ISSN:
1573-4889
Keywords:
stainless steel
;
nickel alloys
;
chromium nitride
;
diffusion
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Nine commercial high-temperature alloys were reacted with NH3 and with N2-5%H2 at temperatures of 1000–1200°C. In all cases extensive internal nitridation developed according to parabolic kinetics. Reaction with N2 produced precipitates of Cr2N plus, at 1000°C, some external CrN, in accordance with thermodynamic prediction. However NH3 produced an external scale of CrN and a near-surface zone of internal CrN as well as a deeper zone of Cr2N at 1100 and 1200°C. The CrN phase is metastable, and results from catalytic dissociation of NH3, which produces a high effective nitrogen activity. This high activity also leads to faster internal-precipitation reactions, whereas reaction rates in nitrogen are in reasonable agreement with Wagner's model of rate control by inwardly diffusing nitrogen at its equilibrium solubility. Precipitate morphologies are complex, reflecting the importance of the energy barrier to homogeneous nucleation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01058247
