Thermodynamic study on pack aluminizing systems of pure titanium and nickel
(1. Centre of Excellence for High Strength Alloys Technology, School of Metallurgy and Materials Engineering,Iran University of Science and Technology, Narmak, Tehran 168463114, Iran;2. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China)
Abstract: Gas aluminizing of pure titanium and nickel samples was carried out in open and closed systems. All the samples were aluminized at 1100 °C for 3 h using pack containing 10%Al+5%NH4Cl+85%Al2O3. Although an α solid solution of Al in Ti was formed on the surface of titanium samples treated in the open set-up, but the samples experienced a mass loss of 32.37%. However, the results of titanium samples treated in the closed set-up showed that a TiAl3 layer and some α solid solution were formed on the surface of these samples without any reduction in mass. Thermodynamic analysis demonstrated that the mass loss of treated titanium samples in the open set-up is due to the continuous formation of titanium chlorides during aluminizing process. Nevertheless, running the experiments in the closed system indicated that the corrosion of titanium samples vanished due to attaining the equilibrium condition. On the contrary, it was observed that nickel samples can be successfully pack aluminized without any mass loss in both open and closed systems. The presence of NiAl and Ni3Al phases on the surface of treated nickel samples was confirmed by XRD and EPMA results in both set-ups.
Key words: pack aluminizing reactions; titanium; nickel; thermodynamics; gas aluminizing