Amorphous Ti–Cu–Ni–Al alloys prepared by mechanical alloying

Ti _x (CuNi)_90–x Al₁₀ (x = 50, 55, 60) amorphous powder alloys were synthesized by mechanical alloying technique. The evolution of amorphization during milling and subsequent heat treatment was investigated by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The fully amorphous powders were obtained in the Ti₅₀Cu₂₀Ni₂₀Al₁₀, Ti₅₅Cu_17.5Ni_17.5Al₁₀ and Ti₆₀Cu₁₅Ni₁₅Al₁₀ alloys after milling for 30, 20 and 15 h, respectively. Differential scanning calorimetry revealed that thermal stability increased with the increasing (CuNi) content: Ti₆₀Cu₁₅Ni₁₅Al₁₀, Ti₅₅Cu_17.5Ni_17.5Al₁₀ and Ti₅₀Cu₂₀Ni₂₀Al₁₀. Heating of the three amorphous alloys at 800 K for 10 min results in the formation of the NiTi, NiTi₂ and CuTi₂ intermetallic phases.     

Martensitic transformation behaviors of rapidly solidified Ti–Ni–Mo powders

For the fabrication of bulk near-net-shape shape memory alloys and porous metallic biomaterials, consolidation of Ti–Ni–Mo alloy powders is more useful than that of elemental powders of Ti, Ni and Mo. Ti₅₀Ni_49.9Mo_0.1 shape memory alloy powders were prepared by gas atomization, and transformation temperatures and microstructures of those powders were investigated as a function of powder size. XRD analysis showed that the B2–R–B19 martensitic transformation occurred in powders smaller than 150 μm. According to DSC analysis of the as-atomized powders, the B2–R transformation temperature (T_R) of the 25–50 μm powders was 18.4 °C. The T_R decreased with increasing powder size, however, the difference in T_R between 25–50 μm powders and 100–150 μm powders is only 1 °C. Evaluation of powder microstructures was based on SEM examination of the surface and the polished and etched powder cross sections and the typical images of the rapidly solidified powders showed cellular morphology. Porous cylindrical foams of 10 mm diameter and 1.5 mm length were fabricated by spark plasma sintering (SPS) at 800 °C and 5 MPa. Finally these porous TiNi alloy samples are heat-treated for 1 h at 850 °C, and then quenched in ice water. The bulk samples have 23% porosity and 4.6 g/cm³ density and their T_R is 17.8 °C.     

Reactive wetting of alumina by Ti-rich Ni–Ti–Zr alloys

Active brazing is a commonly used method for joining ceramic materials. In the present study, the wetting behavior of four Ti-rich ternary Ni–Ti–Zr alloys was investigated through sessile drop experiments on alumina disks of 96 and 99.9 % purity. The microstructure at the metal/alumina interface was analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Three of the analyzed alloys exhibited reactive wetting with final contact angles between 40° and 70°. The reaction phases at the metal/alumina interface had a thickness of about 1 µm and were of a similar composition for all alloys. Dilatometer measurements showed thermal expansion coefficients between 13.2 and 15.8 × 10^?6 °C^?1. The lowest wetting angle of 40° was achieved with the alloy 61Ti–20Zr–19Ni at temperatures above 980 °C.     

Impaired bacterial attachment to light activated Ni–Ti alloy

Ni–Ti alloy due to its unique mechanical properties, is used for many types of implants. Failure of these implants can be attributed to many different factors; however infections are a common problem. In this paper, the attachment of the bacteria, Staphylococcus aureus, to the Ni–Ti surface modified by a range of processes with and without of light activation (used to elicit antimicrobial properties of materials) was assessed and related to different surface characteristics. Before the light activation the number of bacterial colony forming units was the greatest for the samples thermally oxidised at 600 °C. This sample and the spark oxidised samples showed the highest photocatalytic activity but only the thermally oxidised samples at 600 °C showed a significant drop of S. aureus attachment. The findings in this study indicate that light activation and treating samples at 600 °C is a promising method for Ni–Ti implant applications with inherent antimicrobial properties. Light activation was shown to be an effective way to trigger photocatalytic reactions on samples covered with relatively thick titanium dioxide via accumulation of photons in the surface and a possible increase in defects which may result in free oxygen. Moreover, light activation caused an increase in the total surface energy.     

