Structural and phase transitions in technically pure iron under influence of laser radiation

Abstract

The structure and also the phase and element composition of the technically pure iron samples have been investigated before and after the exposure to laser pulse radiation by the methods of metallography, Moessbauer spectroscopy, electron microscopy, and x-ray micro-analysis. It has been shown that carbon in the untreated samples is distributed inhomogeneously and is concentrated in the intergranular areas of crystals. After laser treatment with alloying of the surface, carbon concentration in the α-Fe crystals increases four to five times, while the amount of carbides increases two times. The increase of carbon concentration and the amount of the carbide phases in α-Fe under the influence of laser radiation is caused by rearrangement of carbon in the affected zone. With the use of the concentrated energy beams, one can create the surface layers in solids, with substantial operational advantages to the layers obtained by chemical-thermal treatment. One of the prospective methods of laser technology is implantation of doping elements into the host metals and formation of doped layer. The structure, phase composition, and properties of the affected surface layer depend not only on laser irradiation conditions and composition of the doped layer, but also to a considerable extent on the structure and composition of the bulk material. Mass transport and mixing, not only of atoms of the doped layer but also of the elements from the bulk, take place in the zone of thermal treatment. This is important problem is, however, insufficiently covered in literature. Carbon plays a particularly important role in iron compounds, since even a small amount of it greatly affects alloy properties. Therefore, with the study of laser implantation it is convenient to use as the host material the technically pure iron which contains a low quantity of impurities, including carbon. This allows one to ignore the interaction of impurities with doping atoms when considering mass transport of the implanted elements and the crystallization process. The aim of the present work is to investigate formation of phases and structure elements under the influence of laser radiation and carbon distribution in the untreated and affected samples of technically pure iron.