Ni-free Alloys Research Articles

Effect of Ni addition on the microstructure, conductivities and mechanical properties of as-cast Al-Fe alloys

In this study, the microstructure, conductivity and mechanical properties of as-casted Al-1Fe-xNi (x= 0, 1, 4, 6 and 10, wt%) alloys were systematically investigated. The results exhibited the Al-1Fe-xNi alloys mainly consist of α-Al, Al3Fe, Al3Ni, and Al9FeNi phase. With the increase of Ni addition, the size of α-Al grain decreases and the dimension of Al9FeNi phase increased. The hardness of the as-cast alloys raises with increasing Ni content, whereas the elongation and electrical conductivity decreases and the ultimate tensile strength (UTS) first increases and then decreases dramatically. The Al-1Fe-6Ni alloy exhibited the highest Q-value, which was approximately 11.27% higher than that of the Ni-free alloys. This mechanism of mechanical properties change occurs mainly due to slightly Ni effectively refines the α-Al phase, and the excessive Ni content leads to formation of coarse needle-like or lath-like Al9FeNi phase. Additionally, the grain refinement and precipitation of the second phase upon Ni addition impede electron movement, leading to a decrease in the electrical conductivity of the alloy. The corresponding ductile fracture morphologies of Al-1Fe-xNi alloys are also analyzed. These high-strength Al-1Fe-xNi alloys could be helpful for developing novel Al-Fe alloys with a high strength and ductility.

Development of Ti-Mo-Fe alloys combining different plastic deformation mechanisms for improved strength-ductility trade-off and high work hardening rate

Titanium-based biomaterials are the gold standard for orthopedic implants; however, they are not generally suitable for the manufacture of intravascular stents. Their low strength-ductility trade-off and low work hardening rate are their main limitations. However, Ni-free alloys are desirable for such application in order to avoid allergic reactions caused by the high Ni-content materials currently applied. Therefore, in this study, three alloys of the Ti-Mo-Fe system (Ti-8Mo-2Fe, Ti-9Mo-1Fe and Ti-10.5Mo-1Fe) were designed to present high strength-ductility compromise and high work hardening rate. Their microstructures, mechanical properties and plastic deformation mechanism were investigated. Athermal ω precipitates were observed in the β matrix of all solution-treated alloys. In the solution-treated β matrix of the Ti-9Mo-1Fe alloy, additional nanometer-sized α" particles were detected by transmission electron microscopy (TEM). Although the combined TWIP/TRIP effects were expected by the design method on the Ti-8Mo-2Fe and Ti-9Mo-1Fe alloys, no TRIP effect was actually observed. In fact, stress-induced martensitic (SIM) transformation occurred mainly at the {332}<113> twins/matrix interfaces for all the strained microstructures and acted as a localized stress-relaxation mechanism, delaying the fracture. Based on the electron backscatter diffraction (EBSD) analyses, in the Ti-8Mo-2Fe and Ti-10.5Mo-1Fe alloys, the formation of a dense network of {332}<113> twins was responsible for their high and steady work hardening rates (1370 and 1120 MPa) and large uniform elongations (22% and 34%). The absence of SIM α" as the primary mechanism of plastic deformation and solid solution hardening of Fe resulted in their high strengths (yield strength of 772 and 523 MPa). In Ti-9Mo-1Fe, the formation of mechanical twinning was hindered, resulting in limited strain-hardening capability and low uniform elongation (6%). The nanometer-sized α" particles in its β matrix along with the athermal ω precipitates are thought to impair the mechanical twinning and the ductility of this alloy.

