ISO/TR 26946-2011 pdf download.Standard method for porosity measurement of thermally sprayed coatings.
5 Apparatus
The following equipment is necessary for the porosity measurement of thermally sprayed coatings.
5.1 Cut-off wheels (recommended) or diamond wire or high pressure water-jet cutting equipment, (according to equipment in existence) for sectioning coating samples to a proper size with minimal damage.
5.2 Cleaning apparatus, with ultrasonic equipment.
5.3 Mounting equipment.
5.4 Grinding and polishing equipment, (semi-automated or automated grinding/polishing machines are recommended for consistent reproducibility).
5.5 Scanning electron microscope (recommended) or light microscope, for viewing the inspected sample on a cross-section and obtaining digital images.
5.6 Computer, with analysing software for porosity evaluation on digital images.
All equipment should undergo regular maintenance and calibration to assure reliability and repeatability of the measurement. At the same time, all metallographic personnel should have the proper training to allow them to perform the required functions and analyses.
6 Metallographic preparation
6.1 General
Metallographic preparation of thermally sprayed coatings is critical for the porosity results. The requirements for detail and monitoring will vary from system to system, depending upon the degree of automation in the preparation. The basic steps for the preparation are given in 6.2 to 6.5.
6.2 Sectioning
If sectioning is required, two commonly used methods are abrasive wheel cutting or diamond wire cutting. The first one, which is comprised of a diamond or boron nitride saw (more effective in this purpose) that breaks down readily exposed fresh cutting surfaces, is usually best for a wide range of coatings. Sectioning should be done with the cutting force from coating to substrate and minimal clamping pressure on the sample. It will be better to secure the specimen for sectioning with a soft cushion, such as wood, if possible. The sectioning wheel should be as thin as possible to minimize damage, which must be removed in subsequent steps.
Minimum pressure should be applied on the wheel to minimize possible overheating, with cooling by water if possible. The length of the test specimen should be greater than 1 cm. At least five test specimens should be taken from each sample in different positions.
6.3 Cleaning
Cleaning is an important step for removing all contaminants from the surface of the specimen. Three methods or any combination are recommended.
a) Washing samples with soap and water.
b) Brushing or soaking samples in solvent, such as acetone/alcohol, followed by application of heat treatment to drive off any internal absorption.
c) Cleaning samples by performing an initial/extra vacuum step (if using vacuum impregnation in mounting) to volatilize any entrapped materials.ISO/TR 26946 pdf download.