Amorphisation of Cr–10Co mixture by mechanical alloying

Mechanical alloying of blended chromium and cobalt powders is carried out in order to obtain a nanostructured Cr–10Co alloy. The alloy formation is studied by means of scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and differential scanning calorimetry. The results show that an allotropic transformation of Co from fcc to hcp structure occurs within the first 3 h of milling. After 12 h of milling, nanostructured bcc-Cr(Co) solid solution is obtained. Contamination of the powder by the milling tools and atmosphere for 24 h of milling contributes to the formation of a high degree of structural disorder. In addition to Fe, Cr and Co oxides, Cr(Co) solid solutions with bcc and unusual hcp structures are formed. The differential scanning calorimetry analysis in the temperature range 50–700 °C gives evidence for the presence of both microstrain relaxation and crystallization of the amorphous-like structures. Heating the 24 h-milled powder at 600 °C leads to the formation of bcc-Cr, Fe oxide and tetragonal σ-CrCo phases.