Microstructural characteristics of directionally solidified Ni–43Ti–7Al alloys

Abstract

Ni–43Ti–7Al (at-%) alloy was directionally solidified at different withdrawal rates (2, 20 and 100 μm s^?1) and a constant temperature of 1550°C by liquid metal cooling method. Results show that as the withdrawal rate decreases from 100 to 2 μm s^?1, the cellular arm spacing increases from 39·5 to 126 μm, the size of Ti₂Ni and the stability of the liquid/solid interface also increase, while the volume fraction of Ti₂Ni decreases from 3·1 to 0·9%. Moreover, microstructural analysis reveals that a NiTi+Ti₂Ni anomalous eutectic structure is formed in intercellular regions of directionally solidified samples withdrawn at 20 and 100 μm s^?1. However, in the sample withdrawn at 2 μm s^?1, Ti₂Ni phases represent strip and liquid droplet morphologies in the intercellular region. Finally, the possible explanation to the change of microstructure is discussed.     

Quaternary Ti–Zr–Be–Ni bulk metallic glasses with large glass-forming ability

The glass-forming ability (GFA) of Ti–Zr–Be ternary alloys is dramatically improved by partially replacing Be with Ni. Centimeter-scale fully amorphous samples can be obtained in a wide Ni content range of 4 at.%–12 at.%. In particular, some of the developed Ti–Zr–Be–Ni alloys exhibit a critical diameter up to 20 mm, which is larger than that of other quaternary Ti-based bulk metallic glasses (BMGs). Moreover, Ni addition also enhances the yield strength and compressive plastic strain of Ti–Zr–Be alloys obviously. Based on the experimental results, the effect of substituting elements addition on the glass-forming ability of Ti–Zr–Be alloys has been systematically investigated and an empirical composition design method for the development of novel Ti-based BMGs with large GFA has been proposed.     

Processing maps for Fe–24Ni–11Cr–3Ti–1Mo superalloy

Hot deformation characteristics of a Fe-base superalloy were studied at various temperatures from 1000–1200°C under strain rates from 0·001–1 s^− 1 using hot compression tests. Processing maps for hot working are developed on the basis of the variations of efficiency of power dissipation with temperature and strain rate and interpreted by a dynamic materials model. Hot deformation equation was given to characterize the dependence of peak stress on deformation temperature and strain rate. Hot deformation apparent activation energy of the Fe–24Ni–11Cr–1Mo–3Ti superalloy was determined to be about 499 kJ/mol. The processing maps obtained in a strain range of 0·1–0·7 were essentially similar, indicating that strain has no significant influence on it. The processing maps exhibited a clear domain with a maximum of about 40–48% at about 1150°C and 0·001 s^− 1.     

Microstructure and corrosion behavior of Ti nanoparticles reinforced Ni–Ti composite coatings by electrodeposition

A survey on electrochemical codeposition of Ti nanoparticles in Ni matrix coating is given. The influences of Ti nanoparticle loadings in electrolyte on the microstructure, microhardness and corrosion behavior of Ni–Ti coatings were investigated. The results showed that a pyramidal surface structure evolved into a spherical surface structure of the coatings with increasing Ti nanoparticle loading. The content of Ti in the Ni–Ti coatings first increased and reached the maximum value of 7.1 vol.% at the loading of 16 g/L, then decreased due to agglomeration of nanoparticles. The [2 0 0] preferred orientation gradually evolved to [1 1 1] orientation with increasing Ti nanoparticle loading. At Ti nanoparticle loading of 16 g/L, the minimum crystallite size (44 nm) and maximum microstrain (0.25%) were obtained. The microhardness of the Ni–Ti coatings was improved and obtained the maximum value at the loading of 16 g/L. The anti-corrosion behavior of the Ni–Ti coatings had increased trend with increasing Ti nanoparticle loading. The pitting corrosion and the selective dissolution of Ti nanoparticles happened in corrosion of Ni–Ti coating electrodeposited at the loading of 16 g/L in a 3.5 wt.% NaCl solution.     

Interface microstructure analysis of SiO2 glass ceramic and Ti–6Al–4V alloy joint brazed with Ti–Zr–Ni–Cu alloy

Abstract

In the present paper, SiO₂ glass ceramic was joined to Ti–6Al–4V alloy with 35Ti–35Zr–10Ni–15Cu (wt-%) filler foil. The whole brazing process was performed under vacuum circumstances at different temperatures (850–1000°C) for several holding times (1–30 min). According to results of scanning electron microscopy, energy dispersive spectrometry, electron probe X-ray microanalysis and X-ray diffraction analysis, the reaction products of the interface are Ti₂O, Zr₃Si₂, Ti₅Si₃, Ti based solid solution and Ti₂(Cu,Ni). There is residual TiZrNiCu braze alloy on the SiO₂ glass ceramic/Ti–6Al–4V alloy interface after brazing. Besides, the interface evolution model of the joint was described by four stages: diffusion and solution among atoms, formation of reaction products, precipitation and growth of reaction layers respectively.     

