On the Orowan stress in intermetallic ODS alloys and its superposition with grain size and solid solution hardening

The intermetallic trialurninide Al67Ti25Cr8 was strengthened by nano-scaled dispersions of up to 3 vol.% yttrium and aluminum oxide via mechanical milling. Subsequent powder consolidation, heat treatment, and thermo-mechanical treatment yielded grain growth to an increasing degree, resulting in grain sizes ranging from sub-mu m level to about 0.5 mm. Consequently, the room-temperature yield strength sigma(0), as determined by constant compression rate tests, increases due to three different hardening contributions, namely dispersion strengthening sigma(OR) due to Orowan bypassing, fine-grain strengthening sigma(HP) due to Hall-Petch relation, and, finally, as virtually always present, some solid-solution strengthening as. The analysis of the particle parameters was done using TEM as well as focused ion beam (FIB) imaging. The latter provides the opportunity to directly determine the mean radius r(s) of planar intersections with spherical particles and their nearest-neighbour spacing L since it displays a plane section through the 3-dimensional arrangement of dispersoids. The analysis of the strengthening contributions indicates that a Pythagorean superposition permits an appropriate modeling of the measured yield strength sigma(0).