Microstructure and room and high temperature mechanical properties of ultrafine structured Al-5 wt%Y2O3 and Al-5 wt%La2O3 nanocomposites fabricated by mechanical alloying and hot pressing

Microstructure and yield strength at room temperature and 300 degrees C in Al-5 wt%Y2O3 and Al-5 wt%La2O3 fabricated by mechanical alloying (MA) have been investigated by transmission electron microscopy and compression test. A15 wt%Y2O3 and A1-5 wt%La2O3 were fabricated by MA with powders Al, Y2O3 and La2O3. The alloy powders were consolidated by hot pressing at 550 degrees C under 400 MPa. Yield strengths in the consolidated Al-5 wt %La2O3 at room temperature and 300 degrees C were higher than those in the consolidated Al-5 wt%Y2O3. Vickers microhardness at room temperature in Al-5 wt%La2O3 after the consolidation increased as compared with that before the consolidation. In contrast, Vickers microhardness at room temperature in Al-5 wt%Y2O3 after the consolidation was almost the same as that before the consolidation. X-ray diffraction analyses revealed that in A1-5 wt%La2O3, an intermetallic compound Al11La3 was formed during the consolidation. Al11La3 was finely dispersed in the matrix after the consolidation. In Al-5 wt%Y2O3, however, no intermetallic compound was formed after the consolidation. It is noted that higher yield strength in Al-5 wt%La2O3 than Al-5 wt%Y2O3 at room temperature and 300 degrees C is derived from grain boundary strengthening and dispersion strengthening due to pinning of Al grain growth and retarding of dislocation motion by fine numerous dispersoids. The key factor is the large number density of dispersoids in A1-5 wt%La2O3, which is due to the in-situ formation of intermetallic precipitates Al11La3 during the consolidation.