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Category: Alloys

An alloy is an admixture of metals, or a metal combined with one or more other elements. For example, combining the metallic elements gold and copper produces red gold, gold and silver becomes white gold, and silver combined with copper produces sterling silver.

Nitinol

Nitinol metal alloy is one of the most useful alloys used for various purposes. It has numerous important medical applications.

What is Nitinol?

It is a nickel- titanium metal alloy with some unique properties. It is also known as Nickel titanium. This alloy exhibits the superelasticity or pseudoelasticity and the shape memory properties. It means this unique metal can remember its original shape and shows great elasticity under stress.

Composition of Nitinol

This metal alloy is composed of nickel and titanium. It contains these two elements at approximately equal atomic percentages. Nickel is a known allergen and it might also have carcinogen properties. Due to this reason the nickel content of this alloy has raised great concerns about its usefulness in the medical industry.

Production of Nitinol

Extremely tight compositional control is required for making this alloy. Due to this reason it is very difficult to prepare this alloy. The extraordinary reactivity of titanium is another obstacle in its preparation. Two primary melting methods are presently used for this purpose:

  • Vacuum Arc Re-melting: In this method, an electrical arc is struck between a water cooled copper strike-plate and the raw materials. Water cooled copper mold is used for melting the constituents in high vacuum to prevent carbon introduction.
  • Vacuum Induction Melting: The raw materials are heated in a carbon crucible using alternating magnetic fields. This is also accomplished in high vacuum; however, carbon is introduced in this process.
Nitinol Picture
3D view of Austenite and Martensite structures of the NiTi compound.


Picture 1 – 3D view of Austenite and Martensite structures of the NiTi compound.

Source – en.wikipedia.org

There are no considerable amounts of data showing the product of one method to be better than the other. Both these methods have different advantages to offer. Other methods like induction skull melting, plasma arc melting, and e-beam melting are also used for this purpose on a boutique scale. Physical vapor deposition process is also used in laboratories.

Symbol of Nitinol

This metal alloy is denoted by the symbols of its constituent metals. The formula for this alloy is NiTi.

History of Nitinol

This material derived its name from its constituents and its place of discovery. In 1962, William J. Buehler and Frederick Wang first discovered the unique properties of this metal at the Naval Ordnance Laboratory.

Commercialization of this alloy was not possible until a decade later. This delay was mainly caused by the difficulty of melting, machining and processing the material.

Properties of Nitinol

The shape memory and superelasticity properties are the most unique properties of this alloy. The shape memory property allows this metal to “remember” its original shape and retain it when heated above its transformation-temperature. It happens due to the different crystal structures of nickel and titanium. This pseudo-elastic metal also shows incredible elasticity which is approximately 10 to 30 times more than that of any ordinary metal.

Here are some basic physical and mechanical properties of this alloy:

Physical Properties

Appearance: this is a bright silvery metal.

Density: The density of this alloy is 6.45 gm/ cm3

Melting Point: Its melting point is around 1310 °C.

Resistivity: It has a resistivity of 82 ohm-cm in higher temperatures and 76 ohm-cm in lower temperatures.

Thermal Conductivity: The thermal conductivity of this metal is 0.1 W/ cm-°C.

Heat Capacity: Its heat capacity is 0.077 cal/ gm-°C.

Latent Heat: this material has a latent heat of 5.78 cal/ gm.

Magnetic Susceptibility: Its magnetic susceptibility is 3.8 emu- gm in high temperatures and 2.5 in low temperatures.

Mechanical Properties

Ultimate Tensile Strength: The ultimate tensile strength of this material ranges between 754 and 960 MPa.