Microstructure and Superplastic Behavior of Ni-Modified Ti-Al-Mo-V Alloys

The paper studies the influence of 0.5–1.8 wt.% Ni alloying on the superplasticity, microstructural evolution, and dynamic grain growth effect in a temperature range of 625–775 °C and room temperature mechanical properties of two-phase Ti-Al-Mo-V alloys. Due to a decrease in β transus and an enhancement in the alloy diffusivity, an increase in Ni content significantly improved superplasticity. The Ni-modified alloys exhibited 1.5–3-fold lower flow stress, a 2.5–3-fold greater elongation to failure, and 1.4–1.7-fold higher strain rate sensitivity m coefficient compared to the Ni-free alloy. An intermetallic Ti2Ni compound precipitated in the 1.8 wt.% Ni-modified alloy during low-temperature deformation at 700 °C and decreased superplastic properties. The Ti-4Al-3Mo-1V-0.1B alloy with 0.9 wt.% Ni exhibited a good combination of the superplastic behavior and room-temperature mechanical properties: an elongation to failure of 500–900% at a low-temperature range of 625–775 °C and constant strain rate of 1 × 10−3 s−1 and a yield strength of 885 MPa and ultimate tensile strength of 1020 MPa after pre-straining for 100% in a superplastic regime and strengthening heat treatment.

Strengthening precipitates and mechanical performance of Al–Si–Cu–Mg cast alloys containing transition elements

This study investigated the active strengthening precipitates existing in the structure of 354-type Al–Si–Cu–Mg cast alloys following the addition of Zr as a primary alloying element in addition to Ni and Mn in different amounts and combinations. The investigation comprised three main parts: the first part simulated the formation and dissolution of strengthening precipitates and their precursors using differential scanning calorimetric (DSC) heating analysis of as-quenched samples, the second part presented transmission electron microscopy (TEM) observations of the fine precipitates existing in the structure of the alloys studied, and the third part examined the mechanical performance (tensile properties and hardness values) of the alloys studied. Interpretation of the DSC heating data in accordance to the available literature showed that the alloys are strengthened primarily by θ-Al2Cu and S–Al2CuMg precipitates and their precursors. Furthermore, some of the copper content was consumed in forming Al–Ni–Cu particles instead of the θ-Al2Cu strengthening phase and its precursors and hence the Ni-free alloys contain higher fractions of the θ-Al2Cu phase and its precursors than the Ni-containing alloys. TEM investigations confirmed the results obtained from the DSC heating analysis regarding the combined strengthening effect of θ-Al2Cu and S–Al2CuMg precipitates and their precursors as well as the fraction of θ-Al2Cu phase in Ni-free and Ni-containing alloys. TEM observations revealed, also, that the alloys studied have a secondary strengthening effect which is exerted by precipitates in the form of Alx (Zr,Ti)Si that formed following the addition of Zr. The Mechanical performance showed to be highly dependent on the chemical composition which controls alloys structure and response to the applied heat treatment and hence the formation of the fine precipitates which are mainly responsible to the strengthening effect.

A study on the role of Ni content on structure and properties of Fe–Ni–Si–B–P–Cu nanocrystalline alloys

Amorphous-forming ability (AFA) and thermal stability of melt-spun Fe85-xNixSi2B8P4Cu1 (x = 0–20) alloys and their crystallized structure, magnetic and mechanical properties have been investigated. The increase of Ni content from 0 to 20 at.% gradually improves the AFA with enlarging the critical thickness for amorphous formation from 14 to 38 μm. Adding 5 at.% Ni increases the number density (Nd) of nucleation sites by properly delaying the Cu atoms clustering process during annealing and refines the α-(Fe, Ni) grains, which leads to a magnetic softness improvement of the nanocrystalline alloys. The excessive Ni (≥10 at.%) decreases the Nd due to the overinhibition of the Cu clustering, resulting in the grains coarsening and magnetic softness deterioration. The Fe80Ni5Si2B8P4Cu1 nanocrystalline alloy possesses finer α-(Fe, Ni) grains with an average size of 22 nm, a lower coercivity of 14.3 A/m and saturation magnetic flux density of 1.77 T as compared with those of 40 nm, 105.3 A/m and 1.84 T, respectively, for the Fe85Si2B8P4Cu1 alloy. In addition, the nanocrystalline alloys with 2.5–10 at.% Ni show reduced brittleness compared with the Ni-free alloy owing to the grain refinement, and the alloys with 15–20 at.% Ni possess further decreased brittleness as a consequence of the reduced α-(Fe, Ni) phase volume fraction.

