THIN-FILM SCRATCH TESTING IN 2 DIMENSIONS - EXPERIMENTS AND ANALYSIS

We have modified the microscratch test to create a near plane strain l oading condition. In the Microwedge Scratch Test (MWST), a wedge-shape d diamond indenter tip is drawn along a fine line (i.e., narrow strip of film), while simultaneously being driven into the line. We compare microwedge scratching of zone 1 (voided grain boundaries) and zone T ( metallurgical grain boundaries) thin film specimens of sputtered tungs ten on thermally grown SiO2. Symptomatic of its weak grain boundaries, the zone 1 film displays three separate crack systems. Because of its superior grain boundary strength, the zone T film displayed only one of these-an interfacial crack system. By correlating fracture phenomen a to signature events in the load-displacement curve, we develop gover ning equations for propagating interfacial cracks, including expressio ns for strain energy release rate, bending strain, and mode mixity. Gr ain boundary fracture causes zone 1 films to spall before a stable cra ck is formed. Zone T films survive the bending strains, and hence adhe sions may be inferred from stable crack growth mechanics. We conclude by contrasting and comparing experimental results for plane strain ind entation versus plane strain scratching.