Mechanical alloying of immiscible elements: Experimental results on Ag‒Cu and Co‒Cu

Weakness of the “hot spots” approach to the kinetics of mechanically induced phase transformations

“…10, in substantial agreement with previous work [39], the fcc solid solution is stable up to temperatures of about 350 K. Above such temperatures, it undergoes a demixing process that determines the disappearance of the solid solution by the separation of Ag and Cu. Two exothermal signals are evident, which can be related to a two-stages demixing process [39]. In the first stage atomic-scale diffusivity is observed, with the formation of small demixed domains of Ag and Cu [39].…”

Molecular-dynamics calculations of thermodynamic properties of metastable alloys

“…7 The application of these techniques suggests that mixing of the two components occurs in the Cu-Fe system at the atomic level, even if there is an indication of local compositional fluctuations 5 and, to a limited extent, of modulated structures with a periodicity of a few nm. 4 No investigations at the same level of detail have been performed for other immiscible systems such as Co-Cu and Ag-Cu, so that in these cases the knowledge of the microscopic structure of the metastable alloys obtained by ball milling is very limited and based only on conventional diffractometry which shows the existence of a single crystallographic phase ͑within the limits mentioned above͒ and on differential calorimetry which evidences a heat release of several kJ/mol when these alloys are heated to ϳ1000 K. [1][2][3]8 Another difficulty in understanding the mechanism of alloying in these systems arises from the lack of accurate information ͑both experimental and calculated͒ concerning the enthalpy and the free energy of the different microstructures which could develop during the process of ball milling, including the ideal solid solution which, of course, is not experimentally accessible in the whole range of composition. The enthalpy and the free energy of the ideal solid solution can be calculated 2,3 with the calculation of the phase diagram ͑CALPHAD͒ method or with other more sophisticated approaches such as the free-energy minimization method 9 ͑FEMM͒ or the second-order expansion 10 ͑SOE͒, all of which are of static nature and, therefore, less accurate than a molecular-dynamics ͑MD͒ calculation.…”

Cr-Mo solid solutions forced by high-energy ball milling

“…atom). [9,[13][14][15][16][17] This is to be contrasted with systems with large positive heats of mixing, e.g., Cu-W (⌬H m ഠ 35 kJ/g . atom), [18] Ag-Fe (⌬H m ഠ 25 kJ/g .…”

“…atom), [6] Co-Cu (⌬H m ഠ 6 KJ/g . atom), [7,8,9] Ag-Cu (⌬H m ഠ 7 kJ/g . atom), [10,11] and Cr-Fe (⌬H m ഠ 6 kJ/g .…”