Fretting wear study of surface modified Ni–Ti shape memory alloy

A combination of shape memory characteristics, pseudoelasticity, and good damping properties make near-equiatomic nickel–titanium (Ni–Ti) alloy a desirable candidate material for certain biomedical device applications. The alloy has moderately good wear resistance, however, further improvements in this regard would be beneficial from the perspective of reducing wear debris generation, improving biocompatibility, and preventing failure during service. Fretting wear tests of Ni–Ti in both austenitic and martensitic microstructural conditions were performed with the goal of simulating wear which medical devices such as stents may experience during surgical implantation or service. The tests were performed using a stainless steel stylus counter-wearing surface under dry conditions and also with artificial plasma containing 80 g/L albumen protein as lubricant. Additionally, the research explores the feasibility of surface modification by sequential ion implantation with argon and oxygen to enhance the wear characteristics of the Ni–Ti alloy. Each of these implantations was performed to a dose of 3 × 10¹⁷ atom/cm² and an energy of 50 kV, using the plasma source ion implantation process. Improvements in wear resistance were observed for the austenitic samples implanted with argon and oxygen. Ion implantation with argon also reduced the surface Ni content with respect to Ti due to differential sputtering rates of the two elements, an effect that points toward improved biocompatibility.     

Structure,Composition, and Properties of Arc PVD Mo–Si–Al–Ti–Ni–N Coatings

Using an arc physical vapor deposition process, we have produced nanostructured Mo–Si–Al–Ti–Ni–N coatings with a multilayer architecture formed by Mo₂N, AlN–Si₃N₄, and TiN–Ni and a crystallite size on the order of 6–10 nm. We have studied the physicomechanical properties of the coatings and their functional characteristics: wear resistance, adhesion to their substrates, and heat resistance. According to high-temperature (550°C) wear testing and air oxidation (600°C) results, the coatings studied here are wearand heat-resistant under appropriate temperature conditions. Their properties are compared to those of Mo–Si–Al–N coatings.     

Laser cladding composite coatings by Ni–Cr–Ti–B4C with different process parameters

To investigate the effect of laser process parameters on microstructure and properties of composite coating, the composite coatings were manufactured by laser cladding Ni–Cr–Ti–B₄C mixed powder on Q235 mild steel with different process parameters. The coatings are bonded with the substrate by remarkable metallurgical binding without cracks and pores. The composite coatings are consisted of in situ synthesized solid solution Ni–Cr–Fe, intermetallic compound (IMC) Ni₃Ti, Cr₂Ti, and ceramic reinforcements TiB₂, TiC. Results of scanning electron microscopy (SEM) revealed that the ceramic reinforcements became coarser with higher specific energy (E_s). There were independent ceramics TiB₂, TiC, eutectic ceramic TiB₂–TiC in coatings, and eutectic alloy–ceramic was detected. Compared with the substrate, the microhardness of coatings was increased significantly, and the maximum microhardness of coatings was approximately five times as high as the substrate. The wear resistance of coatings was improved dramatically than the substrate. Compared to the coatings with lower E_s, higher E_s led to lower microhardness and worse wear resistance ascribing to more Fe diffused into the coating from the substrate.     

Phase transition and mechanical properties of constraint-aged Ni–Mn–Ga–Ti magnetic shape memory alloy

Ni–Mn–Ga Heusler-type ferromagnetic shape memory alloys are attractive materials for micro-actuator, but the relatively poor ductility and low strength of Ni–Mn–Ga alloys have triggered a great deal of interest. In this study, we attempt to introduce some ductile second phase in the alloy by partially substituting Ti for Ga and constraint aging treatment. The results show that the martensitic transformation temperature first decreases and then increases slightly with the increasing of constraint-aging temperature, which can be attributed to the decrease of Ni content in the matrix and strengthening effect of the second particles. It is found that the amount of the Ni-rich precipitates by constraint-aged samples is more and the size of the second phase particle is smaller than that of the free-aged samples. The compressive stress and ductility can be significantly improved by the constraint-aging treatment, and the maximum compressive stress for constraint-aging alloy is about 1400 MPa, which is the highest value up to date compared with the 400 MPa in solution-treated Ni–Mn–Ga–Ti alloy and about 900 MPa in Ni–Mn–Ga–Ti alloy free-aged at 1073 K for 3 h. Scanning electron microscopy observations of fracture surfaces confirm that the Ni-rich second phase play a key role in improving the compression stress and ductility of Ni–Mn–Ga–Ti alloy.     

