Nitridation of Ni-based alloys: thermodynamics, kinetics and deformation phenomena accompanying internal precipitation

A. Kodentsov, J.K. Kivilahti, F.J.J. Loo, van

Research output: Contribution to journalArticleAcademicpeer-review

4 Citations (Scopus)
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Abstract

When a moderately stable phase is precipitated out during an internal reaction, the behaviour of the penetrating atoms within the diffusion zone can be interpreted based on thermodynamic considerations. Evidence for "up-hill" diffusion of the penetrating species through the matrix towards the precipitation front during the internal nitridation of Ni-Cr alloys at 1125 °C and 6000 bar of N2-pressure was predicted. Such behaviour of nitrogen is opposite to the boundary conditions in Wagner's description of internal reactions. A volume change associated with the precipitation reaction resulted in a stress gradient between alloys surface and the internal nitridation front. Stress relief occurred mainly by transport of nickel to the gas/metal interface. Pipe diffusion-controlled creep is the dominant stress accommodation mechanism during nitriding of dilute Ni-Cr alloys at 700 °C under a flowing NH3 + H2 gas mixture.
Original languageEnglish
Pages (from-to)501-511
JournalRare Metals
Volume25
Issue number5
DOIs
Publication statusPublished - 2006

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