发现在IN718合金冲击试样断口表面上存在一层极薄的无位错纳米晶层,晶粒尺寸约为20～30nm.在冲击断裂过程中,塑性变形主要集中在裂纹尖端附近的微小区域内.随着裂纹的扩展,沿断口表面形成一极薄的高度塑性变形层,可能是不同方向的位错将其分割成极小的区域.断口表层原子位置的重组释放出高密度的热流导致严重塑性变形层瞬间升温,引发再结晶和纳米晶组织的形成.分析表明,高度塑性变形层愈宽,吸收的冲击功愈多,冲击性能愈好.IN718合金的成分偏析降低高度塑性变形层的宽度和冲击性能.快速加载的冲击性能可能比拉伸等性能对成分偏析更加敏感.
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