A novel pillar indentation splitting test for measuring fracture toughness of thin ceramic coatings

Journal Article · Fri May 16 00:00:00 EDT 2014 · Philosophical Magazine (2003, Print)

DOI:https://doi.org/10.1080/14786435.2014.913110· OSTI ID:1213311

Sebastiani, Marco ^[1]; Johanns, K. E. ^[2]; Herbert, Erik G. ^[2]; Carassiti, Fabio ^[1]; Pharr, George Mathews ^[3]

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1. Univ. of Rome (Italy)
2. Univ. of Tennessee, Knoxville, TN (United States)
3. Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Fracture toughness is an important material property that plays a role in determining the in-service mechanical performance and adhesion of thin ceramic films. Unfortunately, measuring thin film fracture toughness is affected by influences from the substrate and the large residual stresses that can exist in the films. In this paper, we explore a promising new technique that potentially overcomes these problems based on nanoindentation testing of micro-pillars produced by focused ion beam milling of the films. By making the pillar diameter approximately equal to its length, the residual stress in the pillar’s upper portion is almost fully relaxed, and when indented with a sharp Berkovich indenter, the pillars fracture by splitting at reproducible loads that are readily quantified by a sudden displacement excursion in the load displacement behavior. Cohesive finite element simulations are used to analyze and develop, for a given material, a simple relation between the critical load at failure, pillar radius, and fracture toughness. The main novel aspect of this work is that neither crack geometries nor crack sizes need to be measured post test. Furthermore, the residual stress can be measured at the same time with toughness, by comparing the indentation results from the stress-free pillars and the as-deposited film. The method is tested on three different hard coatings formed by physical vapor deposition: titanium nitride, chromium nitride, and a CrAlN/Si₃N₄ nanocomposite. Results compare well to independently measured values of fracture toughness for the three brittle films. The technique offers several benefits over existing methods.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1213311
• Journal Information: Philosophical Magazine (2003, Print), Vol. 95, Issue 16-18; ISSN 1478-6435
• Publisher: Taylor & Francis
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
fracture toughness
nanoindentation
pillar
residual stress
micron scale