Tensile, Creep Properties and Microstructural Correlations in an Extruded Ti-48Al Alloy

Abstract

In this study, new combinations of heat treatment and extrusion conditions was employed to produce fine-grained, nearly lamellar microstructures in a binary Ti-48 at.% Al alloy. The effect of subsequent heat treatment on microstructure was studied and room temperature tensile properties were determined for some representative microstructures with relatively high volume fractions of lamellar grains. High tensile strengths and ductilities (upto 2.3%) were obtained and microstructural factors thought to be responsible for these are discussed. Constant load tensile creep properties for the same microstructures were evaluated in the temperature range of 700 to 815°C for stresses from 103 to 241 MPa. This data was used to determine minimum creep rates, activation energies and stress exponents and their dependence on microstructure. A significant effect of microstructure, particularly volume fraction of lamellar grains on the creep rates was observed, and creep rates comparable to those reported in quarternary Ti-48Al alloys with similar microstructures were obtained. The various results suggest that it is possible to obtain an attractive and balanced combination of room temperature ductility and high temperature creep resistance in these materials by suitably varying thermomechanical processing and heat treatment conditions.