Effect of Ga on the Wettability of CuGa10 on 304L Steel
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BRAZING is an important joining technique, which is applied in most industrial fields. It is used, for instance, in the production of automotive and aerospace components, of cooling units or of electronic devices.[1-3] Compared to welding, brazing essentially has two advantages: (i) during brazing, only the braze filler is molten, whereas the base material remains solid. Thus, the base material keeps its shape and the risk of forming brittle phases since alloying can be reduced; (ii) with this method, also different classes of materials such as metals and ceramics can be joined.[4] The selection of braze fillers is generally accompanied by strict requirements. For example, the working (brazing) temperature, the temperature at which the brazing process shall be carried out, has to match the solidus and liquidus temperatures of the braze fillers. Besides, the deformability of the fillers has to be sufficient in order to ensure easy production of the filler, which can have complex shapes, and to guarantee a long service life of the joint. However, one of the most important criteria constitutes the wetting behavior of the braze filler on the base materials to be joined. The contact angle, h, is a commonly used parameter for the quantification of the wetting behavior of a liquid on a solid substrate. The contact angle depends on the FRANK SILZE, Ph.D. Student, IVAN KABAN, Researcher, UTA KU¨HN, Department Head, and SIMON PAULY, Researcher, are with the Institute for Complex Materials (ICM), IFW Dresden, Helmholtzstraße 20, 01069 Dresden, Germany. Contact e-mail: [email protected] GUNTHER WIEHL, R & D Programm Manager, is with the Umicore AG & Co. KG, Rodenbacher Chaussee 4, 63457 Hanau-Wolfgang, Germany. JU¨RGEN ECKERT, Director, is with the Institute for Complex Materials (ICM), IFW Dresden, and also with the Technische Universita¨t Dresden, Institut fu¨r Werkstoffwissenschaft, 01062 Dresden, Germany. Manuscript submitted September 5, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
surface tension of the solid cs, the surface energy of the liquid cl, and the energy of the solid-liquid interface csl as follows from the Young equation[5-7]: c csl cos h ¼ s : ½1 cl For h > 90 deg, no wetting occurs, the cases with h < 90 deg and h = 0 deg are defined as partial wetting and complete wetting, respectively.[8] As Eq. [1] indicates, the surface tension is a decisive physical parameter for the wetting behavior. Therefore, to gain a better understanding of the wetting process, the surface tension of the liquid braze fillers should be analyzed, which can be done by means of the sessile drop technique for example.[9,10] Next to the surface tension of the liquid also possible oxide layers, the surface roughness and capillary effects influence the spreading behavior of a liquid on a substrate.[7,8,11-13] In the case that there is a reaction between the substrate and the liquid, the wetting process can be significantly affected and this generally also reflects in the contact angle.[14] In other words, brazing is a complex process gove
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