Andrei N. Didenko

High dislocation density structures and hardening produced by high fluency pulsed-ion-beam implantation

Abstract The paper presents a review of experimental data on the “long-range effect” (a change in dislocation structure and in physicomechanical properties at distances considerably greater than the ion range value in ion-implanted metallic materials and semiconductors). Our results of electron microscopy studies of high density dislocation structure in ion-implanted metallic materials with different initial states are given. It has been shown that the nature of the dislocation structure and its quantitative characteristics in the implanted metals and alloys depend on the target initial state, the ion type and energy and the retained dose. The data obtained by different workers are in good agreement both with our results and with each other as well as with the results of investigation of macroscopic characteristics (wear resistance and microhardness). It has been established that the “long-range effect” occurs in metallic materials with a low yield point or high plasticity level and with little dislocation density in their initial state prior to ion implantation.

Observation of deep dislocation structures and “long-range effect” in ion-implanted α-Fe☆

Abstract The results of experimental investigations of “long-range effect” by ion implantation into α-Fe are presented. C, Fe, W, Hf and Ar ions were implanted into α-Fe in continuous and pulse-periodic regimes. The ion energy varied in the range 40–150 keV and the irradiation dose varied in the range 1 × 10 15 -1 × 10 18 ions cm -2 . It has been established that dislocation structures are formed in the near-surface layer of pure metals by ion implantation. The thickness of the near-surface layers with the dislocation structure induced by ion implantation is in the range 20–100 μm. Stress measurements and calculations in the near-surface layers by ion implantation show that the stresses are considerably greater than the yield strength. The stresses result in the plastic deformation of the near-surface layers of the irradiated materials. The plastic deformation is the main reason for the dislocation structure development.

The mechanisms of the long-range effect in metals and alloys by ion implantation

Abstract The main features of the long-range effect in metals and alloys are studied by high-dose ion implantation. The results of a transmission electron microscopy study of the dislocation structures formed in copper by ion implantation are given as an illustration. It is shown that the long-range effect is determined by the microstructure of the initial state of the target and by the structural-phased state formed in the alloyed surface layer. A mathematical model of defect structure formation in the sublayer beneath the alloyed surface layer of the implanted target is proposed. The main principle of the model is that the dislocations under stresses in the alloyed layer are ejected from it and then move by inertia until they are stopped; the dislocation path value in the sublayer exceeds the projected ion range. The model calculations correlate well with experimental results.

Defect structures in metals exposed to irradiation of different nature

Abstract The regularities of the defect structure formation in near-surface layers of metals and alloys under irradiation of different types are presented. Three types of irradiation were used to treat the targets: high-dose ion implantation (HDII), high-power ion beam (HPIB) and high-power pulsed microwave (HPPM). In the case of HDII the continuous and repetitively-pulsed regimes were used. Different ions (B, C, Ar, Fe, Ni, Hf, Cu, Mo, Pb, Zr, La, W, Dy) of 40–200 keV energy were implanted to the irradiation dose of 1 × 10 16 to 1 × 10 18 ion cm −2 in α-Fe, Cu and Mo metals and Ni 3 Fe, Cu-Co-Al and VT18U alloys. Two-component pulsed HPIB (50% C + 50% H) was used to treat α-Fe. The energy of ions was 300 and 400 keV, the ion current density was 60, 100 and 200 A cm −2 and the pulse duration was about 100ns. Cu, α-Fe, Ni and Mo metals were exposed to HPPM with wavelengths of 2.85 and 10.0 cm. The microwave power flux density was varied from 2 to 400 kW cm −2 , whereas the pulse duration was varied from 50 to 300 ns. The exposure to HDII, HPIB or HPPM irradiation leads to the generation of dislocations in the near-surface layer of metallic materials. The thickness of the near-surface layer with induced dislocation structure depends on the type of irradiation and is equal to several micrometres for HPPM, tens of micrometres for HDII and hundreds of micrometres for HPIB. The defect structures induced by irradiations mentioned above are similar to the defect structures formed in metals and alloys during plastic deformation at one-axis tension or compression. The main reason for defect structure formation in the metals exposed to irradiation is the high level of stresses originating in the target near-surface layer. The mechanisms of stress origination, the value and the nature of the stresses are determined by the type of irradiation.

Dislocation structures and strengthening of ion-implanted metals and alloys

This article surveys the empirical data on the “long-range effect” (changes in defect structure and physicomechanical properties at distances considerably exceeding the mean free path of ions) seen in the ion implantation of metallic materials and semiconductors. Results are presented from electron-microscope studies of dislocation structures formed in ion-implanted metallic materials which are initially in different states. It is shown that the character of the dislocation structure and its quantitative characteristics in ion-implanted metals and alloys depend on the initial state of the target, the species and energy of the ions, and the radiation dose. Data obtained on the change in microstructure with depth is combined with data from other authors and correlated with the results of a study of macroscopic characteristics (wear resistance, microhardness). It is established that the “long-range effect” is seen in metallic materials which, in addition to having a low yield point or a high degree of plastic strain, also have a low dislocation density prior to ion implantation. Mechanisms by which the defect structure might be modified by ion implantation are explored.

Microstructure of the near-surface layers of ion-implanted polycrystalline Cu

Abstract Investigation of the submicrostructure formed in the near surface layers of ion implanted polycrystalline Cu was carried out using transmission electron microscopy. Ni and Hf ions were implanted in the pulsed-periodical regime at an accelerating voltage of 40 kV. Irradiation doses were equal to 1 × 1017 ion cm-2 for Hf and 2.0 × 1017 and 4.6 × 1017 ion cm-2 for Ni. It has bees established that a developed dislocation submicrostructure was formed in Cu under ion implantation. The near-surface layers with the induced submicrostructure exceeded 100 μm. The dislocation density in the indicated layer increases approximately 15–40 times as compared with that in the initial state for recrystallization Cu and 20%–30% for work-hardened Cu. With increase in ion flux from 0.09 × 1014 to 0.35 × 1014 ion cm-2 s-1 the maximum dislocation density increases; further ion flux does not result in the dislocation density growth. The change in the temperature of irradiated Cu (343–523 K) does not result in the change of a dislocation structure character in the target near-surface layer.