Properties Of NiTi Alloy Research Articles

Elastocaloric effect of NiTi shape memory alloys manufactured by laser powder bed fusion

To address the challenges posed by the complex processing of NiTi alloys, the additive manufacturing technology has been employed for the preparation of NiTi alloys samples. Up to now, there is limited research on the elastocaloric effects of NiTi alloys manufactured by LPBF. This study focused on the utilization of laser powder bed fusion (LPBF) to fabricate NiTi samples, with a particular emphasis on the influence of laser power, scanning speed and hatch spacing on the microstructure and properties of NiTi alloys. The results indicated that the process parameters affect the stress hysteresis of superelasticity by influencing the Ni content in the NiTi alloys. The higher Ni content, the lower the stress hysteresis. In addition, the critical stress for plastic deformation of the texture in the <001> direction in NiTi alloys is the smallest. When only the P was changed, the proportion of the texture in the <001> direction in the sample increased with the increase of P, the proportion of plastic deformation increased, and the degree of recovery also gradually decreased. Furthermore, at a specific temperature, 10 K higher than the end temperature of austenite transformation, each sample exhibited good superelasticity. In particular, the 1st cooling capacity of the sample with the best elastocaloric effect reached 11.0 K, which was superior to other results obtained by LPBF under similar compressive strain levels.

Determination of the Effect of TiN Coating on Self-Fitting Properties of Dental Implants Made of NiTi Alloy.

Design and material research continues to increase dental implants' success rates, which is a widely applied treatment type. The size and morphology of the implant-bone interface are essential for implant stability. Our study produced a dental implant with two artificial tooth roots from NiTi alloy to increase the implant-bone contact surface. The properties of NiTi alloy, such as transformation temperature and composition, were determined by material characterization tests. Using NiTi alloy's shape memory effect, these artificial roots at body temperature were programmed with appropriate heat treatments for the self-fitting feature. Dental-implant-like models are coated with TiN to prevent Ni ion release. The corrosion tests were performed in Ringer's solution to determine the effect of TiN coating on Ni ion release. The nickel ion emission values showed that the TiN coating inhibited the release. In addition, it was determined that the TiN coating increased the shape memory transformation time of the NiTi alloy. In in vitro tests of NiTi and TiN-coated NiTi implants, it was observed that they completed self-fitting by deforming the trabecular bone, but the placement in the cortical bone was not complete. During the use of a shape memory implant, it should complete its transformation without contacting the cortical bone and should not cause a stress concentration.

Effect of a constant laser energy density on the evolution of microstructure and mechanical properties of NiTi shape memory alloy fabricated by laser powder bed fusion

As the key parameter in the laser powder bed fusion (L-PBF), the laser energy density can directly determine the comprehensive quality of NiTi shape memory alloys (SMAs). However, the specific role of laser parameters under the energy density value is rarely discussed. In this work, the effect of specific laser power and scanning speed variation on the properties of NiTi alloy under the same energy density (62.5 J/mm3) was studied. Results show that the phase transformation temperatures decrease as the Ni content was increasing with the simultaneous increases in laser power and scanning speed. Under the influence of Ni content, the SMA samples with low phase transformation temperatures were fully austenite at room temperature. In the cyclic compression test at Af + 15 °C, the sample built under the lowest laser power and scanning speed showed the best superelasticity effect. Higher scanning speed resulted in a stronger <100>//BD texture, and the increase of laser power produced a deeper molten pool, which remelted the solidified part at the bottom and further enhanced the <100>//BD texture. The TEM characterization shows that more Ni4Ti3 precipitates with larger sizes are obtained in the sample with the lowest laser power and scanning speed. The finite element analysis shows the lowest peak temperature in the molten pool under the lowest laser power and scanning speed, which can promote the precipitation of Ni4Ti3 particles. The promoted formation of Ni4Ti3 precipitates enhanced the austenite stability and further enhanced the superelasticity of NiTi alloy fabricated at the lowest laser power. The present work shows that the specific laser parameter under the constant energy density value can further improve the comprehensive performance of L-PBF NiTi SMAs.

