Hydrogen Absorption in Advanced Aerospace Materials

The research program in Advanced Aerospace Materials is directed at reducing the detrimental effects associated with the absorption of hydrogen in structural materials. In particular, intermetallic alloys of Ti are of considerable interest for applications as high-temperature structural materials because of their low density, high strength, and resistance to oxidation at high temperatures. However these alloys also have lower than desired ductility at room temperature, and may be susceptible to various forms of hydrogen embrittlement. The primary goal of our studies is to identify the mechanisms of hydrogen absorption in Ti alloys, and to determine whether other elements (e.g. Nb, V, or Ta), added to the alloy to improve mechanical properties, might in fact be contributing as well to increasing, or decreasing, hydrogen uptake. We use the technique of Elastic Recoil Detection Analysis (ERDA) to measure the concentration of hydrogen in the material as a function of hydrogen exposure for various surface treatments, hydrogen pressures and sample temperatures. X-ray photoemission and Auger electron spectroscopy are used to determine the amount and chemical state of the various elements on the sample surface. ERDA is an extension of the Rutherford scattering process to the case where the target atom is lighter than the incident ion. In our measurements, incident He+ ions collide with protons, ejecting them from the sample. The protons are counted, and the concentration of hydrogen in the sample is calculated using well-understood scattering cross sections and kinematics.

The samples selected for study are: `₂-Ti₃Al, ~-TiAl and ~-21S (Ti-15Mo-2.7Nb-3Al-0.2Si). These alloys are among those being considered for aerospace applications, either directly or as matrix material for composite structures. These samples are polycrystalline and may contain multiple phases. Thus it is extremely valuable to characterize the microstructure of the surface as well as possible. We use a scanning electron microscope with x-ray analysis to characterize the grain structure and composition of the surface of our samples.

Contact Information

Mail:	Dr. Richard J. Smith
	Department of Physics
	Montana State University
	Bozeman, MT 59717