Nickel-free Alloys Research Articles

The influence of Ni on the contributions of the superplastic deformation mechanisms of the Al–Zn–Mg–Cr alloys

The Ni influence on the superplastic characteristics, the microstructure evolution and the contributions of the superplastic deformation mechanisms for Al-Zn-Mg-Cr-based alloys have been investigated. The alloys contained dispersoids enriched with Cr, Mg and a minor of Zn of a mean size of 140 nm and in addition the Al3Ni phase in the alloy with nickel. Al3Ni phase increased homogeneity and stablity grain structure during elevated annealing temperature and during superplastic deformation at 440°C. The mean grain size decreases from 7.7 to 7.3 µm before the onset of the deformation and from 10 to 8.6 µm after straining of 0.69. The dislocations aggregations near Al3Ni particles were revealed. The microstructure evolution was compared at the testing condition providing a similar value of the strain rate sensitivity coefficient m≈0.6. The grain boundary sliding contribution is twofold larger and the intragranular dislocation slip is three times smaller in the alloy with Al3Ni particles compared to nickel-free alloy. Al3Ni particles leads to more equiaxed finegrain structure and an increase elongation to failure.

Influence of fabrication methods on the microstructures and hardness of Ti-Ni, Ti-Nb and Ti-Ta for biomedical applications

Ti-based alloys namely, Ti-Ni, has been used as biomedical material due to its superior properties. However, it has been reported recently that nickel is toxic to the human body and thus alternative nickel-free alloys has been rigorously studied. The best candidate materials are Ti-Nb and Ti-Ta which are known to be biocompatible. These alloys maybe produced either via casting or through powder metallurgy route. Both production and fabrication methods produced dense and porous materials respectively which have different applications in biomedical field. This paper describes the influence of production and fabrication methods on the microstructures and hardness of nickel-free Ti-alloys, namely, Ti-Nb and Ti-Ta alloys with Ti-Ni as a reference alloy. The alloys were produced by three different methods: casting in vacuum induction furnace, compaction of powders followed by microwave sintering and compaction of powders followed by spark plasma sintering. The presence of porosity was analysed on the as cast and sintered samples by Archimedes drainage method while microstructures analysis was done using standard materials characterisation techniques such as optical and electron microscopy as well as X-ray diffractometry. Hardness test was also conducted by Vickers hardness test. It was found that the alloys with different production and fabrication methods give slight variation in the microstructures in terms of grain size and structures, porosity intensities and pore size. As-cast Ti alloys have the lowest amount of porosity and highest hardness values while Ti alloys fabricated by microwave sintering have the highest porosity content with lowest hardness values.

Nickel Free Alloy for Cardiovascular Stents Application Against Restenosis Associated with Nickel: A Review

The commercialized coronary stents are generally made of biomedical stainless steels (316L) and biomedical cobalt-based alloy (for example L605 alloy) due to their good combination of properties, especially their excellent mechanical properties. However, there are above 10% nickel content in these stents materials, which was known to trigger the inflammation and allergic responses around stents implant location, and contradiction associated with in-stent restenosis when the nickel ions began to release from stents for various corrosion. Consequently, the potential adverse effect of nickel ions release has prompted the development of many nickel free alloy stents materials. In this paper, the controversy of nickel and in-stent restenosis, and the development of nickel free alloy for cardiovascular stents application are reviewed. Nickel free cobalt alloy maybe a good choice for stent materials, but further research is needed. Many research results have proved the high nitrogen nickel-free stainless steel is a good potential stents material and suitable for clinical use, therefore the austenitic high nitrogen nickel-free stainless steels may offer an alternative to further improve the performance of the current coronary stents.

Magnetic properties and induced anisotropy of nanocrystalline Fe72.5–x Ni x Cu1.1Nb1.9Mo1.5Si14.3B8.7 alloys

The effects of the substitution of nickel for iron on the magnetic properties, uniaxial anisotropy induced by magnetic field, and crystallization process of the nanocrystalline Fe72.5–x Ni x Cu1.1Nb1.9Mo1.5Si14.3B8.7 FINEMET alloys modified with molybdenum have been studied. Nickel additions of up to 3 at % have been shown to increase the Curie temperature and magnetization of the alloy, whereas nickel additions of more than 6 at % lead to the decrease in these parameters as compared to those for the initial nickel-free alloy. Nickel additions of 6‒7 at % cause a linear increase in the induced uniaxial magnetic anisotropy constant. Nickel additions of more than 6 at % restrain the crystallization of the alloy and lead to substantial decrease in its magnetic hysteresis characteristics.

