Two technique of coatings were performed by applying pack cementation
technology, the first one was aluminizing diffusion coated low alloy steel substrate
whereas the second one was single step simultaneous Co-deposition silicon- aluminum
diffusion coated low alloy steel substrate. The pack mixture used for producing both
coating systems in pack cementation process was composed of (30% Al, 2% NH4Cl and
the filler 68% Al2O3) , (30% Al , 5% Si , 2% NH4Cl and 63% Al2O3 ) respectively. The
pack temperature was 1000◦C and the diffusion time was 3 hr. XRD exhibits the phases
formed on both coated systems are Fe2Al5 , FeAl3 and FeSi . Uncoated low alloy steel
substrate and the both two coating systems were subjected to exposure environment
deposit salts mixture of (50%Na2SO4 and 50%NaCl) with weight (2mg /cm2), using
cyclic oxidation method in the experiments at temperature of 750◦C for 100hr each
cycle of 5hr. It was found that the oxidation kinetic for uncoated low alloy steel will give
evidence that the oxides formed on this alloy are non – protective. The XRD analysis
exhibited the phases are Fe2O3 , Fe3O4. It was found they followed linear rate law, and
spalling was observed. After these hot corrosion tests were undertaken, It was found that
the oxidation kinetics for both coated systems in environment consist of salt mixture
(50% NaCl +50% Na2SO4) followed parabolic law (protective oxidation behavior). XRD
exhibits the oxides formed on both coated systems are Al2O3, SiO2.