Staff

Abstract:
NiTi exhibits an excellent wear resistance, which can be further enhanced by ion implantation. However, there are some limitations to the implantation effects: only a thin layer of about 100 nm can be created. In this paper, the effect of nitrogen ion implantation on the NiTi wear response is investigated. The different loads and durations of tests are taken into account to show that the implanted layer has the most beneficial effect only in a certain range of contact pressure. It was found that the wear volume changes in a nonlinear manner with respect to the load and sliding length, for both non- and implanted samples. For the latter, two distinct stages can be distinguished in the wear process: an initial stage characterized by a low wear-rate and a low coefficient of friction, and a second stage in which the wear-rate drastically increases. The duration of the first stage is longer for lower loads. This specific behavior is explained by differences in the hardness distribution, energy dissipation due to the normal load, and differences in the microstructure of the wear tracks. Our results show that the lifetime of NiTi can be improved by ion implantation, thus boding well for applications in harsh environments.

Keywords:
ion implantation, NiTi shape memory alloy, sliding wear, pseudoelasticity, abrasion, dry friction, surface treatments

Abstract:
D6A and C75S spring steels were implanted by nitrogen ions at an energy of 65 keV and a fluence of 6 × 10^17 ions/cm2. The hardness and tribological properties of implanted samples were studied. In a reciprocating ball-on-plate wear test, a relatively low contact pressure was applied (9 mm diameter ball under load up to 0.5 N). In the implanted samples two stages of wear process can be distinguished. In the first stage a low friction coefficient and low wear rate are observed while in the second stage their values considerably increase. The duration of the first stage depends on the applied load (contact pressure). At low contact pressure, the wear life can be extended considerably, and at high contact pressure the first stage practically disappears and the effect of ion implantation is negligible. The evolution of wear process in the second stage is similar to that of non-implanted sample. Analysis of morphology and chemical composition of wear tracks with SEM reveals different mechanisms at different stages of wear in implanted samples wear. At the first stage, adhesive and abrasive wear predominate, while in the second stage, oxidative and fatigue mechanisms occur that are similar to those observed for a non-implanted material.

Keywords:
ion implantation, indentation, sliding wear, scanning profilometry, surface topography, electron microscopy

Abstract:
Harsh environments, such as nuclear power plants, require the development of materials with stable properties when exposed to radiation/bombardment conditions. In this work, a bulk high-entropy alloy (HEA) was implanted with nitrogen ions accelerated at 50 kV to induce and study crystal structural defects. X-ray powder diffraction (XRD) showed that the studies HEA consisted of two phases—σ and body-centered cubic (BCC)—and underwent the σ to BCC phase transformation due to ion bombardment. Unexpectedly, XRD peaks of implanted samples could not be assigned to any known simple nitride, a finding that suggests the creation of new high- or medium-entropy ceramics. Studies of the mechanical and tribological properties with the use of nanoindentation and scratch tests revealed a hardening of both phases of the implanted surface and higher wear resistance. There were also surprising increases in the hardness-to-Young’s modulus ratio and elastic recovery for both phases. The results are promising not only for the nuclear applications, but also for space applications, mechanical engineering, and tribology.

Keywords:
high-entropy alloys, high-entropy ceramics, ion implantation, irradiation, phase transformation

Abstract:
The inception of high-entropy alloy promises to push the boundaries for new alloy design with unprecedented properties. This work reports entropy stabilisation of an octonary refractory, HfMoNbTaTiVWZr, high-entropy thin film metallic glass, and derived nitride films. The thin film metallic glass exhibited exceptional ductility of ≈60% strain without fracture and compression strength of 3 GPa in micro-compression, due to the presence of high density and strength of bonds. The thin film metallic glass shows thermal stability up to 750 °C and resistance to Ar-ion irradiation. Nitriding during film deposition of HfMoNbTaTiVWZr thin film of strong nitride forming refractory elements results in deposition of nanocrystalline nitride films with compressive strength, hardness, and thermal stability of up to 10 GPa, 18.7 GPa, and 950 °C, respectively. The high amount of lattice distortion in the nitride films leads to its insulating behaviour with electrical conductivity as low as 200 S cm−1 in the as-deposited film. The design and exceptional properties of the thin film metallic glass and derived nitride films may open up new avenues of development of bulk metallic glasses and the application of refractory-based high entropy thin films in structural and functional applications.

