Letteratura scientifica selezionata sul tema "Polycrystalline Ni-Ti"

The polycrystalline ZrO2?3mol.%Y2O3 was brazed to Ti-6Al-4V using a Ti47Zr28Cu14Ni11 (at.%) amorphous ribbon at 1123 K in a high vacuum. The microstructure of the interface and evolution mechanism of the joint was investigated. The experimental result showed that the typical interfacial microstructures of the joints consisted of ZrO2/TiO+TiO2+Cu2Ti4O+Ni2Ti4O/?-Ti+(Ti,Zr)2(Cu,Ni) eutectic/(Ti,Zr)2(Cu,Ni)/acicular Widmanst?ten structure/Ti-6Al-4V alloy. The microstructure of the brazed joint was related to the solution and chemical reaction among atoms during brazing. According to the mechanical property tests the joint brazed at 1123 K for 30 min obtained the maximum shear strength 63 MPa. Both the white block intermetallic compound (Ti,Zr)2(Cu,Ni) and the coarse ?-Ti+(Ti,Zr)2(Cu,Ni) eutectic structure should be avoided forming in the brazed joint.

Biomimetic apatite deposition behaviors and mechanical performance for as-rolled and annealed Ni-Ti plates were investigated. Apatite nucleation and growth on Ni-Ti in SBF (simulated body fluid) was not appreciably influenced by heat treatment. But, the apatite deposition rate increased slightly by NaOH surface treatment. The nodular apatite on the deposited layer is favored on a macro-scale since the surface energy of polycrystalline apatite particles can be reduced by forming nodules. The weight gain after apatite deposition for Ni-Ti (0.004 g/cm2) after 10 days were found to be smaller that that of NaOH treated Ti-6Al-4V, but it was comparable to that of non- NaOH-treated Ti-6Al-4V (0.004 g/cm2). The stress-strain responses of annealed Ni-Ti displayed the pseudoelastic behavior associated with stress-induced martensite formation with the transition stress for the martensite formation equal to 320 MPa. On the other hand the cold worked Ni-Ti displayed no appreciable pseudoelastic region and the yield stress was ~500MPa. A good biomimetic apatite formation and excellent mechanical performance of Ni-Ti suggests that Ni-Ti can be an excellent candidate material for orthopedic implants.

The thin Ti layers were inserted in the interfaces of base Al/Ni multilayer foils to form the Al/Ti/Ni/Ti (ATNT) foils through magnetron deposition. Al and Ni were determined in the as-deposited foils, while the absence of Ti was due to the strongly textured polycrystalline structure. TEM analysis implied an asymmetric interface structure between the Ni/Ti/Al interfaces and Al/Ti/Ni interfaces. After annealing at 473 K and 573 K for 3 h, the phase composition was the same as the initial state, which changed to be Al3Ni2, Ni3(AlTi), Ni and a small amount of Al3Ti when the treating temperature reached 673 K. Further increasing the annealing temperature to 773 K and 873 K leads to the appearance of stable AlNi. The obtained results implied that the inserted Ti layers impeded atomic interdiffusion and the formation of Al3Ni at the early stage, but had less impact on the final products. This further indicated that adding the inserted transition layer provides a reference to balance the storage stability and reaction performance of Al/Ni foils with regard to the applications.

The radiotracer technique was used to measure the grain boundary diffusion of44Ti and63Ni in slightly Ni-rich polycrystalline NiTi compound in the temperature range of 673 - 923 K. The temperature dependence of the grain boundary triple productP(P=sδDgb,sis the segregation coefficient,δis the grain boundary width, andDgbis the grain boundary diffusion coefficient) for Ti and Ni was determined. The triple products of both Ti and Ni grain boundary diffusion in NiTi reveal a unique behavior with significant deviations from an Arrhenius-type dependence. Probable evolution of the grain boundary structure with temperature was used to interpret this phenomenon.

