The Apparent Contact Angle and Wetted Area of Active Alloys on Silicon Carbide as a Function of the Temperature and the
- PDF / 1,802,930 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 38 Downloads / 188 Views
THE knowledge about the wetting and the spreading behavior of liquid metals on ceramics is crucial in many fields of applications, such as joining[1,2] or manufacturing of composite materials.[3] Since the 1950s, extensive work has been carried out in order to achieve a sufficient wetting of engineering ceramics, using a variety of metallic alloys.[1,2,4–9] A brief excerpt of the results of these works carried out on silicon carbide can be seen in the following Table I. The listed values and references concentrate on liquid metal–ceramic systems, which are of relevance for the joining context [low apparent contact angles at temperatures above 1073 K (800 C)]. Such investigations lead to an improved knowledge about the wetting properties of liquid metals, and consequently about their applicability for joining purposes. Therefore, many of the developed so-called active alloys are nowadays commercially available and used in a broad field of application. Despite this fact, the reproducibility of the wetting and consequently of the joints is still subjected to a high variance.[2] A good example for such a scattering in the wetting properties WOLFGANG TILLMANN, Head, and JAN PFEIFFER and LUKAS WOJARSKI, Research Associates, are with the Institute of Materials Engineering, TU Dortmund University, Dortmund, Germany. Contact e-mail: jan.pfeiff[email protected] Manuscript submitted October 21, 2014. Article published online May 7, 2015 3592—VOLUME 46A, AUGUST 2015
can be seen when the works of Ljungberg[8] and Tillmann[2] are compared. The first named observed for an AgCuTi alloy at 1173 K (900 C) almost total wetting. In Reference 2 measurements on a comparable alloy at the same temperature yielded significantly higher values of the contact angle.[2,8] The reason for this discrepancy is the sensitivity of the wetting properties to a large amount of influencing factors. Small changes in the joining temperature, the substrate preparation, or the atmosphere cause a former stabile joining process to change in an unpredictable way. Thus, it is not feasible to compare the results of studies carried out by different authors quantitatively. It is merely possible to evaluate the plausibility of new results by a qualitative comparison with other published values.[2,8,16–19] Besides the studies named, which focus on the applicability of the high temperature wetting, a large number of investigations concerning the fundamentals and principles of the inherent processes leading to wetting/non-wetting have been carried out. The developed approaches are summarized and reviewed in the contributions of de Gennes et al.[19] and Asthana and Sobczak.[20] Recently, a comprehensive review concerning the fundamentals and theories of wetting is part of the contribution of Kaplan et al.[21] The starting point in most descriptions is usually the Young-Dupree equation. This equation reveals the connection between the contact angle, the surface, and interfacial energies of a system consisting of a solid, a liquid, and a vapor phase (cf. Eq. [1]).[22] METALLURGICAL AND
Data Loading...
