Amorphous phase forming ability in (W-C)-based sputtered films

The effect of adding transition metals, Me, to the structure of (W-C)-based films obtained by sputtering has been studied by the means of electron probe microanalysis (EPMA), secondary ion mass spectrometry (SIMS), low angle X-ray diffraction (XRD), hot stage transmission electron microscopy (TEM), Mossbauer spectroscopy, extended X-ray absorption fine structure (EXAFS), magnetic measurements and differential thermal analysis (DTA). The results obtained for the films in the as-deposited conditions show two types of structures with different degrees of structural order. Films with Ti, Cr or Au are crystalline with a metastable structure of beta-(W,Me)C1-x with 1-x extending from near unity down to about 0.6. In opposition to these, films with Me = Group VIIIA transition metal, show crystalline --> amorphous state transitions for Me percentages in the range 5-10 at.%. The structure of these films consists of small beta-MC1-x crystallites with a size of a few unity cells, surrounded by a disordered phase rich in element Me. Concerning the results obtained at increasing temperatures, the chemical and structural behaviour of the W-Me-C films depend on the affinity of carbon for the element Me. Strong or moderate carbide-forming elements (Ti or Cr) improve the stability of the crystalline phase at high temperatures; the films formed by W, C and a weak or non carbide-forming metal (Fe, Co, Ni, Pd or Au) change structurally in the temperature range studied. (C) 1998 Acta Metallurgica Inc.