Assessing the factors underlying the high yield strength of laser powder bed fusion processed niobium

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2024-09, Vol.910, p.146896, Article 146896
• Main Authors: Chesetti, Advika, Banerjee, Sucharita, Krishna, K.V Mani, Soni, Vishal, Varahabhatla, S.M., Sharma, Abhishek, Mantri, Srinivas Aditya, Nartu, M.S.K.K.Y., Dahotre, Narendra B., Banerjee, Rajarshi
• Format: Article
• Language: English
• Subjects: Additive manufacturing; Atom probe tomography; Laser powder bed fusion; Mechanical properties; Niobium
• ISSN: 0921-5093
• DOI: 10.1016/j.msea.2024.146896

The present study focuses on the factors underlying the substantially higher yield strength (YS) and ultimate tensile strength (UTS) in laser powder bed fusion (LPBF) processed niobium, as compared to electron beam additive manufacturing (EBAM) or conventionally processed Nb. LPBF builds of pure Nb, with a relative density of 98 %, exhibited an YS of 490 MPa, UTS of 609 MPa, and ductility of 9 % with appreciable strain hardenability. Detailed electron backscatter diffraction analysis revealed a high density of sub-boundaries within the BCC Nb grains. Additionally, the LPBF Nb sample contained ∼1200 ppm of oxygen and ∼380 ppm of nitrogen, part of which segregated to the grain boundaries, as revealed by atom probe tomography (APT). The individual strengthening contributions from grain boundaries, dislocations, and oxygen and nitrogen interstitials have been quantitatively estimated, giving an overall computed YS of 506 MPa, in close agreement with the experimentally measured value of 490 MPa. This quantitative assessment also revealed that solid solution strengthening from oxygen and nitrogen can be of the same order of magnitude as strengthening from dislocations and sub-boundaries in LPBF processed Nb.