Stage sequence in mechanochemical synthesis of nanometric solid solutions in metal systems

Formation of the solid solutions by mechanical alloying (MA) of metals with a negative mixing enthalpy is characterized by the formation of an intermediate intermetallic phases. In high-energy planetary ball mills, the low melting component melts, serves as surfactant and accelerate comminution of solid metal, wets the surface of solid particles; intermetallic compounds are formed at the interface. Typically, an intermetallic compound with very high content of low-melting component is formed at this stage of the process; the synthesis of this intermetallic phase lasts till complete consumption of low-melting component. This type of MA behavior is also observed in the systems with higher melting points, in which metals differ in their plasticity. Usually, the diffraction reflections of a more plastic component broadens rapidly and finally disappear, along with the formation of an intermetallic compound with high content of this component. One can assume that at this stage of MA, more plastic component may be subjected to a severe plastic deformation coating the particles of less plastic component thus accelerating dispersion similarly to what happens during liquid metal embrittlement. The increase of the content of newly formed intermetallic compound is observed until practically complete consumption of the plastic component; only after this, the formation of solid solution between the solvent metal and the intermetallic compound starts.