Oxidation and crystallographic features of the new prototype structure Ti₄NiSi₄

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• 作者：N. Chaia^a ; M. Franç ; ois^a ; S. Mathieu^a ; ^{stephane.mathieu@univ-lorraine.fr} ; E. Elkaï ; m^b ; F. Rouillard^c ; M. Vilasi^a
• 关键词：A. Silicides ; various ; B. Crystal chemistry of intermetallics ; B. Oxidation ; B. Phase transformation ; C. Coatings ; G. Corrosion- and erosion-resistant applications
• 刊名：Intermetallics
• 出版年：2013
• 出版时间：September, 2013
• 年：2013
• 卷：40
• 期：Complete
• 页码：1-9
• 全文大小：2265 K

文摘

The oxidation resistance and the crystal structure of the new Ti₄NiSi₄ compound were investigated. This compound was manufactured both as a single-phase and as the outer layer of a protective coating for vanadium alloys. The recorded oxidation rates were very low at 650?¡ãC and 750?¡ãC in air, which represents a more severe environment than those envisaged for the targeted application: fuel cladding for sodium-cooled fast reactors. The powder XRD measurements performed at the synchrotron SOLEIL allowed for the crystallographic structure determination of Ti₄NiSi₄ (S.G. Pnma; a?=?15.63931; b?=?5.08321; c?=?12.75151) with high confidence factors (R_wp?=?0.07; R_Bragg?=?0.067). Its structure consists of atomic planes stacking along the b-axis with planes at coordinates y?=?0, ?, ? and ?; it can therefore be considered as a pseudolamellar structure. It has been suggested that this peculiar feature induces a low activation energy for the phase transformation of Ti₄NiSi₄ into Ti₄Ni₄Si₇, which thus renders the transformation possible at moderate temperature. This structural rearrangement is accompanied by the liberation of Ti and Si, which leads to the formation of both TiO₂ and SiO₂ oxidation products, which are responsible for the high environmental resistance observed at 650?¡ãC in air.