Metallurgical and Materials Transactions A

, Volume 27, Issue 10, pp 2966–2977

A high-resolution transmission electron microscopy study of the precipitation process in a dilute Ti-N alloy

Authors

  • D. Sundararaman
    • Metallurgy DivisionIndira Gandhi Centre for Atomic Research, Kalpakkam
  • S. Ranganathan
    • Centre for Advanced Study, Department of MetallurgyIndian Institute of Science
  • V. S. Raghunathan
    • Metallurgy DivisionIndira Gandhi Centre for Atomic Research, Kalpakkam
Transformations

DOI: 10.1007/BF02663846

Cite this article as:
Sundararaman, D., Ranganathan, S. & Raghunathan, V.S. MMTA (1996) 27: 2966. doi:10.1007/BF02663846

Abstract

The precipitation processes in dilute nitrogen alloys of titanium have been examined in detail by conventional transmission electron microscopy (CTEM) and high-resolution electron microscopy (HREM). The alloy Ti-2 at. pct N on quenching from its high-temperatureβ phase field has been found to undergo early stages of decomposition. The supersaturated solid solution (α″-hcp) on decomposition gives rise to an intimately mixed, irresolvable product microstructure. The associated strong tweed contrast presents difficulties in understanding the characteristic features of the process. Therefore, HREM has been carried out with a view to getting a clear picture of the decomposition process. Studies on the quenched samples of the alloy suggest the formation of solute-rich zones of a few atom layers thick, randomly distributed throughout the matrix. On aging, these zones grow to a size beyond which the precipitate/matrix interfaces appear to become incoherent and theα′ (tetragonal) product phase is seen distinctly. The structural details, the crystallography of the precipitation process, and the sequence of precipitation reaction in the system are illustrated.

Symbols

TiN

δ nitride phase with NaCl structure

Ti2N

equilibrium ε nitride phase with tetragonal (antirutile) structure

Ti6N

one of the superstructures of hexagonal α-Ti-N alloy that presumably undergoes structural change to a tetragonal one during a precipitation reaction

α

low-temperature phase of titanium (hcp)

α′

intermediate off-stoichiometric nitride phase in any composition between 16 and 33 at. pct with antirutile structure

α′′

nitrogen supersaturated α-Ti (hcp)

β

high-temperature allotropie phase of nitrogen-alloyed titanium (bcc)

Copyright information

© The Minerals, Metals & Material Society 1996