THE MICROSTRUCTURES AND COMPRESSIVE DEFORMATION BEHAVIORS OF NANOCRYSTALLINE Al-5 at. Ti COMPACTS PREPARED BY UHP-HP

摘要

Two types of bulk nanocrystalline Al-5 at.% Ti alloys have been prepared by ultra high pressure hot pressing (UHP-HP) method of mechanical alloyed powders and their mechanical properties have been investigated through compression tests at room temperature and high temperatures (300, 400 and 500℃). TiH_2 and Al_3Ti acted as effective dispersoids to prevent grain growth during the consolidation process. A full density was reached within 250 s at 120℃ under 4.8 GPa, in specimen A120, and its microstructure was nanocomposite type with grain size less than 50 nm The consolidation temperature of 120℃ is about 300-400℃ lower than the conventional temperatures. Abnormal grain growth was observed and some Al grains grew up over 500 nm in specimen A300 prepared at 300℃. Specimen A300 had a microstructure consisting of the large Al grains and nano-sized Al_3Ti dispersoids. The mechanical properties and the deformation behaviors of specimens A120 and A300 were very different in the compression tests. The compressive stress of specimen A120 was 1010 MPa and that of specimens A300 was 467 MPa at room temperature. The strength of specimen A120 decreased greatly with increasing ductilities at 300-500℃. Specimen A300 showed very small change in ductility and strength with temperature.