料浆法制备Mo表面硅化物涂层的研究

采用料浆法制备MoSi2涂层,研究了料浆中Si与MoSi2粉末的配比、包渗时间、NaF含量对制备涂层的影响.结果表明:在Mo表面形成了两层硅化物层,其中外层是MoSi2,内层是硅化物Mo5Si3;Si主要参与在Mo的表面上硅化物层的形成,MoSi2也能少量参与形成涂层;NaF则起到Si的活化剂作用,没有NaF无法形成硅化物层,但其加入量增多对涂层的厚度影响并不大;随着包渗时间的延长,内外两层硅化物厚度都增加,但外层厚度增加较大.     

Properties of wear-resistant coatings of eutectic chromium-carbide alloys

Conclusions The increased hardness and wear resistance of electric-spark coatings compared with thermally sprayed ones is due to the presence of oxide and nitride phases in the alloyed layer, whose phase composition — unlike that of a thermally sprayed layer — is not identical with the starting phase composition. The presence of a secondary structure on the working surface of the electrode in ESA and its role in the formation of the alloyed layer have been established.Translated from Poroshkovaya Metallurgiya, No. 9(261), pp. 42–46, September, 1984.     

Addition of vanadium to silicide master alloys for plasma-deposited coatings

Conclusions An investigation was carried out into the effect of vanadium on the structure and phase composition of some alloys of the Si-Ti-Cr system. The microstructure of resultant alloys is the same as that of similar vanadium-free materials. Vanadium is concentrated in the refractory phase, entering into the composition of a complex (Cr, Ti, V)Si₂ disilicide. The remaining structural components are, as in the vanadium-free ternary alloys, free silicon and a eutectic. A study was made also of the effect of vanadium on the oxidation kinetics of alloys of the Si-Ti-Cr system exposed for 100 h to air at 1300C. Alloying with vanadium substantially slows down the rate of oxidation of these alloys and changes the law of oxidation from parabolic, characterizing the ternary alloys, to logarithmic for the vanadium-containing alloys. The 100-h rate of oxidation of an alloy of optimum composition at 1300C is 0.04 mg/cm² · h. The optimum particle size of Si-Ti-Cr-V alloy powders intended for the application of coatings by gasothermic spray-deposition has been established.Translated from Poroshkovaya Metallurgiya, No. 5(233), pp. 46–50, May, 1982.     

Influence of silicide coatings on the mechanical properties of the NT-50 alloy

We have investigated the effect of silicide coatings on the ultimate strength of NT-50 alloy over the temperature range ?196...+1100 °C. From 196 to 800 °C the ultimate strength of silicidated specimens was lower than that of the initial and annealed alloy whereas from 900 °C it was slightly higher. We have also examined the effect of silicide coatings on the relative elongation of NT-50 alloy samples. Over the temperature range ?196...+1100 °C, the relative elongation of specimens annealed in a vacuum of 6.7 · 10^?3 Pa at 1250 °C for 4 h was found to be lower than that of the silicidated specimens. This is attributed to the dissolution of the residual gases (O₂, N₂, H₂, CO, and CO₂) under vacuum annealing.     

Formation of chromium-copper coatings on diamond

The mechanism of chromium and chromium-copper formation is determined, which is mainly by transfer of metal ions to the reaction surface (of diamond) and carbon diffusion (from diamond) into the coating. Introduction of copper oxides into the chromium metallizer promotes an increase in coating thickness due to the additional contribution to transfer of chromium of CuO, Cu, and CrO. With reduction of copper oxides this contribution is reduced, which gives rise to a slower coating thickness growth rate. Slower growth is also caused by accumulation in the metallizer of chromium oxides and carbides which block evaporation as well as inhibiting diffusion of carbon into the body of the coating.     

Wear resistance of heat-treated ion-plasma coatings from iron-based eutectic alloys

Translated from Poroshkovaya Metallurgiya, No. 7(355), pp. 40–44, July, 1992.     

Diffusional breakdown of nickel protective coatings on copper substrate in silver-copper eutectic melts

Diffusion couples with electrolessly plated nickel diffusion barriers between copper substrates and silver-copper eutectic alloys were tested at 800 °C and 850 °C, respectively. Growth of (Cu, Ni, Ag) ternary solid solution into the melt was observed at both temperatures. The growth pattern changed from cellular to dendritic as the temperature was increased from 800 °C to 850 °C. The nonplanar growth morphology can be explained in terms of constitutional supercooling in the melt. Kinetics of (Cu, Ni, Ag) solid solution growth were found to be controlled by interdiffusion at the interface of the nickel barrier and the growing solid-state phase. Local breakdown of the nickel diffusion barrier started once the (Cu, Ni, Ag) solid solution reached the copper substrate. Silver diffused from the silver-copper melt, through the ternary solid solution, dissolving copper and forming silver-copper liquid along copper grain boundaries. Ultimately, the nickel barrier was totally converted to the ternary solid solution, broke up, and floated into the liquid. Dissolution of the copper substrate occurred subsequently. A thin layer of chromium undercoating proved to be very effective in extending the protection time of the nickel diffusion barrier, due to the extremely low solubility of both copper and silver in chromium at these test temperatures.     

Oxidation behavior of niobium aluminide intermetallics protected by aluminide and silicide diffusion coatings

The isothermal and cyclic oxidation behavior of a new class of damage-tolerant niobium aluminide (Nb₃Al-xTi-yCr) intermetallics is studied between 650 °C and 850 °C. Protective diffusion coatings were deposited by pack cementation to achieve the siliciding or aluminizing of substrates with or without intervening Mo or Ni layers, respectively. The compositions and microstructures of the resulting coatings and oxidized surfaces were characterized. The isothermal and cyclic oxidation kinetics indicate that uncoated Nb-40Ti-15Al-based intermetallics may be used up to ∼750 °C. Alloying with Cr improves the isothermal oxidation resistance between 650 °C and 850 °C. The most significant improvement in oxidation resistance is achieved by the aluminization of electroplated Ni interlayers. The results suggest that the high-temperature limit of niobium aluminide-based alloys may be increased to 800 °C to 850 °C by aluminide-based diffusion coatings on ductile Ni interlayers. Indentation fracture experiments also indicate that the ductile nickel interlayers are resistant to crack propagation in multilayered aluminide-based coatings.     

On the mechanism of deterioration of composite eutectic coatings by cavitation

The effect of structure, phase composition and method of preparation on the cavitation resistance of composite eutectic coatings was investigated. It was established that a finely dispersed columnar eutectic structure provided maximum resistance to crack growth. Methods for producing the desired coating structure by the use of concentrated energy sources are proposed. Ukraine National Technical University “KPI.”. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 36–43, July–August, 1998.     

Structure formation of powders and coatings of eutectic iron base alloys

Translated from Poroshkovaya Metallurgiya, No. 7(331), pp. 29–34, July, 1990.