Atomistic modeling of ternary additions to NiTi and quaternary additions to Ni–Ti–Pd,Ni–Ti–Pt and Ni–Ti–Hf shape memory alloys

The behavior of ternary and quaternary additions to NiTi shape memory alloys is investigated using a quantum approximate method for the energetics. Ternary additions X to NiTi and quaternary additions to Ni–Ti–Pd, Ni–Ti–Pt, and Ni–Ti–Hf alloys, for X=Au, Pt, Ir, Os, Re, W, Ta,Ag, Pd, Rh, Ru, Tc, Mo, Nb, Zr, Zn, Cu, Co, Fe, Mn, V, Sc, Si, Al and Mg are considered. Bulk properties such as lattice parameter, energy of formation, and bulk modulus of the B2 alloys are studied for variations due to the presence of one or two simultaneous additives.     

High temperature strain glass in Ti–Au and Ti–Pt based shape memory alloys

Strain glass is a frozen short-range strain ordered state found in shape memory alloys recently, which exhibits novel properties around the ideal glass transition temperature T₀. However, the T₀ of current strain glass systems is still very low, limiting their potential applications and experimental studies. In this paper, we reported two new strain glass systems with relatively high T₀. In Ti₅₀Au_50-xCr_x alloys, the strain glass appears at x = 25, and exhibits a T₀ of 251 K, while in Ti₅₀Pt_50-yFey alloys, the strain glass takes place at y = 30, and shows a T₀ of 272 K. Both of them are comparable with the highest T₀ value reported so far. Moreover, the phase diagrams of main strain glass systems in Ti-based alloys were summarized. It is found that the influence of the martensitic transformation temperature of the host alloy on the T₀ of the strain glass is limited. This work may help to design new strain glass systems with higher T₀ above ambient temperature.     

Plastic deformation properties of Zr–Nb–Ti–Ta–Hf high-entropy alloys

We have investigated the plastic deformation properties of single-phase Zr–Nb–Ti–Ta–Hf high-entropy alloys from room temperature (RT) up to 300 °C. Uniaxial deformation tests at a constant strain rate of 10^?4?s^?1 were performed, including incremental tests such as stress relaxations, strain-rate changes, and temperature changes in order to determine the thermodynamic activation parameters of the deformation process. The microstructure of deformed samples was characterized by transmission electron microscopy. The strength of the investigated Zr–Nb–Ti–Ta–Hf phase is not as high as the values frequently reported for high-entropy alloys in other systems. At RT we measure a flow stress of about 850 °C. We find an activation enthalpy of about 1 eV and a stress dependent activation volume between 0.5 and 2 nm³. The measurement of the activation parameters at higher temperatures is affected by structural changes evolving in the material during plastic deformation.     

Influence of aluminum doping in Li–Co–Ti ferrite

The crystallographic and magnetic properties of low aluminum doped lithium cobalt titanium ferrites, Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄(0.0≤x≤0.5), in the scope of spinel structure and ferrimagnetic property were investigated. Ferrites were doped with aluminum in the range of 0.0–0.5 and were synthesized by using the conventional ceramic methods. Using X-ray diffraction and Mössbauer spectroscopy, we confirmed the formation of crystallized particles. All of the samples showed a single phase with a spinel structure, and the lattice parameters linearly decreased as the doped aluminum content was increased. The particle size of the samples also decreased as the doped aluminum content increased. Until x=0.4 in Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄, the Mössbauer spectra could be fitted with two Zeeman sextets, which is the typical spinel ferrite spectra of Fe³⁺ with A- and B-sites. However, for x=0.5, the Mössbauer spectrum could be fitted with two Zeeman sextets and one doublet. From the variation of the Mössbauer parameters and the absorption area ratio, the cation distributions were determined. The magnetic behavior of the samples showed that an increase in the aluminum contents led to a decrease in the saturation magnetization, whereas the coercivity decreased until x=0.4 and then increased. The minimum coercivity was 52.4 Oe at x=0.4 in Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄.     

Structural-colored silk based on Ti–Si bilayer

In this Letter, Ti–Si bilayer was deposited on white silk to achieve coloration of the silk. By controlling the thickness of the Ti layer and Si layer, the saturation and the hue of the color on the silk could be preciously modulated, respectively. The structural colors on the silk could cover the major colors in the International Commission on Illumination 1931 chromaticity diagram, and it exhibits good durability, which is demonstrated by rubbing and stretching treatments. The developed textile coloration method may provide an eco-friendly technology in the silk dyeing industry.     