The features of electrochemical deposition of copper layer on titanium and tantalum flexible substrates, as well as modes of sequential electrochemical deposition of tin layer on Cu/Ti and Cu/Ta and nickel layer on Sn/Cu/Ti and Sn/Cu/Ta from corresponding electrolyte solutions were studied by cyclic voltammetry. Deposition potentials for each metal layer were determined taking into account the type of substrate, and a wide set of the Cu-Sn-Ni/Ti and Cu-Sn-Ni/Ta stable precursor films were synthesized. The stage of annealing in an active sulfur atmosphere (sulfurization) has been optimized in order to obtain the Cu2NiSnS4 stable compounds. Based on the obtained XRD and Raman spectroscopy data, it was found that annealing in active sulfur atmosphere at 550 °C for 60 minutes is necessary to synthesize the Cu2NiSnS4 stable single-phase compounds with polycrystalline structure on Ta and Ti substrates

In order to clarify the effect of strain rates on phase transformation behaviors of Ni-Ti alloy, a compressive test using a cylindrical specimen of polycrystalline Ni-Ti alloy of Ti-50.69 at% Ni was carried out at a high strain rate and a low strain rate. The transformation temperatures were determined by a differential scanning calorimeter (DSC) using a sample cut from a compressed specimen. The transformation temperatures of the specimens before deformation were Ms= 303 K, Mf = 287 K, As = 297 K and Af = 319 K, respectively. The compressive test was carried out using specimen heated from liquid nitrogen temperature to room temperature. A universal testing machine as a static test apparatus and a Split Hopkinson Bar apparatus for a dynamic test were used. The specimen had a reoriented martensite phase after deformation because the superelastic effect was not observed upon unloading. Two reverse transformations during heating and a forward transformation during cooling were observed by DSC measurement. The first reverse transformation corresponds to that of thermal-induced martensite by immersion in liquid nitrogen and the second reverse transformation corresponds to that of reoriented martensite with slips in a polycrystalline matrix introduced by plastic deformation. The reverse transformation of the martensite phase with a slip exhibited strong strain rate dependency. Plastic strains and strain rate had strong influence on the shape recovery. The interaction between the temperature elevation by a conversion of plastic work and slip generated by dynamic plastic deformation is a complicated problem.

The transformation behavior of shape memory alloys is simulated for complex loadings of stress, strain and temperature. Calculations are made by using the “Accommodation Model” which is a constitutive model for shape memory alloys considering the accommodation behavior of the transformation strain. Calculated results are presented for the transformation behavior in the axial and shear stress state. These results are compared with those obtained by the experiment where tube specimens of the Ti-Ni shape memory alloy are subjected to the axial and torsion loading. The proposed constitutive model can predict the transformation behavior including the plastic strain effect of polycrystalline Ti-Ni shape memory alloys under non-proportional multiaxial loading condition.

This study aims to explore the impact of e-beam irradiation on the mechanical and structural characteristics of four different polycrystalline metals (Ni, Cr, V, and Ti), in both bulk and thin film forms. Thin metal films are fabricated using magnetron sputtering. The primary goal is to identify suitable metal candidates for growing thin films, which could serve as exit windows for e-beam accelerators. This selection is based on their properties, power dissipation capabilities, and the effects of irradiation on mechanical attributes such as hardness, ductility, defect density, and strength. For the bulk polycrystalline metal samples, a series of nanoindentation tests has been conducted before and after e-beam irradiation to investigate changes in hardness and elastic modulus. Additionally, to compare performance with the bulk samples, thin metal films are subjected to the same procedure before and after irradiation, allowing for the evaluation of film hardness, moduli, and creep properties. Results indicate that irradiated bulk samples of Ni, Cr, and V become harder, whereas Ti experiences softening. There is no significant irradiation effect on modulus for all for polycrystalline metal samples. To understand the underlying reasons behind these effects, both the fabricated metal films and bulk metal samples undergo comprehensive characterization tests for their microstructural properties, elastic behavior, and chemical composition. This involves the utilization of SEM with EDS, FESEM and AFM to analyze microstructure and surface attributes of the films, followed by X-ray diffraction to gain insight into film morphology and lattice orientation.

