Phase equilibrium and the formation of a graded diffusion layer by bondingL1(0)- and L1(2)- alloys in the Ti-Al-Mn system

In order to clarify the phase equilibrium in the Ti-Al-Mn system, the verti cal section and the microstructure of the L1(0)/L1(2) two phase alloys have been determined experimentally. In addition, diffusion bonding of L1(0)-ty pe and Lit-type alloys in the Ti-Al-Mn system was carried out to study a fu nctionally graded diffusion layer. The Ti-43Al-5Mn(L1(0)) and Ti-61Al-14Mn( L1(2)) alloys were bonded at 1473 K for 1 h under 30 MPa pressure, and anne aled at 1423 K for 48 h in a vacuum (similar to 10(-4) Pa). The resulting d iffusion layer had Al-rich L1(0) phase layer of about 70 mu m and L1(2)+L1( 0)(coherent precipitated) two phase layer of about 70 mu m. The formation o f the L1(2)+ L1(0) (coherent precipitated) two phase microstructure is caus ed by the presence of the Ti-rich Lit phase field at higher temperatures. I t was found that such diffusion layers have a gradual composition, a good l inear expansion coefficient, and an excellent oxidation resistance for func tionally graded materials.