Acta Metallurgica Sinica (English Letters) ›› 2012, Vol. 25 ›› Issue (2): 141-152.DOI: 10.11890/1006-7191-122-141

• 研究论文 • 上一篇    下一篇

Oxygen-penetration-induced large hardness enhancement in nanoscale Nb/Ti multilayers

赵宇新,赖文生   

  1. 清华大学
  • 收稿日期:2011-09-19 修回日期:2012-01-01 出版日期:2012-04-25 发布日期:2012-04-11
  • 通讯作者: 赖文生

Oxygen-penetration-induced large hardness enhancement in nanoscale Nb/Ti multilayers

Yuxin ZHAO, Wensheng LAI   

  1. Advanced Material Laboratory, Department of Materials Science & Engineering, Tsinghua University, Beijing 100084, China
  • Received:2011-09-19 Revised:2012-01-01 Online:2012-04-25 Published:2012-04-11
  • Contact: Wensheng LAI

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摘要： Nb/Ti multilayers with different modulation periods were prepared by magnetron sputtering deposition. Microstructure and mechanical properties were investigated by XRD, SEM and Nanoindentation. It turns out that hardness of samples increases with decreasing modulation wavelength (Λ) with the exception of the smallest one with Λ = 6 nm. Through scrutinizing other results in literature, we found that coherent stress rather than modulus mismatch played the more important role for hardness enhancement with decreasing Λ of the bcc-hcp multilayers. Annealing of samples in low (or high) vacuum at 400 °C for 30 minutes led to large (or medium) enhancement of hardness, while the modulated structure was still maintained. It was found that annealing in low vacuum resulted in oxygen penetration into the multilayers as revealed by auger electron spectroscopy, but hardly changed metallic sheet resistivity. XRD results suggested that some niobium oxides were formed in Nb layers and oxygen distributed interstitially in Ti layers. The large hardness enhancement after annealing is mainly due to the strengthening effect from dispersive distribution of nano-scale niobium oxides and interstitial oxygen in the multilayers. In addition, interfaces between adjacent layers were more distinct after annealing which indicated good thermal stability of laminated structure.

Abstract: Nb/Ti multilayers with different modulation periods were prepared by magnetron sputtering deposition. Microstructure and mechanical properties were investigated by XRD, SEM and Nanoindentation. It turns out that hardness of samples increases with decreasing modulation wavelength (Λ) and then dropped at small Λ Through scrutinizing other results in literature, we found that the coherent stress rather than modulus mismatch played more important role for hardness enhancement with decreasing Λ of the bcc-hcp multilayers. Annealing of samples in low (or high) vacuum at 400 ℃ for 30 min led to large (or medium) enhancement of hardness, while the modulated structure was still maintained. It was found that annealing in low vacuum resulted in oxygen penetration into the multilayers as revealed by auger electron spectroscopy, but hardly changed metallic sheet resistivity. XRD results suggested that some niobium oxides were formed in Nb layers and oxygen distributed interstitially in Ti layers. The large hardness enhancement after annealing is mainly due to the strengthening effect from dispersive distribution of nano-scale niobium oxides and interstitial oxygen in the multilayers. In addition, interfaces between adjacent layers were more distinct after annealing which indicated good thermal stability of laminated structure.

Key words: Nb/Ti multilayer, Hardness, Microstructure, Annealing, Nanoindentation