Optimisation of Nickel Aluminising by CVD

Abstract

Results Concerning Nickel Aluminisation with Application of Chemical Vapour Deposition Method Are Presented. Two-Step Processing under Investigation Consists of Al Chloride Formation in the Primary Vessel and Al Deposition in the Secondary One. the Initial Gas Stream Is Composed of Hcl Dissolved in H2at Various Ratios. it Was Shown that the Choice of the [HCl]/[H2] Ratio and the Determination of the Optimum Temperature to Produce Most Preferential β-Nial Phase May Be Done with the Use of Thermodynamic Calculations. the Results Obtained with Application of Factsage Program Confirm Essential Influence of both Initial [HCl]/[H2] Ratio (in the Range between 0,05 and 100) and the Temperature in the Second Vessel (1123 K – 1323 K) on Aluminium Chloride Partial Pressures and Hence Aluminium Content in its Gaseous Donors and at the Substrate Surface (boundary Condition for Interdiffusion in Ni-Al System). it Was Confirmed that β-Nial Growth Is Favoured at Low [HCl]/[H2] Ratios and High Temperatures for which Alcl and AlCl2Partial Pressures Increase with Respect to that of AlCl3. the Thermodynamic Predictions Remain in Agreement with CVD Experiments. the Presented Thermodynamic Data May Be Used as a Source of Essential Information for Designing Further Experiments in this Field as Well as for Modelling of Solid-State Diffusion in Ni-Al System.