The internal nitriding behavior of Co-3Cr, Co-3Al, and Co-3Ti (a/o) over the range of 700-1,100 C

Journal Article · Thu Oct 01 04:00:00 EDT 1992 · Oxidation of Metals; (United States)

DOI:https://doi.org/10.1007/BF00666910· OSTI ID:6999980

Chen, I C; Douglass, D L ^[1]

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1. Univ. of California, Los Angeles (United States)

Internal nitridation of Co containing 3 a/o of either Cr, Al, or Ti was studied over the range of 700-1,100C in NH[sub 3]/H[sub 2](6:94 ratio). The kinetics of thickening of the reaction zone followed the parabolic rate law, suggesting that solid-state diffusion was rate controlling. Activation energies obtained were 51.2 Kcal/mol for Co-3Cr, 46.6 Kcal/mol for Co-3Ti, and 27.9 Kcal/mol for Co-3Al. XRD showed only CrN, AlN, and TiN. Deep etching revealed that AlN formed hexagonal plates near the surface when formed at high temperature, the precipitates becoming more massive (blocky morphology) near the reaction front. TiN formed elongated dendritic precipitates, whereas CrN tended to form spheroids. The precipitate size varied with temperature, decreasing with decreasing temperature. In some cases, nitriding formed a case but no visible precipitates even at very high magnifications in the SEM. The solubility of nitrogen in cobalt was determined by long-time equilibration and subsequent chemical analyses. The diffusivity of nitrogen in cobalt was determined from measured permeabilities and the experimentally determined solubilities. Mechanisms are discussed, and the behavior of internal nitridation is compared with internal carburization and oxidation in cobalt alloys.

• OSTI ID: 6999980
• Journal Information: Oxidation of Metals; (United States), Journal Name: Oxidation of Metals; (United States) Vol. 38:3-4; ISSN OXMEAF; ISSN 0030-770X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
ACTIVATION ENERGY
ALLOYS
ALUMINIUM ALLOYS
ALUMINIUM COMPOUNDS
ALUMINIUM NITRIDES
AMMONIA
CARBURIZATION
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHROMIUM ALLOYS
CHROMIUM COMPOUNDS
CHROMIUM NITRIDES
COBALT ALLOYS
COBALT BASE ALLOYS
COHERENT SCATTERING
COMPARATIVE EVALUATIONS
CRYSTAL STRUCTURE
DATA
DIFFRACTION
DIFFUSION
ELECTRON MICROSCOPY
ELEMENTS
ENERGY
EVALUATION
EXPERIMENTAL DATA
HARDENING
HYDRIDES
HYDROGEN
HYDROGEN COMPOUNDS
INFORMATION
KINETICS
MICROSCOPY
MICROSTRUCTURE
MORPHOLOGY
NITRIDATION
NITRIDES
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
NUMERICAL DATA
OXIDATION
PERMEABILITY
PNICTIDES
REACTION KINETICS
SCANNING ELECTRON MICROSCOPY
SCATTERING
SOLUBILITY
SURFACE HARDENING
SURFACE TREATMENTS
TEMPERATURE RANGE
TEMPERATURE RANGE 1000-4000 K
TITANIUM ALLOYS
TITANIUM COMPOUNDS
TITANIUM NITRIDES
TRANSITION ELEMENT COMPOUNDS
X-RAY DIFFRACTION