Process And Performance Of 316L Stainless Steel Bulks By Laser Engineered Net Shaping Technology

As a novel laser additive manufacturing technology based on laser cladding process with synchronous powder feeding, laser engineered net shaping technology has been gradually considered as an important part in fabrication of metal components. In the production of bulk specimens by laser engineered net shaping technology, the plan and realization of laser scanning path are the key to assure high quality and high precision. Therefore, a study about the influence of laser scanning path on microstructure and properties is of great essence and significance.First of all, in this dissertation, the influence of three main technological parameters (i.e. powder feed rate, laser power, and laser beam scanning speed) on the microstructure and morphology of cladding layer has been studied systemically through single-pass laser cladding. Secondly, the influence of overlapping rate and z-axis increment on the specimens has been studied through multi-pass overlapping and multi-layer overlapping experiments. Finally, based on above-mentioned optimized technological parameters, three laser scanning patterns are used to fabricate bulk specimens. Subsequently, influence of laser scanning path and post-heat treatment on microstructure and properties of the as-deposited builds has been investigated. The main results and conclusions are summarized as follows:(1) Compared to powder feed rate and laser power, laser beam scanning speed has a significant influence on the height and the width of single cladding layer. As for microstructure, powder feed rate mainly affects the grain morphology evolution, and laser power and laser beam scanning mainly affect grain size.(2) The surface smoothness of as-deposited builds is greatly influenced by the overlapping rate. The surface smoothness is the highest when the overlapping rate is 50% or 66.7% and the surface state meets the required overlapping quality. An appropriate z-axis increment (i.e. ?Z= 0.3 mm) is successfully used to fabricate the thin-walled part.(3) Laser scanning path has a significant effect on the microstructure and properties of bulk specimens, and the specimen fabricated by weaving scanning path has the best mechanical properties. After solid solution treatment, the tensile strengths of all the as-deposited alloys decrease and the elongations increase. As for electrochemical performance, the thin-walled specimen has the worst electrochemical corrosion resistance and the other specimens are similar in electrochemical corrosion resistance. Additionally, solid solution treatment could improve the electrochemical corrosion resistance of bulk specimens.