Production of in situ Al-TiB 2 nanocomposite powder was studied by using mechanical alloying (MA) of pure Ti, B and Al powder mixture in a planetary ball mill. A double step process was proposed to prevent the formation of undesirable phases such as Al 3 Ti intermetallic compound. The prepared Al-TiB 2 powder was consolidated by spark plasma sintering () followed by hot extrusion with a pre heating temperature of 400 ?C. Two Al matrix composites containing 10 and 20 wt.% TiB 2 were studied to evaluate the effect of TiB 2 content on mechanical behavior. The structural characteristics of powder particles and consolidated samples were studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and conventional and high resolution transmission electron microscopy (TEM). Differential scanning calorimetery (DSC) was used to study the stability of powders at high temperatures. Hardness and tensile behavior of extruded samples was also evaluated. The results showed that the double step MA process leads to the in situ formation of TiB 2 particles in the Al matrix with a fine and uniform distribution. The resulting composite powder showed phase stability at high temperatures so that no undesirable phase such as Al 3 Ti was identified in the annealed powder as well as extruded samples. The TiB 2 particles size in as-milled Al-20wt.%TiB 2 powder ranged from10 nm to 1mm although most of them were smaller than 100 nm. Hot extrusion did not increase the TiB 2 particles size significantly. Furthermore the average Al grains in the as-milled powder was measured to be 15 nm which increased to 35 nm after hot extrusion. These results show that the prepared Al-20wt.%TiB 2 nanocomposite has good thermal stability against grain growth and particle coarsening. Extruded Al-20wt.%TiB 2 showed a hardness value of 180 VHN and yield and tensile strength of 480 and 540 MPa, respectively which are much higher than those reported for similar composites made by other processes. In addition, mechanical properties showed no drastical decrease up to 300 ?C. Key Words : in situ Al-TiB 2 nanocomposite, mechanical alloying,, Hot extrusion
