THERMAL STABILITY AND TENSILE PROPERTIES OF A MECHANICALLY ALLOYED Al-Ti-O BASED MATERIAL

摘要

The microstructure, hardness, and tensile properties of a mechanically alloyed (MA) Al-0.35wt%Li-lwt%Mg-0.25wt%C+7.5vol%TiO_2 material have been characterised, as-extruded, and after heat treatments at 773K, 823K, 873K and 928K. In the as-extruded condition, 'spherical-shaped' Al_3Ti, monoclinic TiO (M-TiO), cubic TiO (C-TiO), 'unreacted' TiO_2 (brookite, anatase, and rutile), MgO, and A1_4C_3 were the main phases identified by TEM. After 24h at 928K, the major dispersed phases included Al_3Ti, α-Al_2O_3, Al_4O_3, and MgO. Al_3Ti became more elongated and faceted after heat treatment at 928K, and there was evidence of substantial Al_3Ti coalescence. Hardness increased by ～ 4%, 3%, 10% and 23% after 504h at 773K, 24h at 823K, 24h at 873K and 24h at 928K, respectively. The starting grain size (0.49 +- 0.18μm) was unaffected by heat treatment for 24h at 773K (0.46 +- 0.18μm) and was only increased by ～ 0.1μm after 168h at 928K. Compared to 24h at 928K, the hardness was reduced by ～ 4% after 168h at this temperature. After heat treatment for 48h at 823K, the room temperature (RT) yield strength (YS) and ultimate tensile strength (UTS) were increased by ～ 7% and 13%, respectively, while elongation to fracture suffered a reduction of ～ 45% compared to the as-extruded condition. RT strength and elongation to fracture were not greatly affected following heat treatment for 48h at 773K. SEM showed ductile fracture surfaces after RT testing, as-extruded, and following heat treatment for 48h at 823K.