Typical Elongation to Fracture: 15.5 percent

Typical Yield Strength: 560 MPa in high temperature; 100 MPa in low temperature

Approximate Elastic Modulus: 75 GPa in high temperature; 28 GPa in low temperature

Approximate Poisson’s Ratio: 0.3

Making Nitinol Devices

Hot working of this material is relatively easy than cold working. The enormous elasticity of this material makes cold working difficult by increasing roll contact. This results in extreme tool wear and frictional resistance. These reasons also make machining of this alloy extremely difficult. The fact that this material has poor thermal conductivity does not help in this purpose. It is relatively easy to perform Grinding, laser cutting and Electrical Discharge Machining (EDM) on this metal.

Heat treatment of this material is very critical and delicate. The heat treatment-cold working combination is important for controlling the useful properties of this metal.

Nitinol Wires

Nitinol is used for making shape-memory actuator wire used for numerous industrial purposes. This wire is used for guidewires, stylets and orthodontic files. This wire is ideal for applications requiring high loading and unloading plateau-stresses as well as for eyeglass frames and cell phone antennas. However, the main uses of this wire are in stents and stone retrieval baskets.

Nitinol Stent

This alloy is used for manufacturing endovascular stents which are highly useful in treating various heart diseases. It is used to improve blood flow by inserting a collapsed Nickel titanium stent into a vein and heating it. These stents are also used as a substitute for sutures.

Nitinol Basket

Nickel titanium wire baskets are well-suited for many medical applications as it is springier and less collapsible than many other metals. This basket instrument is highly useful for the gallbladder.

Uses of Nitinol

Here are some of the main applications of Nitinol metal alloy:

Medical Applications

  • This alloy is very useful in dentistry, especially in orthodontics for wires and brackets that connect the teeth. Sure Smile (a type of braces) is an example of its orthodontic application.
  • It is also used in endodontic mainly during root canals for cleaning and shaping the root canals.
  • In colorectal surgery, it is used in various devices for the purpose of reconnecting the intestine after the pathology is removed.
  • Nitinol stents are another significant application of this metal in medicines.
  • Its biocompatible properties make useful in orthopedic implants.
  • Nitinol wires can be used for marking and locating breast tumors.
  • The use of Nitinol tubing for various medical purposes is increasing in popularity.

Industrial Uses

  • Nitinol wires are used in model heat engines made for demonstration purposes.
  • This material is used in temperature controls. Its shape changing properties can be used for activating a variable resistor or a switch for controlling the temperature.
  • This metal is often used in mechanical watch springs.
  • It is used as microphone boom or a retractable antenna in cell phone technology for its mechanical and flexible memory nature.
  • Nitinol spring is used in various industries for the purpose of utilizing the superelastic properties of this metal.
  • Nitinol sheets are used for punching, stamping and deep drawing.

Other Uses

  • It is also used as an insert for golf clubs for its shape changing abilities.
  • It is a popular choice for making extremely resilient glass-frames.
  • Nitinol is used for making self-bending spoons used in magic shows.

Availability of Nitinol

Nickel titanium is available in various forms including wires, tubes, sheets and springs. NDC is one of the leading manufacturer and supplier of this metal alloy. However, there are many other suppliers of Nitinol wires, tubes, springs etc. Different forms of this metal are also available online at reasonable prices.

Nitinol is counted among the most useful metal alloys with numerous industrial and medical applications. It is often the best choice for many applications that require enormous motion and flexibility. However, this material has shown fatigue failure in many demanding applications. Experts are working hard for the purpose of defining the durability limits of this metal alloy.

References:

http://www.nitinol.com/nitinol-university/nitinol-facts/

http://www.memry.com/nitinol-iq/nitinol-fundamentals/physical-properties

http://jmmedical.com/resources/221/Nitinol-Technical-Properties.html

http://www.colorsproject.com/nitinol_articles_science_digest_1982_sanders.pdf

http://www.dynalloy.com/AboutNitinol.html

Ultimet

Ultimet is a Cobalt alloy and is widely used in factories and industries. Haynes International, Inc produces this “high performance alloy”.

