Radiation Hardening of Ni-Ti Alloy Under Implantation of Inert Gases Heavy Ions

The consistent patterns of changes in nano- and micro-hardness of Ni-Ti alloy with the shape memory effect after implantation of [40]Ar{8+} and [84]Kr{15+} ions depending on phase composition and implantation parameters have been experimentally studied. It has been shown that softening by 4 and 14% near the surface of the two-phase Ni-Ti alloy after implantation of [40]Ar{8+} and [84]Kr{15+} ions is connected with the differences in the nanostructure. Hardening of the near-surface layer of this alloy maximum by 118% at h=~3 pm and single-phase alloy in the entire region of the [40]Ar{8+} and [84]Kr{15+} ions range and in the out-range (h>R[p]) area have been detected. The role of the current intensity of the ions beam in the change of nanohardness for the two-phase Ni-Ti alloy has been established

Specific features of deformation of the nitinol alloy after electrolytic hydrogenation

Specific features of the effect of hydrogenation on the susceptibility of a Ni–Ti alloy with shape memory to deformation are determined with the use of metallographic, electrochemical, and mechanical studies. Three sections are detected in the tensile curves of the specimens of nickel–titanium alloy in the initial state. The first section is linear due to the elastic deformation of the alloy with initial austenitic struc-ture. The second section is nonlinear and associated with pseudoelastic structural transformations of the original austenitic structure into a martensitic structure. The third section is also linear and caused by the elastic deformation of martensite formed in the course of deformation of austenite. After hydro-genation of the Ni–Ti alloy, the pseudoelastic structural transformation starts at a somewhat lower level of stresses than without hydrogenation. In this case, the specimens are destroyed after the termination of this transformation for a much lower level of plasticity than in the nonhydrogenated alloy. It is assumed that the electrolytic hydrogenation of the alloy promotes the formation of a very brittle hydride phase on the surface of Ti-type inclusions revealed in the structure of alloy in the initial state. Its thickness is determined by the duration of the process of hydrogenation rather than by the current used for hydro-genation

Features of radiation damage of Ni-Ti alloy under exposure to heavy ions of gaseous elements

The consistent patterns of changes in structural and phase state, hardening and temperature ranges of martensitic transformations in Ni-Ti alloy with the shape memory effect after implantation of heavy ions 16O3+, 40Ar8+ and 84Kr15+ under comparable parameters have been experimentally studied. It is found that under the impact of 84Kr15+ ions, a two-layer surface structure with radiation-hardened second layer is formed, radiation-stimulated phase transformation B19'>B2 occurs in the near-surface layer and out-range area, and the martensitic transformation temperature increases toward higher values after implantation of 40Ar8+ and 84Kr15+ ions

