Fabrication of W and Mo layers with multi-modal structures on Ti sheets through intense plastic deformation induced by ball collisions

Abstract

Tungsten (W) and molybdenum (Mo) layers were fabricated onto Ti surfaces through intense plastic deformation induced by ball collisions initiated through a mechanically vibrated vial. The Ti disk was affixed to one side of the vial with either W or Mo targets affixed to the opposite side. During processing, ball collisions continually introduced the target material to the Ti surface, yielding mechanical alloying and formation of the desired alloyed layer. The as-fabricated W and Mo layers contained Fe component that was introduced from the milling media. The composition of the as-fabricated W layer corresponded to tungsten–iron heavy metal alloys. The introduction of Fe components could be favorable since the interaction between components resulted in the formation of complex multi-modal heterogeneous structures. There was an observed co-existence of alternating nanolaminated amorphous/crystalline structures, elemental flakes with polycrystalline nanograins, and nanocrystalline grains under 10 nm isolated by the amorphous phase. Structural formation in the W layer developed slowly compared to the Mo layer, which was related to the mechanical characteristics of the initial materials and the atomic reactivity with the Fe component. The as-fabricated surface alloyed W and Mo layers exhibited very high hardness values (883 HV and 933 HV, respectively) that were comparable to the hardness of tempered steel.