E. V. Kozlov

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.

Dislocation structure in coarse-grained copper after ion implantation

Abstract We have investigated the dislocation structures formed in the near surface region of ion implanted coarse-grained copper (grain size 460 μm) using transmission electron microscopy. Ti and Zr ions were implanted into copper using a vacuum arc ion source. The ion energy was about 100 keV and the applied (incident) dose was 1 × 10 17 cm −2 . We find that Ti and Zr ion implantations produce a developed dislocation structure in the Cu subsurface layers. The dislocation structure changes form cell-net and cell dislocation structures at shallow depth to individual randomly distributed dislocations at greater depth. The maximum dislocation density in copper is 6.1 × 10 9 cm −2 for Ti and 11.4 × 10 9 cm −2 for Zr. The thickness of the modified copper layer with high dislocation density is up to 20 μm for Ti and 50 μm for Zr. Microhardness measurements vs. depth and dopant concentration profiles are presented. The long range effect is explained in terms of a model of static and dynamic mechanical stresses formed in the implanted surface layer.

Thermodynamics of substructure transformations under plastic deformation of metals and alloys

The paper is devoted to behavior of the energy stored in deformed metals and alloys. The study is based on the well-known theoretical approaches and on the electron microscopy data obtained by the authors during investigation of the deformed Cu-Al and Cu-Mn f.c.c. alloys. Influence of the solid solution hardening value on the mechanisms of dislocation substructure evolution was studied. The accumulated energy for the substructure being formed at plastic deformation was evaluated. Ways of improvement of such evaluations were considered.

Rare-earth metals (REMs) in nickel aluminide-based alloys: II. Effect of a REM on the phase composition of a multicomponent Ni3Al-based alloy

The hardening mechanisms are studied in the cast high-temperature next-generation materials that are based on the intermetallic compound Ni3Al and are low alloyed with refractory (W, Re, Mo, Cr) and reaction- and surface-active (REM, Ti, etc.) metals. The interaction of the main impurities (C, O, Si, S) with three characteristic representatives of the REM group (namely, Y, La, Ce), which can be used for alloying, is analyzed. The reported data on the behavior of some REMs in the alloys based on nickel monoaluminide NiAl are considered. The effect of the REMs on the phase compositions of real multicomponent semicommercial Ni3Al-based VKNA alloys produced by directional solidification is investigated, and the excess phases precipitating upon alloying are revealed. Alloying with refractory metals and REMs is shown to lead to the formation of nanophases that stabilize the dendritic or single-crystal structure of VKNA-type cast alloys and strengthen the interface boundaries in them.

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.

Action of test temperature on evolution of dislocation structure of nickel single crystals with the [001] compression axis

Types of dislocation substructures produced on straining nickel single crystals with the [001] compression axis are identified in the temperature range from 77 to 673 K. The change in the volume fractions of the substructural types is shown to be correlated with the deformation stages in the work-hardening curves in the strain temperature range studied. Qualitative and quantitative descriptions of the evolution of the dislocation substructures are given. Pathways by which a cellular substructure can be transformed into a microbanded or fragmented substructure and a plausible fragmentation mechanism for the microbanded substructure are discussed.

Instability of the crystal lattice of CuPd alloy

The results of structural investigations (x-ray structural analysis, small-angle scattering and electron microscopy) of the B2→Al deformation phase transition and the kinetics of the recovery processes of deformed CuPd alloy are presented. It is established that the phase transition occurs in regions of local plastic deformation and the B2→Al deformation transition helps to enrich these regions with palladium.

Evolution of the dislocation structure and the hardening mechanisms of multiple slip oriented Ni3Ge single crystals

We studied the evolution of the dislocation structure of Ni3Ge single crystals deformed by compression at room temperature. It is shown that the distribution of dislocations is spatially uniform in the studied alloy. The uniformity in the dislocation distribution is produced by relatively high amounts of the frictional stresses of the dislocations. On the basis of the obtained values of the dislocation structure parameters, the contributions of the various mechanisms in the dislocation drag are determined. It is shown that the resistance to deformation is determined primarily by overcoming reactive and unreactive “forest” dislocations, the total contribution of which is 0.9 of the applied stress.