Formation of Ti1–x Si x and Ti1–x Si x N films by magnetron co-sputtering

The paper reports on surface morphology, structure and microhardness of TiSi–N films formed by cosputtering from two target-facing unbalanced magnetrons, equipped with pure Ti and Si targets, on an unheated substrate rotating in front of both targets. The ratio Si/Ti in the TiSi–N film was achieved by modifying the magnitude of currents in the individual magnetrons and by the addition of nitrogen to the film. The rotation of the substrate has a strong effect on the film deposition rate and its morphology. The deposition rate is 3 times lower than that of the film deposited on a stationary substrate. The surface roughness of a polycrystalline Ti film deposited on the rotating substrate is considerably higher than that on a stationary substrate. On the contrary, the surface of an amorphous Si film is smooth and there is no difference between the roughness of Si films sputtered on stationary and on rotating substrates. The hardness of the film increases with increasing Si content and with the addition of nitrogen to the TiSi film. The Ti(26 at.%)Si(8.5 at.%)N(65 at.%)-film sputtered on an unheated rotating steel substrate, held at a floating potential, exhibited the best result with a hardness of 29 GPa.     

High-strength and ductile glassy-crystal Ni–Cu–Zr–Ti composite exhibiting stress-induced martensitic transformation

We present a Ni-based crystal-glassy composite material having superior strength paired with a considerable ductility of 15%. The formation of a metastable crystalline phase in a glassy matrix during solidification has been proven capable of promoting a strain-induced martensitic transformation leading to enhanced plasticity under compression at room temperature. Underlying mechanisms of plastic deformation are discussed in terms of the interplay between dislocation slip in the crystalline phase and shear deformation in the glassy matrix. We suppose that the strain-induced martensitic inclusions serve as strong barriers for shear band propagation, promoting shear band branching and multiple shear band formation, thus extending the ductility and preventing a premature brittle fracture. The acoustic emission technique has been employed to clarify the kinetics of transformation and stages of plastic deformation.     

Investigating Thin Ti–O–N Films Deposited via Reactive Magnetron Sputtering

Infrared spectroscopy and atomic emission analysis help establish the corrosion resistance of Ti?O–N films deposited on steel substrates via reactive magnetron sputtering, along with potential biological activity by detecting nitric oxide in model solutions after contact with Ti–O–N coatings. Differential thermal analysis and scanning electron microscopy allow the thermal stability of the films to be judged at temperatures of up to 1300°C.     

Microstructure investigations and magnetic after-effect in amorphous and nanocrystalline Fe–Zr–Ti–B–Cu alloy

The microstructure evolution and low field magnetic properties i.e. initial magnetic susceptibility, stabilization field and magnetic after-effect as disaccommodation of the amorphous and nanocrystalline Fe₈₀Zr₄Ti₃B₁₂Cu₁ alloy were investigated. The heat treatment of the as-quenched Fe₈₀Zr₄Ti₃B₁₂Cu₁ alloy at 773 K for 1 h leads to its nanocrystallization. It was stated that initial magnetic susceptibility increases and intensity of disaccommodation decreases with increasing of annealing temperature. The magnetic after-effect of the investigated nanocrystalline samples is connected with relaxation processes that occur in the amorphous matrix.     

Effect of Ti4+ substitution on the hyperfine properties of Li–Sb–Ti ferrites using Mössbauer spectroscopy

Mössbauer investigations were carried out at room temperature on the ferrite system Li_0.6?+?0.5tFe_2.3???1.5tTi_tSb_0.1O₄ (0.0 ≤ t ≤ 1.0 in steps of 0.2). The effect of Ti^4?+? concentration on the various hyperfine interactions like Isomer shift, quadrupole splitting and internal magnetic field have been studied. The spectra exhibited well-defined Zeeman sextets at low substitution level, corresponding to the A and B sites. The sample with t = 1.0 showed paramagnetic behaviour. The results obtained have been discussed.     

Magnetic properties of Fe–Ti–O composite films obtained via solid-phase synthesis

The results from investigating the magnetic and magneto-optical properties of Fe–Ti–O composite films with compositions above the percolation threshold, prepared via a solid-phase reaction with oxygen exchange in layered FeO/Ti structures, are presented. Features of the magneto-optical spectra of prepared films are compared to the spectra of continuous metal films.     

