Microstructure and room and high temperature mechanical properties of ultrafine structured Al-5 wt%Y ₂ O ₃ and Al-5 wt%La ₂ O ₃ nanocomposites fabricated by mechanical alloying and hot pressing

Microstructure and yield strength at room temperature and 300 °C in Al-5 wt%Y ₂ O ₃ and Al-5 wt%La ₂ O ₃ fabricated by mechanical alloying (MA) have been investigated by transmission electron microscopy and compression test. Al-5 wt%Y ₂ O ₃ and Al-5 wt%La ₂ O ₃ were fabricated by MA with powders Al, Y ₂ O ₃ and La ₂ O ₃ . The alloy powders were consolidated by hot pressing at 550 °C under 400 MPa. Yield strengths in the consolidated Al-5 wt%La ₂ O ₃ at room temperature and 300 °C were higher than those in the consolidated Al-5 wt%Y ₂ O ₃ . Vickers microhardness at room temperature in Al-5 wt%La ₂ O ₃ after the consolidation increased as compared with that before the consolidation. In contrast, Vickers microhardness at room temperature in Al-5 wt%Y ₂ O ₃ after the consolidation was almost the same as that before the consolidation. X-ray diffraction analyses revealed that in Al-5 wt%La ₂ O ₃ , an intermetallic compound Al ₁₁ La ₃ was formed during the consolidation. Al ₁₁ La ₃ was finely dispersed in the matrix after the consolidation. In Al-5 wt%Y ₂ O ₃ , however, no intermetallic compound was formed after the consolidation. It is noted that higher yield strength in Al-5 wt%La ₂ O ₃ than Al-5 wt%Y ₂ O ₃ at room temperature and 300 °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 Al-5 wt%La ₂ O ₃ , which is due to the in-situ formation of intermetallic precipitates Al ₁₁ La ₃ during the consolidation.