In this project, we performed a preliminary set of sintering experiments to examine nanocrystal-enabled diffusion bonding (NEDB) in Ag-on-Ag and Cu-on-Cu using Ag nanoparticles. The experimental test matrix included the effects of material system, temperature, pressure, and particle size. The nanoparticle compacts were bonded between plates using a customized hot press, tested in shear, and examined post mortem using microscopy techniques. NEDB was found to be a feasible mechanism for low-temperature, low-pressure, solid-state bonding of like materials, creating bonded interfaces that were able to support substantial loads. The maximum supported shear strength varied substantially within sample cohorts due to variation in bonded area; however, systematic variation with fabrication conditions was also observed. Mesoscale sintering simulations were performed in order to understand whether sintering models can aid in understanding the NEDB process. A pressure-assisted sintering model was incorporated into the SPPARKS kinetic Monte Carlo sintering code. Results reproduce most of the qualitative behavior observed in experiments, indicating that simulation can augment experiments during the development of the NEDB process. Because NEDB offers a promising route to low-temperature, low-pressure, solid-state bonding, we recommend further research and development with a goal of devising new NEDB bonding processes to support Sandia's customers.
The effects of heat treatment parameters were examined in complex electrical contact alloys containing Pd-Ag-Cu-Au-Pt. These alloys (Paliney tradename, Deringer-Ney Inc., Bloomfield, CT) are strengthened by precipitation reactions. During processing such as glass-to-metal joining in hermetic connectors, if the cooling rate is too slow, discontinuous precipitation (DP) of lamellar 2nd phases can spoil the strengthening effect. Two different solutionizing temperatures were employed and the effects of cooling rates between 6 C/min and >200 C/min were studied. Novel metallographic techniques were developed to reveal the microstructure of these corrosion resistant alloys and quantitative image analysis (QIA) was used to determine the amount of 2nd phase precipitates. Vickers and Knoop microhardness testing was performed to determine the effects of heat treatment parameters on mechanical properties.