Titanium-nickel alloys

GoldJilloys, Wrought Type. Two types of wrought gold alloys were formerly recognized by the ADA specification no. 7 for the fabrication of orthodontic and prosthetic dental appHances, ie, type I, high-precious-metal alloys, and type II, low-precious-metal alloys (gold color). Alloys of this type are seldom used in the United States they have been replaced by stainless steels and nickel—titanium alloys. 

The most common SMAs are nickel-titanium alloys and copper alloys of various kinds. Nitinol, a specific alloy of nickel (Ni) and titanium (Ti), is probably the most widely used. (The word nitinol comes from the chemical symbols of its two metal components, along with an abbreviation for the Naval Ordnance Laboratory, where this alloy was discovered and studied in the early 1960s.) Although nickel and titanium alloys tend to be more expensive than copper materi-... 

Alloy with Memory. In seeking a way to reduce the brittleness of titanium, U.S. Navy researchers serendipitously discovered a nickel-titanium alloy having an amazing memory. Previously cooled clamps made of the alloy (nitinol) are flexible and can be placed easily in position. When warmed to a given temperature, the alloy hardware then exerts tremendous pressure. Use of conventional clamps for holding bundles of wires or cables in a ship or aircraft structure requires special tools. For this and other applications in industry and medicine, nitinol has been in demand. The alloy, however, is not easy to produce because only minor variations in composition can affect the snap back" temperature by several degrees of temperature. 

As previously mentioned, the nickel—titanium alloys have been the most widely used shape memory alloys. This family of nickel—titanium alloys is known as Nitinol (Nickel Titanium Naval Ordnance Laboratory in honor of the place where this material behavior was first observed). Nitinol have been used for military, medical, safety, and robotics applications. Specific usages include hydraulic lines capable of F-14 fighter planes, medical tweezers, anchors for attaching tendons to bones, eyeglass frames, underwire brassieres, and antiscalding valves used in water faucets and shower heads (38,39). Nitinol can be used in robotics actuators and micromanipulators that simulate human muscle motion. The ability of Nitinol to exert a smooth, controlled force when activated is a mass advantage of this material family (5). 

Thompson SA. An overview of nickel-titanium alloys used in dentistry. Int Endod J 2000 33(4) 297-310. 

Next-generation metallic biomaterials include porous titanium alloys and porous CoCrMo with elastic moduli that more closely mimic that of human bone nickel-titanium alloys with shape-memory properties for dental braces and medical staples rare earth magnets such as the NdFeB family for dental fixatives and titanium alloys or stainless steel coated with hydroxyapatite for improved bioactivity for bone replacement. The corrosion resistance, biocompatibility, and mechanical properties of many of these materials still must be optimized for example, the toxicity and carcinogenic nature of nickel released from NiTi alloys is a concern. ... 

The structure of alloys and structural changes at certain temperatures can explain the memory effect of special alloys (see E5.6) like Nitinol , a nickel-titanium alloy [4]. The structure as well as the much greater electric conductivity explains the difference between the copper-gold structures (CuAu and Cu3Au) and... 

Problem In 1965 some scientists produced a very special nickel-titanium alloy which can remember its programmed form. They called this kind of alloy memory metal and the special compound Nitinol , because it was discovered in the Nickel-Titanium Naval Ordonnance Laboratory. The memory metals are often used in engines, motors and other pieces of equipment, for which it is important to have a certain form at a certain temperature, e.g. for closing a valve. The conversion temperature of the Nitinol composition NqTq is approximately 50°C. Samples of such memory metals, like nitinol wires, can be obtained from Educational Innovations (teachersource.com). 

Wever DJ, Veldhuizen AG, Sanders MM, Scha-KENRAAD JM and Van Horn JR (1997) Cytotoxic, allergic and genotoxic activity of a nickel-titanium alloy. Biomaterials 18 1115-1120. 

How can the frames "remember" their original shape when placed in warm water The answer is a nickel-titanium alloy called Nitinol that was developed in the late 1950s and early 1960s at the Naval Ordnance Laboratory in White Oak, Maryland, by William J. Buehler. (The name Nitinol comes from Mckel T/tanium Naval Ordnance Laboratory.) Nitinol has an amazing ability to remember a shape originally impressed in it. 

A nickel-titanium alloy with "shape memory" is discovered. The alloy reverts to its original shape after being deformed. Dental braces are one of many applications. 

Nickel-titanium alloys, based upon the equi-atomic intermetallic compoimd NiTi, have very low values of elastic modulus (approximately 35 GPa), compared to stainless-steel alloys (approximately 160-180 GPa) [4]. As a consequence, nickel-titanium alloys have considerable clinical importance for endodontic instruments, permitting negotiation of curved root canals with much greater facility than traditional stainless-steel instruments [5], and for orthodontic wires that have a much more favourable light-force delivery for tooth movement than traditional stainless-steel orthodontic wires [6,7],... 

