A study of transient liquid-phase bonding of Ag-Cu using differential scanning calorimetry
- PDF / 394,749 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 34 Downloads / 211 Views
ENT liquid-phase (TLP) bonding is a material joining process that produces a high quality bond at the interface of the parts to be joined.[2] The TLP bonding, which is also known as diffusion brazing,[3] is a brazing or soldering variation; and, as such, it depends on the formation of a liquid at the faying surfaces by an interlayer that melts at a temperature lower than that of the substrate. The TLP bonding is distinguished from other brazing processes by the resolidification of this liquid at a constant temperature. The interlayer is rich in a melting point depressant, and upon heating through the eutectic temperature, the interlayer will either melt or react with the base metal to form a liquid. During an isothermal hold above the melting temperature of the interlayer, the melting point depressant (solute) is removed from the liquid phase through extensive long-range diffusion into the base metal (solvent). The resulting solid/liquid interfacial motion via epitaxial growth of the substrate is termed ‘‘isothermal solidification.’’[2] A homogeneous bond between the substrates is formed when isothermal solidification is complete, which is when the two solid/liquid interfaces meet at the joint centerline. The TLP bonding shows great potential for joining materials that are not easily joined by conventional fusion welding processes.[4–8] One reason that TLP bonding is not yet in widespread use is that the experimental approach used to determine the process parameters can be time consuming and costly. This experimental approach typically involves a determination of the liquid fraction remaining in the joint metallographically from a series of samples quenched from the process temperature at different hold times.[9] The width of a solidified liquid phase is identified by a eutectic micro[1]
M.L. KUNTZ, Research Assistant, Y. ZHOU, Associate Professor and Canada Research Chair, and S.F. CORBIN, Associate Professor, are with the Department of Mechanical Engineering, University of Waterloo, Waterloo, ON, Canada, N2L 3G1. Contact e-mail: [email protected] Manuscript submitted December 2, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A
structure and measured from a cross section of the joint. Unfortunately, the solid/liquid interface is usually not planar but irregular and scalloped, which makes measurement of the eutectic width difficult and prone to measurement error.[10] In some studies of isothermal solidification kinetics, the eutectic width is assumed to be representative of the liquid width before cooling.[11–15] Nakao et al.[16] and MacDonald and Eagar[10] used the lever rule to account for primary solidification, which has been shown to occur epitaxially during cooling.[17] Both of these methods assume ideal conditions that are unlikely during solidification. MacDonald and Eagar[18] have explained that experimental setup can also be a source of significant error. The apparent overall isothermal solidification time can be reduced by the squeezing of liquid from the interface due to excessive force in the assembly. Liquid
Data Loading...
