Characterisation of diffusion bond TiAl–Ti 6242 joints

Abstract

The γ-TiAl based titanium aluminides are considered as candidates to replace the current materials in engineering applications at high temperatures due to their light weight and high temperature properties. On the other hand, Ti6242Si alloys offer tensile and long-term creep strength which is achieved through microstructural tailoring of alloys with increased α stabiliser content. The equiaxed, duplex and lamellar microstructures that meet the modern engine design demands qualify these alloys for aero-engine applications. Both materials are well studied for processing, characterisation and structural applications [1–3]. However, fully utilisation of these materials for demanding engineering applications necessitate advanced joining technologies where homogeneous material properties are retained with high deformation and crack resistant bonds.The present paper reports on a systematic study being carried out on the diffusion bonding of γ-TiAl intermetallics and equiaxed α/β Ti6242Si alloy. Emphasis is put on the diffusion bonding process parameters of industrial interest, characterisation and properties of the joints. The process variables including temperature, pressure and time are optimised to produce joints with sound microstructure, bond quality and strength. The chemical composition and phase morphologies are studied using scanning electron microscopy and energy dispersive X-ray (EDX) analysis. Mechanical characterisation includes the standard tensile and micro tensile tests at ambient to high temperatures. Deformation, crack initiation and crack growth behaviours are studied on fracture surfaces and side surfaces of the tested diffusion bond joints.