Surface oxide layer fracture and the subsequent exposure of clean metallic surfaces are critical in various solid-state processes for powder consolidation and additive manufacturing. We resolve this process by deforming individual spherical powder particles inside a scanning electron microscope. We reveal three fracture modalities, i.e., meridian, radial, and circumferential cracking that sequentially activate with particle flattening. Real time measurements of load and displacement upon particle flattening also reveal a significant strengthening effect by surface oxide. We attribute the strengthening to two mechanisms: the composite strengthening and the strain gradient strengthening.

中文翻译：

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粉末颗粒压扁过程中的表面氧化层强化和断裂

表面氧化层破裂以及随后暴露的清洁金属表面对于粉末固结和​​增材制造的各种固态工艺至关重要。我们通过在扫描电子显微镜内使单个球形粉末颗粒变形来解决这个过程。我们揭示了三种断裂模式，即子午裂纹、径向裂纹和周向裂纹，它们依次随着颗粒压扁而激活。颗粒压扁时负载和位移的实时测量也揭示了表面氧化物的显着强化效应。我们将强化归因于两种机制：复合强化和应变梯度强化。