Advanced Materials Research Vols. 816-817

Abstract: In DRAM products, the copper interconnections with larger grain size are preferred for lower electrical resistance and better circuit performance. We studied the copper properties which are the evolution of the grain size, distribution of the grain, and the metal line texture formation during self-annealing. And we were able to evaluate the thermal budget in the DRAM process by performing thermal excursion stress test. We found out that the condition with self-annealing time affects copper grain size and stress migration. It has been measured by the EBSD analysis system and TOF-TEM. Compared with the conventional copper anneal process which has no time delay, the self-annealing process with time delay showed the more bamboo microstructure at dram damascene process. In addition, we observed that the self-annealing process helped enhanced thermal stress stability, which is caused by lower hillock deformation to copper top surface after a batch furnace at 400°C, N2 ambient for three times.

Abstract: We investigated the growth and structure properties of C-Mg thin films obtained for the first time by Thermionic Vacuum Arc (TVA) deposition. The TVA technology is suitable for producing nanostructured materials because of the high power density of the vapor plasma generated by accelerated electron flux from the cathode and high energy of the ions incident on the depositing film, both these properties ensuring a high dispersion of the evaporated material. The properties of the deposited C-Mg thin films were investigated in terms of wettability and morphology. The surface free energy (SFE) was determined by means of Surface Energy Evaluation System (See System) indicating a hydrophobic character and the morphology were determined from BF-TEM image performed by Philips CM 120 ST TEM system.

Abstract: Sandwich construction has found extensive application in aeronautical, marine structures and container production due to high strength to weight ratio. This paper documents the compressive strength of Kevlar balsa sandwich structure with epoxy matrix subjected to edge wise compressive loads. Different modes of failure were also observed under the said loading. General modes of failure are buckling, shear crimping, dimpling and wrinkling of faces. In edge wise compression testing of Kevlar balsa sandwich, shear crimping and wrinkling of faces were the modes of failure to be observed, with each mode of failure exhibiting different compressive strength.

Abstract: The layered double hydrotalcites (LDH) with molar ratio Zn:Al=2:1 was prepared by urea method. The mixed oxides were prepared by calcining the LDH at different temperatures and a series of dye-sensitized solar cells were assembled by the corresponding oxides and the dye Ruthenizer 535-bisTBA (N719). The basic parameters were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), thermogravimetric and differential thermal analysis (TG-DTA) and UV-Vis absorption spectrum. The photovoltaic behaviors of solar cells were characterized and the best efficiency was 0.015% when the calcining temperature was 500°C.

Abstract: The effects of spindles vibrational behavior on the stability lobes and the chatter behavior of machine tools are discussed. Multi-segment spinning spindle models, developed based on the Euler-Bernoulli beam bending theory, have revealed that the system exhibits coupled Bending-Bending (B-B) vibration and its natural frequencies are found to decrease with increasing spinning speed. It has also been observed from the experimental data that an average spindle goes through three stages of operation, namely settling, normal operation and failure. As spindle fundamental frequency changes, the stability lobes change, i.e., the originally selected cutting parameters could lead to chatter. It is shown that using the experimental results, it is possible to establish an expression for the variation of spindle's fundamental frequency in terms of machine hours, which can in turn be used to predict chatter-free cutting parameters through calibrated models and the stability lobes.

Abstract: Acicular ferrite (AF) can significantly improve the performance of steels and can be promoted through special inclusions. The present experimental steel was a low carbon Ti-Zr deoxidized and microalloyed steel. The welding heat affected zone (HAZ) simulation indicated that under high heat input (100 kJ/cm) and peak temperature (1400°C) conditions, the HAZ exhibited high impact toughness (150 J, -20°C) and desired microstructure. Isothermal heat treatment data suggested that grain boundary ferrite formed at ~600°C and AF formed at ~500°C. Intragranular plates sheaves formed at ~450°C. MnS coherent precipitation on ZrO₂TiO_x inclusions promoted AF nucleation.

Abstract: With the weight-reduction requirement for transportation tools, more and more carbon fiber reinforced plastics (CFRPs) will be applied. It is known that the plastics will have a brittle fracture under impact loads, and therefore, their resistance capability on impact damage is a crucial factor which restricts the application of CFRPs. The present paper studies the impact damage and residual stiffness of the CFRPs through experiments. The identical specimens were impacted repeatedly by pendulum with a specified constant energy, and then, their residual bending stiffness and strength were measured by three-point-bending tests. Finally, the relationship between the residual stiffness and impact numbers were established. The results will be used in damage-based stiffness predition for CFRPs material and structures.

Abstract: Selective laser melting (SLM) is a relatively new additive manufacturing (AM) technology which uses laser energy for manufacturing in a layered pattern. The unique manufacturing process of SLM offers a competitive advantage in case of very complex and highly customized parts having quasi-static mechanical properties comparable to those of wrought materials. However, it is not currently being harnessed in dynamic applications due to the lack of reliable fatigue data. The manufacturing process shows competitive advantages particularly in the aerospace and medical industry in which Ti-6Al-4V is commonly used, especially for high performance and dynamic applications. Therefore, in this exploratory research, high cycle fatigue (HCF) tests were performed for as-built, polished and shot-peened samples to investigate the capability of SLM for these applications. As-built samples showed a drastic decrement of fatigue limit due to poor surface quality (R_a ≈ 13 µm) obtained from the SLM process. Polishing improved the fatigue limit to more than 500 MPa, the typical value for base material. The effect of shot-peening proved to be antithetical to the expected results. In this context, fractographic analysis showed that very small remnant porosity (less than 0.4%) played a critical role in fatigue performance.

Abstract: This paper presents a general calculation method of steel hardenability. First use non-linear fitting method to establish a general relationship between hardenability coefficient and end-quench distance, and then use SVM method to establish the relationship between alloying elements and hardenability coefficients. It solves the limited applicability and poor precisions problems of the currently applied calculation methods for hardenability. It gives an enhancement scheme to make sure the accuracy of the model when the data are not complete enough. Experimental data show that using this method can effectively improve the hardenability prediction accuracy and can be widely used.

Abstract: Since the generation of prestressed concrete, the causes for losses of prestress have been always analyzed and studied and many achievements are made. However, as the losses of prestress result from many factors, it is very complicated to calculate various losses of prestress accurately. The formulas and methods used in the concrete codes of various countries for calculation of prestress losses vary according to their different purposes. This paper focuses on US code ACI 318-05, Eurocode EN 1992-1-1 and Chinese code GB 50010-2010 (the code for design of concrete structures), and carries out a comparative analysis in terms of losses of prestress for the three codes above.