R-phase, which serves as an intermediate phase to facilitate the transformation between martensite and austenite. Formation of the R-phase is reported to arise from the presence of dislocations and precipitates [11]. A substantial dislocation density is expected in the vwought nickel-titanium endodontic instruments and orthodontic wires, which are subjected to extensive mechanical deformation during manufacturing processes [12], Microstructural precipitates are a consequence of the inevitable deviation of the nickel-titanium alloy composition from the equi-atomic NiTi composition [13,14],... 

The manufacturing of nickel-titanium rotary endodontic instruments, which involves machining of a wire blank into a variety of cross-sectional shapes that depend upon the particular product, is described in a recent review article [20], In that article it is stated that the nickel-titanium alloy for these instruments is in the superelastic condition, for which the alloy has the austenitic structure. This statement is highly plausible, because extensive reversible elastic strain (up to approximately 10% for uniaxial tension) could then occur in the instrument when the stress in the root canal reaches the level that causes transformation from austenite to martensite [21], The first published verification [22] of this superelastic condition was obtained by our research group from DSC experiments on nickel-titanium rotary instruments in the as-received condition. A subsequent study evaluated the rotary instruments after clinical use [23]. 

Since our pioneering study on as-received [22] nickel-titanium endodontic instruments, other DSC studies have confirmed that as-received instruments are in the superelastic condition, which persists after numerous sterilization cycles [28,29]. As would be expected, mechanical properties of these instruments are related to the phase transformation behaviour of the nickel-titanium alloy [30]. Accordingly, suitable elevated-temperature heat treatment may favourably alter the mechanical properties of these instruments [31,32], as was previously found for nickel-titanium orthodontic wires [21,33]. 

Recently, the integration of actuators into structures has also been researched. Shape Memory Alloys (SMA)-based actuators can be embedded into composites in the form of large diameter, plastically deformed wires. SMA are nickel/titanium alloys with a surprising property if plastically deformed at a low temperature (in a martensitic phase), they can recover the original shape and dimensions though heating above a definite temperature. When SMA are embedded and then heated, the restraints on free deformation imposed by the host composite originate a distributed stress which deforms the structure or modifies its vibrational response. 

Next we applied this assay to the assessment of a nickel-titanium alloy [18]. We selected MOLT-3 that was the most sensitive against nickel ion (see Fig. 11). Nickel-titanium (NiTi) alloys were made by an arc melting method. Those alloys varied greatly in composition (Table 3) and phase (Fig. 12). First these alloys were sterilized by soaking them in 70 % ethanol solution. Then they were immersed in phosphate buffer and incubated at 36.5 °C for 25 h. We collected the extract and added it to a MOLT-3 culture plate (the ratio of extract to supernatant was 1 1). After a 4-day culture, we measured the viable cell number of each culture condition. The order of the viable cell numbers was coupon 5> coupon 2> coupon 1, coupon 3> coupon 4 (Fig. 13). We also measured the nickel concentration of the extract by atomic absorptirai spectrophotometry. The order of the nickel concentration was coupon 4> coupon 1, coupon 3> coupon 2> coupon 5 (Table 4), which was... 

Fig. 12 Nickel Titanium constitution diagram and presumed phase of nickel-titanium alloys...

Fig. 13 Relative viable cell number of each culture condition added to an extract of nickel-titanium alloy. No addition of extract was used for the control culture ctmditirai (n = 3). Nickel ion indicates 84 pM of nickel chloride solution was added to the supernatant of MOLT-3...

Ogawa A, Akatsuka R, Tamauchi H, Hio K, Kanematsu H (2011) Influence of nickel-titanium alloy components on biological functions. BMC Proc 5 79... 

Another point of comparison between the devices concerns material choice. Nitinol (nickel/titanium alloy) is used in the ASO, the GHSO and the DAW devices. Nitinol is a shape-memory alloy and it reverts back to its previous... 

For instance, equiatomic nickel-titanium alloy (nitinol) is a very attractive material for biomedical applications. However, the high nickel content of the alloy and its potential influence on biocompatibility is an issue for nitinol-composed devices. Corrosion resistance of nitinol components from implantable medical devices should be assessed according to regulatory processes and standard recommendations. It is now well known that nitinol requires controlled processes to achieve optimal good life and ensure a passive surface, predominantly composed of titanium oxide, that protects the base material from general corrosion. Passivity may be enhanced by modifying the thickness, topography, and chemical composition of the surface by selective treatments [46]. 

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