Electron energy-loss spectroscopy and first-principles calculation studies on a Ni–Ti shape memory alloy

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• 作者：Zhiqing Yang ; Wim Tirry ; Dirk Lamoen ; Svetlana Kulkova ; Dominique Schryvers
• 关键词：Ni– ; Ti ; Precipitate ; EELS ; First-principles calculations ; Bulk modulus
• 刊名：Acta Materialia
• 出版年：2008
• 出版时间：February 2008
• 年：2008
• 卷：56
• 期：3
• 页码：395-404
• 全文大小：588 K

文摘

Electron energy-loss spectroscopy (EELS) investigations and first-principles calculations were carried out on different aspects of a Ni–Ti shape memory alloy. The composition of lens-shaped precipitates is determined to be Ni₄Ti₃ by model-based EELS quantification and the Ni-depleted zone in the B2 matrix surrounding those precipitates is quantified. EELS spectra show that the intensity of the normalized Ni L₃ peak of both the Ni₄Ti₃ precipitates and Ni-depleted zones is higher than that of matrix regions with the nominal composition, which is confirmed by first-principles simulations. The total amounts of 3d electrons, however, are the same for both elements in the different Ni–Ti structures and regions. The Young’s and bulk moduli of the B2 matrix with 51 at. % Ni and the Ni₄Ti₃ precipitates were evaluated and the precipitates are found to be harder than the matrix, while first-principles calculations indicate that the bulk modulus for the Ni₄Ti₃ precipitate is higher by 5 % than that for the equiatomic NiTi B2 phase.