Evaluation of the Shape Memory Effect by Micro-Compression Testing of Single Crystalline Ti-27Nb Ni-Free Alloy.

In this work, micro-compression tests are performed at various temperatures with Ti-27Nb (at.%) single crystalline pillars to investigate anisotropic deformation behavior, including the shape memory effect. In non-tapered single-crystal pillars with loading directions parallel to [001], [011], and [111], transformation strain and stress show orientation dependence. [001]-oriented micropillars with aspect ratios of 2 and 1.5 demonstrate temperature-dependent transformation stress during micro-compression at various temperatures. Although more stress is required to induce martensite transformation in the pillar with the lower aspect ratio, the temperature dependence of ~1.8 MPa/K observed in both pillars is in good agreement with that of bulk Ti-27Nb.

A Comparison of the Compositional, Microstructural, and Mechanical Characteristics of Ni-Free and Conventional Stainless Steel Orthodontic Wires.

Ni-free orthodontic wires were introduced to mitigate concerns associated with the use of Ni-containing alloys in orthodontics. However, limited information is available on their properties and therefore, the aim of this study was to characterize the elemental composition, the microstructure, and the mechanical properties of Ni-free orthodontic wires and compare them with their stainless steel (SS) counterparts. Four Ni-free and four conventional SS wires were included in this study. All the wires were initially imaged with a Scanning Electron Microscopy (SEM) and their elemental compositions were determined by X-ray Energy Dispersive Spectroscopy (EDX). Then, their microstructure was assessed by X-ray Diffraction (XRD) and the indentation modulus, elastic index, Martens Hardness and Vickers Hardness by Instrumented Indentation Testing (IIT). All the wires demonstrated surface cracks and pores oriented parallel to their long axis. The elemental composition of Ni-free alloys showed an increased Mn and Cr content while both SS and Ni-free wires shared the same dominant austenite structure. In conclusion, despite the differences in elemental composition, Ni-free wires demonstrated a similar microstructure and comparable mechanical properties with their conventional SS counterparts and thus may be considered as a promising alternative for patients with Ni supersensitivity.

Effect of Ni addition on microstructure and mechanical properties of Al–Mg–Si–Cu–Zn alloys with a high Mg/Si ratio

The effect of adding 0.03wt% Ni on the microstructure and mechanical properties of Al-Mg-Si-Cu-Zn alloys was systematically studied. The results reveal that the number density of spherical Fe-rich phases within grains increases with the addition of Ni, accompanied by the formation of Q (Al3Mg9Si7Cu2) precipitates around the spherical Fe-rich phases. Additionally, Ni addition is beneficial to reducing the grain size in the as-cast state. During the homogenization process, Q phases could be completely dissolved and the grain size could remain basically unchanged. However, compared with the Ni-free alloy, the Fe-rich phase in the Ni-containing alloy is more likely to undergo the phase transformation and further form more spherical particles during homogenization treatment. After thermomechanical processing, the distribution of Fe-rich phases in the Ni-containing alloy was further greatly improved and directly resulted in a greater formability than that of the Ni-free alloy. Accordingly, a reasonable Ni addition positively affected the microstructure and formability of the alloys.

Magnetic Properties of the Fe63.5Ni10Cu1Nb3Si13.5B9 Alloy Nanocrystallized in the Presence of Tensile Stresses

The effect of 10 at % Ni, which was introduced into the classic Finemet Fe73.5Cu1Nb3Si13.5B9 at the expense of the Fe content, on the magnetic properties of the composition has been considered. The alloy was subjected to nanocrystallizing annealing in the presence of tensile stresses and in their absence. It is shown that, similarly to the Ni-free alloy, in the Fe63.5Ni10Cu1Nb3Si13.5B9 alloy subjected to thermomechanical treatment, the magnetic anisotropy with the easy magnetization direction across the ribbon axis (transverse induced magnetic anisotropy) is induced. It was found that the 10 at % Ni addition almost does not affect the value of magnetic anisotropy constant induced under thermomechanical treatment and decelerates the process of magnetic anisotropy inducing at σ ≤ 200 MPa. The Ni-containing alloy subjected to nanocrystallizing annealing (at 520°C) in the presence of tensile stresses and in their absence demonstrates the more than 200-fold increase in the coercive force as the annealing time increases from 1 to 4 h, whereas the coercive force of the Ni-free alloy is almost unchanged. This is likely to be related to the appearance of new structural components in the Ni-alloyed composition upon annealing.

