The role of mechanical alloying time on the thermal and mechanical behavior of Al/Ni reactive composites

Reactive composites are a new group of composite materials consisting of two or more materials that cannot ignite or explode in the Environmental conditions, but can release a lot of energy due to shock and severe impact loads. This study aimed to investigate the effect of milling time on the microstructure, thermal and mechanical properties of the Al-Ni composite. For this purpose, the Al-Ni compound with a 2:1 Al:Ni molar ratio was milled for 0.5, 1, 2, 4 and 6 hours in attrition mill and mixed. Then the samples were cold press and sintered at 400 ˚C under argon atmosphere for one hour. The microstructure of samples was analyzed by field emission scanning electron microscope (FESEM) and XRD. To investigation of thermal properties DSC and DTA analysis and for mechanical properties compression test and Hopkinson test were used. The DSC analysis results showed that by increasing the milling time, the reaction start temperature decreased from 650.34 °C in the sample milled to 0.5 hour to 645.84 °C the sample milled to 6 hour and the reaction heat (enthalpy) decreased from 26.87 J/g to 14.84 J/g. The results of compression and Hopkinson tests of samples after 6 hours milling time showed 21 and 42 percent increase in compressive strength, respectively compared to samples after 0.5 hours milling time. Also, the results showed that the compressive strength increased by changing the strain rate from 0.01 s-1 (in the pressure test) to 1000 s-1 (in the Hopkinson test).