Thermodynamic and Kinetic Study of Phase Transformations in Solder/Metal Systems

AbstractDiffusion in both the Pd‐Sn and Cu‐Sn systems has been investigated using differential scanning calorimetry. Averaged interdiffusion coefficients for the PdSn4, PdSn2 and Cu3Sn intermetallics have been calculated, where equilibrium concentrations in the diffusion couples are assumed. There is an obvious hierarchy within the Pd‐Sn system where diffusion is fastest in the most Sn‐rich intermetallic. Comparisons within each system, including consideration of the solute diffusion coefficients in pure Sn, provide evidence that in the most Sn rich phase (e.g. PdSn4) the interstitial diffusion of metal atoms is the dominant reaction mechanism. In contrast, the diffusion coefficient for the Cu‐rich phase Cu3Sn was found to be five orders of magnitude smaller than the solute diffusion coefficient for Cu in pure Sn.</jats:p

A Study of the Kinetics and Energetics of Solid State Reactions in Pd/Sn Diffusion Couples

ABSTRACTUsing differential scanning calorimetry, supplemented by measurements from scanning electron microscopy images, we have investigated solid state reactions in Pd/Sn multilayer composites to form PdSn4 and PdSn3. Planar diffusion couples of Pd and Sn were prepared by means of mechanical co-deformation in a rolling mill. A phase formation sequence was determined using differential scanning calorimetry and x-ray diffraction. Growth of the PdSru phase was studied from room temperature to the melting point of Sn. For temperatures between 430 and 460K diffusion limited growth of PdSn4 was observed. From heat flow data over this limited temperature range, the form of the reaction constant was found to be k2 −k0 exp(−Ea / kbT), where k0= 0.16 cm2/s and &amp;Epsilon;n= 0.8 eV/atom. Also determined was a heat of formation, ΔHf = −27±1 kJ/mol for PdSn4 from Pd and Sn.</jats:p

Combining in situ and online approaches to monitor interfacial processes in lubricated sliding contacts

In this study, “within the environment” and “within the contact” in situ tribology techniques are combined in order to study the interfacial processes in lubricated metallic (i.e., aluminum-based) sliding conditions. The evolution of the roughness follows the trend of the coefficient of friction closely, with initially low values followed by higher roughness during steady state. Similarly, the transfer film behavior correlates well with the roughness of the worn surfaces and the subsurface microstructure of the worn surfaces. The effect of normal load on the running-in behavior is also studied in terms of differences in the interfacial processes

Metallic transfer films studied in situ and ex situ: The case of cold-sprayed Al-Al2O3

The presence of A12O3 particles in the composite coating promoted the formation of nanostructured aluminum in the transfer film, which contributed to its stability, as observed by in situ tribometry. This was linked to lower wear rates and more stable friction compared to the unreinforced cold sprayed aluminum. Here, the combination of in situ tribometry and ex situ analysis was a useful approach to reveal mechanisms specifically related to the transfer film, which were responsible for improved tribological performance. Other questions remain, which will be subject of future work, regarding the microstructural evolution in the wear track, mechanical properties of the third bodies, and the role of A1203 particles in the dynamic formation of nanocrystalline aluminum.Peer reviewed: YesNRC publication: Ye