Investigation and application of Fe-Al intermetallic compound formed by atmospheric-controlled IH-FPP

In the present study the authors attempted to propose a new method to form Fe-Al intermetallic layer on a steel surface by using atmospheric-controlled IH-FPP (AIH-FPP). Surfaces of structural carbon steel as well as high-speed tool steel were modified by AIH-FPP using aluminum particles. Optical microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy revealed formation of solidified Al layer and underlying Fe₂Al₅ layer on the AIH-FPP-treated carbon steel substrate. Because of the existence of the intermetallic compound layer, the AIH-FPP-treated surface showed high hardness. It was assumed that deposition of aluminum particles and subsequent diffusion between aluminum deposit and substrate occurred during AIH-FPP process, forming the intermetallic layer. Longer anneal time after peening and higher temperature in AIH-FPP process increased in the thickness of the intermetallic layer and decreased in that of the solidified Al layer. AIH-FPP performed on the tool steel also formed Fe₂Al₅ layer and Al solidified layer. AIH-FPP temperature suitable for creating intermetallic was slightly higher for tool steel substrate than for carbon steel, implying that intermetallic layer formation was affected by carbon content in the substrate. Hot filament chemical vapor deposition (HF-CVD) successfully deposited thin film comprising diamond crystals on the AIH-FPP-treated steel substrate on which the intermetallic layer was formed. Graphite was contrastingly deposited on untreated steel substrate because of graphitization catalytic effect of Fe elements. It was clarified that the AIH-FPP using aluminum particles was a possible treatment to form hard intermetallic compounds and a candidate as a pre-treatment of CVD diamond coating for steel substrates.