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How can I characterise the density of thermal spray coatings?


Frequently Asked Questions

The liquid displacement method to evaluate bulk material density (ASTM B962 and B963) can be readily adapted to thermally sprayed coatings. An alternative liquid displacement method consists of producing coatings on a thin mild steel strip, after which the steel strip is dissolved away by immersion in an acid solution. The remaining strip is used for density measurement. The strip is accurately weighed prior to being coated with a lacquer of known density, and again after coating. The coated strip is suspended in a beaker of de-mineralised and de-aerated water and weighed while immersed. The coating density can then been calculated.

It is often necessary to measure the porosity levels in a coating as well as the density. A cross section of the coated test piece is prepared (mounted and polished) and observed using an optical or scanning electron microscope (SEM). Pores and oxide area are determined using an image analyser, and the level of porosity calculated as volume fractions.

The porosity level can also be determined using commercially available mercury intrusion porosimetry (MIP). The method consists of evacuating the sample and immersing in mercury at low pressure. The mercury is then pressurised; corresponding volumes of intruded mercury are measured at a series of pressures. The pore diameter can be calculated. This method enables the total porosity and pore distribution to be determined.

B962 - Standard Test Methods for Density of Compacted or Sintered Powder Metallurgy (PM) Products Using Archimedes’ Principle

B963 -Standard Test Methods for Oil Content, Oil-Impregnation Efficiency, and Surface-Connected Porosity of Sintered Powder Metallurgy (PM) Products Using Archimedes’ Principle

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