within hard rock mass is studied using the unified rock mass strength material. For comparison, the Hoek-Brown empirical strength criterion is also chosen for the rock mass material modeling. The computation results show that the plastic zone calculated using the unified rock mass strength criterion is smaller than that using the Hoek-Brown empirical strength criterion. The railway tunnel lining structure is designed according to the unified rock mass strength criterion and greatly makes use of the rock mass potential strength, which decreases engineering cost.

Abstract: Large numbers of experimental results show that carbides Me3C (Me means Fe, Ni, Co, Mn) are the primary carbon source to form diamond structure under the high temperature and high pressure (HPHT). In this paper, based on the empirical electron theory of solids and molecules (EET), the valence electron structure (VES) and interface structure factors of diamond and various carbides are calculated, and the boundary condition of electron movement in the improved Thomas- Fermi-Dirac theory by Cheng (TFDC) is applied to the carbide/diamond interfaces. It is found that the electron density of crystal plane in Me3C formed by C-C bonds is continuous with that in diamond at the first order of approximation. Compared with Ni-based carbides [Ni3C, (NiMn)3C)], the electron density difference of Fe-based carbides [Fe3C, (FeNi)3C, (FeMn)3C]/diamond interfaces is lower, and that of (FeNi)3C/diamond interface is minimum. The results show that the energy needed to transform carbon atomic groups into diamond structure is lower for Fe-based carbides than Ni-based carbides.