Interfacial phenomena in welding

The understanding of the interfacial phenomena in welding is crucial to the understanding of the welding process and weld metal properties. The interfacial tension force is the dominant force for fluid flow in welding. The variation of interfacial tension as a function of temperature and composition of the melt is not well understood. Further compounding this effect is the role of plasma during welding. Important questions such as how plasma affects the nature of the interface and thus the interfacial tension tension forces and vaporization losses of alloying elements remain unanswered.; Both theoretical and experimental studies were conducted to obtain a fundamental understanding of the nature of the interfacial tension and a physical concept of the interface within an ambient which contains excited and charged species. A combination of Gibbs and Langmuir's adsorption isotherms was used to develop an analytic formalism of interfacial tension as a function of both temperature and composition of binary metal-surface active systems. Theoretical predictions of surface tension behavior as a function of temperature and composition were compared with existing data and fair agreement was observed. The variation of the temperature coefficient of surface tension and its effect on fluid flow was examined from a theoretical and experimental standpoint. Using a radio frequency power generator an inductively coupled plasma was generated and interfacial tension was measured both in the presence and absence of the plasma. The variables were temperature, plasma composition and plasma intensity of emission. A hypothesis was proposed to explain the observed reduction in surface tension in the presence of an argon plasma on the basis of plasma-induced enhanced surface segregation of surface active species. Interfacial tension of pure liquid copper in a hydrogen plasma was not different than that observed in inert gas systems. To further corroborate this effect and to study the nature of the interface, vaporization rate experiments were carried out, in conjunction with emission spectroscopy, to develop a physical concept of the interface in proximity of the liquid metal.