Transformation to Ni5Al3 in a 63.0 At. Pct Ni-Al alloy

Autor:	I. E. Locci, Gary M. Michal, K. Vedula, P. S. Khadkikar
Rok vydání:	1993
Předmět:	Phase boundary Nial Materials science Metallurgy Metals and Alloys Nucleation Intermetallic Analytical chemistry Condensed Matter Physics Microstructure Mechanics of Materials Martensite Orthorhombic crystal system Grain boundary computer computer.programming_language
Zdroj:	Metallurgical Transactions A. 24:83-94
ISSN:	2379-0180 0360-2133
DOI:	10.1007/bf02669606
Popis:	Microstructures in a 63 at. pct Ni-Al alloy, produced by a powder metallurgy process, have been investigated in detail in as-quenched and aged (823 to 923 K) conditions. The parent L10 martensite plus B2 NiAl microstructure in the as-quenched state transformed nearly completely to the orthorhombic Ni5Al3 phase upon aging at 823 K for 720 hours. The volume fraction of Ni5Al3 formed as a function of aging time at 823 K was observed to obey cellular reaction kinetic behavior. The specimens aged at 823 K for short times indicated that nucleation of the Ni5Al3 phase occurred preferentially at grain boundaries. Transmission electron microscopy (TEM) observations of short-time aged specimens revealed a complex microstructure consisting of shortrange ordered domains of Ni2Al in a matrix of 7R martensite, in addition to new variants of 3R martensite and Ni5Al3. Aging at 873 and 923 K for 720 hours produced a stable two-phase microstructure consisting of NiAl and Ni5Al3. A quantitative phase analysis was carried out to calculate the (NiAl + Ni5Al3)/Ni5Al3 phase boundary locations. The measured lattice parameters of Ni5Al3 formed at 823, 873, and 923 K indicated an increase in tetragonality of the phase with increasing nickel content.
Databáze:	OpenAIRE
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