Laser 3D printing of CoCrFeNiTix high entropy alloys

• Main Author: Huang, Sheng
• Other Authors: -
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering
• Online Access: https://hdl.handle.net/10356/175820
• Institution: Nanyang Technological University

Selective laser melting (SLM), which is an important metal three-dimensional (3D) printing or metal additive manufacturing (AM) technique, has become increasingly popular, mainly due to its capability of producing customised fully dense metal parts with complex geometries that are unattainable by traditional manufacturing processes. With the appearance of high entropy alloys (HEAs), a whole new field of alloy design with better design freedom has been realized. One notable HEA system is the CoCrFeNiTix series which can potentially achieve high specific strength. However, few studies have been conducted on laser 3D printing of CoCrFeNiTix HEA parts in spite of the advantages of SLM process. As such, this project aims to manufacture CoCrFeNiTix HEA via the SLM route. This project successfully optimized the SLM scanning parameters for CoCrFeNiTi0.5 HEA to achieve a part porosity of <1.5%. The porosity contributors for SLM-printed CoCrFeNiTix HEA parts were identified. They are mainly the long cracks due to high thermal residual stress, the spherical pores due to vaporization of Ti powder, and the short cracks due to the Ti-rich brittle phases. It was noted that the microstructure of SLM-printed CoCrFeNiTi0.5 HEA is strikingly different from those produced via casting method. Moreover, four kinds of CoCrFeNiTix (x = 0, 0.1, 0.5, and 1.0) HEA parts were 3D-printed using SLM in order to study the effects of Ti additions on microstructure and mechanical properties of CoCrFeNi base system. With increasing Ti additions into CoCrFeNi, the formation of Ti-rich phases and intermetallic compounds occurred. Also, Ti additions could generally strengthen the CoCrFeNi base system. However, a softening effect was observed when a minor amount of Ti (x = 0.1) was added. Furthermore, it was found that the usage of blended powders inherently imposes a maximum limit on the amount of Ti addition into the CoCrFeNi base system due to severe Ti segregation. This project shows that the SLM process could be adopted to print high-performance CoCrFeNiTix HEA parts.