Development and characterization of titanium-based bulk metallic glasses

The amorphous structure of bulk metallic glasses results in outstanding properties, which are able to outshine the properties of common metallic biomaterials. In particular, Ti-based bulk metallic glasses are interesting candidates for the use as biomaterial or as structural material in lightweight applications. However, the usage of known Ti-based bulk metallic glasses with casting thicknesses of several millimeters is strongly limited due to the large content of rare, expensive and harmful elements. In this work, we design Ni-free Ti-based bulk metallic glasses with a low Cu-content, being suitable for the application as biomaterial. On the basis of the binary Ti-Ni system, novel glass forming alloys are developed by the addition of sulfur. In order to increase the glass forming ability and to reduce the Ni-content, Ti was substituted with Zr and Ni with Cu. Finally, it is possible to produce synchrotron X-ray amorphous samples with a diameter of 3 mm for the Ni-free alloy Ti40Zr35Cu17S8. Furthermore, it is shown that industrial grade raw materials can be used for the synthesis of amorphous samples of this alloy without diminishing the glass forming ability or the mechanical properties. Characterization by mechanical and electrochemical tests proves the superiority of the novel alloys over commercial amorphous and crystalline alloys. All in all, a new class of Ni-free Ti-based bulk metallic glasses with unprecedented properties is developed, being highly attractive for a widespread use.

Influence of Ni substitution for B on crystallization behavior, microstructure and magnetic properties of FeBCu alloys

Abstract The crystallization, microstructure and magnetic properties of Fe83NixB16−xCu1 (x = 0, 1, 2, 4) alloys are investigated by Mossbauer spectroscopy, X-ray diffractometry and magnetometry. The substitution of Ni for B in the Fe83B16Cu1 alloy enriches Fe clusters in melt-spun ribbons and promotes the nucleation of α-Fe(Ni), which is beneficial to the formation of high volume fraction of nanocrystals after crystallization. Furthermore, the addition of 1–2 at.% Ni widens the annealing temperature range for the alloys with low HC. Excellent magnetic properties with high saturation magnetic flux density (BS) of 1.83 T and low coercivity (HC) of 9.2 A/m are obtained by annealing the Fe83Ni2B14Cu1 melt-spun ribbons. In addition, the nanocrystalline alloy with x = 2 possesses a lower saturation magnetostriction (19 ppm) than that of the Ni-free alloy (25 ppm).

Galvanic coupling and mechanical properties of low Ni orthodontic brackets with representative types of orthodontic wires

Abstract Aim To characterise the mechanical properties and galvanic coupling of Ni-free orthodontic brackets with stainless steel (SS) and Nickel-Titanium (NiTi) orthodontic wires. Methods Three Ni-free bracket types (Topic [TOP], Equilibrium [EQU] and Orthos [ORT] made of Ni-free alloys), one conventional (Mini 2000 [MIN]) made of SS alloy and an SS and a NiTi wire were examined in the present study. All brackets and wires were embedded in epoxy resin and, after metallographic grinding and polishing, the Martens hardness (HM), the indentation modulus (EIT), and the elastic index (ηIT) were recorded, employing Instrumented Indentation Testing (IIT) by monitoring force over indentation depth curves during a loading-unloading cycle. The galvanic coupling of all bracket-wire combinations was tested in 0.1M NaCl-0.1M lactic acid and 0.3% (wt.) NaF solutions by noting the potential differences over 48 hours. The mechanical properties were statistically analysed by one-way ANOVA and Tukey multiple comparison tests at alpha = 0.05. Results Significant differences were identified in the mechanical properties of the materials tested. The TOP (2372 ± 182 N/ mm2), ORT (wing) (2418 ± 164) and SS wire (2302 ± 85) showed significantly higher HM compared with all other materials tested. The MIN (base) (1115 ± 81) and ORT (base) (1237 ± 101) showed the lowest HM while MIN (wing) (1520 ± 138), EQU (1620 ± 139) and NiTi wire (1526 ± 42) demonstrated intermediate HM values. The ORT (wing) (101 ± 6 GPa) displayed the highest EIT while NiTi wire (24 ± 5) showed the lowest. The latter had the highest elastic index (59 ± 5%) with MIN (base)(15 ± 3) possessing the lowest. The potential difference for all bracket wire combinations was found below the threshold for the initiation of galvanic corrosion (200 mV) apart from MIN coupled with NiTi wire in the NaF solution. Conclusions The mechanical properties of Ni-free brackets are significantly different compared with the SS bracket assessed. Galvanic testing revealed that conventional and Ni-free brackets are compatible with both SS and NiTi wires in media containing chloride and fluoride ions.

