Sintering behavior of Al-AlN-nanostructured composite powder synthesized by high-energy ball milling

High strength Al-AlN composites were synthesized via high-energy milling and sintering technique. Al-X wt.% AlN (X = 0, 2.5, 5 and 10) composite powders were milled in a planetary ball mill for 25 h. Morphology, particle size distribution, crystallite size, micro-strain, and microhardness of milled powders were studied. Ball-milled powders were degassed at 400 °C for 30 min. After uniaxial cold compaction, composite compacts were sintered at 650 °C for 20, 30 and 60 min under N2 atmosphere. Effects of reinforcement content, degassing treatment and sintering time on the sinterability of powders were investigated. The results revealed that the sinterability was degraded by increasing the reinforcement content, particularly above 5 wt.% AlN. Nevertheless, the sinterability of compacts was improved by degassing treatment. Near full density (>99% of theoretical density) compacts were produced by consolidation of degassed powders reinforced with AlN particles up to 5 wt.%. Additionally, rate of densification was reduced at higher reinforcement content.