Setting the functional properties of TiNi alloys during ion-plasma coating deposition process

The aim of the present work is to study the influence of the technological parameters of the ion-plasma treatment (IPT) on the functional properties of a TiNi shape memory alloy and its biocompatibility. The object of the study was the Ti–50.8 at. % Ni alloy, widely applied in medical devices. IPT was carried out by vacuum-arc evaporation of a titanium cathode at different values of the bias potential (0, –100, and –500 V), followed by TiN deposition. The functional properties of the TiNi alloy after IPT were investigated using differential scanning calorimetry. The biocompatible properties were evaluated using atomic emission spectrometry to measure a nickel concentration after one year holding TiN-coated TiNi samples in the 0.9 % NaCl solution. It has been determined that by setting the temperature regime of heating of Ti–50.8 at. % Ni alloy samples due to the technological parameters of the IPT process, it is possible to change the interval of realization of thermoelastic martensitic transformations, and, consequently, the temperature response of devices made of this alloy, i. e. to set the necessary functional properties. The comparative analysis of the characteristic temperatures after heat and ion-plasma treatments allow us to conclude that the proposed method for calculation of the TiNi substrate temperature is correct at IPT. The calculated temperature of the TiNi samples was ~275 °C at the zero potential, which is sufficient to shift the characteristic temperatures of the alloy. The substrate temperature during deposition was ~400 °C at a – 100 V bias and above 600 °C at a – 500 V bias, respectively. The Ni concentration in the model solution did not exceed 0.14 mg/l after one year holding, which indicates the high biocompatibility of the TiN-coated TiNi samples.

A review on NiTi alloys for biomedical applications and their biocompatibility

As per the growing demand in commercial and biomedical industries, NiTi alloys secured a good position in the market. A brief explanation regarding the properties of Ni-Ti alloys and their applications has been discussed here. Ni-Ti is a smart material which can exhibit thermal induced shape memory effect at lower operational temperatures and how it is useful in the biomedical application is metioned with details. There are several biocompatibility tests needed for a bio-material to be selected as a final product in the biomedical industry. Some tests like haemocompatibility, lysis and thrombogenicity, cytotoxicity test-methyl thiazole tetrazolium (MTT) assay are the most important for the biomedical implants. All the detailed methods and procedures are explained and can help to get an idea about the selection of materials.

An updated review on TiNi alloy for biomedical applications

Abstract This manuscript has provided an overview of the development of TiNi alloys and their applications in biomedicine. The microstructures and properties of TiNi alloys are first introduced. The breakthroughs in the manufacturing and applications in biomedicine of TiNi alloys in recent years have been achieved by scientists and are presented in the present paper. It is well known that the properties of TiNi alloys are affected by the modification methods on the surface of bulk TiNi alloys. The main preparation technologies of TiNi alloy coatings are evaluated, with particular attention to several spray technologies. Then, the biocompatibility, strong anticorrosion and antiwear properties, and mechanism of TiNi alloys are also described in detail. Several advanced manufacturing processes of TiNi alloys are also briefly outlined such as selective laser melting and spark plasma sintering. The performance of TiNi alloy coatings prepared by thermal spraying techniques are fully qualified for medical applications. Thermal spraying techniques have great prospects in reducing the cost and improving the quality of TiNi alloy medical products.