Composition of Ultimet

It is a metal alloy that consists of various alloying elements. The elements are used in the following proportions to produce this alloy:

  • Cobalt (as balance) – 54%
  • Chromium- 26%
  • Nickel- 9%
  • Molybdenum- 5%
  • Iron- 3%
  • Tungsten- 2%
  • Manganese- 0.8%
  • Silicon-0.3%
  • Nitrogen- 0.08%
  • Carbon-0.06%

Properties of Ultimet

Following are some of the physical properties of this metal alloy:

  • The density of this metal alloy is 8.47 g/cm3.
  • It melts in a temperature somewhere between 2430-2470 °F.
Ultimet Picture

Applications of Ultimet

This alloy is widely used for various industrial purposes. Following are some of the uses of Ultimet:

  • This alloy has high corrosion resistance abilities. In fact its resisting abilities are comparable to that of the Hastelloy alloys. Hastelloy is the trademark name for 22 highly corrosion resistant alloys, all of which are produced by the Haynes International, Inc.
  • Ultimet is also a very efficient wear and gall resistant material.
  • The electrogalvanising rolls of this alloy are successfully used in the production of galvanized steel. This steel is used for automobiles In Europe and the Far East.
  • It is also commonly used in agitators, blenders, dies, fan blades, nozzles, glass plungers, valve parts and screw conveyors.

Material Safety Data Sheet (MSDS)s of Ultimet

This material can be harmful for humans in the cases mentioned bellow:

Inhalation

If a person inhales the fume or dust of this alloy while welding, he may experience reduced lung function, nasal irritation, breathing difficulty etc. The victim should immediately seek medical advice. Artificial respiration must be given to the victim in case breathing has stopped.

Ingestion

If the metal is ingested by accident, the victim should take medical assistance. Sometimes it is advisable to drink 1-2 glasses of water and dilute the material.

Eyes

Direct eye contact with this material may cause eye irritation. The affected eye should be immediately washed with plenty of clean water. It is not advisable to rub or keep the eyes closed. Medical advice should be taken if the irritation continues.

Skin

Ultimet dust or fume may cause skin irritation. But the affected skin can be treated by regular first aid. The affected area should be washed properly with soap. The victim should seek medical assistance in case the irritation continues or blisters appear.

Ultimet is a highly useful alloy and it is the answer for various welding, corrosion and other industrial needs.

References:

http://www.vegasfastener.com/Haynes-Ultimet-1233.php

http://www.haynesintl.com/UltimetAlloy/ULTIMETAlloyPF.htm

http://www.wolframalpha.com/input/?i=ultimet

Stellite

Stellite alloys are a group or a range of cobalt-chromium alloys. They are designed to be resistant to wear and corrosion. These alloys may also have some portions of tungsten or molybdenum and some small but critical amounts of carbon. Stellite is a trademarked name of Deloro Stellite Company supplying Stellite alloys like Stellite3, Stellite 6, Stellite 12 and Stellite 21. Deloro Stellite Company also supplies other products like casting, machinery, welding, coating, knives and many others. The alloy was invented in the early 1900s by American metallurgist Elwood Haynes as a proper substitute for easily staining silverware.

Identification of Stellite

The CAS Registry Number for Stellite alloys is 12638-07-2.

Composition of Stellite

There are many types of Stellite alloys composed of varying quantities of cobalt, chromium, molybdenum, tungsten, iron, nickel, boron, aluminum, carbon, manganese, phosphorus, silicon, titanium and sulfur in different proportions. Most Stellite alloy compositions contain at least four to six of the listed elements.

Stellite alloy Picture


Picture 1 – Stellite alloy

Chemical Formula of Stellite

Stellite alloys do not have any specific chemical formula as various types of alloys are formed by combining a number of elements in different proportions. The various types of Stellite alloys are represented by using numbers, such as Stellite 1, Stellite 6K and Stellite 706.

Types of Stellite

A special form of Stellite known as Talonite is manufactured by hot-rolling and hardening a specific alloy combination. Talonite combines the properties of hardness, machinability and wear resistance. It is important to note that not all types of Stellite alloys can be processed to create Talonite.

