The Effects of Ar-Bombardment on the Dissolution and Reprecipitation of Carbonitrides Implanted Into Low Carbon Steel
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THE EFFECTS OF Ar-BOMBARDMENT ON THE DISSOLUTION AND REPRECIPITATION OF CARBONITRIDES IMPLANTED INTO LOW CARBON STEEL STELLA M.M. RAMOS, L. AMARAL, M. BEHAR, A. VASQUEZ AND F.C. Instituto de Fisica, UFRGS, 91500 Porto Alegre, Brasil
ZAWISLAK
ABSTRACT The effects of Ar post-bombardment on the dissolution and reprecipitation of carbonitrides present in N2 implanted 1020 low carbon steel are investigated using conversion electron M~ssbauer spectroscopy (CEMS). The results are compared with similar experiments where samples of the same steel were post-bombarded with He. The experimental data show that the Ar is more efficient in the dissolution of precipitates and also more efficient in the precipitate retention at 450 °C, for the same peak concentration.
INTRODUCTION In previous works we have reported results showing the effects of alpha particle post-bombardment on nitrides and carbonitrides produced by N implantation into Fe [1] and into low carbon steel [2) respectively. In both cases the alpha irradiation affected the thermal behaviour of the precipitates by raising the temperature at which they started to dissolve. Besides these results, particular effects have been found for each case. The alpha bombardment produced partial nitride dissolution in the Fe matrix [11 whereas for the low carbon steel complete dissolution and reprecipitation of carbonitrides have been observed at low bombardment fluences [2,3]. As discussed previously [3] the above effects are strongly dependent on the kind of precipitates involved in the process as well as on the type of matrix in which the precipitates are formed. An extension of this research is to investigate the influence of the type of ions used in the post-bombardment experiments. Therefore, in the present work we report results of Ar post-bombardment effects on carbonitrides produced by N implantation in low carbon 1020 steel samples. The N implanted samples have been annealed, Ar post-bombarded and further thermally treated. The characterization and evolution of the precipitates are followed, at each 5 7 stage, using Fe conversion electron M8ssbauer spectroscopy (CEMS). It is shown that the Ar post-irradiation produces carbonitride dissolution and reprecipitation. In addition we show that the thermal behaviour of the precipitates is affected by the presence of the Ar in the N implanted region.
EXPERIMENTAL Mechanically polished discs of 1020 low carbon steel (C=0.2; Mn=0.9 wt%) were implanted at the HVEE 400 kV ion implanter of the Institute of Physics, Porto Alegre. The N' implantation was performed at 150, 80 and 40 keV in order to obtain a plateau from the surface up to around 120 nm. The typical im6 2 planted fluence was 6x101 N2 /cm and the N concentration at the plateau was around 40%. The Ar was implanted4t an energy of 150 keV, leaving the Ar particles in the N implanted regiojfThe samples we e studied as a function of 4 2 the Ar fluence in the range from 101 to 1.Oxi1O Ar/cm . The implantation 2 density current was always lower than 1 jiA/cm , thus during the im
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