Advanced Materials Research Vols. 652-654

Abstract: Optical metallographic examination, scanning electron microscope as well as energy dispersive X-ray spectrometry was operated to the interface of titanium/steel laminates manufactured by explosive welding. Three types of microcosmic defects as brittle Ti-Fe intermetallic compound, shearing crack, and brittle Ti-Fe-O layer were found at the interface of titanium/steel laminates. The reasons for above three microcosmic defects were analysed.

Abstract: Analysis of the causes of welding residual stress and the mechanism of VSR, also give the sufficient condition of the exciting force. Firstly, use the thermal - structural coupling and cell life and death of the welding process simulation, get the welding residual stress. Consistent with the theory. Secondly, build the VSR simulation process based on the use of the harmonic response analysis and welding simulation. select the appropriate VSR process parameters through the simulation results. Finally, VSR process simulation, analysis showed that the peak of residual stress after VSR treatment decreased by about 33%, and achieved good results. The numerical simulation analysis provides a strong basis for rational selection of the parameters of the VSR.

Abstract: The welding temperature field of twin-wire submerged arc welding (SAW) in an X80 pipeline steel welded joint was analyzed using a three-dimensional (3D) finite element (FE) model. Taking into account nonlinear relationships between temperature and mechanical properties, a coupled thermo-mechanical FE solution was used to obtain the temperature distribution for varying set of welding conditions. Effect of welding speed, inter wire spacing on welding temperature field were studied and presented. It is found that welding speed and inter wire spacing play a significant role in deciding the temperature distribution of twin-wire submerged arc welding. Simulation results were well consistent with theoretical analysis.

Abstract: In this paper, experimental investigations on femtosecond laser (pulse duration:164 fs, wavelength:780 nm) micromachining of polycarbonate have been carried out in air. The lateral and vertical machining precision was evaluated by scanning electron microscopy and profilometer. The morphological changes were observed by scanning electron microscopy. The ablation mechanism varied with the laser pulse energy was discussed. The diameter and depth of the ablated crated are influenced by the laser pulse energy and the number of laser pulses. The relation between the diameter and ablation depth of the crater and the key parameters of femtosecond laser is obtained. Femtosecond laser micromachining of polycarbonate have a potential application of the fabrication of polycarbonate-based devices.

Abstract: Recast layer, micro cracks and thermal deformation limited the improvement of the surface quality of laser processing in precision machining of hard and brittle material. This paper presents a new method which combines low-pressure water jet with laser processing. A comprehensive study on the influence of laser processing parameters on surface quality of an Al2O3 ceramic sheet is presented. The experiment was conducted using ND: YAG laser machine and low-pressure water jet was used as assist. The surface quality of normal laser processing and low-pressure water jet assisted laser processing was comparative analyzed using a 3-D microscopy. Experiment proves that the composite processing of low-pressure water jet assisted laser processing can obtain good surface quality, slight moltenslag and thermal deformation, compared with the normal laser processing.

Abstract: Using high power Nd3+:YAG pulse laser for precision cutting stainless sheet, study the effects of the laser cutting technological parameters on quality of cutting surface and joint-cutting width. The data of single factor experiment proved： With the increasing of scanning velocity, the joint-cutting width decreased; the width increased with the increasing of scanning velocity, laser current, impulse frequency and impulse width; the increasing of impulse frequency may improve the processing quality and ultimate cutting speed; the data of two-factors experiment proved: when the output power and impulse width are fixed, the impulse frequency will be increased, the joint-cutting width will be decreased; when the output power and impulse frequency are fixed, the impulse width will be increased, the joint-cutting width will be decreased.

Abstract: A femtosecond laser machine consisting of femtosecond fiber laser, trepanning head, linear motor stages system and Siemens 840D system has been integrated for industry application. The femtosecond laser source is all fiber system which contains a fiber mode-lock laser at 1053 nm with a repetition rate of 3.9 MHz, a double-cladding gain fiber amplifiers and a PCF amplifier. An acoustical modulator has employed to tune repetition rate from 3.9 MHz to 100 KHz. An in-line fiber chirped grating is used to stretch the pulse duration to 700 ps. After the PCF amplifier pulse is compressed to sub-ps with 50% efficiency based two grating compressor. The system outputs an average power of 15 W at 100 KHz and 800 fs. Using four wedges trepanning head, cylinder hole is drilled in 1mm thickness SiC ceramics in 30 s.

Abstract: Laser shock peening (LSP) is widely known as a cold-worked surface treatment, and this technology has been to greatly improve the fatigue life of many metallic components. Our works focused on laser shock peening with Nd: glass laser system (pulse duration 30ns) and square laser spot size of 4mm×4mm for TC17 titanium alloy. Surface morphology, residual stresses and fatigue performance had been studied for TC17 alloy specimens and blades processed by LSP treatment. The results show that plastic strains in shocked dents become more homogeneous than ones produced by original circle spot with gaussian energy distribution. Surface residual stresses which measured using x-ray diffraction method showed different characteristic as varying specimen thickness, and LSP with overlapping ratio of 8% provided uniform residual stresses on peened surface. Low fluence peening which was implemented at borderline of peened surface was effective to diminish the stress gradient. Compared with mechanical shot peening, LSP attained smoother surface, lower microhardness and better fatigue performance. In a word, Square-spot LSP is an excellent way to improve fatigue life of titanium blade.

Abstract: Laser processing glazing ceramics is a new application of laser technique. This article presents the study of laser processing speed of glaze cladding. It found that the laser processing speed affected the morphology of glaze cladding significantly. Within the experimental conditions, rise of processing speed can decrease the depth of melted zone and the width of glaze cladding, vice versa.