Design of a Fatigue Resistant Ni-free PdTi-base SMA

Two main challenges in the design of reliable shape memory alloys for medical devices are improving fatigue life and addressing biocompatibility issues such as Ni hypersensitivity. This study presents the optimized design of a low-Ni (Pd,Ni)50(Ti,Al)50 alloy and the characterization of a peak-strengthened Ni-free (Pd,Fe)50(Ti,Al)50 superelastic alloy. Precipitate size, phase fraction, and phase composition are measured using Atom Probe Tomography (APT). From this data, thermodynamic and kinetic descriptions of the 2-phase field containing coherent L21 Heusler precipitates in a B2 matrix are developed. The optimum radius for precipitation strengthening in these systems is determined via experimentally calibrated strengthening models to be 2.3nm. Enhanced fatigue resistance of a peak-strengthened Ni-free alloy design is validated via thermal and mechanical cycling.

Influence of carbon addition on mechanical properties and microstructures of Ni-free Co–Cr–W alloys subjected to thermomechanical processing

We report the effects of carbon concentration on the microstructures and tensile deformation behaviors of thermomechanically processed Ni-free Co–29Cr–9W–1Si–C (mass%) alloys designed for use as disk materials in CAD/CAM dental technology. The alloy specimens, which contained carbon in different concentrations, were prepared by casting and subsequent hot rolling. Overall, the developed Ni-free alloys with added carbon showed an excellent combination of high strength and high ductility. The precipitates were identified in all of the alloy specimens. Intermetallic compounds, i.e., the Laves and σ phases, were formed in the low-carbon alloys, whereas the precipitates changed to M23C6 carbide when the carbon concentration exceeded 0.1mass%. Carbon concentrations less than 0.1mass% exhibited minimal contribution to strengthening, but the formation of the M23C6 carbide particles increased the alloy strength. On the other hand, elongation-to-failure increased with increasing carbon content when the carbon concentration is relatively low. However, the coarse M23C6 carbide particles formed by higher concentrations of carbon were detrimental to ductility. Thus, a maximum elongation-to-failure was obtained at carbon concentrations of around 0.1mass%. The results of the current study can aid in the design of biomedical Co–28Cr–9W−1Si-based alloys containing carbon.

Corrosion Behavior of Soldered and Laser-Welded Ni-Free Co-Cr Alloy Joints in Sodium Chloride Solution

This paper investigates the quality and corrosion property of Ni-free Co-Cr alloy joints soldered and laser welded using filler. The soldered and laser-welded test specimens were sectioned at the center and rejoined by either soldering or laser welding using appropriate fillers. The joint area was analyzed using microfocus X-ray and the percentage of porosity, as a measure of joint quality, was calculated. The corrosion behavior of soldered and laser-welded test specimens was evaluated using a potentiodynamic polarization technique in a 0.9 wt.% NaCl solution, pH 2.3, at 37°C. The results indicated that the amount of porosity and cracks in soldered joints were less than those of the laser-welded joints, leading to a lower corrosion rate.

