Evaluation of Fracture Toughness of Ultra-Thin Amorphous Carbon Coatings Deposited by Different Deposition Techniques

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The successful performance and reliability of thin coatings is often limited by their mechanical properties. Generally, harder coatings are more brittle and easily damaged by shock loads in practical applications. A necessary criterion for evaluating brittleness of thin coatings is to measure fracture toughness of the coatings. In this paper, the nanoindentation fracture of ultra-thin (100 nm thick) amorphous carbon coatings on Si substrate deposited by filtered cathodic arc (FCA), direct ion beam (IB), electron-cyclotron resonance plasma chemical vapor deposition (ECR-CVD), and sputter (SP) deposition processes was studied using a cube corner indenter. Based on the analysis of the energy release in cracking, the fracture toughness of the coatings was calculated. It is found that among the coatings tested, the FCA coating has the highest fracture toughness, followed by the ECR-CVD, IB, and SP coatings. The higher deposition kinetic energy, plasma density and electron temperature are believed to be responsible for the higher fracture toughness values for the FCA and ECR-CVD coatings.