Effect of biaxial cyclic severe deformation on structure and properties of Ti-Ni alloys

In this work, biaxial cyclic severe deformation of Ti-50.0 at.% Ni shape memory alloy was performed using MaxStrain module of Gleeble system at 250 °C with ultimately high accumulated true strain of e = 11. The martensitic transformations, structure and crystallographic texture features were studied using DSC, X-ray diffractometry, and TEM from three mutually perpendicular sides. The maximum completely recoverable strain was determined by a thermomechanical method, and the hardness was measured. A true nanocrystalline structure with grain/subgrain size of 50 nm has been formed in bulk Ti-Ni samples for the first time. The resulting structure is crystallographically isotropic and provides the completely recoverable strain of 9.6% that exceeds the best result attained for bulk equiatomic Ti-Ni alloys. The texture factor in a combination with the structure factor contribute to the completely recoverable strain only until accumulated strain reaches e = 9.5 at higher deformation temperatures.

A Modified Embedded Atom Method Potential for High Temperature and Solid-Liquid Interfacial Properties of Ti-Ni Alloys

A Modified Embedded Atom Method Potential for High Temperature and Solid-Liquid Interfacial Properties of Ti-Ni Alloys

Effect of Zirconium, Niobium and Chromium on Structure and Properties of Ni-Ti Alloy

This work deals with the possibility of modification of the phase composition and improvement of the properties of the NiTi alloy by alloying with other elements. After the production by conventional melting metallurgy as well as powder metallurgy, the Ni-Ti alloys contain in addition to the NiTi shape memory phase a lot of other phases, for example Ti2Ni, Ni3Ti, Ni4Ti3. Some of these phases can have an undesirable effect on the properties of the Ni-Ti alloy. A possible solution is the addition of alloying elements to destabilize these phases. The aim of this work is to describe the effect of Zr, Nb and Cr as alloying elements in the amount of 1 and 3 wt. % on microstructure, phase composition, hardness and transformation behavior of the Ni-Ti alloy produced by powder metallurgy using reactive sintering. Alloying by chromium leads to increase of hardness and microhardness of the NiTi phase whereas the addition of the alloying elements niobium and zirconium increases the temperatures of phase transformations.

Properties of Ni-Ti-(Fe,Co,Al) Shape Memory Alloys Prepared by Self-Propagating High-Temperature Synthesis

Shape memory, superelasticity and pseudoplasticity are the exceptional properties of Ni-Ti alloys, which are listed among SMAs (Shape Memory Alloys). The carrier of these properties is the intermetallic NiTi phase. In addition to this phase, the Ti2Ni phase is always present, which is hard and brittle, and therefore it is undesirable in the Ni-Ti alloys. The aim of this work was to determine the influence of selected alloying elements (iron, cobalt and aluminium) in two different amounts (1 wt. % and 3 wt. %) on the microstructure, phase composition and amount of the Ti2Ni phase, hardness and transformation temperature of Ni-Ti-X alloy. The samples examined were prepared by self-propagating high-temperature synthesis at sintering temperature of 1100 °C. By altering the selected elements, the Ti2Ni phase was not reduced, on the contrary aluminium increased its amount. The Ni-Ti alloys alloyed with these three alloying elements proved to be harder. The phase transformations were observed only in the sample with 1 wt. % of aluminium at heating and cooling curves from differential scanning calorimetry.

Changes in Microstructure and Properties of Ni-Ti Alloy after Addition of Ternary Alloying Element

In this work, the influence of alloying element in equimolar Ni-Ti alloy was investigated. Selected alloying elements (cobalt, chromium, niobium) were added into Ni-Ti46 wt. % powder mixture. The samples were prepared by self-propagating high-temperature synthesis at temperature of 1100 °C with the use of high heating rate (300 °C/min). The changes in microstructure, phase composition, temperature of reaction between Ni-Ti-X powders, phase transformation temperatures and mechanical properties were studied.

Ni-Ti Alloys Produced by Powder Metallurgy

This paper deals with the influence of alloying elements on the properties of Ni-Ti alloys. The base alloy was the binary alloy Ni-Ti with 54 wt. % Ni and 46 wt. % Ti. Alloying elements (aluminium, iron and vanadium) in an amount of 5 wt. % were added to this alloy. All samples have been prepared by the method of powder metallurgy - reactive sintering at 1100 °C for 20 minutes. Microstructure, phase composition (especially amount of the Ti2Ni phase), process of sintering and the formation temperature of intermetallic phase NiTi, transformation temperatures and mechanical properties have been examined in these alloys. The corrosion characteristics were measured on the Ni-Ti and NiTiV5 alloys.