Plasma oxidation of NiTi alloy for medical application

V diplomskem delu smo izvedli plazemsko oksidacijo Ni-Ti zlitine z namenom tvorbe zaščitne oksidne plasti TiO2 na Ni-Ti kovinski podlagi. S tem smo povečali korozijsko odpornost in biokompatibilnost zlitine, kar je zelo pomembno za uporabo žilnih opornic iz Ni-Ti zlitine v medicini. Plazemska obdelava vzorcev je potekala v vodikovi in kisikovi plazmi pri tlaku 30 Pa z različnimi časi obdelave od 5 do 20 s. Primerjalni vzorec je bila neobdelana Ni-Ti zlitina. Vzorce smo analizirali z metodami rentgenske fotoelektronske spektroskopije (XPS), masne spektrometrije sekundarnih ionov (ToF-SIMS) in vrstične elektronske mikroskopije (SEM), da bi ugotovili kemično sestavo površine in oksidnih plasti ter morfologijo in mikrostrukturo oksidnih plasti. Za določanje biološkega odziva smo opravili in vitro biološke teste s polno človeško krvjo, da bi ugotovili, ali se trombociti na površino vežejo in aktivirajo. Pokazali smo, da se s časom obdelave v plinski plazmi povečuje debelina oksidne plasti, ki je iz TiO2 in ne vsebuje niklja. Barva vzorcev po plazemski obdelavi je odvisna od debeline oksidne plasti. Dobljena zaščitna oksidna plast zmanjša adhezijo in aktivacijo trombocitov iz polne krvi na Ni-Ti zlitini.The main aim of the research off my thesis was to form a protective oxide layer TiO2 on the Ni-Ti metal surface by carrying out the plasma oxidation of the Ni-Ti alloy. With the plasma treatment the corrosion resistance and the biocompatibility of the Ni-Ti alloy were increased, which are very important properties for medical applications. The plasma treatment was performed at pressure of 30 Pa in hydrogen and oxygen plasma with a different treatment times ranging from 5 s to 20 s. The untreated sample of Ni-Ti alloy was taken for comparison. All samples were analyzed by the X-Ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Scanning Electron Microscopy (SEM) to determine the chemical composition of the surface and the oxide layers and the morphology and microstructure of the oxide layers. In order to asses biocompatibility of samples in vitro biological tests with a whole blood were performed. We have shown that TiO2 oxide rich layer is formed with plasma, which does not contain Ni. The thickness of the TiO2 oxide layer increases by plasma treatment time. Changes of the colour of samples reflect the change of the oxide layer thickness. It was shown that the protective oxide layer of TiO2 on Ni-Ti alloy reduces adhesion and activation of platlets from whole blood

Structural Evolution of Ni-Ti Alloy Wires Produced by Hot and Cold Rotary Forging

Ni-Ti shape memory alloys (SMA), have interesting functional properties such as shape memory effect and superelasticity that enable their use in different segments. These functional characteristics are obtained through the thermomechanical processing (hot and cold). The hot deformation may promote the intended metallurgical transformations and the microstructural changes are improved by final cold deformation. These processes influence the final mechanical properties of the materials and, by consequence, their applications. This work focused on a Ni-rich Ni-Ti alloy, which may be used in the orthodontic archwires since the alloys used for this purpose need to show superelastic characteristics at room and oral temperature. It is sought by the mechanical and thermal treatments that the material displays an austenite finish temperature below room temperature. In this work, the characteristics of the thermomechanical processing are studied using samples representative of the different processing steps. For each processing step, the effect of the process parameters on the phase transformation temperature, superelasticity and shape memory effects was assessed and correlated to its microstructure. The structural analysis of each sample was performed by different techniques, which allowed the identification of the thermomechanical processing evolution. It was noticed that the austenite finish temperature was close to room temperature for all the steps. For all the samples, an austenite matrix at room temperature was observed. Different heat treatments were applied to identify the most suitable changes to be proposed along the rotary forging steps. Thermomechanical treatments were performed to understand and verify the structural evolution (by X-ray diffraction, using synchrotron radiation) and the mechanical behavior during the hot and cold deformations. These treatments allowed us to observe and discuss restoration phenomena, such as dynamic recovery and recrystallization. In addition, orthodontic archwires were studied in a reverse engineering approach to identify their structural characteristics and the corresponding functional behavior. The characterization of commercial functionally graded NiTi orthodontic archwire was performed and the introduction of graded functionality in conventional archwires was analyzed. This study aimed to contribute to the development of processing strategies that will give rise to more consistently uniform characteristics of Ni-Ti shape memory alloys and a minimization of the failures occurring during processing

An in vitro comparison of cyclic fatigue resistance of ProTaper universal and GT series X files

