State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049, China.
Nanoscale. 2018 Nov 29;10(46):21827-21841. doi: 10.1039/c8nr07129b.
Two kinds of crystalline/amorphous nanolaminates (C/ANLs), i.e., Ag/Cu-Zr and Mo/Cu-Zr, with a wide range of modulation ratios η (thickness ratio of the amorphous layer to the crystalline layer) from 0.1 up to 9.0 were, respectively, prepared using magnetron sputtering. The hardness and the strain rate sensitivity m were measured for comparison through nanoindentation testing. The mechanical properties displayed a strong η-dependence, which was tuned by the crystalline phases. With the increase of η, the hardness increased in the Ag/Cu-Zr nanolaminates while it decreased in the Mo/Cu-Zr ones. However, the two C/ANLs showed similar variations in m that was reduced gradually from positive values at small η to negative values at large η. Microstructural examination demonstrated that the amorphous Cu-Zr layers in both the C/ANLs showed a deformation-induced crystallization (DIC) phenomenon within the nanoindentation deformation zone. The DIC was highly dependent on η and became more intense in the Mo/Cu-Zr than in the Ag/Cu-Zr C/ANLs. The η- and constituent-dependent DIC behaviors were rationalized in light of the stress field applied on the amorphous layers that is sensitive to both the amorphous layer thickness and the crystalline constituents. This DIC-induced negative m in amorphous layers competed with the positive m in crystalline layers, leading to a negative-to-positive change in m on reducing η. The underlying deformation mechanism was revealed to be the cooperation between dislocation activities in the crystalline layers and shear transformation zone motions in the amorphous layers. Furthermore, a modified mechanistic model was utilized to quantitatively describe the η-dependent hardness at different crystalline constituents.
两种晶态/非晶态纳米叠层（C/ANLs），即 Ag/Cu-Zr 和 Mo/Cu-Zr，调制比 η（非晶层厚度与晶态层厚度之比）从 0.1 到 9.0 不等，分别采用磁控溅射法制备。通过纳米压痕测试测量了硬度和应变速率敏感性 m 进行比较。力学性能表现出强烈的η依赖性，由晶相调节。随着 η 的增加，Ag/Cu-Zr 纳米叠层的硬度增加，而 Mo/Cu-Zr 纳米叠层的硬度降低。然而，两种 C/ANL 在 m 方面表现出相似的变化，即从小 η 时的正值逐渐减小到大 η 时的负值。微观结构检查表明，两种 C/ANL 中的非晶态 Cu-Zr 层在纳米压痕变形区内均表现出变形诱导结晶（DIC）现象。DIC 高度依赖于 η，在 Mo/Cu-Zr 中比在 Ag/Cu-Zr C/ANL 中更为强烈。基于对施加在非晶层上的应力场的考虑，合理化了 η 和组成依赖性的 DIC 行为，该应力场对非晶层厚度和晶态成分均敏感。这种在非晶层中引起的 DIC 诱导的负 m 与晶态层中的正 m 竞争，导致 η 降低时 m 从负到正的变化。揭示的变形机制是晶态层中的位错活动与非晶层中的剪切转变区运动之间的合作。此外，利用改进的机械模型定量描述了不同晶态成分下 η 依赖性的硬度。
