Process optimization of directed energy deposition for 316L/TiB2

• Main Author: Ang, Yao Ting
• Other Authors: Yeong Wai Yee
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Materials; Engineering::Manufacturing; Engineering::Aeronautical engineering
• Online Access: https://hdl.handle.net/10356/150558
• Institution: Nanyang Technological University

Directed energy deposition (DED) is a popular additive manufacturing (AM) method that is efficient and flexible due to its high energy density. It is ideal in repair and reinforcement cladding applications. It can also create metal matrix composites and functionally graded materials that can be customized for various requirements. 316L stainless steel is a suitable material for DED and has high corrosion resistance, ductility, and biocompatibility. Its weak strength can be overcome by the addition of reinforcement particles such as TiB2 to form metal matrix composites. In this project, the effects of process parameters were studied for the mechanical and microstructural properties of 316L/TiB2. Laser power, scanning speed and hopper speed was varied using the Taguchi L9 array. It was found that the process parameters had a negligible effect on the bulk density of deposited 316L/TiB2. Tumble mixing was also not suitable for the powder preparation for DED of 316L/TiB2. The Taguchi method was effective in optimizing the process parameter for Vickers hardness. The optimal parameter was found to be 1000 W, 600 mm/min, 400 rpm laser power, scanning speed and hopper speed respectively. However, Vickers hardness of the deposited 316L/TiB2 was found to have no significant difference from DED of pure 316L in other literature. The microstructure morphology of the deposited 316L/TiB2 was made of columnar and equiaxed grains. Columnar grains were located within layers while equiaxed grains were located at interlayer zones. Fine sub-grains were also observed within the columnar and equiaxed grains. The sub-grain boundary was confirmed to be enriched with Mo and Cr atoms. Black precipitates that contained Ti atoms were found to be formed at the sub-grain boundaries. Trace amounts of Ti atoms were also found in the sub-grain boundaries. Low TiB2 content had a negligible effect on the microstructural and mechanical properties of 316L.