Microstructure characterisation and CTE study of Fe-42Ni-Nb invar alloys

• Published in: Materials science and technology Vol. 27; no. 3; pp. 655 - 660
• Main Authors: Xu, P. Q., Zhao, X. J., Xu, G. X., Li, L. N., Yu, Z. S.
• Format: Journal Article
• Language: English
• Published: London, England Taylor & Francis 01.03.2011; SAGE Publications; Taylor & Francis Ltd
• Subjects: Alloys; Casting; CTE; Ferrous alloys; Invar alloy; Low expansion alloys; Materials science; Melting; Microstructure; Nickel; Precipitation hardening; Rare earth; Rare earth metals; Temperature; Thermal expansion; Transmission electron microscopy; Invar alloy; Rare earth; Microstructure; CTE
• ISSN: 0267-0836; 1743-2847
• DOI: 10.1179/026708309X12512744154324

Invar alloy has low coefficient of thermal expansion; however, the week strength always limits its application. To circumvent this problem, the authors have designed Fe-42%Ni-Nb invar alloy using midfrequency vacuum induction melting technique. The microstructures of this alloy were characterised by means of XRD, SEM and TEM. The multicomponent composition (NiFeCMnNb) is chosen such that upon chill casting of the alloy the liquid undergoes a metastable reaction, forming a strengthening NbC precipitated phase on γ-(Fe, Ni) solid solution. As a result, the alloy achieves the low coefficient of thermal expansion α 30-100 =6·14 × 10 −6 K −1 ranged from room temperature to 100°C. The results show: in NiFe invar alloys, the primary phases are γ-(NiFe), FeNi 3 ) Ni and Fe 2 C; and with the addition of carbon, manganese and rare earth niobium, NiFeCMnNb invar alloy achieves such primary phases as γ-(NiFe) and Nb y C x ; and TEM structure consists of superfine structure and its matrix is γ-(NiFe).