Structural investigations of detonation-deposited tungsten carbide-cobalt coatings

Conclusions The phase composition of detonation-deposited VK type coatings differs from that of the starting mixtures. A deposited layer contains about 40–50% of the tungsten carbide WC present in the starting mixture, metallic tungsten and cobalt, the intermetallic compounds Co₇W₆ and Co₃W, traces of W₂C, and a small amount of complex carbides. The amount and particle size of the tungsten carbide in a coating are determined by the particle size distribution of the powder being deposited and detonation process parameters. Our investigations have shown that the optimum powder particle size range for the process of detonation deposition of hard-metal mixtures may be taken to be 5–40 m. During detonation deposition under the conditions investigated the usual hard-metal structure and composition are not obtained. Most of the starting tungsten carbide decomposes with the formation of tungsten and cobalt intermetallic compounds. Attempts should now be made to improve deposition conditions so as to increase the phase and structural homogeneity of layers being deposited. In coatings deposited by an optimum method the ductile Co binder will be present in an amount close to that in a sintered VK type hard metal. The fracture of coatings and basis metal on the antivibration shelves of compressor blades has a fatigue character. Crack initiation takes place in the surface and inner layers of detonation-deposited coatings as a result of their considerable brittleness, which is due to the presence of metastable intermetallic phases as well as of defects in the form of pores and blowholes.Translated from Poroshkovaya Metallurgiya, No. 10(238), pp. 24–29, October, 1982.     

Wear resistance of detonation-deposited composite coatings containing molybdenum disulfide

Translated from Poroshkovaya Metallurgiya, No. 1(313), pp. 25–28, January, 1989.     

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.     

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.     

Phase composition and residual stresses in thermal barrier coatings

The phase composition and the residual stresses in multilayer thermal barrier coatings, which consist of an external ZrO₂–8Y₂O₃ ceramic layer, an intermediate gradient (metal ceramic) layer, and a transient metallic NiCrAlY sublayer, are studied. It is shown that an increase in the specific volume of the metallic sublayer as a result of the formation of thermal growing oxide Al₂O₃ generates high compressive stresses in this sublayer. The ceramic layer undergoes tensile stresses in this case. A method is proposed to estimate the stresses in gradient coatings from X-ray diffraction results.     

Protective properties of detonation-deposited coatings from powders alloyed with aluminum and boron

Conclusions The corrosion resistance of detonation-deposited coatings from aluminum- and boron-containing PKh20N80 alloy, nickel, and stainless steel powders markedly surpasses that of constructional steel. The electrochemical properties of such detonation-deposited coatings are determined by their composition and thickness. The basis material is effectively protected against corrosion by 600-Mm-thick coatings. Under conditions of corrosive and mechanical wear detonation-deposited coatings from aluminum- and boron-containing 20% Cr-80% Ni alloy, nickel, and stainless steel powders operate satisfactorily under loads of not more than 5 MPa. The results of service tests have demonstrated the usefulness of detonation-deposited coatings from alloyed powders. Coating with powder of composition III was found to increase the useful life of certain parts of spraying equipment two to two and a half times.Translated from Poroshkovaya Metallurgiya, No. 8 (272), pp. 52–55, August, 1985.