Standard Test Method for Adhesion Strength and Mechanical Failure Modes of Ceramic Coatings by Quantitative Single Point Scratch Testing

Importancia y uso:

5.1 This test is intended to assess the mechanical integrity, failure modes, and practical adhesion strength of a specific hard ceramic coating on a given metal or ceramic substrate. The test method does not measure the fundamental “adhesion strength” of the bond between the coating and the substrate. Rather, the test method gives a quantitative engineering measurement of the practical (extrinsic) adhesion strength and damage resistance of the coating-substrate system as a function of applied normal force. The adhesion strength and damage modes depend on the complex interaction of the coating-substrate properties (hardness, fracture strength, modulus of elasticity, damage mechanisms, microstructure, flaw population, surface roughness, and so forth) and the test parameters (stylus properties and geometry, loading rate, displacement rate, and so forth).

5.2 The test method as described herein is not appropriate for polymer coatings, ductile metal coatings, very thin (<0.1 μm) ceramic coatings, or very thick (>30 μm) ceramic coatings.

Note 2: Under narrow circumstances, the test may be used for ceramic coatings on polymer substrates with due consideration of the differences in elastic modulus, ductility, and strength between the two types of materials. Commonly, the low comparative modulus of the polymer substrate means that the ceramic coating will generally tend to fail in bending (through-thickness adhesive failure) before cohesive failure in the coating itself.

5.3 The quantitative coating adhesion scratch test is a simple, practical, and rapid test. However, reliable and reproducible test results require careful control of the test system configuration and testing parameters, detailed analysis of the coating damage features, and appropriate characterization of the properties and morphology of the coating and the substrate of the test specimens.

5.4 The coating adhesion test has direct application across the full range of coating development, engineering, and production efforts. Measurements of the damage mechanisms in a coating as a function of applied normal forces are useful to understand material-process-property relations; quantify and qualify the mechanical response of coating-substrate systems; assess coating durability; measure production quality; and support failure analysis.

5.5 This test method is applicable to a wide range of hard ceramic coating compositions (carbides, nitrides, oxides, diamond, and diamond-like carbon) applied by physical vapor deposition, chemical vapor deposition, and direct oxidation methods to metal and ceramic substrates.

5.6 Ceramic coatings can be crystalline or amorphous, but commonly have high relative density with limited porosity (<5 %). Porous coatings can be tested, but the effects of porosity on the damage mechanisms in the coating must be carefully considered.

5.7 The test method, as defined with the 200 μm radius Rockwell diamond stylus, is commonly used for ceramic coating thicknesses in the range of 0.10 to 30 μm. Thinner coatings may require a smaller diameter stylus and lower normal forces for reliable results. Thicker coatings may require larger diameter stylus and higher normal forces. Any variations in stylus size and geometry and designated normal force ranges shall be reported.

5.8 Specimens commonly have a flat planar surface for testing, but cylinder geometries can also be tested if they are properly fixtured and aligned and the scratch direction is along the long axis of the specimen. The physical size of the test specimen is determined primarily by the capabilities and limits of the test equipment stage and fixturing.

5.9 The test is commonly conducted under unlubricated conditions and at room temperature. However, it is feasible and possible to modify the test equipment and test conditions to conduct the test with lubrication or at elevated temperatures.

5.10 Coated specimens can be tested after high temperature, oxidative, or corrosive exposure to assess the retained properties and durability (short-term and long-term) of the coating. Any specimen conditioning or environmental exposure shall be fully documented in the test report, describing in detail the exposure conditions (temperature, atmosphere, pressures, chemistry, humidity, and so forth), the length of time, and resulting changes in coating morphology, composition, and microstructure.

Subcomité:

C28.04

Volúmen:

15.01

Número ICS:

25.220.99 (Other treatments and coatings)

Palabras clave:

adhesion test; ceramic coating; critical scratch load; hard coatings; scratch adhesion; scratch test;