Twinning mediated anisotropic fracture behavior in bioimplant grade hot-rolled pure magnesium

• Published in: Journal of Magnesium and Alloys
• Main Authors: Prakash C. Gautam, Somjeet Biswas
• Format: Article
• Language: English
• Published: KeAi Communications Co., Ltd. 2024-09-01
• Subjects: Magnesium; Elastic-plastic fracture toughness; Twins; Texture; Strain incompatibility
• Online Access: http://www.sciencedirect.com/science/article/pii/S2213956724003141

Bioimplant grade hot-rolled magnesium with equiaxed microstructure and basal texture was examined for fracture toughness (FT) anisotropy using fatigue pre-cracked single-edge notch bending specimens with the notch, an ∥, ⊥ and 45° to rolling direction (RD). Due to adequate crack-tip plasticity, the size-independent elastic-plastic fracture toughness (JIC) were determined. Anisotropic JIC was observed due to different twin lamellae formation w.r.t. notch owing to the initial basal texture with {101¯0} and {112¯0} poles mostly ∥ and ⊥ to RD. The out-of-plane tensile stresses activated the {101¯2}〈101¯1〉 extension twins (ET) as usual with matrix-ET Σ15b coincident site lattice boundary (CSLB) interfaces. While the in-plane tensile stress ⊥ to the crack-tip activated {101¯1}〈101¯2〉 contraction twins (CT) that transform into {101¯1}-{101¯2} double twins (DT) with matrix-DT Σ23b and Σ15a CSLBs. For an∥ RD, large DT lamellae fraction formed at ∼30° and few ETs at ∼30° and ∼90° to the notch with crack growth mainly via the Σ23b/Σ15a CSLB interfaces during FT. While, significant DT and ET lamellae developed at ∼0° and ∼60° with cracking via the matrix-DT Σ23b/Σ15a and matrix-ET Σ15b CSLBs for an⊥ RD. The DT and ET lamellae activated at ∼15°, and the crack propagated through Σ15b for an∼45∘ to RD. The JIC and the crack-tip plastic zone decreases, while the elastic component of the J-integral (Jel) and the ET formation increases from an∥, ⊥,  to ∼45∘ to RD. The strain incompatibility of matrices was higher with the geometrically hard ETs than DTs. Thus, brittle interlamellar cracking occurred through the Σ15b interfaces. In contrast, almost similar and higher crack-tip plasticity occurred in matrix and DT domains during crack propagation via Σ23b/Σ15a CSLBs. Crack growth through Σ23b/Σ15a led to high JIC, both Σ15b and Σ23b/Σ15a led to moderate JIC, and Σ15b least JIC for an ∥, ⊥ and 45° to RD, respectively.