Structure of surface layers produced by non-vacuum electron beam boriding

The structure and mechanical properties of boronized layers produced on low carbon steel substrates by non-vacuum electron-beam cladding were studied. This process provides high performance and high thickness of coatings and can be used to process large workpieces. In this study, we investigated coatings obtained by one, two or three passes of the electron beam. The thickness of the coatings varied from 0.6 to 1.0 mm, and the maximum hardness achieved was 21 GPa. Structural analysis revealed the oriented growth of eutectic colonies near the primary crystals of iron borides, which was explained by the commonality of the boride phases in the primary Fe2B and eutectic Fe2B. The eutectic colonies formed during electron-beam cladding consisted of a continuous framework of borides crystals and segregations of α-Fe in the form of oriented fibers. Coatings produced by electron-beam cladding had higher contact-fatigue endurance than those produced by pack boriding.