Properties of Stellite

Stellite alloys are non-magnetic alloys which are highly resistant to corrosion. A range of different alloy compositions are prepared by combining different elements in varying proportions and the properties of an individual alloy composition might vary from an alloy of a different composition. Different alloy compositions are used for different purposes and valued for their functional flexibility. The alloy Stellite 100 is mostly used nowadays for cutting tools as it is very hard and is capable of maintaining a great cutting edge even when exposed to high temperatures. The alloy is also resistant to processes such as hardening and annealing that might result from excessive heat. Other Stellite alloys are manufactured to combine the properties of corrosion resistance, wear resistance and the ability to tolerate extreme temperatures.

Stellite alloys can be characterized as having great hardness and toughness. They are also normally highly resistant to corrosion. The extreme harness of these alloys frequently makes it difficult to work with them and so anything made from these alloys are normally very expensive. Usually, Stellite parts are precisely cast to avoid any need of further excessive machining. Stellite alloys are more frequently machined by grinding instead of cutting. These alloys usually have very high melting points resulting from the combined content of cobalt and chromium.

Uses of Stellite

The various uses of Stellite alloys are discussed below:

  • Stellite alloys are used in the process of hardfacing.
  • They are also applied in the manufacturing of saw teeth and acid-resistant machine parts.
  • The invention of Stellite alloys greatly improvised the manufacturing of poppet valves as well as the valve seats for valves. These alloys revolutionized the exhaust valves of internal combustion engines. The interval between maintenance of the valves and re-grinding of the valve seats was lengthened to a significant degree by reducing the erosion of the valves from hot gases.
  • The first third of M60 machine gun barrels (starting from the chamber) and the M2HB machine gun are lined with Stellite. Stellite alloys were also used to make the shoulders and locking lugs of Voere Titan II rifles.
  • Stellite alloys are also frequently used to make the cast structure used for dental prosthesis.
  • During early 1980s, experiments were conducted in United Kingdom to see if precision-cast Stellite alloys could be used to create artificial hip joints as well as other bone replacements.
  • Stellite alloys have been used to manufacture turning tools for lathes. Stellite alloys have greater cutting abilities compared to carbon steel tools as well as some high speed steel tools. They are especially capable of cutting difficult materials like stainless steel. Improvements in tipped tools over the years have greatly reduced the use of Stellite alloys in lathes.

Material Safety Data Sheet (MSDS)s of Stellite

Reactivity of Stellite

Stellite alloys are normally very stable materials. However, they can react with oxidizing agents and mineral acids to form explosive hydrogen gas which can cause fire hazards.

Toxicological Properties

Under normal circumstances, handling of Stellite alloys hardly poses any risk of health hazards. However, machining or welding with these alloys can produce dust, fumes and small particles of component alloy elements. These particles can pose a serious threat to human health when they enter the body in excess of maximum exposure limits.

Health Hazards

Inhalation: Inhaling particles of Stellite alloy generated from grinding, welding or similar processes can cause asthma and metal flume fever. Component materials like boron, chromium, cobalt, copper, manganese, molybdenum, nickel and vanadium are respiratory irritants.

Ingestion: Stellite particles normally do not enter the human body through ingestion. However in some cases a person’s hands, clothing or foods and drinks can get contaminated with dusts from Stellite alloy materials and the particles may enter the body through activities such as smoking, eating, drinking and nail biting. Ingesting Stellite particles can cause vomiting, diarrhea, nausea and abdominal pain.

Skin: Irritation, sensitization or allergic dermatitis can occur from the some of the components of Stellite alloys. When the skin comes in contact with vanadium, copper and nickel, it may result in dermatitis. Exposure of the skin to cobalt might cause allergic skin reactions and dermatitis. Skin exposed to manganese might suffer from excessive sweating. Vanadium and boron exposure causes skin irritation.

