MICROSTRUCTURE AND PROPERTIES OF DUPLEX DELTA-AL-3(TI, V) BETA-(TI, V) ALLOYS/

The microstructures of multiphase intermetallic alloys with compositio ns Al70Ti10V20 and Al62Ti10V28 based on the trialuminide Al3Ti have be en characterized, following chill casting and postsolidification heat treatment, using a combination of scanning electron microscopy and tra nsmission electron microscopy (TEM). Evidence of a eutectic reaction o f the form L --> delta-Al-3(Ti, V) + zeta-Al8V5, not previously report ed in the Al-Ti-V system, has been observed in both alloys solidified at sufficient levels of undercooling. The zeta phase is replaced by me tallic beta-(Ti, V) phase during subsequent heat treatment in the rang e 1073 to 1273 K, and differential thermal analysis (DTA) of samples p reannealed at 1173 K revealed an endothermic peak at similar to 1560 K , consistent with equilibrium eutectic melting of the form (delta + be ta) --> L. Although the chill-cast alloys retained metastable intermed iate high-temperature phases, duplex metallic-intermetallic microstruc tures, containing uniform fine-scale distributions of metallic beta-(T i, V) solid solution in a delta-Al-3(Ti, V) intermetallic matrix, have been produced in both alloys during isothermal heat treatments at tem peratures in the range 1073 to 1273 K. For both alloys, the bulk Vicke rs hardness of such microstructures remained in excess of that of bina ry Al3Ti, while in the Al62Ti10V28 alloy, where the increased volume f raction of beta phase took the form of a near-continuous network withi n delta matrix, there was evidence arising from indentation tests of a substantial improvement in the cracking resistance compared to both c hill-cast ternary alloy and binary Al3Ti.