Processing and surface properties of Al-AlN composites produced from nanostructured milled powders

Al-AlN nanostructured composites were fabricated via the powder metallurgy method using mechanically milled aluminum powder mixed in a planetary ball-mill with different content of AlN (0, 2.5, 5, 10 wt.%) as the reinforcement. After milling for 25 h, powders were degassed and die-pressed uniaxially in a steel die and then sintered at 650 degrees C for different times. The sinterability, tribilogical and corrosion behavior of composites were investigated at predefined conditions. Sinterability of composites was degraded with increasing the reinforcement content. Wear resistance was improved by increasing volume fraction of AlN and this improvement was more pronounced at higher fraction of reinforcement. The potentiodynamic polarization was used for corrosion testing in 0.05 and 0.5 mol/L NaCl solutions. According to the results of the experiment, the amount of the second phase did not exhibit any detectable influence on the corrosion current density. In the diluted solution, E-pit was reduced in the diluted solution as a result of decrease in the amount of reinforcing particles. In the concentrated solution, E-pit was equal or lower than E-corr for all the specimens. The SEM observations revealed that regular cracks were distributed all over the surface and corrosion products had covered the surface. (C) 2009 Elsevier B.V. All rights reserved.