Evaluation of strength of DLC films at high temperature by static and cyclic indentation test with AE technique

Abstract

This study aims to evaluate strength of a diamond-like carbon (DLC) film on a metal for glass press molding at high temperature. Static and cyclic indentation tests at high temperature up to 300℃ with AE monitoring technique were performed. AE monitoring reveled crack generation load or cyclic number during the indentation tests. The static strength of the films at each temperature was determined from maximum stress in the film in the radial direction induced by sink-in deformation due to static indentation. The maximum stress at each temperature was estimated with indentation loads at first AE generation and FEM analysis. Thermal stress in DLC film was at each temperature also calculated. The film strength estimated by taking the thermal stresses into account was decreased with an increase of temperature. In cyclic indentation test, AE due to cracks in film was detected after 1.0×10⁴ cycles at the load where no crack generated under one loading cycle. The cyclic number to crack initiation for the sample in 300℃ was 1/50 smaller than that in room temperature.