Premium
Radiotracer studies of carbon permeation through oxide scales on commercial high temperature alloys and model alloys
Author(s) -
Grabke H. J.,
Ohla Klaus,
Peters Jörg,
Wolf Irene
Publication year - 1983
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19830341002
Subject(s) - oxide , materials science , chromia , alloy , carbon fibers , nucleation , graphite , permeation , gravimetric analysis , layer (electronics) , metallurgy , penetration (warfare) , chemical engineering , composite material , chemistry , biochemistry , operations research , membrane , composite number , engineering , organic chemistry
Chromia‐ and alumina‐forming commercial high temperature alloys and model alloys were preoxidized at 900 or 1000 °C in H 2 ‐H 2 O at a low oxygen potential. The oxide layers were characterized by different methods. The carbon permeation through the oxide layers was studied by exposing the preoxidized specimens to an atmosphere CO‐CO 2 ‐H 2 ‐H 2 O, tagged with radiocarbon, for long time. The carbon was detected by stepwise polishing and measuring the radioactivity. A slow carbon ingress occurs through chromia layers, differences in the protection by the oxide scale could be tested by the radiotracer method for the different alloys. The alumina layer on Fe‐6 Al is not protective, but no carbon ingress could be detected for an alloy Fe‐6Al‐0.5Ti. Autoradiography, AES and X‐ray structure analysis showed the presence of Ti(O,C) beneath the outer Al 2 O 3 ‐layer. The oxicarbide improves the nucleation and adherence of the Al 2 O 3 and prohibits the carbon penetration. The results were confirmed by gravimetric experiments, after preoxidation samples were exposed to CO‐CO 2 ‐H 2 ‐H 2 O at high carbon activity (a c = 1.02), carburization and graphite deposition were retarded or prohibited by dense and well adherent oxide layers.