Wettability of two-phase composites by molten metals

Translated from Poroshkovaya Metallurgiya, No. 6(354), pp. 40–44, June, 1992.     

Forecasting Capillary Characteristics for Aluminum Nitride Ceramic ― Liquid Metal Systems

A test has been devised that allows one to determine the work of adhesion and wettability in a system composed of aluminum nitride ceramics with a liquid metal without the need for experimental examination. A correlation is examined between the work of adhesion on the one hand and that criteria or others on the other that have been proposed by various researchers. Forecasts are made for the work of adhesion and wetting angle for a series of metals that have not been examined previously. An experimental check has been made on the forecast adhesion activity for some elements.     

Diamond-hard alloy macrocomposite material: Development and application

A new diamond-hard alloy macrocomposite material consisting of diamond grits (0.5–0.8 mm or more in size) and a WC-Co matrix has been developed. The material is characterized by high mechanical properties of the matrix (the same as for WC-Co monolithic hard alloys) while diamonds remain completely intact (no graphitization or dissolution in cobalt melt). This process does not require superhigh pressures. Hard-alloy samples sintered beforehand in conditions that ensure the maximum mechanical properties (1450–1500°C, 30–60 min holding) are used as initial materials. Hollows (cells) or ditches of specific sizes (depth, width) are made in these samples with mechanical or electrophysical methods, and then diamond crystals (grits) commensurate with the hollows, cells, or ditches are placed in them. Vacuum infiltration (brazing) at moderate temperatures (900–1150°C) with adhesion-active alloys (or metallized diamonds) is the final stage in the formation of the composite. Therefore, strong adhesion-mechanical fixation of diamond grits in the hard-alloy matrix is ensured. The new material is efficiently used in diamond bits.     

High-strength oxide ceramics joints obtained by diffusion bonding with the use of platinum and palladium gaskets

Alumina and zirconia ceramics joints were made by diffusion bonding through platinum and palladium gaskets in air at temperatures between 1300 and 1550°C. The instrumentation and the procedure for these joints manufacturing are described. The effects of temperature, pressure and exposition time on 3-pt bending strength of resulting joints were established. The maximum bending strength of the samples reached 500 MPa. During thermal resistance testing the samples withstood several hundreds of thermal cycles at temperatures up to 800°C in air.     

Wetting and contact reaction in systems of rare-earth oxides with copper-titanium alloys

Conclusions The wetting angles of rare-earth metal oxides of the yttrium group with copper and copper-titanium alloys are higher than for Al₂O₃, which qualitatively agrees with the greater changes (in absolute values) in the free Gibbs energies for the formation of rare-earth oxides in comparison with Al₂O₃.The nonstoichiometric nature of the rare-earth oxides in respect to oxygen and the higher mobility of the oxygen anion substantially influence the kinetics of wetting, increasing the duration of the change in the wetting angle with energy possibilities for the melt to absorb the oxygen from the substratum.The highest reaction resistance in the metal alloys is exhibited by rare-earth oxides with the minimum capacity for nonstoichiometry undergoing deoxidizing treatment.Translated from Ogneupory, No. 8, pp. 13–16, August, 1985.     

Investigation of interaction of metal melts and zirconia

The wetting of zirconia by a number of pure metals was studied. The wetting of zirconia by Cu-Ga-Ti, Cu-Ga-Zr, Cu-Ge-Ti and Cu-Ge-Zr alloys was studied. For Cu-Ga-Ti the minimal contact angle was near 60^°, for Cu-Ga-Zr it was near 30^°. Cu-Ge based alloys wet the zirconia worse because of the low solubility of titanium and zirconium in germanium. The wetting of different zirconia ceramic by a few molten alloys was compared. Contact angles for equal alloys are close. The substrate structure influences the wetting: polycrystal zirconia is wetted by active alloys worse than monocrystal form. The kinetic of ZrO₂ variation of stoichiometry in contact with active alloys was investigated. The dark zone dimension was found to very according a to parabolic law; and the diffusion coefficients of F-centers in ZrO₂-ceramic were calculated. For Cu-Ga-Ti on zirconia adsorption of titanium on the substrate surface and the formation of a TiO layer close to zirconia was revealed. Similarly, for Cu-Ga-Zr adsorption of zirconium on substrate was also found. Interface reactions were described, showing negative Gibbs energy. The average F-centers concentration was calculated. Metals wet better nonstoichiometric than stoichiometric zirconia. At contact to noble metals melts in a vacuum nonstoichiometric (black) zirconia becomes white. Obviously Zr–O bond are weak in black zirconia and a larger quantity of zirconium/metal bonds forms, so the black zirconia is wetted better. When in contact to noble metals some part of zirconium diffuse into metal and so the oxygen deficit disappears. Finally, The brazing of zirconia to metal was briefly discussed.