Enhancing micro-hardness of additively manufactured Inconel-625 through post-processing heat treatment

• Main Author: Low, Zi Tung
• Other Authors: Dong Zhili
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Materials::Functional materials
• Online Access: https://hdl.handle.net/10356/166772
• Institution: Nanyang Technological University

Climate change is a global issue that has prompted a shift towards renewable energy and advanced transportation technologies. While hydrogen is a promising alternative to fossil fuels due to its abundance and clean burning properties, there remain challenges associated with transporting hydrogen, particularly its impact on pipeline steels due to hydrogen-induced cracking and other forms of corrosion. Hence, it is important to understand the effects of hydrogen in weld heat-affected zones to ensure the safety and long-term reliability of hydrogen storage and transportation, as well as protecting existing infrastructure from hydrogen-related corrosion. The scope of this project is to develop a hydrogen barrier coating for repurposing existing oil and gas pipelines to transport and store pressurized hydrogen gas. This study focuses on the effects of post process heat treatment on microhardness of additively manufactured Inconel (In) 625. Four different print parameters were used to deposit In625 onto hot-rolled In625 substrates via laser metal deposition (LMD). The samples were then post-processed with two heat treatment conditions, annealing and quenching. The microstructure and mechanical properties of the samples were characterized using electron backscattered diffraction (EBSD) and Vickers hardness test before and after the post-process heat treatment. Several important factors affecting the hardness values of the printed samples were identified. These factors include the presence of interlayer cooling during the printing process, laser power, and post-process heat treatment. Understanding and controlling these factors can help to optimize the laser metal deposition process for Inconel 625 and improve the quality and performance of printed parts.