Surface film softening effects in MoSi₂

Surface film softening, which is associated with the generation of mobile dislocations at a film-substrate interface and their motion into the substrate, has been demonstrated previously for bcc metals and B2 ordered alloy substrates. MoSi₂ exhibits features of limited dislocation mobility and plasticity similar to these materials and would also be expected to exhibit film-enhanced plasticity, but at much higher temperatures. In this investigation, 150 nm thick films of SiO₂, MoSi₂ and ZrO₂ were deposited on MoSi₂ substrates by electron beam deposition at approximately 50 °C in an attempt to observe film softening. In initial experiments, hot hardness testing was utilized primarily to maintain deformation conditions characteristic of dislocation glide. ZrO₂-coated MoSi₂ demonstrates a large film-induced softening in hardness tests carried out at 0.5-1 kgf loads over the temperature range 25-1300 °C.