Les dernières avancées réalisées dans le domaine de l’instrumentation canalaire ont permis de rendre le traitement endodontique plus rapide et plus efficace. L’amélioration des limes endodontiques au travers des géométries instrumentales, mouvement de travail ou propriétés mécaniques du matériau constitutif de l’instrument ont rendu le traitement plus sûr dans la préservation de l’organe dentaire et des tissus parodontaux environnants. Néanmoins, peu de recherches se sont portées sur l’utilisation d’Alliage à Mémoire de Forme (AMF) différents du Nickel-Titane (Ni-Ti). Ce travail se propose d’étudier une potentielle utilisation en endodontie d’un nouvel AMF doté de propriétés antimicrobiennes très prometteuses : le Cuivre-Aluminium-Béryllium (Cu-Al-Be) monocristallin. Cette étude se fait au travers d’une approche expérimentale, au moyen d’un dispositif d’essais innovant, capable d’appliquer des chargements combinés ou séparés de flexion et de torsion. Ces chargements sont les principales sollicitations appliquées aux limes endodontiques lors du traitement canalaire. Une approche numérique vient compléter les études expérimentales, avec un modèle éléments-finis représentatif des chargements appliqués par le dispositif d’essais. Un programme de génération de modèles géométriques de limes endodontiques est développé et permet de représenter les réponses obtenues expérimentalement à l’aide de deux lois de comportement thermomécaniques adaptées aux AMF polycristallins et monocristallins. Enfin, à l’aide de ces deux outils, un plan d’expérience capable de déterminer l’influence des paramètres géométriques d’une lime endodontique sur sa réponse mécanique est réalisé et apporte une aide précieuse à la décision pour le choix d’une géométrie et d’une utilisation adaptée pour ces limes endodontiques en Cu-Al-Be monocristallin
Recent enhancements in canal instrumentation area have significantly improved the endodontic treatment making it faster and more efficient. The improvement of endodontic file quality through the instrument geometry, operating motion, and material properties made the endodontic treatment safer and thereby preserving the tooth and the surrounding periodontal tissues. Nevertheless, few research works investigated the possibility of using an alternative shape memory alloy (SMA) to the Nickel-Titanium (NiTi). This PhD work focuses on investigating the possibility of use in endodontic of Cu-based SMA having promising antimicrobial properties I.e. the Copper-Aluminum-Beryllium (Cu-Al-Be) single crystal SMA. The present study is based on an experimental approach using an original testing device able to apply bending and torsion loading in separate or combined way. Such solicitations are mainly induced by the curvature of the dental canal while the mechanical preparation. A numerical approach completes this experimental part by considering a finite element model representative of the file geometry, the thermomechanical behavior of the Cu-based single crystal or NiTi polycrystal SMAs and the bending- torsion loading and boundary conditions. A developed numerical tool allowed to build a parametrized geometry of an endodontic file and mesh it with tetrahedral finite elements in order to numerically analyze its response under combined bending-torsion loading. Based on these two approaches, an experience plan was carried out in order to analyze the influence of geometrical parameters on the response of endodontic files made of Cu-based single crystal SMA. It could be a precious tool for decision aid in choosing endodontic file geometry and its adapted use for root canal preparation

Abstract This investigation deals with a study of the friction, wear and corrosion behavior of vacuum plasma sprayed quasicrystalline (QC) Ti41.5Zr41.5Ni17 coatings. During pin on disc experiments, a change in the mode of wear has been found to occur with corresponding changes in normal load and sliding velocity. The low thermal conductivity of quasicrystals and its brittleness play a vital role in determining the friction and wear behavior of such materials. When these coatings are subjected to rubbing for a longer period of time, wear occurs by subsurface crack propagation and subsequent delamination within the coated layer. By comparing the QC to its polycrystalline counterpart during potentiodynamic measurements according to ASTM G 31, higher currents were found over the whole range of potentials for QC when immersed in 1MHCl solution.

Abstract Modern polycrystalline Ni-base superalloys for advanced gas turbine engines have been a key component that has contributed to technological advances in propulsion and power generation. As advanced turbine engine designs are beginning to necessitate the use of materials with temperature and strength capabilities beyond those exhibited by existing materials, new alloying concepts are required to replace conventional Ni-base superalloys with conventional γ-γ’ microstructures. The phase stability of various high Nb content Ni-base superalloys exhibiting γ-γ’-δ -η microstructures have been the subject of a number of recent investigations due to their promising physical and mechanical properties at elevated temperatures. Although high overall alloying levels of Nb, Ta and Ti are desirable for promoting high temperature strength in γ-γ’ Ni-base superalloys, excessive levels of these elements induce the formation of δ and η phases. The morphology, formation, and composition of precipitate phases in a number of experimental alloys spanning a broad range of compositions were explored to devise compositional relationships that can be used to predict the microstructural phase stability and facilitate the design of Ni-base superalloys.