Advanced Materials Research Vols. 538-541

Abstract: The butt-joint of 0.3 mm SUS 321 plate was welded successfully by micro-pulse laser and the processing parameters were optimized through orthogonal experimental design. The effect of the processing parameters on the microstructure and mechanical properties of the joint with OM, electronic precision stretching machine and other analysis and detection methods. The results indicate that the butt-joint will possesses highest tensile strength of 550 MPa when the optimized processing parameters are the percentage of pulse power of 18, pulse width of 4 ms, pulse frequency of 2 Hz, and the strength of the joint is 98% to the strength of basic metal. The microstructures of joint with high tensile strength are composed of small equiaxial grains in the weld center zone and columnar grains in fusion zone. The microhardness of the joint is higher than that of basic metal.

Abstract: The silver nanoparticles colloid was prepared by pulsed laser ablation in distilled water under various laser repetition rates. The particles size, morphologies and absorption spectroscopy of the obtained nanoparticles colloids were characterized by ultraviolet to visible (UV-Vis) spectrometer and transmission electron microscopy (TEM). The average diameter and its distribution were analyzed by Image-ProPlus software. The results showed that the average diameter of the silver nanoparticles prepared at the laser repetition rate of 10 HZ was the smallest (D=29.75 nm), also, the distribution of particle size decreases with increasing the laser repetition rate.

Abstract: The paper presents a study on analysis of thermal elasto-plastic stress during pulsed laser heating a K418 alloy plate. Based on elasto-plastic constitutive relationship, a spatial finite element model was established to simulate the whole process. The distribution and evolutions of temperature and stress field was calculated. The stresses induced during the process are highly heterogeneous because of the recurrent changing temperature field. The stresses during the process fluctuate as the temperature field changes. High level tensile residual stresses reside in the fusion zone after the laser process. Compared to all other stress components, longitudinal stress is the highest and will have considerable influences over the distortion level and failure of the material.

Abstract: The laser quenching of GCr15 steel by wide band scanning technology was researched. Hardness and depths of laser transformation hardening zones of samples were also measured experimentally. Temperature field and residual stress field in the laser hardening process were numerically simulated by ANSYS software. The calculated results are in good agreement with the experimental results. The distribution of residual stress is closely related to the temperature distribution made by laser heating process. Then the distribution of residual stresses of the laser surface hardened layers was analyzed by using the X-ray diffraction (XRD). Compressive stresses were detected on the surface of the harden layer after the laser transformation hardening process, and the residual stress value of the surface of samples increases with the increasing of laser power. But the residual stress value of surface melting zones of samples is small.

Abstract: Cellular structures exhibit favorable properties for multifunctional applications, such as light weight, high load-bearing combined with high heat exchange capability. This paper is to seek optimal cellular structures as the core architectures of parts manufactured by selective laser melting (SLM) technology, which provides required mechanical properties. Design features for characterizing optimal structural performance are discussed. Some preliminary design rules are developed to improve the manufacturability and the quality of cellular structures, the orientation of strut is designed as ±45° or 90°. Compression tests are also carried out to seek cellular structures of synthetically optimal mechanical properties. Comparing the effects of the unit cell architecture and the relative density on mechanical properties, it reveals that unit cell architecture is dominant rather than the relative density, and the truss lattice with [90°,±45°] structure is the overall best performing among the selected cellular structures.

Abstract: Two image generating algorithms based on square partial scrambling are raised to implement micro-pits with approximate uniformity distribution of YAG laser texturing roll. Micro-pits can be uniformly distributed to ensure the area-uniformity of the micro-pits distribution. Micro-pits can be partial scrambled and optimized according to the evaluation standard to ensure the direction-uniformity of the micro-pits distribution.Partial scrambling image generating algorithms based on square-aligned-array arrangement and square-staggered-array arrangement are both effective image generating algorithms of uniformity distribution. The latter is more effective.

Abstract: In coal-water-slurry (CWS) boilers, the nozzle is eroded continuously by the abrasive action of the CWS, and there are high temperature and temperature gradient inside nozzle, which may cause large tensile stress and lead to an increased erosion wear of the nozzle. In this paper, Al2O3/(W,Ti)C+Al2O3/TiC laminated ceramics were developed to be used as nozzles in CWS boilers. The purpose is to reduce the tensile stresses at the nozzle during the CWS burning process. The value of the residual stresses, which arise from a mismatch between the coefficients of thermal expansion of the constituent phases and neighbouring layers, was calculated by means of the finite element method. The erosion wear behavior of the laminated nozzles was investigated and compared with an unstressed reference nozzle. Results showed that the laminated ceramic nozzles exhibited an apparent increase in erosion wear resistance over the unstressed reference one. It is suggested that laminated structures in ceramic nozzles is an effective way to improve their erosion wear resistance in industrial CWS boilers.

Abstract: The friction and wear properties of GCr15/45# steel frictional pairs lubricated by n- Al2O3 additives under ultrasonic vibration or not were studied. The scanning electron microscope(SEM), X-ray photoelectron spectroscopy(XPS) and energy dispersive spectrometer (EDS) were carried out to analyse the wear scar surface. The effect mechanism of ultrasonic vibration on friction pairs was discussed. The results indicated that ultrasonic vibration could decrease the friction and wear of GCr15/45# friction pairs, when the content of n-Al2O3 was 0.5wt%, the effect of ultrasonic vibration on friction pairs was most obvious. The friction coefficient, wear volume and wear scar depth under ultrasonic vibration decreased 10%, 34% and 13%, respectively. The friction reduction and anti-wear mechanism of n-Al2O3 was single “micro ball bearing” without ultrasonic vibration, and it changed to “micro ball bearing” and adsorption penetration film with ultrasonic vibration, so the friction coefficient and wear volume was reduced.

Abstract: The sliding wear behavior of Cu-Ag alloy in Cu cladding Al contact wire against 45# steel or bronze block was tested, then surface morphology was investigated in different load and velocity. The results indicated that the worn surface had plastic deformation and many clear furrows and cutting traces along the sliding direction. There were black oxide of copper on the worn surface. The oxide was both abrasive and lubrication. The mechanisms transformed from abrasive attrition into adhesive wear. Spalling pits and adhesive blocks with bronze friction were significantly bigger than that of steel, and the mechanisms was adhesive wear.

Abstract: The microstructures and tribological properties of materials for friction pairs used to space docking were investigated by optical metallographic microscope and a special home-made tribo-tester, respectively. The results demonstrate that friction material appears homogeneous and compact microstructure. Counterpart material presents temper sorbite which keeps martensite morphology and residues a small amount of blocky undissolved ferrite; the porosity of friction material is about 3.7%. Materials for space docking show favorable rigidity; during running-in, friction torque of friction pairs can be enhanced obviously; under different operation conditions, friction pairs for space docking possesses different friction coefficient.