Strain behavior of the hydrogenated submicrocrystalline Ti–6Al–4V alloy

Comparative studies of the influence of 0.002–0.12 mass % hydrogenation on the structure and phase composition of the submicrocrystalline and coarse-grained Ti–6Al–4 V alloys are performed. The evolution of the strain processes in the hydrogenated alloy is studied for both alloys upon tension at a temperature of 293 K depending on the hydrogen content and alloy state. It is established that the presence of hydrogen in the nanostructured Ti–6Al–4 V alloy in the solid solution leads to a decrease of its yield stress and an increase of its tensile strength and total strain before failure. The possible reasons for the increased duration of the uniform strain stage and the effect of strain hardening of the alloy in the presence of hydrogen in the solid solution are discussed.     

Ultrasonic cavitation erosion of gas nitrided Ti–6Al–4V alloys

Ultrasonic cavitation erosion experiments were performed on Ti–6Al–4V alloys samples in annealed, nitrided and nitrided and subsequently heat treated state. The protective oxide layer formed as a result of annealing and heat treatment after nitriding is eliminated after less than 30 min cavitation time, while the nitride layer lasts up to 90 min cavitation time. Once the protective layer is removed, the cavitation process develops by grain boundary erosion, leading to the expulsion of grains from the surface. The gas nitrided Ti–6Al–4V alloy, forming a Ti_xN surface layer, proved to be a better solution to improve the cavitation erosion resistance, compared to the annealed and nitrided and heat treated state, respectively. The analysis of the mean depth of erosion rate at 165 min cavitation time showed an improvement of the cavitation erosion resistance of the nitrided samples of up to 77% higher compared to the one of the annealed samples.     

Thermal analysis of precipitation reactions in a Ti–25Nb–3Mo–3Zr–2Sn alloy

A study was undertaken on a Ti–25Nb–3Mo–3Zr–2Sn alloy using differential scanning calorimetry (DSC) in order to improve understanding of the precipitation reactions occurring during aging heat treatments. The investigation showed that isothermal ω phase can be formed in the cast and solution treated alloy at low aging temperatures. An exothermic peak in the temperature range of 300 to 400°C was detected for precipitation of the ω phase, with approximate activation energy of 176 kJ/mol. The ω phase begins to dissolve at temperatures around 400°C and precipitation of the α phase is favoured at higher temperatures between 400°C and 600°C. An exothermic peak with activation energy of 197 kJ/mol was measured for precipitation of the α phase. Deformation resulting in the formation of the stress induced α″ phase altered the DSC heating profile for the solution treated alloy. The exothermic peak associated with precipitation of the ω phase was not detected during heating of the deformed material and increased endothermic heating associated with recovery and recrystallisation was observed.     

Directional solidification of Ti–49 at.%Al alloy

Ti–49Al (at.%) alloy was directionally solidified in Bridgman-type directional solidification furnace. The specimens were directionally solidified under an argon atmosphere with the different growth rate (V=5–30 μm/s) at a constant temperature gradient (G=12.1 K/mm), and with the different temperature gradient (G=2.8–12.1 K/mm) at a constant growth rate (V=10 μm/s). The dendritic spacings (λ ₁) were measured from both transverse and longitudinal sections of the specimens. The dependence of λ ₁ on the growth rate (V) and temperature gradient (G) were determined by using linear regression analysis. According to the experimental results, the value of λ ₁ decreases with the increase of values of V and G. The experimental results were compared with the current theoretical and numerical models, and similar previous experimental results.     

Substrate-induced stress and transformation characteristics of a deposited Ti–Ni–Cu thin film

This article presents the investigation results on the transformation characteristics of a sputter-deposited Ti–Ni–Cu shape memory alloy thin film and its relation to the substrate-induced stress. Experimental results show that, with the substrate attachment, the transformation interval increases while the transformation hysteresis decreases in comparison with those of the same thin film in the free-standing condition. By assuming a stress distribution through the film thickness, a layer-by-layer transformation sequence in the substrate-attached film is proposed and the transformation interval and hysteresis are analysed. The analysis results show qualitative agreement with the experimental observations, suggesting that the approach taken is plausible. This approach may also be used to examine the transformation characteristics of other thin films having thermally induced phase transformations.