Structure and selected properties of laminate composite Ti6Al2Cr2Mo titanium alloy – Ti-Al intermetallic phases
Tadeusz Wierzchoń, Maciej Ossowski Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa
Quarterly No. 3, 2006 pages 50-53
DOI:
keywords: laminate composite, titanium alloy Ti6Al2Cr2Mo, Ti-Al intermetallic phases, magnetron sputtering, glow discharge oxidizing, surface layer, structure, corrosion resistance, wear resistance
abstract The rapid progress in engineering enhances the demands for materials with improved mechanical properties, in particular the resistance to frictional wear, to corrosion, erosion etc. These demands can be satisfied by e.g. applying various surface engineering techniques which permit modifying the microstructure as well as the phase and chemical composition of the surface layers of the treated parts. The processes of glow discharge assisted oxidizing combined with magnetron sputtering of aluminum (aluminum alloys) coatings and diffusion welding yielded gradient-type materials that were laminate composites with the following arrangement of the layers: Ti6Al2Cr2Mo titanium alloy/Ti-Al intermetallic phases/Ti6Al2Cr2Mo titanium alloy (or a multiple of this system) with a diffusion layer of the Al2O3+TiAl3+TiAl+Ti3Al type formed on the surface. These composites are new materials, with the density lower than that of titanium alloys and a good resistance to frictional wear (Fig. 5) and corrosion (Fig. 6). The temperature of the fabrication of these composites does not exceed 700oC. The individual zones of the composites have a diffusion character, and their microstructure, thickness and phase composition can be modified by modifying the process parameters, in particular the parameters of the glow discharge assisted oxidizing since these decide about the nano-crystalline or fine-crystalline structure of the individual phases of the surface layer (Fig. 4). The formation of the TiAl3 aluminide in the outer zone of the composite layer, between the Al2O3 and TiAl zones, is advantageous, since the TiAl3 phase has a higher Young modulus and a better resistance to high-temperature oxidation than the other titanium aluminides. The near-surface zone of the composite layer provides therefore double protection against high-temperature oxidation (the Al2O3 and TiAl3 zones). Moreover, the fact that the Young modulus of the individual zones, which decreases with increasing distance from the surface from about 310 GPa in Al2O3, through about 210 GPa in TiAl3, 180 GPa in TiAl and 130 GPa in Ti3Al, to about 120 GPa in the Ti6Al2Cr2Mo titanium alloy substrate.