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

Abstract

Abstract The intermetallic trialuminide 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-mechani-cal treatment yielded grain growth to an increasing degree, resulting in grain sizes ranging from sub-μm level to about 0.5 mm. Consequently, the room-temperature yield strength σ 0 as determined by constant compression rate tests, increases due to three different hardening contributions, namely dispersion strengthening σ OR due to Orowan bypassing, fine-grain strengthening σ HP due to Hall-Petch relation, and, finally, as virtually always present, some solid-solution strengthening σ s. 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 σ 0.