Carbon in Nb-rich γ-TiAl based alloys
Intermetallic γ-TiAl based alloys are light-weight high-temperature structural materials of great technological interest. They have the potential to partly replace the heavier Ni based super alloys for applications as compressor and turbine blades in gas turbines and aero engines [1]. TiAl alloys are two-phase alloys consisting of tetragonal γ-TiAl and small amounts of hexagonal α2-Ti3Al. In order to extend their service range to higher temperatures research activities have been focused on high Nb bearing TiAl alloys. These so-called third generation or TNB alloys exhibit a significant increase in strength combined with improved creep properties and oxidation resistance [2].
Microstructure and Properties of TiAl-Based Alloys Melted in Graphite Crucible
This paper presents the chemical and phase composition, microstructure, and selected properties both at room temperature and at the temperature corresponding to the expected operating conditions of three successive generations of TiAl-based alloys (Ti-47Al-2W-0.5Si, Ti-45Al-8Nb-0.5(B,C), and Ti-45Al-5Nb-2Cr-1Mo-0.5(B,C)-0.2Si) melted in a vacuum induction furnace with high-density isostatic pressed graphite crucibles. The obtained results of mechanical and physical properties of the produced alloys were compared to the properties of reference alloys with similar chemical composition and melted in a cold copper crucible furnace. The effect of increased carbon content in the produced alloys due to the degradation of the graphite crucible during melting is higher strength properties, lower plastic properties, higher coefficient of thermal expansion, and improved creep resistance. It was shown that the proposed technology could be successfully used in the production of different generation TiAl-based intermetallic alloys.
Surface characterization and failure analysis of thermally aged, polyimide bonded titanium
This study of high temperature stable adhesive systems using 6Al-4V titanium adherends found that certain adhesive/adherends exhibit a change from cohesive to adhesive failure mode during long term 450 F thermal aging. Lap-shear specimens which exhibited adhesive failures were subjected to failure analysis using scanning transmission electron microscopy (STEM) and surface analysis techniques. Data is presented which supports the conclusion of interfacial failures for these samples.