Abstract:
The changes in the optical, structural, mechanical properties, and chemical composition of Y3Fe5O12/Gd3Ga5O12 (YIG/GGG) single crystal structures grown by liquid phase epitaxy, particularly at the interface between the film (Y3Fe5O12) and the substrate (Gd3Ga5O12), are studied. Different complementary techniques, including optical microscopy, local spectrophotometry, electron probe microanalysis, micro-Raman spectroscopy, and nanohardness analysis are used. The main finding of the study is an experimental approach, in which the probe of the measuring device (light beam, electron beam, nanoindenter) is directed to the surface of the studied sample in a direction perpendicular to the direction of structure growth, and the surface is scanned along this direction. It allows to obtain the profiles of changes in refractive properties, nanohardness, optical absorption, chemical composition, and intensity of phonon spectrum bands at the transition from the GGG to YIG. It is established that the lengths of the scanning intervals, at which the changes of various properties of a specimen occur, differ significantly. The obtained results are affected by the size of the probes and by the sensitivities of both the particular measuring method and the particular physical property of the material to changes in the chemical composition and crystalline structure of the sample.

Keywords:
electron probe microanalysis, gadolinium gallium garnet, interface, nanohardness, Raman scattering, spectrophotometry, yttrium iron garnet

Abstract:
Tungsten borides (WBx; x = 2.5 or 4.5) with an increasing substitution of tungsten by zirconium from 0 to 24 at.% were synthesized by spark plasma sintering (SPS) for the first time. The influence of the holding time (2.5–30 min) on the densification behavior, microstructure evolution and development of the properties of W–Zr–B compounds were studied. The samples were characterized using scanning electron microscopy (SEM) for microstructure analysis, X-ray diffraction (XRD) for phase identification, Vickers micro-indentation for microhardness measurements, tribological tests to determine the coefficient of friction and specific wear rate, as well as measurements of electrical conductivity. The XRD results confirm the presence of the WB4 phase in the microstructure, despite the high sintering temperature (1800 °C) and small overstoichiometric excess of boron (4.5) addition in the sintered samples. This is caused by the high heating rate (400 °C/min), short holding time (2.5 min) and addition of zirconium. The Vickers hardness (HV) values measured at 1 N are 24.8 ± 2.0 and 26.6 ± 1.8 GPa for 24 at.% zirconium in WB2.5 and for 0 at.% zirconium in WB4.5, respectively. In addition, the hardest sample (W0.76Zr0.24B2.5) showed electrical conductivity up to 3.961·10^6 S/m, which is similar to WC–Co cemented carbides. The friction and wear test results reveal the formation of a boron-based film which seems to play the role of a solid lubricant.

Abstract:
The difference in wear behaviour of superelastic NiTi and conventional Ti6Al4V alloys with similar elastic limits was investigated. Reciprocating dry-sliding wear tests were performed with a ball-on-plate tribometer machine at different normal loads and sliding times. Mechanical properties were also examined using different microindentation tests, and wear track morphologies and chemical compositions in the scar area were characterised by scanning electron microscopy and energy dispersive spectrometry. Superelasticity of the NiTi alloy was significantly beneficial to its tribological properties, and wear resistance of the NiTi alloy was up to forty times higher than that of the Ti6Al4V alloy. Such a significant difference cannot be attributed only to the relatively small difference in hardness (H) or H/E ratios (E - elastic modulus) of the materials but, rather, a difference in strain energy, which dissipates in the material and results from normal load of the sliding ball. To estimate this energy, spherical microindentation tests in wear scar were carried out. Understanding the difference between tribological behaviour of the NiTi shape memory alloy and the conventional Ti6Al4V material provides insight into wear progression, and an investigation of its mechanisms can effectively prevent the destruction of components, prolonging their safe service life.

