Analysis of cracking induced by scratching of tungsten coatings on polyimide substrate

Tungsten films were deposited on Upilex S polyimide substrates using a triode discharge system. Films 200, 400 and 600 nm thick were produced at three different argon deposition pressures (0.2, 0.7 and 1.2 Pa). The behaviour of the metallic coating–polymeric substrate composite was studied by sliding indentation. Three different scratching tests were carried out: in increasing load mode (ILM), in increasing load mode with multipass (ILM-M), and in constant load mode (CLM). These scratchings induced transversal crack formation but no coating delamination in the range of the studied parameters (applied load L≤30 N, load gradient≤15 N mm−1). The critical load, Lci was defined as the load at which cracks occurred in the coating homogeneously throughout the scratch. The superscript i denotes the number of scratches in multipass mode.