Processing map and hot deformation mechanism of novel nickel-free white copper alloy

Hot compression test of a novel nickel-free white alloy Cu–12Mn–15Zn–1.5Al–0.3Ti–0.14B–0.1Ce (mass fraction, %) was conducted on a Gleeble–1500 machine in the temperature range of 600–800 °C and the strain rate range of 0.01–10 s–1. The constitutive equation and hot processing map of the alloy were built up according to its hot deformation behavior and hot working characteristics. The deformation activation energy of the alloy is 203.005 kJ/mol. An instability region appears in the hot deformation temperature of 600–700 °C and the strain rate range of 0.32–10 s–1 when the true strain of the alloy is up to 0.7. Under the optimal hot deformation condition of 800 °C and 10 s–1 the prepared specimen has good surface quality and interior structure. The designed nickel-free alloy has very similar white chromaticity with the traditional white copper alloy (Cu–15Ni–24Zn–1.5Pb), and the color difference between them is less than 1.5, which can hardly be distinguished by human eyes.

Metallic ions released from stainless steel, nickel-free, and titanium orthodontic alloys: Toxicity and DNA damage

The aims of this study were to determine the amounts of metallic ions that stainless steel, nickel-free, and titanium alloys release to a culture medium, and to evaluate the cellular viability and DNA damage of cultivated human fibroblasts with those mediums. The metals were extracted from 10 samples (each consisting of 4 buccal tubes and 20 brackets) of the 3 orthodontic alloys that were submerged for 30 days in minimum essential medium. Next, the determination of metals was performed by using inductively coupled plasma mass spectrometry, cellular viability was assessed by using the tetrazolium reduction assay (MTT assay) (3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide), and DNA damage was determined with the Comet assay. The metals measured in all the samples were Ti(47), Cr(52), Mn(55), Co(59), Ni(60), Mo(92), Fe(56), Cu(63), Zn(66), As(75), Se(78), Cd(111), and Pb(208). The cellular viability of the cultured fibroblasts incubated for 7 days with minimum essential medium, with the stainless steel alloy submerged, was close to 0%. Moreover, high concentrations of titanium, chromium, manganese, cobalt, nickel, molybdenum, iron, copper, and zinc were detected. The nickel-free alloy released lower amounts of ions to the medium. The greatest damage in the cellular DNA, measured as the olive moment, was also produced by the stainless steel alloy followed by the nickel-free alloy. Conversely, the titanium alloy had an increased cellular viability and did not damage the cellular DNA, as compared with the control values. The titanium brackets and tubes are the most biocompatible of the 3 alloys studied.

Metallic ion content and damage to the DNA in oral mucosa cells of children with fixed orthodontic appliances

Although the metal devices used in orthodontic treatments are manufactured highly resistance to corrosion, they may still suffer some localized corrosion resulting from the oral cavity conditions. The corrosion causes the release of metals from the alloys used for their manufacture. In this report, we evaluated the in vivo metal ions release of three alloys (stainless steel, titanium and nickel-free) usually used in the orthodontics treatments and its genotoxicity. We applied to 15 patients, between 12 and 16 years, 4 tubes and 20 brackets. Samples from oral mucosa were taken before the treatment and 30 days later. The concentration of the titanium, chromium, manganese, cobalt, nickel, molybdenum and iron were detected using inductively coupled plasma mass spectrometry (ICP-MS). The genotoxicity was measured with a comet assay (Olive moment). The oral mucosa cells in contact with the stainless steel alloy displayed the greatest titanium and manganese concentrations and those in contact with the nickel-free alloy presented the greatest concentration of chromium and iron. Both alloys, stainless steel and nickel-free, induced a higher DNA damage in the oral mucosa cells than the titanium alloy, in which the Olive moment was similar to controls. Based on the results of our study, we can conclude that titanium brackets and tubes are the most biocompatible of the three alloys.