Keywords:
wear mechanisms, unlubricated friction, non-ferrous alloys, titanium

Abstract:
In this work we apply N+ ion irradiation on vertically aligned carbon nanotube (VACNT) arrays in order to increase the number of connections and joints in the CNT network. The ions energy was 50 keV and fluence 5 × 10^17 ions cm^−2. The film was 160 μm thick. SEM images revealed the ion irradiation altered the carbon bonding and created a sponge-like, brittle structure at the surface of the film, with the ion irradiation damage region extending ~4 μm in depth. TEM images showed the brittle structure consists of amorphous carbon forming between nanotubes. The significant enhancement of mechanical properties of the irradiated sample studied by the cyclic nanoindentation with a flat punch indenter was observed. Irradiation on the VACNT film made the structure stiffer, resulted in a higher percentage recovery, and reduced the energy dissipation under compression. The results are encouraging for further studies which will lead to create a class of materials - ion-irradiated VACNT films - which after further research may find application in storage or harvesting energy at the micro/nanoscale.

Keywords:
vertically aligned carbon nanotubes, ion irradiation, nanoindentation

Abstract:
In this work, (W,Ti)B2 films with different stoichiometric ratio Ti/W deposited on silicon and 304 stainless steel by radio frequency magnetron sputtering are presented. The coatings were deposited from plasma spark sintered targets obtained from the mixture of pure boron, tungsten and titanium powders. It is shown that during plasma spark sintering process using overstoichiometric boron and a low content of titanium change the WB2 to WB4 phase with almost no secondary phases. Subsequently, the impact of titanium content on the films properties is investigated systematically, including the chemical and phase composition, crystalline structure, surface and cross-section morphology. Simultaneously, nano-indentation test and ball-on-disk tribometery are performed to analyse the hardness and tribological properties of the films. It is shown that deposited films with titanium content of 3.6 and 5.5 at.% are formed in the zone T of the Thornton's Structural Zone Model. In opposite to α-WB2 magnetron sputtered coatings they are more flexible and hard nanocomposite coatings. The results show that the addition of titanium is apparently changing the film structure from nanocrystalline columnar to amorphous, very dense and compact structure with the addition of TiB2 phase. That films are simultaneously hard (H > 37.5 GPa), have high hardness to effective Young's modulus ratio values (H/E* > 0.1) and elastic recovery (We > 60%) appropriate for tough and resistant to cracking materials. The presented (W,Ti)B2 films exhibit also tribological and corrosion properties better than unalloyed coatings.

Keywords:
superhard films, ternary tungsten borides, RF magnetron sputtering, wear resistance, corrosion

Abstract:
The manuscript presents experimental investigations of an unusual behaviour of shape memory alloys (NiTi) having different characteristic temperatures in wear test. The studies are focused on the different wear mechanism at varying loads and sliding times and include a description of the phenomena accompanying the wear process. The ball-on-plate reciprocating sliding wear tests were conducted on NiTi shape memory alloys against a sapphire ball. We show that the wear resistance of NiTi is affected by its specific stress-strain characteristic. The understanding of the tribological behaviour of NiTi, a knowledge of the course of wear and an examination of its mechanisms can enable an effective prevention of the destruction of devices components and prolong their safe working life.

Keywords:
wear behaviour of NiTi SMA, friction coefficient, superelasticity, shape memory effect

Abstract:
Spatial changes of optical and mechanical properties of doped lithium niobate (LN, LiNbO3) single crystals are investigated. The crystals are doped with copper ions by thermal diffusion at elevated temperatures. LiNbO3 crystal absorption spectra are recorded in a direction perpendicular to the direction of diffusion. The concentrations of copper ions are calculated using the Smakula–Dexter formula. To determine a relation between changes of optical and mechanical properties, the hardness profiles of the doped crystals are investigated by the nanoindentation technique. Young's modulus and hardness are specified in accordance with the Oliver–Pharr method.

Abstract:
The main goal of the proposed paper is to present the results of the nitrogen ion implantation effects on mechanical and corrosion properties of NiTi shape memory alloy. Local pseudoelasticity phenomena of NiTi were determined using the ultra-low load applied system. The load–penetration depth curves show that lower nitrogen fluence improves mechanical properties in the near surface layer but higher ion fluence leads to degradation of pseudoelasticity properties. Corrosion resistance of NiTi in the Ringer solution was evaluated by means of electrochemical methods. The results of potentiodynamic measurements in the anodic range for implanted NiTi indicate a decrease of passive current density range in comparison with non-treated NiTi, without any signs related to Ni release. The results of impedance measurements recorded at the corrosion potential show a capacitive behaviour for all samples without clear predominance of one of them. It can be explained by the fact that this result concerns the first stage of corrosion exposition. It is shown that nitrogen ion implantation leads to formation of modified surface of improved physicochemical properties

Abstract:
Reactive spark plasma sintering (SPS) of WB2/WB3 ceramics from elements is studied; the sintering pressure dependence of the ratio of WB3 to WB2 in samples produced by SPS is discussed. Regardless of the sintering pressure, the obtained samples are very hard ~20 GPa. WB3 superhard films prepared by pulsed laser deposition (PLD) from selected SPS targets are presented.

