| Despite its critical role in many manufacturing processes, reactive wetting remains a poorly understood phenomenon. During reactive wetting, a broad spectrum of physicochemical processes may occur over a wide range of time scales and length scales. The primary challenge has been to identify the driving forces and the rate-controlling mechanisms of reactive wetting.; In the present work, the isothermal wetting and spreading behavior of two binary metallic systems, Bi-Sn and Au-Sn, were experimentally studied using the sessile drop method in a gaseous flux atmosphere. Wetted radius and apparent dynamic contact angle were measured as a function of time. Sequential quenching and metallographic analysis were employed to investigate the temporal evolution of the solid/liquid interface, the total contact angle and intermetallic compound formation. Discussion of equilibrium states, fluid flow, mass transport and associated metallurgical reaction are presented.; In the dissolutive Bi-Sn system, the spreading of various Bi-Sn alloys on pure Bi substrates was studied at 250 °C. The macroscopic total contact angle was found to be close to 90° during the spreading for majority of the Bi-Sn alloys investigated. The contact line mobility relationship, based on the apparent dynamic contact angle, showed certain similarities to a universal correlation for partially wetting inert systems. A set of equations describing the equilibrium state in the dissolutive system is presented. The analysis indicates that both the equilibrium upper and lower contact angles are dependent on the initial alloy composition, although the sum is a constant.; In the compound forming Au-Sn system, the spreading of pure Sn and an eutectic Au-Sn (80 wt.% Au) alloy was studied on Au and zeta-phase substrates. The spreading of pure Sn on Au exhibited three unique behaviors over the temperature range of 250-430 °C: (1) 250-280 °C, limited spreading was accompanied by the formation of multiple intermetallic compounds; (2) 315-415 °C, rapid spreading and concurrent appearance of transient intermetallic solidification were observed; (3) 430°C, extensive spreading was observed in the form of a thick film (∼20 mum) supplied by a central dissolution crater whose liquid/vapor interface exhibited a curvature reversal. Despite a substantial concentration difference, the eutectic Au-Sn alloy showed similar extensive spreading behavior to pure SN at 430 °C. However, at this temperature, the eutectic Au-Sn alloy did not show a zero or near zero contact angle on the zeta-phase substrates. |
