CREEP-BEHAVIOR OF AN AL-2.0 WT PCT LI ALLOY IN THE TEMPERATURE-RANGE 300-DEGREES-C TO 500-DEGREES-C

The elevated temperature deformation behavior of an Al-2.0 wt pct Li a lloy in the temperature range 300-degrees-C to 500-degrees-C was studi ed using constant extension-rate tension testing and constant true-str ess creep testing under both isothermal and temperature cycling condit ions. Optical microscopy and transmission electron microscopy (TEM) we re employed to assess the effect of deformation on microstructure. The data showed that the stress exponent, n, has a value of about 5.0 at temperatures above the alpha + deltaAlLi solvus (approximately 380-deg rees-C) and that subgrains form during plastic deformation. Models for dislocation-climb and dislocation-glide control of creep were analyze d for alloys deformed in the temperature range of stability of the ter minal AlLi solid solution. A climb model was shown to describe closely the behavior of this material. Anomalous temperature dependence of th e activation energy was observed in this same temperature range. This anomalous behavior was ascribed to unusual temperature dependence of e ither the Young's modulus or the stacking fault energy, which may be a ssociated, in turn, with a disorder-order transformation on cooling of the alloy.