WB3 coatings were prepared on Si (100) substrates using a nanosecond, Nd:YAG laser operating at a 355 nm wavelength. The phase analysis, crystallography, and orientations have been studied using X-ray diffraction (XRD). A WB2 to WB3 phase transformation from 8.2% WB3 in a sintered target to 93.3% WB3 in a deposited film was observed. Additionally, the surface of a SPS sintered WBx target after the ablation process was examined. XRD studies show that already during the laser ablation there is a significant WB2 to WB3 phase transformation. Vickers hardness of sintered samples was measured in macro- and micro-scale, and PLD films in the nanoscale.

Keywords:
Films, Tungsten borides, SPS – sintering, Pulsed laser ablation/deposition

Abstract:
This work presents fabrication and characterization of Al–Al2O3 composite materials with a 5%, 10%, 15% and 20% volume fraction of reinforcing phase particles. The spark plasma sintering method was applied for the purpose of fabricating these materials. The obtained Al–Al2O3 composites were characterized with an porosity from 1.27% to 5.07%. It was proven that as the content of hard ceramic particles increases in the composite, its density, hardness, and compression as well as tensile strength increase. The conducted study showed that a composite with 20% alumina content is characterized by a larger hardness (1355 MPa) and compression strength (247 MPa).

Keywords:
Spark plasma sintering, Composite material, Aluminum, Alumina

Abstract:
A shape-memory alloy (SMA) is expected to be applied as intelligent or smart material since it shows the functional characteristics of the shape memory effect and superelasticity. Most SMA elements, with these characteristics, perform cyclic motions. In these cases, the fatigue property of SMA is one of the most important issues in view of evaluating functional characteristics of SMA elements. The fatigue properties are complex since they depend on stress, strain, temperature and their hysteresis. If an SMA is implanted with high-energy ions, the thermomechanical properties of the material may change, resulting in long fatigue life. In the present study, the nitrogen ion implantation was applied to modify the surface of a TiNi SMA tape and the influence of implantation treatment on the bending fatigue properties was investigated.

Keywords:
shape-memory alloy, titanium-nickel alloy, superelasticity, nitrogen ion implantation, fatigue, bending

Abstract:
In the paper a change of material (mechanical) parameters of NiTi shape memory alloy subjected to ion implantation treatment is investigated. The spherical indentation tests in micro- and nano-scale and tension test have been performed to study an evolution of local superelastic effect in different volumes of nonimplanted and nitrogen ion implanted NiTi alloy. The differential scanning calorimetry has been applied to measure the change of characteristic temperatures due to ion implantation treatment. The structure of implanted material has been investigated using electron microscopy technique. It has been found that the ion implantation process changes the properties not only in a thin surface layer but also in bulk material. In the layer the pseudoelastic effect is destroyed, and in the substrate is preserved, however its parameters are changed. The characteristic phase transformation temperatures in substrate are also modified.

Keywords:
Ion implantation, NiTi shape memory alloy, Micro- nano-indentation

Abstract:
The state of the art in ion implantation of superelastic NiTi shape memory alloys is analyzed. Various technological applications of the shape memory effect are outlined. The principles and techiques of ion implantation are described. Specific features of its application for modification of surface layers in surface engineering are considered. Key properties of shape memory alloys and problems in utilization of ion implantation to improve the surface properties of shape memory alloys, such as corrosion resistance, friction coefficient, wear resistance, etc. are discussed.

