Understanding the Microstructure Evolution of 8Cr4Mo4V Steel under High-Dose-Rate Ion Implantation

Abstract

In this study, the effect of microstructure under various dose rates of plasma immersion ion implantation on 8Cr4Mo4V steel has been investigated for crystallite size, lattice strain and dislocation density. The phase composition and structure parameters including crystallite size, dislocation density and lattice strain have been investigated by X-ray diffraction (XRD) measurements and determined from Scherrer’s equation and three different Williamson–Hall (W-H) methods. The obtained results reveal that a refined crystallite size, enlarged microstrain and increased dislocation density can be obtained for the 8Cr4Mo4V steel treated by different dose rates of ion implantation. Compared to the crystallite size (15.95 nm), microstrain (5.69 × 10−3) and dislocation density (8.48 × 1015) of the dose rate of 2.60 × 1017 ions/cm2·h, the finest grain size, the largest microstrain and the highest dislocation density of implanted samples can be achieved when the dose rate rises to 5.18 × 1017 ions/cm2·h, the effect of refining is 26.13%, and the increment of microstrain and dislocation density are 26.3% and 45.6%, respectively. Moreover, the Williamson–Hall plots are fitted linearly by taking βcosθ along the y-axis and 4sinθ or 4sinθ/Yhkl or 4sinθ(2/Yhkl)1/2 along the x-axis. In all of the W-H graphs, it can be observed that some of the implanted samples present a negative and a positive slope; a negative and a positive slope in the plot indicate the presence of compressive and tensile strain in the material.

Effect of Dose Rate on Tribological Properties of 8Cr4Mo4V Subjected to Plasma Immersion Ion Implantation

“…For the samples that underwent ion implantation at a total dose of 2.215 × 10 20 ions/cm 2 , the new Fe 2-3 N peaks emerged in the X-ray diffraction patterns. This was particularly notable at the high dose rate of 5.18 × 10 17 ions/cm 2 •h ion implantation, as indicated in references [41,47]. Meanwhile, in comparison to the samples implanted at a dose rate of 1.04 × 10 18 ions/cm 2 •h, those treated at dose rates ranging from 2.60 × 10 17 to 7.85 × 10 17 ions/cm 2 •h exhibited broadened diffraction peaks.…”

“…This setup guaranteed uniform temperature conditions for both samples throughout the treatment process. The temperature was meticulously determined based on the Rockwell hardness of the implanted GCr15 steel and subsequently calculated using a scientifically established equation, as referenced in [41]. by interactions with high-energy ions.…”

“…As can be seen in Figure 2f, the evolution trend of roughness initially decreases and then increases with the implantation dose rate. This increase in surface roughness may be due to changes in lattice parameters, particularly the augmented formation of dislocation density, during the high-dose-rate implantation process [41,44]. The values of Rq and Ra tend to rise to 24.3 nm and 18.9 nm, respectively, as the treating temperature increases.…”

“…This phenomenon suggests that the high-dose-rate ion implantation leads to a partial substitution of nitrogen ions at the iron sites. Furthermore, during the ion implantation process, this high-dose-rate implantation is likely to cause changes in lattice parameters within the surface layer [41,46].…”

“…Processes 2024, 12, x FOR PEER REVIEW 7 of 19 rate of 5.18 × 10 17 ions/cm 2 •h ion implantation, as indicated in references [41,47]. Meanwhile, in comparison to the samples implanted at a dose rate of 1.04 × 10 18 ions/cm 2 •h, those treated at dose rates ranging from 2.60 × 10 17 to 7.85 × 10 17 ions/cm 2 •h exhibited broadened diffraction peaks.…”