Microstructure and properties of duplex δ-Al3(Ti, V)/β-(Ti, V) alloys

The microstructures of multiphase intermetallic alloys with compositions Al₇₀Ti₁₀V₂₀ and Al₆₂Ti₁₀V₂₈ based on the trialuminide Al₃Ti have been characterized, following chill casting and postsolidification heat treatment, using a combination of scanning electron microscopy and transmission electron microscopy (TEM). Evidence of a eutectic reaction of the form L → δ-Al₃(Ti, V)+ζ-Al₈V₅, not previously reported in the Al-Ti-V system, has been observed in both alloys solidified at sufficient levels of undercooling. The ζ phase is replaced by metallic β-(Ti, V) phase during subsequent heat treatment in the range 1073 to 1273 K, and differential thermal analysis (DTA) of samples prean-nealed at 1173 K revealed an endothermic peak at ∼1560 K, consistent with equilibrium eutectic melting of the form (δ+β) → L. Although the chill-cast alloys retained metastable intermediate high-temperature phases, duplex metallic-intermetallic microstructures, containing uniform fine-scale distributions of metallic β-(Ti, V) solid solution in a δ-Al₃(Ti, V) intermetallic matrix, have been produced in both alloys during isothermal heat treatments at temperatures in the range 1073 to 1273 K. For both alloys, the bulk Vickers hardness of such microstructures remained in excess of that of binary Al₃Ti, while in the Al₆₂Ti₁₀V₂₈ alloy, where the increased volume fraction of β phase took the form of a near-continuous network within δ matrix, there was evidence arising from indentation tests of a substantial improvement in the cracking resistance compared to both chill-cast ternary alloy and binary Al₃Ti.