Abstract:
A shape memory alloy (SMA) is expected to be applied as intelligent material since it shows the unique characteristics of the shape memory effect and superelasticity. Most SMA elements, with these characteristics, perform cyclic motions. In these cases, fatigue of SMA is one of the important properties in view of evaluating functional characteristics. The fatigue properties are complex since they depend on stress, strain, temperature and time. If SMA is implanted by high energy ions, the thermomechanical properties may change, resulting in long fatigue life. In the present study, the nitrogen ion implantation was applied to modify TiNi SMA wire surface and the influence of implantation treatment on the tensile deformation and bending fatigue properties was investigated.

Keywords:
shape memory effect, titanium-nickel alloy, nitrogen ion implantation, superelasticity, fatigue

Abstract:
New investigation results of N +, Mo, W, N and Ni high dose ion implantation of 1018cm – 2 influence on alloys physical and mechanical properties are presented in this article. Increasing of alloys wear resistance by abrasion of the surface layer, increasing of nanohardness, corrosion resistance, and changes of surface NiTi morphology are obtained. The correlation between the change of the elemental composition (after implantation) and the increase in mechanical properties of the alloy is observed. In other words, a nanostructure of oxycarbides and oxynitrides is formed in the surface layer as a result of high-dose ion implantation, which improves wear resistance, corrosion resistance and nanohardness of material. At the same time, the bulk properties of NiTi after implantation (pseudoplasticity and shape memory effect) do not change, which makes ion implantation an effective tool for improvement materials properties.

Keywords:
Implantation, NiTi, Shape memory effect, Pseudoelastic, Properties

Abstract:
An attempt to evaluate mechanical properties changes (superelastic phenomena) in the shape memory NiTi alloy (austenitic form) due to ion implantation (N+, fluences of 1x10^17 and 4x10^18 cm-2 ) has been made. We applied the differential scanning calorimetry technique and spherical indentation (micro- and nanoindentation scale) test to study superelastic effect. The results of investigations of selected functional properties, i.e. characteristic temperatures, total and recovered penetration depth on the implanted and non-implanted NiTi samples are presented.

Keywords:
superelastic phenomena, shape memory alloy, nitinol, nitrogen ion implantation

Abstract:
The results of X-ray diffraction studies on structural changes in the near-surface layers in the NiTi alloy caused by nitrogen-ion implantation with the energy E = 50 keV and the fluence D = 1018cm°2 are presented. X-ray diffractometry, using the Philips diffractometer type X’Pert in the Bragg–Brentano geometry, was used to identify the phase composition of NiTi alloy. For layer by layer analysis of structural changes in the near-surface layers, the D8 Discover Bruker diffractometer with polycapilar beam optics was used. The ion-implanted NiTi alloy in the near-surface layer exhibits five phases: the dominating austenite phase, two martensitic phases and a small amount of the Ni4Ti3 and NTi phases. Along with the decreasing thickness of the near-surface layer investigated in material an increasing fraction of the Ni4Ti3 and NTi phases was observed. With the thickness of this layer about 340 nm, besides still existing the austenite, Ni4Ti3 and NTi phases, only one martensitic phase is present in the alloy. Further decrease of the thickness of the near-surface layer to about 170 nm leads to the increasing fraction of the Ni4Ti3 and NTi phases.

Keywords:
X-ray diffraction, ion implantation, shape memory alloy, nitinol, phase composition

Abstract:
W przedstawionej pracy zastosowano metodę implantacji jonowej (jako techniki konstytuowania warstw wierzchnich) do modyfikacji własności stopu z pamięcią kształtu (SMA-Shape Memory Alloy) NiTi (w postaci martenzytycznej). Przedmiotem badań było określenie zmian własności kompozytu „warstwa implantowana+rdzeń” (rys. 2) po implantacji azotem (1x1018j/cm2, 65keV) na stopie NiTi oraz określenie wpływu implantacji jonowej na własności lokalnego efektu pamięci kształtu (EPK). Przedstawiono badania wybranych charakterystyk funkcjonalnych: temperatur charakterystycznych implantowanego stopu NiTi, a także zmian trwałych odkształceń w zależności od temperatury. Wykorzystano test mikroindentacji i profilometrii skaningowej. Metodą transmisyjnej mikroskopii elektronowej (TEM) badano mikrostrukturę stopu NiTi, a pomiary RBS zastosowano do oszacowania profili rozkładów pierwiastków po implantacji jonowej. W pracy potwierdzono, że zachowanie materiału NiTi bardzo zależy od temperatury. Pokazano, również, że test wgniatania wgłębnika kulistego w powierzchnie może posłużyć do identyfikacji implantowanej warstwy.

