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Reducing the defect density and improving the performance of selective laser melting-forming parts are significant for the development of selective laser melting (a great potential powder additive manufacturing method). Therefore, many methods like layer-by-layer laser remelting have been applied in the selective laser melting process. To investigate the influence of the layer-by-layer laser remelting process on the selective laser melting 316 L SS specimens, a three-dimension mesoscale remelting numerical simulation model in the single powder layer is established, and the microstructure and performance (surface quality, mechanical properties) are measured and analyzed with the different number of layer-by-layer laser remelting. The numerical simulation results show that the remelting process can effectively inhibit the defect. Nerversless, when the number of remelting is large, the over-melting phenomenon occurs, which is harmful to surface quality on the remelting surface. The experimental results also show that surface roughness, microhardness, ultimate strength, and strain can be effectively improved by controlling remelting times. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is a popular additive manufacturing technique for metal material. Microstructure and defects of fabricated parts by SLM are closely associated with double scanning track. In this study, the single/double track formation simulation of 316L stainless steel was established to study the influence of process parameters on the forming and the defects during the SLM process. In addition, the impact of melt pool flow on single/double track forming and defects was analyzed. Experiments verified the numerical simulation. Results show that the volume energy density (VED) has significant influence on the formation and defects of SLM, and the optimized volume energy density (VED) range is obtained by numerical simulation and experiments. [ABSTRACT FROM AUTHOR]

Laser micromachining has proven to be a useful tool for the precision processing of semiconductors. In the hybrid laser-water jet micromachining process investigated in this research, a laser is used for heating and softening the work material (polycrystalline silicon, in this case), while a water jet is employed for shearing the softened material and subsequently removing it due to the high-velocity of the liquid jet impingement, as well as for cooling the material. Specifically, the use of a low-pressure water jet to assist with the laser etching of polycrystalline silicon was investigated in this study. The energy efficiency of the processing as well as the width, depth, and surface microstructure of the groove etched in the polycrystalline silicon using the composite process were considered. With increasing jet velocity, the integrated energy initially decreased before increasing and the overall groove depth decreased, then increased, and finally decreased again. When the incidence angle was 30°, the groove width in the polypolycrystalline silicon increased as the jet velocity increased from 8 and 28 m s−1, and the use of a low-pressure jet to assist with the laser etching resulted in etched surfaces smoother than those obtained in air and hydrostatic conditions. The experimental results prove that the low-pressure water-jet-assisted laser etching technique can overcome the problems of micro-crack, slag, and recast layer formation that affect traditional laser etching and consequently improve the quality of machined parts. [ABSTRACT FROM AUTHOR]

The microstructure, surface quality, and thermal shielding properties of the coatings prepared by the methods of magnetron sputtering and electroplating are studied. The results show that the Cr–Ag coating prepared by means of magnetron sputtering is smoother, its porosity and emissivity are lower, and the hardness is higher than that of the coating prepared by means of electroplating. [ABSTRACT FROM AUTHOR]