Abstract Single crystal sapphire is an anisotropic material and its mechanical behavior depends on the crystallographic orientation. In this work, a systematic study is performed to investigate the effect of crystallographic orientation on the deformation and cracking of sapphire by means of nanoindentation using spherical indenters. It aims also at determining the physical origin of the ''pop-in" appearing in the nanoindentation curves. For that purpose, nanoindentations were performed where the load was increased until the detection of the ''pop-in", followed by direct unloading. After SEM and TEM observation of the indents, it is concluded that the deformation mechanisms of sapphire depend on the tip radius and the applied indentation stress: exclusively twin formation for the smaller 1 and 2 μm tip radii indenters and twin formation together with crack propagation for larger 10 μm tip radius spherical indenter. It was also determined that the cracks propagate preferentially in the ( 10 1 ¯ 2 ) ''R-plane". Therefore, this study is supplement to and enrichment of existing studies on deformation and cracking behavior of sapphire under spherical nanoindentation.

中文翻译：

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蓝宝石中的纳米压痕变形和开裂

摘要 单晶蓝宝石是一种各向异性材料，其力学行为取决于晶体取向。在这项工作中，通过使用球形压头进行纳米压痕，系统研究了晶体取向对蓝宝石变形和开裂的影响。它还旨在确定纳米压痕曲线中出现的“pop-in”的物理起源。为此，在增加负载的情况下进行纳米压痕，直到检测到“pop-in”，然后直接卸载. 对压痕进行 SEM 和 TEM 观察后，得出结论，蓝宝石的变形机制取决于尖端半径和施加的压痕应力：较小的 1 和 2 μm 尖端半径压头的完全孪生形成和较大的 10 μm 尖端半径球形压头的孪生形成和裂纹扩展。还确定了裂纹优先在( 10 1 ¯ 2 )“R面”扩展。因此，本研究是对现有球形纳米压痕下蓝宝石变形和开裂行为研究的补充和丰富。