Objective : The aim of this study was to compare the cyclic fatigue resistance of two nickel-titanium (NiTi) endodontic instruments from ProTaper and GT series X files. Study Design: Cyclic fatigue test was realized with instruments from ProTaper: F1 and F3 (Denstply Maillefer, Ballaigues, Switzerland) and GT-X: 20.06 and 30.08 (Dentsply Tulsa Dental, Tulsa, Oklahoma, United States of America). A total of 320 instruments were rotated in 4 curved artificial canals with different angles and radius of curvature. The time and cycles to failure were calculated. The data was compared using a Mann-Whitney, Kruskall-Wallis, and Kolmogorov-Smirnov tests, with a significance level of p<0.05. Results: GT-X files rotated for a significantly longer period of time before separation occurred, thus GT-X files where more resistant to the cyclic fatigue compared with ProTaper. Conclusion : GT-X files have a greater resistance to cyclic fatigue, this fact can be caused by the use of the Ni-Ti alloy "M-Wire"

Microstructure Evolution of a New Precipitation-Strengthened Fe–Al–Ni–Ti Alloy down to Atomic Scale

Ferritic materials consisting of a disordered matrix and a significant volume fraction of ordered intermetallic precipitates have recently gained attention due to their favorable properties regarding high-temperature applicability. Alloys strengthened by Heusler-type precipitates turned out to show promising properties at elevated temperatures, e.g., creep resistance. The present work aims at developing a fundamental understanding of the microstructure of an alloy with a nominal composition of 60Fe&ndash;20Al&ndash;10Ni&ndash;10Ti (in at. %). In order to determine the microstructural evolution, prevailing phases and corresponding phase transformation temperatures are investigated. Differential thermal analysis, high-temperature X-ray diffraction, and special heat treatments were performed. The final microstructures are characterized by means of scanning and transmission electron microscopy along with hardness measurements. Atom probe tomography conducted on alloys of selected heat-treated conditions allows for evaluating the chemical composition and spatial arrangement of the constituent phases. All investigated sample conditions showed microstructures consisting of two phases with crystal structures A2 and L21. The L21 precipitates grew within a continuous A2 matrix. Due to a rather small lattice mismatch, matrix&ndash;precipitate interfaces are either coherent or semicoherent depending on the cooling condition after heat treatment

Differential Scanning Calorimetry (DSC) Analyses Of Superelastic And Nonsuperelastic Nickel-Titanium Orthodontic Wires

The purpose of this study was to determine the transformation temperatures for the austenitic, martensitic, and rhombohedral (R) structure phases in representative as-received commercial nitinol (NiTi) orthodontic wire alloys, to reconcile discrepancies among recent publications. Specimens were examined by differential scanning calorimetry (DSC) over a temperature range from approximately −170° C to 100° C, with a scanning rate of 10° C per minute. Two different pathways, with the intermediate R structure either absent or present, were observed for the transformation from martensitic to austenitic NiTi, whereas the reverse transformation from austenitic to martensitic NiTi always included the R structure. The enthalpy (ΔH) for the transformation from martensite to austenite ranged from 0.3 to 35 calories per gram. The lowest ΔH value for the nonsuperelastic Nitinol wire is consistent with a largely work-hardened, stable, martensitic microstructure in this product. The DSC results indicate that the transformation processes are broadly similar in superelastic, body-temperature shape-memory, and nonsuperelastic NiTi wires. Differences in bending properties for the NiTi orthodontic wires at room temperature and 37° C are due to the relative proportions of the metallurgical phases in the microstructures

Development of a safe and quick method for removal of intermaxillary fixation with superelastic Ni-Ti wire

To improve emergency intermaxillary fixation release, a novel method of intermaxillary fixation, in which super-elastic nickel-titan (Ni-Ti) alloy wires were applied at 2 places (Method A) was developed. Method A was compared to the previous method (Method B : fixing the jaw at 3 places with stainless steel wires), in terms of the time required to remove the wires and the number of pieces of cut wire left in the oral cavity and pharynx. The average time for removing the wires was 14.5 ± 9.9 (mean ± SD) seconds for Method A, and 79.1 ± 53.1 seconds for Method B. The average time was significantly shorter in Method A than in Method B (p < 0.01). The number of pieces of cut wire left was zero with Method A. These findings suggest that the novel method (Method A) provides quick and safe wire removal and improves the safety and quality of dentistry in emergency cases