Formation of Graded Diffusion Layer by Bonding of L1₀-and L1₂-Alloys in the Ti-Al-Cr System

Abstract

Diffusion bonding of L1₀-type and L1₂-type alloys in the Ti-Al-Cr system was carried out to study graded diffusion layer. The Ti₅₂Cr₅Al₄₃(L1₀) and Ti₂₅Cr₁₄Al₆₁(L1₂) alloys were bonded at 1473 K for 1 h under 30 MPa, and annealed at 1423 K for 48 h in a vacuum(-10^-4Pa). The resulting diffusion layer had Al-rich L1₀ phase layer of about 50μm and L1₂/L1₀ (coherent precipitated) two phase layer of about 50μm. The formation of the L1₂/L1₀ two phase layer is caused by the presence of the Ti-rich L1₂ phase field at higher temperatures. It was found that such diffusion layers have a preferable composition gradient and a graded linear expansion coefficient for functionally graded materials.