ALUMINUM HALIDES
The most popular aluminum halides for CVD applications is aluminum trichloride AlCl3
Aluminum monochloride AlCl
Aluminum monochloride is a precursor prepared in situ according to the reaction:
2 Al + AlCl3 → 3 AlCl (at high temperature, on cooling AlCl3 is formed.
Aluminum trichloride AlCl3
AlCl3 for Al coatings by CVD
Al films have been deposited on Si and SiO2 substrates from AlCl3 precursor, formed in situ and transported to substrate by vapor phase transport, starting from Al and HCl as precursors:
3 HCl + Al → AlCl3 + 3/2 H2 (900 – 1000 °C)
Process conditions were following: temperature gradient from 150 to 550 °C, partial pressure of HCl and H2 0.2 and 0.8 Torr.
Al film growth rate was 50 nm/ min, grain size 400 nm, resistivity of films 3.4 – 3.7 μWcm.
AlCl3 for aluminide (Ni,Pd)Al coatings by CVD
Palladium modified nickel aluminide coatings were prepared by CVD method on nickel-based superalloy, with the target of using them as an alternative for Pt-modified aluminide coatings in turbine blades of aircraft engines. The aluminide coating was obtained in low-activity CVD process using BPXPRO3242 equipment of IonBond company at the temperature 1050°C for 8h. In order to obtain a thermodynamically stable conditions the CVD process consisted of several heating stages. The gas atmosphere (AlCl3+H2) was prepared in an external generator and transported into the retort with samples.
The microstructure investigations of Pd-modified nickel aluminide coatings were conducted by the use of optical microscope and SEM equipped with an EDS, the phase composition was identified by XRD. The surface roughness parameter - Ra of modified aluminide coatings was evaluated using perthometer
The microstructure of palladium modified aluminide coatings (3 and 7 μm thick) consisted of (Ni,Pd)Al phase and two zones: outer and internal one. Low activity CVD aluminizing at 1050 ºC for 8 h caused the increase of surface roughness parameter of modified coatings. The increase of platinum thickness from 3 to 7 μm causes a greater surface roughness of aluminide coatings. It was found that palladium modification of aluminide coatings increased the oxidation resistance of CMSX 4 Ni-base superalloy. Oxidation resistance was evaluated at 1100ºC for 1000 h in air atmosphere using furnace of Czylok company. . [[i]]
[i]M. Zagula-Yavorska, K. Kubiak, J. Sieniawski, Journal of Achievements in Materials and Manufacturing Engineering 55/2 (2012) 848-854.
http://ww.w.journalamme.org/papers_vol55_2/58296.pdf
“Oxidation behaviour of palladium modified aluminide coatings deposited by CVD method on nickel-based superalloys under air atmosphere”,