Applied Surface Science, Vol.488, 739-752, 2019
Interatomic interactions and structural formations in WFeNi(Ti) and MoFeNi (Ti) layers under intense plastic deformation induced by ball collisions
WFeNi(Ti) and MoFeNi(Ti) alloy layers were fabricated onto Ti surfaces from W, Mo, and Ni targets through ball collisions initiated by a mechanically vibrated vial. Steel balls were used for processing as the Fe source. The as-fabricated alloy structures could be represented as a heterogeneous multi-modal nanocrystalline structure with elemental flakes embedded within a matrix composed of nanocrystalline grains encapsulated within an amorphous phase. The deformation-induced chemical interactions between dissimilar atoms in the WFeNi(Ti) and MoFeNi(Ti) systems affected the structural formation of the alloy layers. Fe atoms in the WFeNi(Ti) alloy system tended to react with Ni, forming fcc (Fe, Ni) phase, while W atoms dissolved into the fcc (Fe, Ni) lattice. In the MoFeNi(Ti) alloy system, Fe tended to react with Mo over Ni, resulting in the formation of a bcc Fe(NiMo) solid solution. Formation of an amorphous phase was mainly related to compositional changes and distortion of the bcc Fe atomic rows with refractory metal atoms. The W and Mo nanocrystalline grains reduced their size continuously during processing via amorphization and wear effects. The Ti particles absorbed oxygen atoms. Chemical interactions between Ti and oxygen atoms made the Ti and oxygen components passive with regard to other present metallic elements. The formation of atomic clusters was related to the attractive bonding forces between dissimilar atoms that bonded the atoms together. The yield stress value of the as-fabricated layers evaluated via nanoindentation was (2.5 +/- 0.4) GPa, which was much higher than the yield stress for tungsten heavy alloys.
Keywords:Nanocrystalline metallic coatings;Tungsten;Molybdenum;Nanocomposite;Mechanical alloying;Solid-state surface modification