Yu. P. Sharkeev

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.

The long-range effect in ion implanted metallic materials: dislocation structures, properties, stresses, mechanisms

Abstract The results of 15 years of systematic experimental and theoretical study are given and the basic concepts of the fundamental phenomena taking place during the interaction of accelerated ions with solid crystals—a long-range effect—are developed. The long-range effect consists of a change in defect structure and/or structural-phased state in the ion-affected zone of the ion-implanted target, which is located directly beyond the implanted zone where the accelerated ions are stopped. The thickness of the ion-affected zone with microstructure modified during ion implantation varies from several up to tens of micrometers and more. The basic features of defect structures formed in the ion-affected zone are adduced. The ion implantation is accompanied by the development of considerable mechanical stresses in the implanted zone, which appear to be static, and dynamic stresses. These stresses are sufficient for the initiation of mechanisms of accumulation of dislocations in the ion-affected zone of the target. The mechanisms of the long-range effect in ion-implanted metallic materials are analyzed.

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 Structure and Physical and Mechanical Properties of a Novel Biocomposite Material, Nanostructured Titanium–Calcium-Phosphate Coating

The paper presents the results of a complex study of the structure, phase composition and physical and mechanical properties of a new biocomposite material, bulk nanostructured titanium–calcium-phosphate coating, as well as its biological testing. The high-strength nanostructured titanium was obtained by multiple uniaxial pressing using an original press-mold within the temperature interval from 1023 to 623 K and the additional rolling deformation in combination with prior-recrystalline annealing. Such a treatment produces improvement in the mechanical properties of titanium up to the level of high-strength titanium alloys, for example, Ti-6Al-4V. It was found that the micro-arc technique of formation of calcium phosphate (Ca-P) coating in aqueous solutions of phosphoric acid, hydroxylapatite and calcium carbonate powders provides the generation of β-tricalcium phosphate that points to high biocompatibility. Adhesion strength of Ca-P coating to nanostructured titanium is no less than 25 MPa. Biological tests in vivo showed that the novel coating promotes implant integration into bone marrow cells and provides the growth of bone tissue on an implant surface. The novel calcium phosphate coating is highly biocompatible, nontoxic and can be used for osteosynthesis.

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.

Mechanism of improvement of TiN-coated tool life by nitrogen implantation

The life of TiN-coated tools can be improved by a post-coating ion implantation treatment, but the mechanism by which this occurs is still not clear. Nitrogen implantation of both physical-vapor-deposited TiN and CVD TiN leads to surface softening as the dose increases, which has been attributed to amorphization. In this study a combination of transmission electron microscopy and atomic force microscopy was used to characterize the microstructure of implanted TiN coatings on cemented carbide for comparison with mechanical property measurements (nanoindentation, residual stress, etc.), made on the same samples. Ion implantation leads to a slight reduction in the grain size of the TiN in the implanted zone, but there is no evidence for amorphization. Surface softening is observed for physical-vapor-deposited TiN, but this is probably due to a combination of changes in surface composition and the presence of a layer of bubbles generated by the very high implantation doses used.

Osteogenic potential of mesenchymal stem cells from bone marrow in situ: role of physicochemical properties of artificial surfaces.

Correlation analysis demonstrated the role of inorganic parameters of the surfaces of calcium phosphate materials in the regulation of osteogenic differentiation of mesenchymal precursors. The progenitor stromal cells were isolated from syngeneic bone marrow immobilized in vitro on calcium phosphate surfaces with different structure, phasic, and elemental composition. After 45 days of subcutaneous ectopic osteogenesis in BALB/c mice, the tissues grown on these matrixes were characterized histologically. It was found that adhesion of bone marrow cells is the initial stage determining their future proliferation (conduction) over the artificial surface and the area of formed tissue plate. The success of histogenesis depends on surface roughness. The optimal roughness class was 4–5 (Russian State Standards), which enables differentiation of progenitor stromal cells under the specific microenvironmental conditions into the connective and adipose tissue cells. Differentiation of the progenitor cells into the stromal cells producing the hemopoiesis-inducing microenvironment also takes place in the foci of active hemopoiesis. Induction of osteogenic potential of the stromal precursors (osteoinduction) is determined by the ratio between calcium and phosphate atoms in surface coatings. In our experimental system, osteogenic differentiation of stromal mechanocytes was blocked only at Ca/P<0.5.

Formation of intermetallic layers at high intensity ion implantation

The experimental results are presented on a study of intermetallic phase formation in the surface zone of metal target at high intensity ion implantation. High intensity ion implantation allow to obtain the surface-alloyed layers of a much greater thickness in comparison with ‘ordinary’ ion implantation. Pure polycrystalline nickel was chosen as the target. The nickel samples were irradiated with the aluminum ions using the vacuum-arc ion beam and plasma flow source ‘Raduga-5’. The RBS and TEM were used for the investigations presented. It was established that the fine dispersed intermetallic precipitates are formed in the surface alloyed nickel layer. The alloyed layer thickness is equal to 150 nm and more, while the ion projected range that is equal to 70 nm. Compositions of these intermetallic precipitates are close to Ni3Al and NiAl phases. The solid solution of aluminum in nickel is also formed. The depth dependence of the formation of intermetallic phases can be deduced from the Ni–Al phase diagram.

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.

Pilot in vitro study of the parameters of artificial niche for osteogenic differentiation of human stromal stem cell pool

The aim of this research is experimental investigation of the topography and evaluation of some parameters of artificial microterritories promoting osteogenic differentiation of stromal stem cells. A technique of short-term culturing of prenatal human lung stromal cells with fibroblastoid morphology on calcium phosphate substrates with known topography was used. Judging from secretory activity of the cell culture (osteocalcin, alkaline phosphatase), stromal stem cells directly interacting with calcium phosphate discs have advantage in manifestation of osteoblast-like functional activity in comparison with cells cultured on plastic. Rough surfaces of calcium phosphate discs stimulate the formation of spatial human fibroblastoid cell culture. The cells with positive reaction to acid phosphatase are located on spheroliths forming the relief of calcium phosphate coatings. The cells with positive reaction to alkaline phosphatase (marker of osteoblasts) populate hollows (niches) of the artifi cial surface. The niche for induction of osteogenic differentiation of human multipotent mesenchymal stem cells is apparently a structural and functional formation. It can be characterized by an index calculated as the ratio of the total area occupied by alkaline phosphatase-positive cells to the area of artifi cial surface occupied by one stained cell.