Phase transformation-induced strength softening in Ti/Ta nanostructured multilayers: Coherent interface vs phase boundary

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• 作者：Z.Q. Hou ; J.Y. Zhang ; ^{jinyuzhang1002@mail.xjtu.edu.cn} ; J. Li ; Y.Q. Wang ; K. Wu ; G. Liu ; ^{lgsammer@mail.xjtu.edu.cn} ; G.J. Zhang ; J. Sun
• 关键词：Ti/Ta multilayers ; Strength softening ; Phase transformation ; Coherent interface ; Phase boundary
• 刊名：Materials Science and Engineering: A
• 出版年：2017
• 出版时间：27 January 2017
• 年：2017
• 卷：684
• 期：Complete
• 页码：78-83
• 全文大小：906 K
• 卷排序：684

文摘

In this work, hcp-to-bcc Ti phase transformation was uncovered in Ti/Ta nanostructured multilayers. The Ti nanolayers were fully transformed to bcc phase when the layer thickness (h) smaller than ~7.5 nm, accompanied with the formation of fully coherent interfaces. While in the greater layer thickness, Ti layers were partially phase-transformed, resulting in the simultaneous existence of bcc/bcc Ti/Ta coherent interfaces and bcc/hcp Ti/Ti phase boundaries. A thermodynamic model was proposed to account for the layer thickness h-dependent Ti phase transformation. The phase transformation caused an unusual size-dependent hardness, i.e., the smaller the layer thickness and the lower the hardness, which was quantitatively addressed by an ad hoc strengthening model.