Selective laser melting (SLM) process has advantages in building free shape and simplification of manufacturing process. Since Ni-base superalloys have lower ductility at lower temperature, it is difficult to produce the parts by means of other process like forging. Therefore, SLM process has already applied to produce Ni-base superalloy parts. However, SLM process needs a long process time comparing to casting and machining. One of the means to solve this problem is an application of the high scanning speed condition under high power laser output. In this research, the optimum fabrication condition of Inconel 718 superalloy by SLM process under high power and high scanning speed condition was investigated. As a result, the optimum fabrication condition was obtained using the process map. However, the relative density of the as-built specimen fabricated under high power and high scanning speed condition is lower than that of the as-built specimen fabricated under the condition of 300 W and 600 mm/s. This may be mainly due to the occurrence of gas-pores by key-hole like phenomenon in melt pool and the increase of spattering at high power and high scanning speed condition.

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This study aims to optimize the process parameters for PBF-LB of Inconel 718 using the surface texture and density of the as-built specimen to fabricate high-quality products. In order to achieve this aim, the melting and solidification phenomena of the melt pool were examined using a high-speed camera, and the process map of laser power and scan speed was constructed by evaluating the surface texture and density of the as-built specimen to optimize the process parameters. In addition, the mechanical properties of the as-built specimens fabricated at the optimum process parameter derived from the process map were examined. Consequently, it was found that the optimum process parameter should be determined by consideration of the melting and solidification phenomena because the phenomena such as spattering and instability of the melt pool change with the process parameters. It was also found that the morphology of the track is affected by the spot size of the laser beam. It was revealed that the similarity of the process maps evaluated by surface texture and density of the specimens results in the correlation between the surface texture and the density. The optimum laser power and scan speed can be determined using the process maps evaluated by the surface texture and density of the specimens. The as-built specimen fabricated at the optimum process parameter showed anisotropic tensile behavior, and the tensile strength of the transverse specimen was higher than that of the longitudinal specimen. The tensile properties of the as-built specimen fabricated in this work were similar to those of the as-built specimen reported by the other works.

In this study, we investigated the influence of the addition of MgO powder to the alkali and alkaline-earth borosilicate (AEB) glass paste on acid durability and peel adhesion characteristics of Ag conductors formed on the alumina substrate with the AEB glass paste. It was determined that the addition of the MgO powder to the AEB glass paste promoted crystal precipitation during the firing process of the printed AEB glass thick-film on the substrate at 850°C. By characterizing the acid corrosion behavior in a H 2 SO 4 aq., the weight loss after immersion for the micro-crystallized AEB glass thick-film with the added MgO powder was reduced by approximately half compared with that of the AEB glass thick-film without the MgO powder. In addition, no cracks were observed on the film surface of the micro-crystallized AEB glass, whereas cracks appeared on the film surface of the non-crystallized AEB glass after the acid corrosion treatment. It is thought that microcrystallization induced by the addition of MgO powder to the glass paste during the firing process is partly involved in improving the acid resistance of the AEB glass thick-film. During the peel adhesion test of the Ag conductor on the alumina substrate in a H 2 SO 4 aq., the Ag conductor formed with the MgO powder-added AEB glass paste exhibited small deterioration of peel adhesion in comparison to the Ag conductor formed using the AEB glass paste without the MgO powder. These results suggest that the correlation between the improved acid durability and peel adhesion characteristics of the Ag conductor formed with the MgO powder-added AEB glass paste was related to the micro-crystallization of the AEB glass induced by the addition of MgO powder to the thick-film pastes during the annealing process at 850°C.

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