Nitinol alloy

The results of the above experiments could be very important in supporting your theory of the crystal-structure reversion. I should appreciate it if you would send me copies of your papers on this subject. Also, we would like to perform some additional acoustic-emission tests with our more sophisticated apparatus and we need some 1/2M diameter stock of Nitinol alloys. Please tell me how I can get some. 

As is explained above, single crystals of size within a fraction of a mm (millimeter) are not available in Nitinol alloy (under microscope the grain size was determined to be in 100 micron range). On the other hand, other conventional martensitic transition systems, such as In-Tl, Au-Cd, Al-Cu all have good size of crystals — in the range of 1 4 cm. 

Cobalt chrome alloys, gold alloys, mercury amalgams, nickel-chrome alloys, nitinol alloys (shape memory and superelastic), stainless steels, tantalum, titanium, and titanium alloys... 

Flgnre 13.18 Schematic representation of typical stress—strain curves of biological tissue and nitinol alloy. 

The original shape (the one that is to be remembered) is created by heating to well above the Af temperatiue (such that the transformation to austenite is complete) and then restraining the material to the desired memory shape for a sufficient time period. For example, for Nitinol alloys, a 1-h treatment at 500 C is necessary. 

Nickel-tin-aluminum catalyst, 24 794 Nickel titanate, 25 47 Nickel-titanium (NiTi) alloy (Nitinol), 22 341, 712... 

Not much has been done in discussing ways to improve medical device surfaces using electrochemical coating methods in particular, with the aim of accomplishing the medically relevant goal, aside from discussion in the relevant literature, of the processing of nitinol (an alloy of nickel and titanium see Section 21.4). 

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-... 

Wilham J. Buehler and his colleagues at the Naval Ordnance Laboratory in White Oak, Maryland, describe the shape-memory alloy known as nitinol. 

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). 

The discovery of the shape memory effect in TiNi by Buehler et al. at the Naval Ordinance Labs occurred during an investigation of the alloy for possible use as a corrosion-resistant knife for underwater activities. The investigators called the alloy nitinol for Nickel, Titanium, and Naval Ordinance Labs. 

The temperature for the acoustic damping capacity change from Nitinol was found to be different for alloys that were prepared at different laboratories (even though both alloys have identical composition). Further, the shape memory response to temperature change, such as how fast and how much force, also varied a great deal from one alloy to another. 

This study led to an important conclusion that what is happening in Nitinol is unique from all other known alloy systems with martensitic transformation. These unique properties include the following ... 

It was based on these uniqueness and commonalities, my colleague and I submitted a paper entitled Crystal Structure and A Unique martensitic Transition of TiNi to a Journal concerned with metals and alloys for publication in 1965. But, the paper was rejected outright by two anonymous reviewers who could not accept our observation that the Nitinol transition was unique. Obviously the reviews contend that by accepting Nitinol transition being unique, may make all other martensitic transformations garden variety. This may upset the theory of martensitic transition formulated thus far. We then, submitted the paper to the Journal of Applied Physics and was accepted for publication and eventually appeared in print [10]. A few months after the appearance of this article, the editor of the very journal that rejected my paper, asked me to review two papers on Nitinol for the journal. Suddenly, I was an undisputed expert in Nitinol Up to this point I had not really start to apply covalent-bond concept but devoting more time in collecting experimental data [14,15], which may be important in support or non-support of covalent-bond concept. 

In 1967, on April 3 and 4, under the sponsorship of ONR (Office of Naval Research) I organized the first International Conference on Nitinol called Symposium on TiNi and Associated Compounds . The conference was held at Naval Ordnance Laboratory, the birthplace of Nitinol. As the chairman of the conference I assisted in selecting the papers from this conference that were later published in block form in the Journal of Applied Physics [16]. Despite these efforts the Nitinol transition remained elusive for sometime. In fact, after more than 30 years since the discovery of memory effect and with more than 139 papers have appeared in various journals on this subject, the investigators still do not agree with one another. At the same time more than 4,000 patents worldwide have been filed on the use of the memory effect or superelasticity in Nitinol. Out of all this, the actual application of Nitinol remains only a handful. In sharp contrast other conventional alloys with martensitic transition has no controversy and in fact they are so well understood that a Crystallographic theory of martensitic transformation was formulated [27],... 

The only way to investigate these alloys was through single crystal X-ray diffraction study. This was particularly worthwhile, because we already have the results of single crystal X-ray diffraction study from Nitinol itself. The results of this investigation are given below. 

The transition band of TiNi (3-d series) bordered by Ms and Mf temperatures are obtained experimentally from a number of Ti (Ni, Co) and Ti (Co, Fe) alloys as shown in Fig. 6. But, the transition band of ZrPd (4-d) series is based on only two X-ray diffraction data and is assumed to be parallel to that of TiNi(3-d) band. It is reasonable, based on these data, to conclude that the crystal structures of the equiatomic compound series of the TiNi, ZrPd, and HfPt are all isotypic and the cause for their diffusionless transition are the same. That is AEd, the d-orbital energy level difference between the two elements change as a function of temperature. It is logical therefore, to conclude that the Nitinol transition is electronic in origin. In order to corroborate this conclusion more data other than crystal structure were obtained as follows. 

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