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.

中文翻译：

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孪晶介导的生物植入物级热轧纯镁的各向异性断裂行为


使用具有缺口、∥、⊥和与轧制方向 （RD） 成 45° 的疲劳预开裂单边缺口弯曲试样，检查具有等轴微观结构和基底织构的生物植入物级热轧镁的断裂韧性 （FT） 各向异性。由于裂纹尖端塑性足够，确定了与尺寸无关的弹塑性断裂韧性 （JIC）。由于初始基部纹理具有 {101 ̄0} 和 {112 ̄0} 极，大部分∥且⊥ RD，因此观察到各向异性 JIC。面外拉伸应力像往常一样激活了 {101 ̄2}〈101 ̄1〉 扩展孪晶 （ET），就像矩阵-ET Σ15b 重合位点晶格边界 （CSLB） 接口一样。而⊥裂纹尖端的面内拉伸应力激活了 {101 ̄1}〈101 ̄2〉 收缩孪晶 （CT），这些收缩孪晶转化为具有基体 DT Σ23b 和 Σ15a CSLB 的 {101 ̄1}-{101 ̄2} 双孪晶 （DT）。对于∥ RD，在 ∼30° 处形成较大的 DT 薄片部分，在 ∼30° 和 ∼90° 处形成少量 ET，在 FT 期间主要通过 Σ23b/Σ15a CSLB 界面扩展裂纹。同时，在 ∼0° 和 ∼60° 处形成显着的 DT 和 ET 薄片，并通过基体 DT Σ23b/Σ15a 和基体 ET Σ15b CSLBs 开裂，用于 ⊥ RD。DT 和 ET 薄片在 ∼15° 处激活，裂纹通过 Σ15b 传播至 ∼45∘ 到 RD。JIC 和裂纹尖端塑性区减小，而 J 积分 （Jel） 和 ET 形成的弹性分量从 an∥、⊥ 增加到 ∼45∘ 再到 RD。基质的应变不亲和性与几何硬质 ET 的不亲和性高于 DTs。因此，脆性层间开裂发生在 Σ15b 界面上。相比之下，在通过 Σ23b/Σ15a CSLBs 进行裂纹扩展过程中，基体和 DT 域中出现了几乎相似且更高的裂纹尖端塑性。 通过Σ23b/Σ15a的裂纹扩展导致高JIC，Σ15b和Σ23b/Σ15a都导致中等JIC，而Σ15b最低的JIC分别是∥、⊥和45°到RD。