Influence of processing parameters on microstructure of metal films produced from high velocity impact of nanoparticle aerosols
The Laser Ablation of Microparticle Aerosol (LAMA) process and the Micro Cold Spray (MCS) process are used for production of thick (> 1μm) films. Both are aerosol processes that produce films by the impact of solid nanoparticles at high velocities (400-1500 m/s). The particles are accelerated through a nozzle onto a substrate. By moving the substrate under the nozzle, it is possible to produce patterned films of variable thickness onto a variety of substrates. While deposition of larger metal particles (> 5 μm) has been extensively studied, there have been comparatively few studies about the parameters that effect film formation when finer (< 1000 nm), metallic particles impact at high velocities. In this dissertation the LAMA and MCS systems are used to produce thick films of metal nanoparticles at a variety of deposition conditions. Each of the experiments aims at examining a processing parameter to study its effect on film formation. Through optical profilometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), four-point probe resistivity, and x-ray diffraction (XRD) deposited film and nanoparticle microstructure are characterized and properties are measured. The effect of impact velocity for silver particles is first examined when impacting particle size and material are fixed, and it is shown that film densities can be increased from 58-86% by increasing impact velocity from 980 m/s to 1440 m/s. The influence of agglomeration morphology on deposition is then studied, and it is shown that the size and shape of silver agglomerates in the feedstock can be controlled through heat treatment and by high rate shearing. It is shown that dense films with high conductivity are favored when agglomerates consist of a small number of primary particles that have a compact morphology. A preliminary study is presented where deposition of different metal particles, including stainless steel, Ni, Cu, Au, and Pt that have a range of stacking fault energies (SFE) and hardnesses are explored.