Original Article

Characterization of molybdenum-modified aluminide coating on 304 stainless steel via slurry aluminizing

¹ School of Materials and Minerals Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia
² University of Ilorin, Faculty of Engineering and Technology, Ilorin, Nigeria
³ Indian Institute of Technology Kharagpur 721302, India

^* e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 6 January 2026
Accepted: 19 January 2026

Abstract

This study investigates the microstructural changes and growth kinetics of intermetallic compounds in Mo-modified aluminide coatings on 304 stainless steels with varying temperatures and times. Molybdenum and alumina were introduced via slurry aluminizing. Heat treatments were conducted at 750 °C, 800 °C, and 850 °C for varying times (6, 8, and 10 h). Aluminide coating was characterized with SEM, EDX, and XRD, revealed the presence of multilayer phases comprising of Fe-Al and Mo-Al intermetallic compounds, along with an alumina scale on the coating surface. Samples heated at 750 °C showed uniform coatings, while those at 800 °C and 850 °C exhibited voids and cracks. The growth kinetics of the coating obey a parabolic law conforming to diffusion-controlled growth. The activation energies calculated for FeAl and Fe₃Al were 360 kJ/mol and 237 kJ/mol, respectively, which is higher than that of coatings containing aluminium (FeAl layer: 180 kJ/mol and and Fe₃Al layer: 260 kJ/mol). The total activation energy (Q) was 26 kJ/mol for coatings containing molybdenum and 53 kJ/mol for coatings with only aluminium. Hardness of the intermetallic layers varied from 378 to 966 HV for Mo-modified coatings as compared to aluminide coating (380 to 1030 Hv). The corrosion behaviour of Mo-aluminide coatings was investigated in 3.5% NaCl using polarization and electrochemical impedance spectroscopy (EIS) tests. Results show improved performance of corrosion resistance due to Mo-rich intermetallic phases, with the 6 h sample exhibiting the best corrosion resistance.