Constitution of Ni3Al–Ni3Mo–Ni3W section of Ni–Al–Mo–W system

Abstract

The isothermal section of the Ni–Al–Mo–W system has been studied at 75 at.-%Ni at temperatures of 1523 and 1273 K. Constitutional data have been determined using electron probe microanalysis, X-ray diffraction, and microscopical examination. The alloys studied lay in the range 12·5–15 at.-%Al, 2·5–7·5 at.-%Mo, and 2·5–7·5 at.-% W. The phases present at 1523 K were γ, γ′, and α (based on the Mo–W continuous series of solid solutions); at 1273 K, NiMo(δ′) was also encountered. The γ/γ′ mismatch values lay in the range ?0·03 to ?0·75%. In the as-solidified state, the alloys consisted predominantly of γ-phase containing γ′-precipitates formed in the solid state.

MST/462     

Characterization of corrosion phenomena of Zr–Ti–Cu–Al–Ni metallic glass by SEM and TEM

Corrosion phenomena are investigated for a Zr₅₉Ti₃Cu₂₀Al₁₀Ni₈ metallic glass immersed in hydrofluoric acid (HF) in open-circuit conditions and by means of electron microscopies (SEM and TEM). Several morphologies develop on the corroded surface and especially large and deep pits. TEM study demonstrates that Cu-rich nanocrystals of 5–10 nm are formed inside the corrosion pits (on their walls) during the corrosion process. These nanocrystals are not only by-products of the corrosion process but they very likely play a role in the development of the corrosion pitting morphology. They could have a dual role: (i) protecting the capped areas against dissolution and (ii) speeding the dissolution of neighboring uncapped areas by the creation of local galvanic cells.     

Ni3AI–Ni3Cr–Ni3Ta section of Ni–Cr–AI– Ta system

Abstract

The constitution of the 75 at.%Ni section of the Ni–Cr–Al– Ta system has been determined at 1523 and 1273 K. Alloys annealed at these temperatures have been studied using electron probe microanalysis and X–ray diffraction, and their microstructures and associated hardness values have also been examined. The isothermal sections at 1523 and 1273 K contain the following phases: γ+γ′+Ni₃Ta, and Ni₆TaAI, with the following three–phase equilibria between them: γ+γ′+Ni₆TaAI and γ+Ni₃Ta+Ni₆TaAl. The γ′–phase contains up to ~9 at.–%Ta. Some observations on as–cast structures have also been made.

MST/208     

Microstructure evolution of directionally solidified Ni–43Ti–7Al alloy during heat treatment

The microstructure change of directionally solidified Ni–43Ti–7Al alloy after heat treatment has been investigated by transmission electron microscopy and back scattered electron imagings in this paper. After solution and aging treatment, the NiTi + Ti₂Ni anomalous eutectic structure nearly cannot be observed and Ti₂Ni phases become spheroidized. The β′-Ni₂TiAl precipitates are nearly spherical at the early stage of aging at 800 °C (0.1–1 h); however, they become aligned along 〈100〉 directions and change to cubic shape after aging for 20 h. In the course of further aging, the coarsened semi-coherent β′ precipitates occur preferentially in intercellular regions. Then the coarsened β′ precipitates begin to occur in intracellular regions with the increasing aging time and aging temperature. These β′ precipitates change the shape to sphere and plate, accompanied with loss of their coherency by introducing interface dislocations surrounding them. Finally, the formation mechanism of β′ precipitates are discussed compared to other studies in the Ni–Ti–Al system.     

Influence of ageing on wear resistance of an Fe–Mn–Si–Cr–Ni–Ti–C shape memory alloy

To further improve the wear resistance of Fe–Mn–Si–Cr–Ni based shape memory alloys, the effects of ageing at 1123 K with and without pre-deformation at room temperature on the precipitation of second-phase particles and their effects on wear resistance were investigated in an Fe–Mn–Si–Cr–Ni–Ti–C alloy. Results showed that the solution treated Fe–Mn–Si–Cr–Ni–Ti–C alloy exhibited much better wear resistance than the solution treated AISI 321 stainless steel; ageing with pre-deformation improved the wear resistance of Fe–Mn–Si–Cr–Ni–Ti–C alloy more effectively than ageing without pre-deformation, especially under the heavy load condition.