材料期刊网

为研究调制周期和界面结构对纳米多层膜应变率敏感性的影响,采用电子束蒸发镀膜技术在Si基片上制备了不同周期(Λ=4 nm,12 nm,20 nm)的Cu/Ni纳米多层膜,采用磁控溅射技术在Si基片上制备了不同周期(Λ=5 nm,10 nm,20 nm)的Cu/Nb纳米多层膜。在真空条件下,对Cu/Ni纳米多层膜进行了温度分别为200和400 ℃、时间4 h的退火处理,对Cu/Nb纳米多层膜进行了温度分别为200、400和600 ℃,时间为4 h的退火处理。采用XRD和TEM表征了Cu/Ni和Cu/Nb纳米多层膜的结构,采用纳米压痕仪获取了不同加载应变率(0.005、0.01、0.05和0.2 s^-1)下纳米多层膜的硬度。结果表明,应变率敏感性受到界面结构和晶粒尺寸的影响,非共格界面密度提高以及晶粒尺寸变大均可导致应变率敏感性下降。当周期变大时,Cu/Ni纳米多层膜的非共格界面密度提高,晶粒尺寸变大,应变率敏感性指数m减小;当周期变大时,Cu/Nb纳米多层膜的非共格界面密度下降,晶粒尺寸变大,m基本不变。随退火温度上升,Cu/Ni和Cu/Nb纳米多层膜应变率敏感性大体上呈现下降趋势,这是由退火过程中非共格界面密度上升和晶粒长大共同引起的。

Different from monolayers of same components, nanoscale multilayers have different mechanical properties owing to their relatively high interfacial density, such as extremely high yield strength, high ductility and outstanding wear resistance. Furthermore, their precise modulation period and unique interfacial structures contribute to investigate the plastic deformation mechanism of metal materials. As the plastic deformation behaviors of nanoscale multilayers were reflected in a thermal activation process, strain rate sensitivity index m can be used to characterize the tendency of material strengthening as the strain rate increases. To investigate the impacts of modulation period and interfacial structures upon strain rate sensitivity of nanoscale multilayers, Cu/Ni nanoscale multilayers with different periods (Λ=4 nm, 12 nm, 20 nm) were prepared on Si substrate with e-beam evaporation technologies, while Cu/Nb nanoscale multilayers with different periods (Λ=5 nm, 10 nm, 20 nm) were prepared on Si substrate with magnetron sputtering technologies. Under vacuum conditions, the Cu/Ni nanoscale multilayers of different periods were annealed at 200 and 400 ℃ for 4 h respectively, and the Cu/Nb nanoscale multilayers of different periods were annealed at 200, 400 ℃ and 600 ℃ for 4 h respectively. Microstructures of Cu/Ni and Cu/Nb nanoscale multilayers were characterized with XRD and TEM. Besides, the hardness of nanoscale multilayers was measured by nano-indentation techniques under different loading strain rates (including 0.005, 0.01, 0.05 and 0.2 s^-1). The results suggested that strain rate sensitivity was impacted by interfacial structures and grain size. Both increased density of incoherent interfaces and grain size could result in weaker strain rate sensitivity. As the period increases, the density of incoherent interfaces and the grain size of Cu/Ni nanoscale multilayers increased, leading to a decline in the strain rate sensitivity. While for Cu/Nb nano scale multilayers, the density of incoherent interfaces decreased and their grain size was enlarged with longer period, the m value kept unchanged as a result. As the annealing temperature increasing, the strain rate sensitivity of Cu/Ni and Cu/Nb nanoscale multilayers generally tended to decline, which should be ascribed to increased density of incoherent interfaces and grain size in the course of annealing.