META-STABLE CONDITIONS OF DIFFUSION BRAZING

作者：Wolczynski W^*; Okane T; Senderowski C; Kania B; Zasada D; Janczak Rusch J

来源：Archives of Metallurgy and Materials, 2011, 56(2): 311-323.

DOI：10.2478/v10172-011-0035-7

• meta-stable equilibrium
• joint formation model
• dissolution
• solidification

A thermodynamic justification for the joint formation is developed on the basis of the diffusion brazing of the Ni/Al/Ni system. The phenomena of dissolution and solidification were included into the description. The first solid/solid transformation is also discussed. Mainly, a description for the isothermal brazing occurrence in the meta-stable conditions is developed. It involves the application of the criterion of higher temperature of the solid / liquid (s/l) interface. The dissolution of the filler metal in the substrate is described by the N(0) - solute concentration within the dissolution zone (liquid film) distinguished at the substrate surface. The selection of the N(0) - parameter by the dissolution is justified by the Thermocalc calculation of the Ni-Al phase diagram for meta-stable equilibrium. According to the model assumptions, the solidification is accompanied by partitioning or by undercooled peritectic reaction resulting in formation of the intermetallic phase. The average Al - solute concentration measured across some Al(3)Ni(2)/Al(3)Ni/Al(3)Ni(2) joints confirms that the N(0) - solute concentralion is conserved within the analyzed joint sub-layers. The Ni-Al phase diagram for meta-stable equilibrium referred to the solidification is also calculated by means of the Thermocalc Software. It allows locating the solidification path, s/l interface path and redistribution path onto the mentioned diagram. Superposition of both calculated phase diagrams is also given to show that the joint formation occurs cyclically under the meta-stable conditions.

• 出版日期2011