The Effect of Microstructure on Unidirectional Chilled Solidification of High Chromium White Cast Iron

This study mainly investigates the characteristics of carbide and the matrix structure of ASTM A532–87 CLASS Ⅲ high-chromium white cast iron under directional solidification. The two components of high-chromium white cast iron were put in a 3-level Furan sand model, which is placed in a cold-water circulation copper model, producing unidirectional chilled solidification. A K-type thermocouple is employed to measure data for solidification temperature with time. The move velocities of the liquidus phase and solidus phase is calculated. The matrix and the growth characteristics of M7C3 carbide are explored. As determined from the experiment, the liquidus temperature gradient GL is 0.45~ 0.9oC/mm, and the solidus temperature gradient Gs is 4.3~6.2oC/mm. Around 300 nm of the primary carbide is formed from the added elemental nickel being less than 0.3 mm from the chilled end and from the nickel-free alloy being less than 5 mm from the chilled end. As the distance from the chilled end increases, the primary carbide gradually becomes coarser, and the distance between eutectic carbide groups is increased. This study employs EPMA to analyze the changes of primary carbide, eutectic carbide and matrix components with distance from the chilled end, as well as changes in the distributions of chemical elements.

Corrosion properties of nickel free austenitic stainless steels in 0·5M H2SO4 and 0·5M H2SO4 plus 0·4M NaCl

The corrosion behaviour of four nickel free austenitic stainless steels were investigated in 0·5M H2SO4 and 0·5M H2SO4 plus 0·4M NaCl solutions by means of potentiodynamic and potentiostatic anodic polarisation testing. The performances of the nickel free alloys are compared to those of an experimental intermediate nickel alloy (4%Ni) and a standard AISI 304 steel grade. Once passivity was reached all alloys displayed similar current densities ip in 0·5M H2SO4, independent from alloying. Mo and Cu were shown to be beneficial in decreasing the active dissolution currents and icrit values. The commercial AISI 304 steel displayed superior resistance to pit initiation during potentiodynamic testing, and AISI 304 steel displayed the highest Epit value of all alloys tested. When tested potentiostatically the N and Mo alloyed nickel free alloys showed excellent resistance to pit initiation and growth. The dominant effect of N was associated with repassivation of incipient pits, while Mo appeared to act at an earlier stage, suppressing initiation.

Impact toughness properties of nickel-free austenitic stainless steels

The Charpy-V impact toughness of six interstitially-alloyed nickel-free austenitic stainless steels was investigated in the temperature range between −196 and 150 °C. Unlike traditional face-centered-cubic steels, the investigated alloys show a marked decrease in impact toughness with decreasing temperature and cleavage-like fracture surfaces at low temperatures. The decrease in impact toughness is due to the combined effects of high strain rate and temperature sensitivity of plastic flow and the strong planarity of the deformation mechanisms of nitrogen-alloyed nickel-free alloys at low temperatures. The effects of the high strain rate and temperature sensitivity of the flow stress on the fracture behavior are discussed based on an analysis of the critical stress for fracture and plastic flow.

Hypersensitivity to conventional and to nickel-free orthodontic brackets

The aim of this study was to evaluate the allergenic potential of orthodontic brackets, comparing the cutaneous sensitivity provoked by metals present in conventional metallic brackets to that provoked by brackets with a low concentration of nickel, known as "nickel-free". A sample was selected from 400 patients undergoing treatment in the orthodontic clinic of the Pontifical Catholic University of Minas Gerais (Belo Horizonte, MG, Brazil), in the period from the beginning of 2002 to the end of 2003. A cutaneous sensitivity patch test containing 5% nickel sulphate was used in 58 patients (30 males and 28 females), aged between 11 and 30, which were using fixed appliances with Morelli brackets in both arches. In a second phase, 30 days later, a comparative test of cutaneous sensitivity was applied to the whole sample with two types of test specimens, in the form of a disc. Two alloys were tested: discs composed of the alloy used in the construction of conventional brackets and discs composed of a nickel-free alloy. The internal part of the forearm was chosen for testing, and 20 test specimens of each experiment (corresponding to the twenty brackets of a complete fixed appliance) were applied. Of the 58 patients evaluated, 16 patients were sensitive to the patch test with 5% nickel sulphate. Out of these 16 patients, 12 developed an allergic reaction to experiment 1 (test specimen with nickel), while in experiment 2, only 5 patients showed sensitivity to that sample. The McNemar test revealed that the nickel-free test specimens provoked less allergic reaction when compared with the conventional alloy (p=0.016).

