Ordering reactions in an Ni25Mo8Cr alloy

• Published in: Acta materialia 1996-04, Vol.44 (4), p.1591-1600
• Main Authors: Kumar, M., Vasudevan, V.K.
• Format: Article
• Language: English
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; General studies of phase transitions; Metals. Metallurgy; Order-disorder and statistical mechanics of model systems; Order-disorder transformations; statistical mechanics of model systems; Physics
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/1359-6454(95)00258-8

The transformations from short- to long-range order in Haynes® Alloy 242, a nominal Ni25Mo8Cr (in wt%) alloy, during isothermal aging at temperatures between 550 and 750°C are reported using microhardness measurements, and optical and transmission electron microscopy. Aging below the critical transformation temperature (∼ 775°C) led to considerable hardening; this hardening was associated with the formation of a very high volume fraction of Ni 2(Mo,Cr) domains/precipitates. The transformation from short- to long-range order was observed to proceed by a mechanism of continuous ordering at temperatures ⩽ 700°C, whereas at temperatures (750°C) close to the critical temperature a first order nucleation and growth mechanism appeared to be operative. The sequence of transformations are correlated with the associated diffraction effects and discussed in terms of theoretical formulations and experimental observations of other studies.