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Title: Identification of a kinetic length scale which dictates alloy phase composition in Ni-Al interfaces on annealing at low temperatures

Ni-aluminides are an important class of intermetallics from technological point of view. Ni-Al phase diagram has been studied in detail experimentally as well as theoretically. It is known that if annealed at low temperature, the first alloy phase is usually NiAl{sub 3} according to Bené's rule. It is also understood that heat of formation may get modified by local densities of the constituents forming the alloy. In this regard, it is important to identify a kinetic length scale for defining “local density” in a system. We have deposited ultrathin multilayers of Ni and Al of layer thickness in tens of nanometres with Ni:Al stoichiometric ratio as 3:1 and 1:3, respectively. Considering these stoichiometry, Ni{sub 3}Al and NiAl{sub 3} are the thermodynamically favoured alloy phases in these samples. We used x-ray reflectivity, polarized neutron reflectivity, x-ray diffraction, and secondary ion mass spectroscopy to follow the alloy formation after annealing and identified the alloy phases at interfaces with nanometre resolution. Diffusion length of Ni and Al was obtained using Darken's law. Our results predict that ‘diffusion length’ is the unique length scale that connects kinetics to local density. In another interesting observation, using “virtual Kirkendall markers” at the interfaces, we showed asymmetrymore » in consumption of Al for alloy formation, at Al on Ni (Al/Ni) and Ni on Al (Ni/Al) interfaces by comparing as-deposited and annealed states with respect to the markers.« less
Authors:
; ; ;  [1] ;  [2]
  1. Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)
  2. UGC DAE Consortium for Scientific Research, Khandwa Road, Indore 452001 (India)
Publication Date:
OSTI Identifier:
22402753
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 116; Journal Issue: 22; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANNEALING; DENSITY; DIFFUSION LENGTH; FORMATION HEAT; INTERFACES; INTERMETALLIC COMPOUNDS; ION MICROPROBE ANALYSIS; NEUTRONS; PHASE DIAGRAMS; REFLECTIVITY; TEMPERATURE RANGE 0065-0273 K; X RADIATION; X-RAY DIFFRACTION