Recent Development of New Alloys for Biomedical Use

Metallic materials are widely used in medicine not only for orthopedic implants but also for cardiovascular devices and other purposes. New alloys for biomedical use are developed all over the world continuously to decrease corrosion, toxicity and fracture during implantation and increase interfacial and dynamical tissue compatibility. Most of efforts are made to develop titanium alloys, especially in β-type alloys whose Young’s modulus is as low as cortical bone. Nickel-free alloy is also necessary to prevent nickel allergy: nickel-free austenitic stainless steels and shape memory alloys are developed. To increase iocompatibility, the controls of surface morphology and surface treatment or modification are necessary.

Ａｌ‐４％Ｃｕ‐１．５％Ｍｇ合金の耐熱性に及ぼすニッケル添加の影響

Softening characteristics and corresponding microstructural changes due to annealing were studied on heattreated Al-4%Cu-1.5%Mg alloys containing Ni up to 4%. Age-hardenability was markedly lowered with increasing nickel content. Neither after annealing nor at elevated temperatures, hardness of nickel contained alloys seemed to be superior to that of nickel free alloy. These results were attributed to the facts that insoluble compounds containing Cu, Ni and Al were formed in nickel contained alloys, and that coarsening of precipitates (S', S) was never checked by nickel addition. It was suggested that nickel addition was not effective on heat resistance of Al-Cu-Mg alloy.

Thermochemical production of nitrogen stainless steels

Laboratory studies have shown that nickel-free fully austenitic stainless steel strip can be produced via a simple thermochemical route. Fe-18Cr alloys containing 0 and 5% Ni and 0 to 25% Mn have been nitrided in nitrogen-hydrogen atmospheres in the temperature range 1373–1573K. Provided the gas atmosphere is sufficiently pure, the rate of uptake of nitrogen into solid solution in austenite is determined by the diffusivity of nitrogen in austenite where, typically it has been found that the nitrogen diffusion coefficient is 2·5 × 10−11 m2s−1 at 1473K. Equilibrium within a 1mm thick sample is established within 4h at 1473K. The solubility of nitrogen in austenite increases with nitrogen pressure and manganese concentration, and decreases with temperature and nickel concentration. Fe-18Cr alloys containing manganese are fully austenitic at 1473K if the nitrogen concentration exceeds 0·4%. However, the minimum partial pressure of nitrogen necessary to give an austenitic structure is lowered by increasing the manganese concentration. The addition of 5% Ni reduces this nitrogen concentration by 0·25% demonstrating that 0·05% N is equivalent to about l% Ni in promoting the formation of austenite. The condition by which the surface of substantial section sizes can be transformed into an austenitic material in nickel-free alloys has been established.

Anodic Polarization Behavior of Nickel-Manganese Alloys in 1N Sulfuric Acid Solution

Abstract The anodic polarization behavior of six alloys in the nickel-manganese system in hydrogen saturated 1N sulfuric acid was investigated at 20 C (68 F) using a potentiodynamic technique. Only the nickel free alloy failed to exhibit passivity. The potential width of the passive region for those specimens exhibiting passivity decreased, and the passive current density increased with increasing manganese content. The corrosion potential decreased with increasing manganese content. The critical current density was nearly constant for all passive specimens except pure nickel. Nickel-manganese alloys exhibited marked secondary passivation at potenitals just slightly more active than those at which visible oxygen evolution occurred. It was also noted that among elements 22 through 29, passivity occurs in the above environment only in the even numbered elements.