Eyes: If the eyes get contaminated by coming in contact with soiled fingers or airborne particles, it might result in irritation or abrasion of the eyes. Particles of Stellite materials can cause irritation of the eyes resulting from mechanical abrasion. Severe allergic conjunctivitis and eye irritation might result when dusts of cobalt enter the eyes. Irritation may also be caused by dusts of copper.

Chronic health effects

Chronic health effects resulting from Stellite alloys are difficult to detect as these alloys are made up of several elements. Effects of chronic inhalation include pulmonary fibrosis, chronic obstructive lung disease, rhinitis and bronchitis. Chronic occupational exposure to dusts of cobalt results in goiter, bloody urine and polycythemia.

Carcinogenicity

Some elements of Stellite alloys have been recognized as carcinogenic substances by The International Agency for Research on Cancer (IARC). Exposure to nickel and nickel compounds, cobalt and cobalt compounds and hexavalent chromium can greatly increase the risk of cancer among workers dealing with these alloys.

Medical Symptoms Aggravated By Exposure

Individuals already having sensitivity to certain elements and are prone to develop allergic reactions to metals like nickel, copper, chrome and cobalt might possibly encounter dermatitis and skin rashes. Persons already suffering from impaired pulmonary function can develop airway diseases and health conditions such as emphysema, asthma and chronic bronchitis, etc. when excessive concentrations of alloy fumes or dusts are inhaled. If any of these health conditions are already present, the inhalation of Stellite alloy particles can aggravate the symptoms. If a person is already suffering from prior damages to the Circulatory, Neurologic (nervous), Renal (kidney) or Hematogic (blood) systems, proper examinations or screening should be conducted for appropriate diagnosis of these patients. They should also be prohibited from entering areas contaminated by dusts of Stellite alloys.

Preventative Measures

Ventilation: The area should be well ventilated to minimize contamination of dust, fume and particles. Air exposure of materials should be kept below the recommended limits of exposure.

Respiratory: If the room is not properly ventilated and the exposure levels of alloy dust is not maintained below the exposure limits, adequate respiratory protection needs to be used by the working personnel. The respirators should be NIOSH-approved and have a proper air purifying filter.

Skin: Rubber or leather gloves should be used while dealing with Stellite alloys to avoid skin contact and for preventing metal abrasions and cuts. Unnecessary and risky skin contact can be easily avoided by using protective coveralls.

Eye: Safety goggles or glasses should be worn while entering a contaminated area.

First Aid Measures

Inhalation: The victim suffering from breathing difficulty due to inhalation of dust particles and fumes should be removed to an area of fresh air. A physician needs to be consulted if the breathing still does not improve.

Ingestion: The victim should drink plenty of water and try to vomit. A doctor should be consulted for ensuring further safety.

Skin: The infected area should be washed nicely with plenty of water. The victim should take a shower if possible. Contaminated clothing should be removed. Medical attention is required if irritation of skin persists.

Eye: The eyes should be washed well with ample amounts of water. A doctor needs to be consulted if eye irritation persists. While working with powders and dusts of Stellite alloys, a person should not wear contact lenses.

Recommended Monitoring Procedures

Environmental Surveillance: Air samples should be taken from the industrial working area for regularly checking the levels of air contamination.

Medical Surveillance: The workers should regularly go through a thorough health check up. Tests like chest x-rays, lung tests and routine physical examinations should be conducted on regular intervals to ensure safety of the workers.

Waste Disposal: Wastes of Stellite alloys should be disposed of by following the relevant Local, Provincial and Federal regulations regarding waste management.

Harmful effects of Stellite usage in nuclear power plants

Stellite alloys should not be used in nuclear power plants as cobalt can be changed to Cobalt-60 in nuclear reactors, which is a harmful radioisotope having a half life of five years and releases strong gamma radiation.

Stellite alloys are often a first choice in many industrial applications and functions. They are highly valued for their high resistivity to corrosion and weariness and hardness.