Keywords:
implantacja jonowa, efekt pamięci kształtu, stopy z pamięcią kształtu, indentacja

Abstract:
In the present study we report the changes in the modified near-surface layer on NiTi shape memory alloy, caused by ion implantation as well as their influence on the structure and mechanical properties of this material. Experimental results of an inhomogeneous structure and tribological properties of implanted NiTi are discussed in this paper.

Keywords:
shape memory NiTi alloy, Ion implantation, DSC, X-ray diffractometry, TEM

Abstract:
The paper presents new results on investigation of structure and physical-mechanical properties of near surface layers of titanium alloys after (W+, Mo+) ion implantation and subsequent thermal annealing under 550 °C for 2 h. Using back scattering (RBS) of helium ions and protons, scanning electron microscopy (SEM) with microanalysis (EDS), (WDS), proton (ion) induced X-ray emission (PIXE), X-ray phase analysis (XRD) with a grazing incidence geometry (0.5° angle), measurements of nanohardness and elastic modulus, friction wear (cylinder-plate), measurements of corrosion resistance in a salt solution, we investigated the VT-6 samples, and determined their fatigue resistance under cyclic loads. Double increase of hardness, decrease of wear and increased fatigue resistance were found, which was related to the formation of small dispersion (nanodimension) nitride, carbonitride, and intermetalloid phases

Keywords:
Implantation, Structure, Ti alloys, Composition, Hardness

Abstract:
The aim of this study was investigation of changes in the modified near-surface layer on the NiTi shape memory alloy, caused by ion implantation as well as their influence on the mechanical and shape memory properties of this material. Surface of NiTi has been modified by nitrogen ion beam at several fluences 1 × 1017 cm−2, 1 × 1018 cm−2 and 2 × 1018 cm−2 at the energy 50 keV. The effect of implantation parameters on surface characteristics and wear properties was investigated using dry-sliding-wear test, depth sensing indentation test and scanning profilometry method. The experimental results have shown how the ion implantation treatment can change the original surface: reducing Ni content in the surface, increasing the surface hardness (furthermore, the hardness improvement extended to the regions much deeper than the implanted layer), and improving the sliding wear resistance. The experimental results of surface treatment conditions and mechanical properties of the modified NiTi alloys are compared, analyzed and discussed in this paper.

Keywords:
Shape memory NiTi alloy, Ion implantation, Wear, Surface characterization

Abstract:
This paper reports the application of nitrogen ion implantation for modification of a shape memory alloy. It is known that the problem of creating a protective surface coating for the shape memory alloy is the most acute for potential applications of this material. Thus, the problem of increasing surface protective properties and, at the same time, simultaneous preservation of functional properties of shape memory materials is a subject of research and development [Pelletier H, Muller D, Mille P, Grob J. Surf Coat Technol 2002;158:309.]. The surface characterization of nitrogen implanted (fluence 1018 cm−2 and energy 50 keV) equiatomic commercial NiTi alloy samples was performed with the assistance of high resolution transmission electron microscopy (HTEM) techniques and modifications of phase composition before and after irradiation are studied at room and martensitic transformation temperatures by X-ray diffraction methods. Differential scanning calorimetry (DSC, TA Instruments) was used to characterize the transformation sequence and transformation temperatures for the initial and surface-modified materials. Experimental results of an inhomogeneous structure of near-surface layers in the ion-implanted NiTi alloy are discussed in this paper

Keywords:
Shape memory NiTi alloy, Ion implantation, DSC, X-ray diffractometry, TEM