On the Elevated-Temperature Strengths of Some Aluminium Cast Alloys for Piston

This investigation was carried out in relation to the effects of heat-treatment and nickel content on the tensile properties, creep and fatigue strengths, at the temperature ranging from room-temperature to 400°C on AC5A (Y alloy), AC8A (Low-Ex.) and AC8B (Alcoa D 132) cast aluminium alloys for piston.The chemical compositions and mechanical properties at room-temperature including the heat-treatments are given in Table I and II, respectively. The specimens were cast into a permanent mould which is in accordance with Japanese Industrial Standard (JIS) H0321.The alloys were compared on the basis of their tensile properties at elevated-temperature after 1000 hour soaking. The creep tests were carried out with the lever-type creep-rupture tester, and the creep strengths were calibrated at 0.1% per 1000 hours. The fatigue tests were conducted on Ono's high-temperature fatigue tester (3000rpm) and fatigue strengths were determined at 107 cycles.The fatigue strength showed lower value at the temperature ranging from room-temperature to 300°C than yield strength. In the case of AC8A and AC8B alloys, however, the creep strength showed the lowest value of the temperature above 200°C. As for the effect of heat-treatment conditions on their strengths, higher values were given by T6 treatment at the temperature up to 200°C, and T5 treatment showed slightly higher strengths than by other treatments at further elevated-temperature. The authors would recommend T5 treatment for the heat-treatment of those alloys for piston.The strengths of nickel-free alloys decreased a little compared with nickel-containing alloys at elevated-temperature. It would appear from the above results that elimination of nickel from the alloys is undesirable. Alcoa F132, however, which has a reduced nickel content of less than 0.50%, is currently in use in U.S.A., and in consideration of the difference in strengths of nickel-free and nickel-containing alloys, it may be acceptable for nickel content of these alloys to approach the lower limit of the current specification.

The thermal conductivity, electrical resistivity, and mechanical properties of a sintered iron-copper alloy. Part 2

1. It was established in this investigation that, when 15% nickel is added to an iron-copper-graphite alloy containing after sintering 1.1% C and 10% Cu, the hardness of the alloy increases by 20–25%, but, at the same time, its mechanical strength, ductility, and impact strength decrease compared with the same properties of a similar nickel-free alloy. 2. Other conditions being equal, sintering in a dissociated ammonia atmosphere reduces the mechanical and impact strengths by approximately 10–15% and slightly decreases the ductility compared with the properties of the same alloy sintered in a hydrogen atmosphere. 3. The tensile and impact strength tests of specimens at 400°C revealed a slight decrease in the mechanical and impact strengths at that temperature. 4. The thermal conductivity increases linearly with increasing temperature. The Lorenz function is greater than its theoretical value, and decreases with increasing temperature. This indicates that heat conduction in this alloy is due to conduction electrons and crystal-lattice conduction. 5. The coefficient of linear thermal expansion at first shows an insignificant increase, but at 400°C attains values characteristic of cast austenite.

Topic of the Month—Catastrophic Corrosion Resulting From Vanadium Pentoxide in Fuel Oil Ash

Catastrophic corrosion resulting from burning fuel oils containing very small concentrations of vanadium is described. Experiments are outlined in which the effects of contamination of fuel oil ash by vanadium and other materials is evaluated after test samples are exposed for varying periods of time at high temperatures. Relative merits of nickel-rich versus nickel-free alloys is mentioned as are experiments involving additives to fuel. Molecular structure of vanadium porphyrin is illustrated and sources of fuel oil containing greatest concentration are listed. 10 references.

PYROLYSIS OF THE LOWER PARAFFINS: III. PRODUCTION OF OLEFINES IN BAFFLED METAL TUBES

Results have been obtained which indicate that the conversion of the lower paraffins to olefines by thermal treatment can be satisfactorily carried out in special alloy steel tubes at 800–820 °C. By using baffled tubes it has been found possible to obtain high rates of conversion at temperatures considerably lower than when using open tubes. Actually the temperature has been brought within the range of usefulness of special alloy steels. Heat-resistant alloys of the 18–8 type have been found unsuitable for this purpose, because nickel appears to catalyze the formation of elementary carbon, but nickel-free alloys containing over 20% of chromium have been found satisfactory.