Materials Science Forum Vols. 532-533

Abstract: A system is developed on a 5-axes automatic scanning for ultrasonic test. It is a system with the host-slave and open-loop mode that contains PC and a 5-axes drive card based on single chip microcomputers. The system drives five stepper motors to carry the detector moving paralleling the normal direction of the detected surface to complete the detect task.

Abstract: In order to obtain the projections with short cracks, a novel subvoxel model is proposed for short crack simulation. Short cracks are modeled in subvoxel space. Giving an initial subvoxel as an initial cracking point, a short crack is simulated according to the random growing mode. If there are multiple initial cracking points, multi-cracks can be simulated easily, and short cracks are visualized using CT. Limited by the resolution of real CT system, it is not possible to detect individual short crack but a group of them. By pre-processing the reconstructed images, new images are obtained, which are very close to actual conditions. The differences between the reconstructed images without short cracks and the images with short cracks are analyzed. Experiment results proved that it is feasible to detect short crack behavior by analyzing the grey level variance of the images.

Abstract: Femtosecond laser pulses are irradiated on a single-side polished single-crystalline silicon wafer. Metamorphic zone appears around the ablated zone and the morphology changes gradually in the metamorphic zone. Typical phenomena of thermal ablation such as melt-resolidification and subtransparent glassy materials occur in the marginal area of the ablated zone. No apparent changes are found among microscopic morphologies of the ablated, metamorphic and unirradiated zones. There are flaws and spallations on the smooth back surface of the wafer, which are caused by the stress inside the sample. Nanomechanical properties of the sample surface hardly change in the small scope of the backside around the ablated zone. While regular changes occur in large scope, which is the conjunct result of such stresses caused by many different collateral damages.

Abstract: By means of optical microscope(OM), scanning electron microscope(SEM), X-ray diffraction(XRD) and shear test, the microstructure and mechanical property of 1Cr18Ni9Ti stainless steel brazed joints with BNi-2 filler by electron beam brazing(EBB) and vacuum brazing(VB) are investigated respectively. The results show that, the microstructures of brazed joint with BNi-2 by EBB are mainly solid solutions of Ni. And the microstructures of brazed joint by VB are composed of two parts: one part is a solid solution of Ni, which lies adjacent to base metal; another part is chemical compound structures present in the centre zone of brazing seam. The shear strength of brazed joint by EBB is higher than that of by VB. This is closely related with the microstructures of brazed joint.

Abstract: The photo-polymerization induced by Two-Photon Absorption (TPA) is tightly confined in the focus because the efficiency of TPA is proportional to the square of intensity. Three-dimensional (3D) micro-fabrication can be achieved by controlling the movement of the focus. Based on this theory, a system for 3D-micro-fabrication with femtosecond laser is proposed. The system consists of a laser system, a microscope system, a real-time detection system and a 3D-movement system, etc. The precision of micro-machining reaches a level down to 700nm linewidth. The line width was inversely proportional to the fabrication speed, but proportional to laser power and NA. The experiment results were simulated, beam waist of 0.413μm and TPA cross section of 2×10-54cm4s was obtained. While we tried to optimize parameters, we also did some research about its applications. With TPA photo-polymerization by means of our experimental system, 3D photonic crystal of wood-pile structure twelve layers and photonic crystal fiber are manufactured. These results proved that the micro-fabrication system of TPA can not only obtain the resolution down to sub-micron level, but also realize real 3D micro-fabrication.

Abstract: Experiment setup of femtosecond laser pump probe was established, the time resolution of time-delay setting reached 67fs. By use of femtosecond laser with width of 30fs and wavelength is 796nm the dependence of transient change of reflectivity on delayed time in GaAs was measured by pump-probe method. By calculating the change of complex index of refraction (%n), free-carrier effect, lattice-temperature and carrier recombination contributions to relaxation curve was analyzed. When the carrier density N is 1.44×1018/cm3, free-carrier contribution to refraction index %nFC is -7.33×10-4, lattice-temperature %nLT is 0.85×10-4. Based on recombination rate equation, recombination lifetime of 980ps was deduced.

Abstract: The connotation of ecological economic booster explosive has been defined firstly in this paper. The ecological economic booster explosives green manufacturing process system architecture and a general framework are provided. They are consisted of an assessing method for manufacturing process, a modeling on rational proportioning for booster explosives, a modeling on optimum control parameters of the manufacturing process and the rapid prototyping method of the pellet used in the capability testing.

Abstract: Based on the metal cutting experiments, the forming model of feed direction burr is proposed in the paper, a physical parameter of determining the generating of typeⅠ feed direction burr — critical tool edge angle rI χ is given. And the main factors which influence rI χ are studied by the experiment, and related theory analysis is made. Furthermore, some new controlling methods and technology to restrain or decrease the feed direction burr in machining are developed.

Abstract: The structure and performance of the hardened layer in this paper has been researched by means of transverse feed grinding 40Cr steel on a plane grinding machine, the result shows that under the action of the grinding temperature field, there are different structural change rules and distributing characteristics of micro-hardness. Although there is always a softened band, which is made up of a transitional area and an unhardened area or a temper area in the hardened layer, the reasonable softened band is conducive to the improvement of wear-resistant quality of a hardened layer under the condition of oil lubrication.

Abstract: The purpose of this experimental research are investigation the growth behaviors of the oxide layer at different pre-dressing conditions in ELID pre-dressing, effects of voltage and duty ratio of the power supply, wheel speed on the oxide layer formation characteristics on the metal bond diamond wheel surface. The results indicated that the oxide layer thickness on the wheel surface increase with pre-dressing time. The oxide layer growth rate is faster in beginning period time of pre-dressing process then slow down. Both the thickness and growth rate of oxide layer increase with the increase of duty ratio and applied voltage. It takes longer time for oxide layer growth rate to reach to stable state in lower duty ratio condition than in higher duty ratio condition. There are no effects of wheel speed on oxide layer growth behaviors in the wheel speed range of 1000rpm to 4000 rpm.