Porosity measurements on detonation-deposited coatings

Typical values of the open and total porosities of good-quality detonation-deposited alumina and VK alloy coatings are 4–6%. To obtain reliable values of porosity for detonation-deposited coatings by the hydrostatic weighing method, the coatings must be vacuum-treated and then impregnated with a liquid for not less than 1 h. The open porosity of an alumina coating does not differ greatly from its total porosity, but in a VK alloy coating the proportion of closed pores may be as high as 40%.