Nitrogen-doping assisted local chemical heterogeneity and mechanical properties in CoCrMoW alloys manufactured via laser powder bed fusion

Wenting Jiang; Ruidi Li; Junyang He; Song Ni; Li Wang; Zibin Chen; Yi Huang; Caiju Li; Jianhong Yi; Min Song

Advanced Powder Materials (Oct 2024)

Nitrogen-doping assisted local chemical heterogeneity and mechanical properties in CoCrMoW alloys manufactured via laser powder bed fusion

Wenting Jiang,
Ruidi Li,
Junyang He,
Song Ni,
Li Wang,
Zibin Chen,
Yi Huang,
Caiju Li,
Jianhong Yi,
Min Song

Affiliations

Wenting Jiang: State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China; College of Materials and Advanced Manufacturing, Hunan University of Technology, Zhuzhou 412007, China
Ruidi Li: State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China
Junyang He: State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China
Song Ni: State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China; Corresponding author.
Li Wang: State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China; Corresponding author.
Zibin Chen: Research Institute for Advanced Manufacturing, Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hong Kong, China
Yi Huang: Department of Design and Engineering, Faculty of Science and Technology, Bournemouth University, Poole, Dorset, BH12 5BB, UK; Materials Research Group, Department of Mechanical Engineering, University of Southampton, Southampton, SO17 1BJ, UK
Caiju Li: Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China
Jianhong Yi: Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, China
Min Song: State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China; Corresponding author.

Journal volume & issue: Vol. 3, no. 5
p. 100217

Abstract

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CoCrMoW alloys with different nitrogen (N) additions (0, 0.05, 0.1, and 0.2 wt%) were prepared via laser powder bed fusion (LPBF). The effects of N content on the microstructure and mechanical properties were investigated. The results indicate that the LPBFed CoCrMoW alloy with 0.1 wt% N addition (0.1 N alloy) shows the best combination of mechanical properties with a yield strength of ∼983 MPa and an elongation of ∼19 %. Both the LPBF process and the N addition impose great effects on suppressing the γ to ε martensitic transformation, resulting in a decrease in the width and amount of ε laths/stacking faults. Besides, the N addition promotes the segregation of elements Mo, W, and Si along the cellular sub-grain boundaries (CBs), forming fine and discontinuous precipitates rich in Mo, W and Si along the CBs in the 0.1 N alloy, but dense and continuous (Mo,W)5Si3 precipitates along the CBs in the 0.2 N alloy. The (Mo,W)5Si3 precipitates with a tetragonal structure were observed and characterized for the first time in the Co–Cr based alloys. The negative mixing enthalpy between the non-metallic elements N, Si and the metallic elements Mo, W, Cr, and the rapid solidification induced segregation of high melting point elements such as Mo and W along CBs during LPBF process, synergistically contribute to the chemical heterogeneity in the alloys. The pure FCC matrix, the slightly increased segregation of Mo, W, Si elements and fine precipitates along the CBs contribute to the good combination of strength and elongation of the 0.1 N alloy. However, though pure FCC phase was present in the 0.2 N alloy, the dense and continuous (Mo,W)5Si3 precipitates along CBs acted as nucleation sites for cracks, deteriorating the elongation of the alloy. Overall, it is possible to tune the mechanical properties of the LPBFed CoCrMoW alloy by adjusting the local chemical heterogeneity.

Published in Advanced Powder Materials

ISSN: 2772-834X (Online)
Publisher: KeAi Communications Co. Ltd.
Country of publisher: China
LCC subjects: Technology: Mining engineering. Metallurgy
Website: https://www.keaipublishing.com/en/journals/advanced-powder-materials/

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