A study of nitride formation during the oxidation of titanium-tantalum alloys Page: 4 of 15
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A Study of Nitride Formation During the Oxidation of Titanium-Tantalum Alloys
R. J. Hanrahan Jr., Y. C. Lu, H. Kung, and D. P. Butt
Materials Science and Technology Division
Los Alamos National Laboratory,
Los Alamos, NM, 87545
Abstract:
The oxidation rates of Ti rich titanium-tantalum alloys are significantly lower in air than
in oxygen. This nitrogen effect has been shown to be associated with the formation of a
nitride layer at or near the scale-metal interface. In the present work we used transmission
electron microscopy and microdiffraction to identify the nitrides formed on Ti5Ta and
Ti40Ta (5 and 40 weight percent Ta alloys) during identical exposures. In both alloys the
nitride develops in contact with the oxygen stabalised a-phase in the substrate. In Ti5Ta
a continuous layer of TiN forms, while in Ti40Ta a discontinuous layer of Ti2N
interspersed with Ta205 (formed from the Ta rich 3-phase) is formed. The nitride layer
acts as an oxygen diffusion barrier, reducing the dissolution of oxygen in the substrate.
Introduction
Most of the previous studies of the oxidation of Ti-Ta binary alloys were conducted in
either pure oxygen or laboratory air. The only exception was Chen and Rosa' who
performed experiments on Ti-4.37%Ta in both pure oxygen and air environments, where
they reported lower oxidation rates in air. They did not discuss the mechanism by which
nitrogen reduced the oxidation rate. However, they did report that TiN was detected near
the scale/metal interface using x-ray diffraction. We have observed that the presence of
nitrogen in the atmosphere consistently results in reduced oxidation rates of alloys
containing from 5 to 60 weight percent tantalum.2 In this paper, in order to further
elucidate the effect of nitrogen on the oxidation mechanism, we present the results of an
investigation of the structure and composition of the nitride layer using cross sectional
TEM.
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Hanrahan, R. J., Jr.; Lu, Y. C.; Kung, H. & Butt, D. P. A study of nitride formation during the oxidation of titanium-tantalum alloys, report, December 1996; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc678256/m1/4/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.