Influence of gas environment of an implanter of structural-phase transformations in tantalum

Full text: It is known, that on structural-phase transformations in ionic-implanted layer essential value has interaction of metals with elements of gas environment of an implanter (C, N, O). In the given work results on ionic-beam alloying of tantalum by ions of nitrogen. As an initial material the polycrystalline foil from tantalum by cleanness of 99.96% thickness 0.5 mm, cut out as rectangular in the sizes 8·1.5 mm2 is used. With the purpose of removal of the deformed layers samples after machining were exposed to electrolytic polishing. Implantation of ions of nitrogen with energy 70 keV dozes l.87·1017 cm-2, 3.74·1017 cm-2 and 5.6·1017 cm-2 was spent in vacuum (1.3·10-3 Pa) at density of a current ∼1 mA·cm-2. Thermal annealing carried out in vacuum (6.6·103 Pa) through 100 deg. C in a range of temperatures 500-1100 deg. C within one hour each sample. Identification of structure of the modified superficial layers was carried under the roentgenograms received with use of a narrow bunch monochromatized CuKα-radiation, directed under a sliding 6 deg. corner to a surface of a sample. At formation of textured phases for specification of results additional shootings were carried out at corners of falling 3.9 and 15 deg. It is established, that after implantation of ions of nitrogen on roentgenograms there is a set of lines from a polycrystalline phase which represents nitride of tantalum TaN with densely packed FCC-structure. Together with lines of this phase the weak set lines of carbonide of tantalum β-Ta2C with HCP- structure which arises due to implantation by a method of feedback of carbon from an atmosphere of residual gases of the accelerator is registered also. Further, the subsequent annealing up to 900 deg. C does not bring essential changes in an observably picture while annealing at 1100 deg. C conducts in addition to formation of phase Ta2C which results partial carbonization from a surface of tantalum in an atmosphere of residual gases of the furnace. Occurrence densely packed phases Ta2C was observed earlier and at implantation of nitrogen in molybdenum. The analysis of the received results in the following. The relation of nuclear radius of nitrogen to nuclear radius of tantalum makes 0.48 In this case, it agrees the assumptions put forward earlier, based on Hegg's rule, at implantation should be formed mainly simple densely packed structures, as has proved to be true in the given work. On the literary data among known nitrides the unique phase having densely packed structure, is phase TaN. For this reason, apparently, implantation of ions of nitrogen results directly in formation of phase TaN with the FCC-lattice though at small dozes it was necessary to expect all over again occurrence of phase Ta2N with lower contents of nitrogen