Hydrogen permeation through coated and uncoated WASPALOY
- PDF / 611,051 Bytes
- 6 Pages / 613 x 788.28 pts Page_size
- 53 Downloads / 238 Views
I.
INTRODUCTION
IT has
been established that hydrogen embrittles many metals, including many Ni-base alloys.t~'2]The embrittlement caused by hydrogen can be manifested as decreased reduction in area in a tensile test or by slow crack growth under constant load.[3] The characteristic of hydrogen which differentiates it from other solutes which might cause embrittlement is its high diffusivity-- several orders of magnitude larger than other solute diffusivities in metals. Therefore, studies of factors influencing hydrogen permeation are important to understanding the kinetics of hydrogen embrittlement. Ni-base alloys have been adopted for high temperature service at high stress levels and where high surface stability is required. These alloys are being used in different types of gas turbines, and now are used in rocket engines, nuclear reactors, chemical plants, and other places where hydrogen might enter from the environment. Knowledge of hydrogen degradation would be useful in predicting mechanical failures near room temperature and after exposure to hydrogen in these critical applications. The material being tested for hydrogen permeation in this report is WASPALOY, a Ni-base superalloy used for disks in hydrogen fueled turbines which operate in a moist hydrogen environment. The conditions studied were Pdcoated and Au-plated WASPALOY in dry hydrogen gas and uncoated WASPALOY in moist and dry hydrogen gas. Since bare materials are often used in engineering applications, the uncoated WASPALOY tested in dry and moist hydrogen gas was intended to yield meaningful data for practical use. Pd-coating was chosen to determine the "true" hydrogen permeation characteristics of WASPALOY. Furthermore, it is well known that metals with extremely low *WASPALOY is a trademark of United Technologies Corporation. T-P. PERNG, formerly Postdoctoral Associate at the University of Illinois, is Associate Professor at National Tsing Hua University, Hsinchu, Taiwan. M.J. JOHNSON, formerly Student Assistant at the University of Illinois, is with IBM in Boulder, CO. C.J. ALTSTETTER is Professor of Physical Metallurgy, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 1304 West Green Street, Urbana, IL 61801. Manuscript submitted June 8, 1987. METALLURGICAL TRANSACTIONS A
hydrogen permeability are suitable as coatings to reduce the quantity of hydrogen penetrating the base alloy. Of these, gold is a good candidate for WASPALOY because it has probably the second lowest hydrogen permeability in metals, next to tungsten, r41 and can be easily coated and used at the high temperatures of interest. A gold-plated specimen of WASPALOY was thus tested in dry hydrogen gas to determine the degree to which hydrogen permeation was reduced by gold plating. From gas phase permeation experiments, hydrogen diffusivity and permeability were calculated from the time lag for diffusion through the specimen and the steady state flux permeating through a metal membrane, respectively. In a bulk diffusion-controlled per
Data Loading...
