A study on the microsturcture of nanocrystalline Al-Ti alloys synthesized by ball milling in a hydrogen atmosphere and hot extrusion

摘要

Nanocrystalline Al-Ti alloy powder was producedby reactive ball milling (RBM) in a hydrogen atmosphere. Themicrostructure of as-RBMed powder was nanocomposite typeconsisted of nano-sized Al and nano-sized TiH2. Thermal analysisof as-milled powder showed that the decomposition of TiR2 andthe subsequent formation of Al3Ti occurred at 37O~48O℃. Thepowder was consolidated by hot extrusion at 500℃. The grain sizeof as-extruded specimens decreased with decreasing consolidationtemperature and shortening consolidation time before hotextrusion. The grain size was about 5O~1OO nm for Al-5at.%Tiand about 1OO~2OO nm for Al-l0at.%Ti. The hardness of Al-5at.%Ti specimens synthesized by RBM and subsequent hotextrusion was 25-75% higher than that of Al-8wt.%Ti alloysproduced by mechanical alloying (MA) in Ar atmosphere and hotextrusion. Room temperature and high temperature (300, 400, 500℃) tensile strengths of RBM Al-Sat.%Ti alloys were superior tothose of MA Al-8wt.%Ti alloys. But the ductility of RBM alloysdecreased. It is considered that the deterioration in ductility ofnanocomposite Al-Ti alloys was attributed to the increase of theinterface area between Al and Al3Ti and its high energy. SEMfractograph showed that fracture progressed intergranularly.