Abstract
The kinetics of formation of iron borides by boronizing of FeAl was studied. FeAl samples were exposed to boronizing process in a solid medium at 875 °C, 940 °C, 1040 °C for 2, 4 and 8 hours. The characterization and morphology of borides layers were studied by XRD analysis and metallographic technique. The results showed that increasing boronizing time and temperature led to thicker boride layers. The thickness of boride layers ranged from 8 to 60 μm with changing boronizing temperatures and times. Depending on treatment temperatures and times, the hardness of the boride layers ranged from 1290 to 1500 HV, while the hardness of the substrate ranged from 340 to 490 HV. XRD analysis revealed that FeB phase was a major phase at all temperatures. However, Fe2B phase was detected as a minor phase at only 1040 °C for 8 hours. The formation of iron borides followed a parabolic growth rate law, showing a diffusion-controlled process.

Key words
boronizing, iron aluminides, borides, kinetics, diffusion-controlled

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