Zhao J T, Zhang J Y, Hou Z Q, Wu K, Feng X B, Liu G, Sun J
State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049, People's Republic of China.
Nanotechnology. 2018 May 11;29(19):195705. doi: 10.1088/1361-6528/aab19a. Epub 2018 Feb 22.
In order to achieve desired mechanical properties of alloys by manipulating grain boundaries (GBs) via solute decoration, it is of great significance to understand the underlying mechanisms of microstructural evolution and plastic deformation. In this work, nanocrystalline (NC) Cu-W alloyed films with W concentrations spanning from 0 to 40 at% were prepared by using magnetron sputtering. Thermal stability (within the temperature range of 200 °C-600 °C) and hardness of the films were investigated by using the x-ray diffraction, transmission electron microscope (TEM) and nanoindentation, respectively. The NC pure Cu film exhibited substantial grain growth upon all annealing temperatures. The Cu-W alloyed films, however, displayed distinct microstructural evolution that depended not only on the W concentration but also on the annealing temperature. At a low temperature of 200 °C, all the Cu-W alloyed films were highly stable, with unconspicuous change in grain sizes. At high temperatures of 400 °C and 600 °C, the microstructural evolution was greatly controlled by the W concentrations. The Cu-W films with low W concentration manifested abnormal grain growth (AGG), while the ones with high W concentrations showed phase separation. TEM observations unveiled that the AGG in the Cu-W alloyed thin films was rationalized by GB migration. Nanoindentation results showed that, although the hardness of both the as-deposited and annealed Cu-W alloyed thin films monotonically increased with W concentrations, a transition from annealing hardening to annealing softening was interestingly observed at the critical W addition of ∼25 at%. It was further revealed that an enhanced GB segregation associated with detwinning was responsible for the annealing hardening, while a reduced solid solution hardening for the annealing softening.
为了通过溶质修饰来操控晶界（GBs）从而实现合金所需的力学性能，理解微观结构演变和塑性变形的潜在机制具有重要意义。在这项工作中，通过磁控溅射制备了W浓度范围从0至40原子百分比的纳米晶（NC）Cu-W合金薄膜。分别使用X射线衍射、透射电子显微镜（TEM）和纳米压痕技术研究了薄膜在200℃至600℃温度范围内的热稳定性和硬度。NC纯铜薄膜在所有退火温度下均表现出显著的晶粒生长。然而，Cu-W合金薄膜呈现出明显的微观结构演变，这不仅取决于W浓度，还取决于退火温度。在200℃的低温下，所有Cu-W合金薄膜都高度稳定，晶粒尺寸变化不明显。在400℃和600℃的高温下，微观结构演变受W浓度的极大控制。低W浓度的Cu-W薄膜表现出异常晶粒生长（AGG），而高W浓度的薄膜则出现相分离。TEM观察表明，Cu-W合金薄膜中的AGG可通过晶界迁移来解释。纳米压痕结果显示，尽管沉积态和退火态的Cu-W合金薄膜硬度均随W浓度单调增加，但在约25原子百分比的临界W添加量时，有趣地观察到从退火硬化到退火软化的转变。进一步揭示，与孪生相关的增强晶界偏析导致了退火硬化，而固溶强化的降低则导致了退火软化。