Influence of Ni on the magnetocaloric effect in Nanoperm-type soft-magnetic amorphous alloys

We have studied the influence of Ni on the magnetocaloric effect (MCE) in Nanoperm-type amorphous materials by investigating a series of Fe84−xNixZr6B10 alloys with x=0, 2, 4 and 6. As expected, the Curie temperature increased with the amount of Ni from 427K for x=0 to 482K for x=6. The maximum magnetic entropy change (ΔSMpk) for an applied field of 1.4T also increased, reaching a value of 1.52J/Kkg for x=6, which is an increase of 25% compared to the Ni-free alloy. The refrigerant capacity first decreased for x=2 and then increased, reaching a maximum value of 93J/kg (ΔH=1.4T) for x=6. For a 5T field change, the value increased to 407J/kg, which is higher than the 355J/kg achieved with Gd5Ge1.9Si2Fe0.1. We confirmed the proposed “master curve” behavior for second-order magnetic transition (SOMT) alloys for the temperature dependence of ΔSM for different alloy compositions of the same series, which makes it easier and faster to find proper candidates for a magnetic refrigerator.

Selective dissolution sensitive to minor alloying in CuZr-based metallic glasses

The selective dissolution behaviour of CuZr-based metallic glasses can be strongly influenced by minor Ni additions. The surface corrosion layers of the Ni-free alloy are changed from a porous Cu-enriched film to a Zr-enriched covered passive film on the Ni-containing alloys, thus, resulting in the elevation of critical potentials. The results indicate that the preferential dissolution of Zr atoms is inhibited by minor Ni alloying, while Cu atoms dissolve. A local bonding controlled mechanism is proposed to understand the switchable behaviour of selective dissolution. It presents us with new insights into the intrinsic corrosion resistance of alloys.

On the transformation-induced work-hardening behavior of Zr47.5Co47.5Al5 ultrafine-grained alloy

The work-hardening behavior of Zr47.5Co47.5Al5 ultrafine-grained alloy, obtained by water-cooled copper mold casting, has been investigated. The Cu- and Ni-free alloy shows high compressive strength combined with large plasticity. The work-hardening behavior and the remarkable enhancement of the ductility and strength origin from the B2 to B33 deformation-induced martensitic transformation associated with the high strength ultra-fine grains. The fracture mode of the alloy is both intergranular and transgranular fracture. Our current finding may offer useful guidelines to design materials with improved strength and ductility as practical engineering and biomedical applications.

The effect of nickel and silicon addition on some oxidation properties of novel Co-based high temperature alloys

Isothermal oxidation was carried out on γ′-strengthened Co–Al–W–B–Ni and Co–Al–W–B–Si superalloys at 800, 900, and 1000°C. Ni-addition to Co–Al–W–B alloys leads to an absence of B within the inner oxide layer and at the grain boundaries, as indicated by ToF-SIMS. As a result, also inner Al2O3-formation is inhibited, which leads to inferior oxidation properties compared to Ni-free alloys. In contrast, Si-addition enhances formation of protective Al2O3 at 900 and 1000°C due to enhanced selective Al-oxidation. Si-containing phases at the oxide/alloy interface, at the grain boundaries, and within precipitates are of subordinate importance but may further improve oxidation resistance.

Corrosion Behavior of Zr-Based Bulk Metallic Glasses by Addition of Ni

Fully amorphous Zr48Cu43-xAl7Ag2Nix(x=0, 2, 4, 6, 8 at. %) alloy system synthesized by Cu mould casting method were utilized to study corrosion behavior due to the poor corrosion resistance of Zr-Cu-Al-Ag alloy system by addition of Ni. High temperature DSC revealed that the Zr-based alloy system still maintained good glass-forming ability and thermal stability with the addition of Ni element. The result obtained from both the immersion test and the potentiodynamic polarization test showed that the addition of Ni element significantly improved the corrosion resistance compared to the Ni-free Zr-based alloy system. SEM graph showed a phenomenon of corrosive pit where there existed corrosion deposits as well as cellular textures and microcracks. In summary, proper addition of Ni could modify the corrosion resistance of the Zr-based alloy system.