References:

http://en.wikipedia.org/wiki/Stellite

http://www.reade.com/western-region-%28usa%29/745

http://armstrongblue.com/Publications/msds__stellite_tips.htm

Manganin

Manganin is the trademarked name for an alloy that consists of three metallic elements – Copper, Nickel and Manganese. This alloy is useful in various industries. Read on to learn more about the composition, properties and uses of this material.

History of Manganin

Edward Weston, an American chemist, was the first person to discover “Manganin” in 1892, while working on the improvement of another metallic alloy. This alloy, which was previously known as “Alloy No. 2”, was discovered by Weston who renamed it as “Constantan”.

Composition of Manganin

This metal alloy consists of the following metals in the following proportions:

  • Copper (Cu): 86%
  • Manganese (Mn): 12%
  • Nickel (Ni): 2%

Chemical Formula of Manganin

The chemical formula of this substance is CuMnNi. It consists of the formulas of all the constituent metals, namely CU for Copper, Mn for Manganese and Ni for Nickel.

Chemical Structure of Manganin


Properties of Manganin

Following are some of the basic properties of this alloy:

  • It has the formula weight (sum of the molecular masses of the atoms in the formula) of 177.18 g/mole.
  • This alloy has a low temperature coefficient of resistance (relative change of the physical properties of a substance with 1 K temperature change).
  • The resistivity of this resistance alloy is 4.55×10-5 ohm centimeters.
  • It is electrically conductive.
  • It has a melting point of 960 °C.
  • The tensile strength of this substance ranges between 300-600 MPa.
  • The electrical resistivity of this alloy varies between 43 and 48 µOhmcm.
  • The density of this alloy is 8.4 g/cm3.
  • It has a specific gravity of 8.5.
  • Its electrical resistance is found to be constant over a range of temperatures.

Uses of Manganin

Manganin has been used for different industrial purposes from the moment of its discovery. The properties of this material make it most efficient for certain applications. It is widely used in industries for manufacturing various substances like:

Shunts

The wire and foil of this material are mainly used to manufacture various resistors – mainly ammeter shunts. Shunt refers to a device that controls the passage of electric current in different points of a circuit. This metal alloy has very low temperature coefficient of resistance. It also has long term stability. These properties make it very useful to be used for making shunts.

A coil of this substance is usually 150 mm wide and 0.025 mm thick.

Gauges

This substance has a low sensitivity to strain (Deformation of a substance due to the stress or strain applied to it) and a high sensitivity to hydrostatic pressure (the pressure applied by a fluid at the state of equilibrium as a result of gravitational force). Due to this reason, it is very useful in gauges to study High-Pressure Shock Waves (an energy carrying wave originated from a variety of mediums like gas, liquid, solid and also through various fields under a high-pressure).

Manganin gauges are extensively used in high-pressure shock wave studies that range from 1 – >400 kilobars (1 bar = 100 000 N/m2 or 14.5 psi). The gauge is bonded in mainstream applications between two flat polymer plates or metallic plates.

Manganin-Constantan Thermocouples are more efficient than Copper-Constantan Thermocouples in the thermometry (temperature measurement) units of Commercial Ultrasound Hyperthermia Systems.

Manganin wire is also seen to be used as an electrical conductor in cryogenic systems. Its use minimizes transfer of heat between points that require electrical connections.

References:

http://www.reade.com/products/4-alloys-metal-inorganic-powder-sheet-a-wire/305-manganin-alloy-manganin-shunt-manganin-strip-manganin-wire-nickel-plated-copper-wire-cu-mn-fe-astm-b267

http://www.isabellenhuette.de/pdf/WIDER_LEG/MANGANIN-ISABELLENHUETTE-R.pdf

http://www.lakeshore.com/temp/acc/am_wirets.html

http://www.ncbi.nlm.nih.gov/pubmed/7714367

http://www.vishaypg.com/docs/11524/mangpatt.pdf

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