Evaluation of strengthening behavior of Al-AlN nanostructured composite by the use of modified Heckel model and response surface methodology

Al-AlN powder mixtures with 0, 5 and 10 wt.% of AlN were mechanically alloyed in a planetary ball mill under argon atmosphere up to 25 h. The compressibility behavior of the obtained samples was investigated in a wide range of compaction pressure from 62.5 up to 875 MPa. It was shown that presence of 10 wt.% of AlN leads to a reduction in the rate of hardening after 15 h milling. The morphological features of the samples showed that after 15 and 25 h milling, a relative steady-state equiaxed powder can be synthesized in the case of Al-10% AlN and Al-5% AlN, respectively. A combined modified Heckel model and response surface methodology (RSM) based on central composite design (CCD) was also employed to study the effect of three factors of AlN wt.%, milling time and compaction pressure on the densification and strengthening behavior of nanostructured Al-AlN composites. All the three factors had statistically significant effect on density (D) and yield strength (YS); while in the case of milling strengthening fraction (MSF) as the response, AlN was statistically insignificant. Second order polynomial models were successfully fitted to the responses in different ranges of low (125-375 MPa) and high (625-875 MPa) pressures. Furthermore, the statistically significant interactions between parameters were comprehensively discussed in each case. (C) 2011 Elsevier B. V. All rights reserved.