Decomposition induced by mechanical milling

The decomposition behavior of FeSn, CoSn, CoIn₂ and Al₃Ni intermetallics under high-energy ball-milling has been investigated using X-ray diffraction, calorimetric and magnetization measurements. Upon milling a large amount of the FeSn inter metallic decomposes into Fe₅Sn₃ and FeSn₂, where the average grain size of the product phases stays nearly constant with milling-time. Similar observations are made for the CoSn intermetallic, which decomposes into Co₃Sn₂ and Sn. It is suggested that the mechanically driven decomposition of FeSn and CoSn results from local melting of powder particles due to high temperature pulses during ball collisions. In contrast to FeSn and CoSn, Al₃Ni exhibits only a small decomposition degree and CoIn₂ does not decompose at all upon milling. The different decomposition behaviors of the studied intermetallics may be attributed to the volume changes occurring with a decomposition process. Whereas the decomposition of FeSn and CoSn into their product phases results in a strongly negative volume change, the decomposition of Al₃Ni and CoIn₂ leads to an increase in volume. Hence, high local stresses under ball collisions are expected to make the mechanically induced decomposition of FeSn and CoSn favorable but rather hinder the decomposition of CoIn₂ and Al₃Ni.