Experimental Examination of Measurement Techniques of Threshold Stress in a Dispersion-Strengthened alloy for High-Temperature Deformation

In order to clarify the problems involved in the measurement of the threshold stress for high-temperature deformation in a dispersion-strengthened alloy, using an Al-1.5 vol%Be alloy in which the strengthening mechanism has been identified, the threshold stress was measured by four different techniques: tensile test, stress relaxation test, creep test and stress abruptly loading test. The measured values were compared with the Orowan stress and the void-hardening stress calculated from the dispersion parameters. The yield stress obtained from the tensile test at room temperature was higher than the Orowan stress: the proportional limit was about 1.3 times and the 0.2% proof stress was about 3 times. For the stress relaxation test, no clear zero-creep stress was observed at high temperatures and the approximately determined zero-creep stress strongly depended on temperature, decreasing as temperature rose. The threshold stress obtained from the creep test agreed approximately with the void-hardening stress or the slightly higher Orowan stress than the void-hardening stress. The threshold stress at high temperatures, 623 and 673 K, obtained from the stress abruptly loading test decreased from the Orowan stress to the void-hardening stress with loading time. From these results, the problems in the measurement of threshold stress are discussed and the stress abruptly loading technique is recommended.