Processing and Superelasticity of Ni-Ti Shape Memory Alloys

In the paper is shown the study of super elasticity of Ni-Ti shape memory alloys from the point of view of stored energy, strain dependencies and martensitic transformations that influence superelasticity of Ni-Ti shape memory alloys [1]. We also present the influence of temperature and alloy composition on the properties of Ni-Ti alloys after plastic deformation and heat treating [2].

Features of Deformation Behavior, Structure and Properties of TiNi Alloys Processed by Severe Rolling with Pulse Current

The possibility of applying electropulse to increase the deformability, nanostructure formation and functional property enhancement of hard deformed TiNi-based alloys during severe plastic deformation is examined. It is shown that electroplastic rolling significantly increases total strain to failure. The formation of nanocrystalline structures by rolling with current depends on the strain degree and pulse current density, which are critical parameters of the new method. For the first time display of the electroplastic effect in coarse-grained and nanostructured TiNi alloys is investigated. It has been shown that the amplitude and direction of stress jumps on tensile stress-strain curves depends on grain size and pulse current regimes. An increase in the recovery strain and superelasticity of material processed by rolling with current is demonstrated.

Surface Properties of TiNi Alloy Treated by Micro-Arc Oxidation under Different Voltages

The effects of micro-arc oxidation (MAO) voltage (370V, 400V, 420V) on the surface morphology, adhesion of film/substrate, corrosion resistance and fretting friction and wear properties after micro-arc oxidation and heat-treatment for 48h of TiNi alloy were investigated. The results show that, as the voltage gradually increases: (1) micro-arc oxidation coatings form, when the voltage increase to 420V, the coating shows a significant micro-arc oxidized porous characteristics; (2) the Ca/P ratio in the coatings also increases, so the Ca/P ratio can be controlled by adjusting the voltage of micro-arc oxidation; (3) the corrosion resistance of MAO coatings can be significantly improved by increasing the output voltage, the corrosion rate and the corrosion potential of 420V are smaller two magnitude than 370V’s; (4) the coating of 420V shows lower friction coefficient with higher resistance, narrower wear scar width; (5) the MAO coatings have formed different types of hydroxyapatite crystals (HA) after immersed in high temperature and pressure reactor for 48h, and the phase composition of the coating are mainly apatite.

Effect of multiaxial deformation Max-strain on the structure and properties of Ti-Ni alloy

The severe plastic deformation (SPD) forming ultrafine-grained (nanocrystalline or nanosubgrained) structure is one of the most effective ways to improve the functional properties of Ti-Ni-based shape memory alloys [1, 2]. In the present work, the SPD of near-equiatomic Ti-Ni alloy was carried out using the multi-axial deformation module Max-strain, which is a part of the physical simulation system "Gleeble 3500". The deformation was performed at a constant temperature of 400°C with speed of 0.5 mm/s in six passes without interpass pauses. The accumulated true strain was about 3. As a result, a mixed ultrafine-grained/subgrained structure with grain/subgrain sizes from 50 to 300 nm and a high density of free dislocations formed. The resulting structure is close to a nanoscale region and provides a significant advantage in the basic functional property – completely recoverable strain – as compared with a conventional recrystallized structure: 7% versus 2%.