Abstract:
The surface layer of an equiatomic TiNi alloy, which exhibits the shape memory effect in the martensitic state, is modified with high-dose implantation of 65-keV N+ ions (the implantation dose is varied from 1017 to 1018 ions/cm2). TiNi samples are implanted by N+, Ni+-N+, and Mo+-W+ ions at a dose of 1017–1018 cm−2 and studied by Rutherford backscattering, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction (glancing geometry), and by measuring the nanohardness and the elastic modulus. A Ni+ concentration peak is detected between two maxima in the depth profile of the N+ ion concentration. X-ray diffraction (glancing geometry) of TiNi samples implanted by Ni+ and N+ ions shows the formation of the TiNi (B2), TiN, and Ni3N phases. In the initial state, the elastic modulus of the samples is E = 56 GPa at a hardness of H = 2.13 ± 0.30 GPa (at a depth of 150 nm). After double implantation by Ni+-N+ and W+-Mo+ ions, the hardness of the TiNi samples is ∼2.78 ± 0.95 GPa at a depth of 150 nm and 4.95 ± 2.25 GPa at a depth of 50 nm; the elastic modulus is 59 GPa. Annealing of the samples at 550°C leads to an increase in the hardness to 4.44 ± 1.45 GPa and a sharp increase in the elastic modulus to 236 ± 39 GPa. A correlation between the elemental composition, microstructure, shape memory effect, and mechanical properties of the near-surface layer in TiNi is found.

Keywords:
double ion implantation, nitinol, shape mempry effect, nanohardness, elastic modulus

Abstract:
Stopy z osnową NiTi należą do grupy najlepszych materiałów z pamięcią kształtu [1]. Szeroki zakres zastosowań w medycynie i technice [2], [3], [4] powoduje zwiększenie roli stanu ich powierzchni. Zagadnienia modyfikacji powierzchni stopu NiTi w kontekście polepszenia jej charakterystyk – z jednej strony, i zachowania funkcjonalnych własności (efektu pamięci kształtu i pseudosprężystości) z drugiej strony, - stawiane są coraz częściej [6], [7]. W przedstawianej pracy jest pokazana próba oceny zmian własności mechanicznych stopu NiTi implantowanego azotem (zakres dawek 1x1017–3x1018j/cm2). Wykorzystano test mikroindentacji. Przedstawiono badania wybranych charakterystyk funkcjonalnych, głównie zmian odkształceń odzyskiwanych i trwałych, a także temperatur charakterystycznych implantowanego topu NiTi w warunkach pokojowej i podwyższonej temperatury.

Keywords:
stopy z pamięcią kształtu, implantacja jonowa, pseudospręzystość

Abstract:
Поверхностный слой эквиатомного сплава TiNi, обладающего эффектом памяти формы в мартенситном состоянии, был модифицирован при помощи высокодозной имплантации ионов N+ с энергией 65keV (доза имплантации составила от 1017 до 1018 ion/cm2). С помощью методов резерфордовского обратного рассеяния ионов (RBS), растровой электронной микроскопии с микроанализом (SEM и EDS),метода XRD в скользящей геометрии, а также измерения нанотвердости и модуля упругости исследовались образцы TiNi после имплантации ионов N+,Ni+−N+,Mo+−W+ дозами от 1017 до ∼1018 cm−2. Между двумя максимумами концентрационного профиля ионов N+ обнаружен пик концентрацииионов Ni+. XRD-анализ в скользящей геометрии образцов TiNi после имплантации ионов Ni+ и N+ показал образование фаз TiNi(B2);TiN; Ni3N. Исследования механических характеристик образцов показали, что висходном состоянии модуль упругости образцов составлял E=56 GPa при твердости H=2.13±0.3 GPa (на глубине 150 nm). После двойной имплантации ионов Ni+−N+, W+−Mo+ твердость образцов TiNi на глубине 150 nm составляла∼2.78±0.95 GPa, а на глубине 50 nm ее значение возросло до 4.95±2.25 GPa при модуле упругости 59 GPa. Отжиг образцов при 550◦C привел к увеличению твердости до 4.44±1.45 GPa и резкому увеличению модуля упругости до значения 236±39 GPa. Обнаружена корреляция между элементным составом, микроструктурой, эффектом памяти формы и механическими свойствами приповерхностного слоя TiNi

Abstract:
Wykonano badania metoda RBS z zastosowaniem jonów N+ i Ne+ rozkładów pierwiastków w NiTi po dużych dawkach implantacji jonów N+(1018 cm-2) oraz podwójnej implantacji jonów N+ (1018 cm-2) i Ni+ (5x1017cm-2). Zaobserwowano obecność dwóch maksimów rozkładu atomów azotu, spowodowaną obecnością atomów Ni. Zjawisko to nie było zaobserwowane po implantacji samych jonów N+. Na skutek obecności atomów Ni powstają naprężenia ściskające, które powodują migrację jonów N poza obszar maksimum rozkładu jonów Ni. Na powierzchni implantowanych próbek NiTi powstają kratery o różnych wymiarach, spowodowane jej rozpylaniem podczas implantacji dużych dawek jonów N+ i Ni+.

