Kumar, P., Michalek, M., Cook, D. H., Sheng, H., Lau, K. B., Wang, P., Zhang, M., Minor, A. M., Ramamurty, U., & Ritchie, R. O. (2023). On the strength and fracture toughness of an additive manufactured CrCoNi medium-entropy alloy. Acta Materialia, 258, 119249. https://doi.org/10.1016/j.actamat.2023.119249
Abstract:
An additively manufactured (nominally equiatomic) CrCoNi alloy was processed by laser powder bed fusion (LPBF). At ambient temperatures (298 K), this medium-entropy alloy displayed a yield strength, σy of ~691 ± 9 MPa, and an ultimate tensile strength, σu of ~926 ± 15.2 MPa; at cryogenic temperatures (77K), yield and tensile strengths increased respectively to σy ~ 944 ± 6 MPa and σu ~ 1382 ± 11 MPa. These strength levels are 57% and 44% higher than that of the wrought alloy, due to strengthening from the solidification cellular structures intertwined with dislocations in the LPBF CrCoNi. The crack-initiation fracture toughness, KJIc was measured to be ~183.7 ± 28 MPa√m at 298 K; this value marginally decreased by ⁓4% to ~176 ± 11 MPa√m at 77 K. These KJIc values of the LPBF CrCoNi were 11% and 35% lower than the wrought CrCoNi alloy at 298K and 77K, respectively. The resistance to crack growth of the LPBF CrCoNi from its hierarchical micro- and meso-structures was evaluated using nonlinear-elastic fracture mechanics by measuring R-curve behavior in the form of the J-integral as a function of crack extension. The specific features of the hierarchical microstructures at different length-scales provide a basis for the strengthening and toughening properties of this additively manufactured medium-entropy alloy. This correlation between the deformation and the hierarchical microstructures at different length-scales may provide future guidance for improving the fracture toughness properties of medium-entropy alloys.
License type:
Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
Funding Info:
This research / project is supported by the Agency for Science, Technology and Research - Structural Metal Alloys Programme
Grant Reference no. : A18B1b0061