Thin coatings with graded elastic properties

Abstract

Thin W—Nb coatings were sputter co-deposited from pure targets on glass substrates with Nb contents from 14 to 70 at%. Pure W coatings (2.5 μm thick) were deposited on Ti-6Al-4V substrates with and without 0.5-μ m thick W—Nb interlayers to assess the influence of graded elastic properties on the adhesion of the W coatings. Two interlayer compositions were studied: 31 and 50 at% Nb. All of the W—Nb coatings were crystalline and solely body centre cubic. The plane strain elastic modulus (E′ _c ) and hardness (H _c ) of the coatings (as measured by nanoindentation) increased with increasing W content. E′ _c increased from 223 ± 16 GPa at 70 at% Nb to 587±91 GPa for a pure W coating. Over the same composition range H _c increased from 8.51±0.25 to 13.49±1.04 GPa. No delamination was observed for any of the coated Ti-6Al-4V samples after adhesion testing by Rockwell C (Rc) indentation or scratch testing (at loads up to 5.00 kg). Through-coating cracks were observed around the rims of the Rc indents and within the scratches (at loads of 1.00 kg and higher). In all cases, the density of these cracks increased in the following order: 50 at% Nb interlayer<31 at% Nb interlayer<no interlayer.