The Internal-Nitriding Behavior of Co-Fe-Al Alloys

1573-4889

INTERNAL NITRIDING ; Co-Fe-Al ALLOYS ; KINETICS ; NITROGEN PERMEABILITIES ; PRECIPITATE MORPHOLOGY

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract Co-10Fe, Co-20Fe, and Co-40Fe alloys containing3 at.% Al were internally nitrided inNH3/H2 mixtures over the range700-1000°C. The kinetics of thickening of theinternal-reaction zone followed the parabolic rate law, suggesting thatsolid-state diffusion was rate controlling. Nitrogenpermeabilities were obtained for each alloy. AlN was theonly nitride to form for all materials and at alltemperatures. At high temperature, the nitride precipitatesformed hexagonal plates near the surface, theprecipitates becoming more blocky near the reactionfront. Precipitate size increased with increasing depthin the alloy and increasing temperature, becauseof competition between nucleation and growth processes.Increasing iron content increased the reacion kineticsdue to increased nitrogen solubility with increasing iron content.

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