Keywords:
RBS, tytan, jony N, jony Ni, implantacja jonowa

Abstract:
In present paper the aspects of complex nitriding of titanium alloys by two methods (thermodiffusion saturation and implantation with nitrogen) were examined. Before implantation both thin oxynitride and thick nitride layers have been formed on the Ti-6A1-4V alloy surface (Fig.l). It was shown that nitrogen implantation allows to modify the coatings. Qualitative and quantitative character of changes is determined by the structural and phase state of titanium surface layer achieved previously. It was investigated that nitrogen implantation improves the surface microhardness both nitride and oxynitride coatings (Fig. 5, 6). Our results reveal that the surface hardening without losses of its quality can be achieved by the implantation of nitrogen in oxynitride layer.

Keywords:
Ti6Al4V alloy, thermodiffusion saturation, ion implantation treatment

Abstract:
Experimental results of an accumulation and return strain behaviour of the modified surface of NiTi alloy, as well mechanical and shape memory behaviour, are shown in this paper.
Surface of equiatomic NiTi shape memory alloy (in martensitic form) has been modified by high dose ion implantation technique using nitrogen ion beam. The low-energy (65 keV) and following high doses have been used: 1x1017j/cm2, 5x1017j/cm2, 1x1018j/cm2. Correlation between subsurface layers elemental composition of NiTi alloy, microstructure and shape memory properties is shown.

Keywords:
ion implantation, Shape memory effect, Differential Scanning Calorimetry (DSC), NiTi alloy, indentation test

Abstract:
Due to superelasticity phenomena, shape memory effect and durability in many environments NiTi shape memory alloys (SMAs) are being intensively adapted for biomedical applications. However, high Ni concentration and its possible release from the surface create a problem of negative effects on biological environment. Therefore a number of surface treatments has been proposed to stabilize a surface passive layer and inhibit Ni dissolution. The main goal of the proposed article is to present results of the effect of nitrogen ion implantation on mechanical and corrosion properties of equiatomic commercial NiTi SMA. Mechanical properties (local superelasticity phenomena) of NiTi samples were determined using ultra-low load indentation system. The differential scanning calorimetry was applied to measure the change of characteristic temperatures due to ion implantation treatment. The load–penetration depth curves show that the lower of applied nitrogen doses improve mechanical properties in the near-surface layer of NiTi. Corrosion resistance of implanted samples carried out in Ringer solution was evaluated by means of electrochemical methods. The results of potentiodynamic measurements in anodic range of polarization curves for implanted samples indicated a decrease of current density in passive range in comparison with non-treated NiTi sample. Therefore an inhibition of Ni release from the alloy can be expected. The results of impedance measurements recorded at the corrosion potential show a capacitive behaviour for all samples without clear predominance of one of them. It can be explained by the fact that this result concerns the case of general corrosion in the beginning of exposition. Prolonged exposition gives rise to the occurrence of local corrosion. It is shown in this work that nitrogen ion implantation (fluences 1017- 1018 ion/cm2, energy 50 keV) leads to a creation of modified surface of improved physicochemical properties with unchanged shape memory effect.

Keywords:
shape memory alloy(SMA), nitinol, ion implantation, superelasticity, corrosion resistance

Abstract:
Inexpensive Tungsten Tetraboride super hard coatings prepared by pulsed laser deposition (PLD) method are investigated. WB4 coatings were prepared on Si (100), by PLD technique using nanosecond, Nd:YAG laser operating at 355 nm wavelenght. Additionally the surface of SPS sintered WBx target before and after ablation process was examined. Phase change of WB2 to WB4 at the surface of target is observed. The phase analysis, crystallography and orientations have been studied using X-ray diffractometry. The surface layer of target after ablation and deposited films are found to be mostly WB4 phase with hardness HV>28 GPa.

Keywords:
laser mikro/nano engineering, thin films, pulsed laser ablation/deposition, tungsten tetraboride WB4