Metastable structures in magnetron sputtered W–Zr thin-film alloys

Abstract

Binary W–Zr thin-film alloys with different metastable structures were prepared by dc magnetron co-sputtering of W and Zr targets in argon atmosphere on unheated and unbiased substrates. The effect of the elemental composition on the formation of different structures and phases was studied in a very wide range of 3–99 at.% Zr. The microstructure and properties of the films were related to the individual metastable structures prepared. We found that W-rich films with an α-W(Zr) solid solution structure can be prepared in much wider range of the elemental composition (up to 24 at.% Zr) than indicated in the equilibrium W–Zr phase diagram. These films exhibited an enhanced hardness (up to 16.1 GPa) and a reduced residual stress (down to −0.05 GPa). Amorphous W–Zr films with a very low surface roughness (down to 0.4 nm) and metallic glass features were prepared with the Zr content between 33 and 83 at.%. The hardness of these films gradually decreased with increasing Zr content due to reducing average bond energy. All films were in the compressive state in contrast to the crystalline ones. The structure of crystalline Zr-rich films with higher than 88 at.% Zr was predominantly dual-phased exhibiting a gradual transition from a metastable β-Zr(W) solid solution (86–96 at.% Zr) through a metastable ω-Zr(W) solid solution (94–100 at.% Zr) to the thermodynamically stable α-Zr phase (99–100 at.% Zr) with increasing Zr (decreasing W) content. We also observed the formation of dual-phase glassy-crystalline structures in the transition zones between fully crystalline and glassy films.