Effect of Hydrogen on the Elastic Modulus and Hardness of Gamma Titanium Aluminides

University Of Puerto Rico Mayaguez, Mayaguez PR

Investigators

Abstract

9988846 Sundaram In preliminary microindentation tests, gamma titanium aluminide (TiAl) samples charged with hydrogen for different times at room temperature exhibited lower values of elastic modulus and hardness compared to uncharged samples. On degassing the samples, the original values of hardness and elastic modulus were recovered. This preliminary result merits additional careful and detailed study of the effect of hydrogen on the elastic modulus and hardness of these materials. The research examines the effect of hydrogen on gamma TiAl by evaluating the elastic modulus and hardness. The alloy selected for the study is Ti-46.5Al-4(Cr,Nb,Ta,B) provided in sheet form in the fully lamellar condition. Hydrogen will be introduced into sheet samples by cathodic charging in an acid environment, both in the galvanostatic and the potentiostatic modes for a variety of charging conditions. X-ray diffraction will detect the formation of hydride on the surface of the samples under various charging conditions. The hydride formed will be characterized using transmission electron microscopy. A vibrational technique will determine the elastic modulus of both charged and uncharged specimens by measuring the transverse frequencies. Microhardness measurements will measure sample hardness. Standard room temperature tensile tests will be carried out to simultaneously evaluate their tensile properties. Selected hydrogen-charged samples will be degassed using a vacuum anneal at 1000o C. These degassed samples will then be subjected to the above tests. It is expected that the results from this investigation will lead to greater understanding of the role of hydrogen on the properties of gamma TiAl. %%% Gamma titanium aluminides are an emerging class of materials with potential for use as advanced turbine engine materials in hypersonic airplanes. Consequently, the behavior of gamma TiAl in the presence of hydrogen is of great technological importance especially under stringent mechanical and thermal environments. ***