Porosity measurements on detonation-deposited coatings

Conclusions 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%.Translated from Poroshkovaya Metallurgiya, No. 4(208), pp. 47–50, April, 1980.     

Electrical conductivity of detonation-deposited hard-alloy coatings

Conclusions A study was made of the electrical conductivity of WC-base detonation coatings at 20–900°C. It is demonstrated that such spray-deposited coatings have a laminar structure, which accounts for the anisotropy of their conductivity. Phase changes occurring in a coating affect mainly its conductivity measured in a direction perpendicular to the deposition axis. Data on anisotropy of conductivity can be utilized for assessing the degree of particle deformation.Translated from Poroshkovaya Metallurgiya, No. 12 (156), pp. 93–96, December, 1975.     

Porosity of detonation-deposited chromium carbide-base coatings

Conclusions The variation of the open porosity of a coating as a function of detonation-deposition process conditions matches that of the quality of the coating as assessed by other parameters. The open porosity of a coating is strongly affected by its surface roughness, and consequently estimates of _op may be high. The size of a specimen for open porosity testing should not be greater than 1.2 times the barrel bore. Under optimum conditions the visible porosity of coatings does not exceed 1%.Translated from Poroshkovaya Metallurgiya, No. 7(259), pp. 17–20, July, 1984.     

Structural state,phase composition,and thermal fatigue resistance of detonation-deposited alumina coatings

Conclusions By suitable choice of gas ratio in the detonating mixture and degree of barrel filling, which determine the kinetic energy and degree of heating of the particles, it is possible to obtain good-quality alumina coatings exhibiting fairly high thermal fatigue resistance. For the application of satisfactory coatings it is necessary to employ powders of predominant particle size 20–40 m annealed at 1400–1700°C. Evidence has been obtained in support of literature reports concerning the beneficial effect of incomplete filling of the barrel of the detonation apparatus, which results in a higher proportion of -Al₂O₃ (up to 30%) in coatings. This is a key factor in the wear and thermal fatigue resistance of the coatings. The weakest structural elements in detonation-deposited oxide coatings under conditions of thermal cycling at 800°C are their interlayer boundaries, whose rupture leads to lamination and crumbling of the coatings.Translated from Poroshkovaya Metallurgiya, No. 5(269), pp. 32–38, May, 1985.