Mechanical Properties of Chemical Etched Biomedical NiTi Alloy Wires

Nickel-titanium alloy wires are widely applied in manufacturing biomedical devices; however, it is difficult to be micro-fabricated. Chemical etching process can successfully micro-fabricate the Ni-Ti alloy. The surface morphology, the etching products and the mechanical properties of the fine NiTi wires after the chemical etching process are investigated in the paper. After etching process, the characteristics of the wire surface are studied by Scanning Electron Microscopy (SEM). The X-Ray Diffraction (XRD) phase identification analysis is used to identify the etching products on the side surface of the etched wire. The Vickers Micro-hardness Test shows that the micro-hardness in peripheral surface is slightly higher than that in bulk. Mechanical properties of NiTi alloy fine wires after etching were studied by means of tensile tests.

Effects of equal channel angular extrusion and subsequent heat treatment on tribological properties of TiNi alloy

The friction and wear properties of TiNi alloy processed by equal channel angular extrusion (ECAE) and subsequent heat treatment processing under dry sliding condition were evaluated on a block on ring M-2000 tribometer. The effects of ECAE and heat treatment on the tribological properties of TiNi alloy were investigated. The worn surface morphologies of TiNi alloy were examined by scanning electron microscopy (SEM) and the wear mechanisms were discussed. The results showed that ECAE and heat treatment contributed to improve the friction and wear behaviours of TiNi alloy remarkably. The friction coefficient and wear loss of TiNi alloy decreased after ECAE and heat treatment. The maximum wear reduction was obtained when the heat treatment temperature after ECAE was 773 K. Adhesion wear and delamination were notable for the initial TiNi alloy. The material delamination was greatly abated when the heat treatment temperature of TiNi alloy processed by ECAE was 773 K.

Mechanical behavior of TiNi shape memory alloy under axial dynamic compression

Intermetallic compound TiNi alloys are known as shape memory alloys (SMAs) because of the thermoelastic martensitic transformation (MT) and reverse martensitic transformation. Apart from the shape memory effect (SME) [1], TiNi alloys also possess excellent pseudoelasticity (PE) [1], wear-resistance [2], corrosion-resistance [3], high damping capacity [4], good bio-compatibility [5] and outstanding mechanical properties [6]. Therefore, TiNi shape memory alloys have attracted considerable attention in recent years as functional materials in a variety of industrial and medical applications. They are called important smart materials due to their ability to perform both sensing and actuating functions [7]. A great number of investigations have been conducted on SME and PE associated with the thermoelastic martensitic transformation. Nevertheless, the transformation behavior and mechanical properties of TiNi alloys are susceptive to thermomechanical treatments such as cold working [8], thermal cycling [9], stress cycling [10], annealing temperature [11], aging of Ni-rich alloys [12] and addition of a third element [13]. Quite a few investigations on pseudoealsticity of TiNi alloys have been carried out by means of the tension test while the mechanical behavior under compression has not been studied. Since the materials are subjected to compression, impact as well as combinations of normal and tangent stresses in many engineering applications, it is needed to investigate, in a detailed way, the factors affecting properties of TiNi alloys under relevant conditions to extend their practical engineering applications. In this article, for the sake of simplicity, the Ni-rich Ti-50.9at% Ni alloy was selected for studying the influence of the strain rate on the mechanical behavior of TiNi alloys under axial dynamic compression and some significant results were obtained. The Ti-50.9at%Ni alloy was melted by the vacuum induction method in a graphite crucible with an argon atmosphere. The alloy ingot was homogenized at 1000 ◦C for 4 hr, then quenched in water. After removing the surface layer, the ingot was forged and rolled into bars of 6 mm in diameter. Before being cut into

Superelasticity in TiNi Alloys and Its Applications in Smart Systems

The superelasticity is one of the most important properties of TiNi alloy, which has been widely used in the smart systems of many fields, such as aerospace, aviation, biomedicine and energy etc. The current state of superelasticity of TiNi alloy has been reviewed with emphasis on the superelasticity, phase transformations, thermo-mechanical treatment and their relationship. The mechanisms of linear superelasticity and non-linear superelasticity have been revealed. Some successful applications based on the superelasticity of TiNi alloys in smart systems have been introduced.