Institute of Fundamental Technological Research

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.

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.

Implantation, NiTi, Shape memory effect, Pseudoelastic, Properties

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

Implantation, Structure, Ti alloys, Composition, Hardness

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.

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

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

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+.

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