Deposition of Intermediate (Barrier) Coatings of Silicon and Germanium on Steel, Titanium or Aluminum Substrates Using Laser Ablation

The paper presents the results of the first stage of the experimental research of intermediate (barrier) silicon and germanium coating deposition on the substrates not proned to the formation of carbides (steel, titanium, aluminum) by laser ablation. These experiments were carried out using modified YAG-Nd3+ solid state laser of LTI-130 type with the wave length of 1064.1 nm. It was shown that the sequence of large numbers of nanosecond pulses which composed the train of laser radiation provided the material ablation under the power of two orders of the magnitude less than that of the single pulse necessary for the ablation process. In the experiments, silicon coatings up to 5 mu m in thickness and germanium coatings of 1-3 mu m in thickness were produced on substrates from steel, aluminum and titanium. It was determined that the roughness of substrate surface for deposition of intermediate (barrier) coatings had a strong influence on the coating structure. Silicon films on substrate surfaces with the roughness <= 10 mu m were denser and more homogeneous and looked like amorphous films without a crystal structure. On surfaces with the roughness >20 mu m a silicon film had a crystal structure with the size of crystallites about 5 mu m. It was shown that unlike the silicon the germanium in the same experimental conditions had the tendency to the formation of films with elements of a crystal structure. Germanium coatings were not homogeneous and consisted of the mixture accumulations of crystallites and amorphous fields.