Terfenol-D , an alloy of the formula Tb x Dy 1− x Fe 2 ( x ≈ 0.3), is a magnetostrictive material. It was initially developed in the 1970s by the Naval Ordnance Laboratory in the United States. The technology for manufacturing the material efficiently was developed in the 1980s at Ames Laboratory under a U.S. Navy-funded program. It is named after terbium , iron (Fe), Naval Ordnance Laboratory (NOL), and the D comes from dysprosium .
124-450: The alloy has the highest magnetostriction of any alloy , up to 0.002 m/m at saturation; it expands and contracts in a magnetic field. Terfenol-D has a large magnetostriction force, high energy density , low sound velocity , and a low Young's modulus . At its most pure form, it also has low ductility and a low fracture resistance. Terfenol-D is a gray alloy that has different possible ratios of its elemental components that always follow
248-490: A capacitance discharge to eliminate oxides before direct current heating, was patented by G. F. Taylor in 1932. This originated sintering methods employing pulsed or alternating current , eventually superimposed to a direct current. Those techniques have been developed over many decades and summarized in more than 640 patents. Of these technologies the most well known is resistance sintering (also called hot pressing ) and spark plasma sintering , while electro sinter forging
372-461: A compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors, helping the alloy resist deformation. Sometimes alloys may exhibit marked differences in behavior even when small amounts of one element are present. For example, impurities in semiconducting ferromagnetic alloys lead to different properties, as first predicted by White, Hogan, Suhl, Tian Abrie and Nakamura. Unlike pure metals, most alloys do not have
496-602: A form of hot pressing, to enable lower temperatures and taking less time than typical sintering. For a number of years, it was speculated that the existence of sparks or plasma between particles could aid sintering; however, Hulbert and coworkers systematically proved that the electric parameters used during spark plasma sintering make it (highly) unlikely. In light of this, the name "spark plasma sintering" has been rendered obsolete. Terms such as field assisted sintering technique (FAST), electric field assisted sintering (EFAS), and direct current sintering (DCS) have been implemented by
620-451: A formula of Tb x Dy 1− x Fe 2 . The addition of dysprosium made it easier to induce magnetostrictive responses by making the alloy require a lower level of magnetic fields. When the ratio of Tb and Dy is increased, the resulting alloy's magnetostrictive properties will operate at temperatures as low as −200 °C, and when decreased, it may operate at a maximum of 200 °C. The composition of Terfenol-D allows it to have
744-466: A gaseous state, such as found in a blast furnace to make pig iron (liquid-gas), nitriding , carbonitriding or other forms of case hardening (solid-gas), or the cementation process used to make blister steel (solid-gas). It may also be done with one, more, or all of the constituents in the solid state, such as found in ancient methods of pattern welding (solid-solid), shear steel (solid-solid), or crucible steel production (solid-liquid), mixing
868-498: A glass of water adhere to each other, which is driven by the temperature difference between the water and the ice. Examples of pressure-driven sintering are the compacting of snowfall to a glacier, or the formation of a hard snowball by pressing loose snow together. The material produced by sintering is called sinter . The word sinter comes from the Middle High German sinter , a cognate of English cinder . Sintering
992-602: A great range of material properties. Changes in density, alloying , and heat treatments can alter the physical characteristics of various products. For instance, the Young's modulus E n of sintered iron powders remains somewhat insensitive to sintering time, alloying, or particle size in the original powder for lower sintering temperatures, but depends upon the density of the final product: E n / E = ( D / d ) 3.4 {\displaystyle E_{n}/E=(D/d)^{3.4}} where D
1116-588: A hard bronze-head, but a softer bronze-tang, combining the alloys to prevent both dulling and breaking during use. Mercury has been smelted from cinnabar for thousands of years. Mercury dissolves many metals, such as gold, silver, and tin, to form amalgams (an alloy in a soft paste or liquid form at ambient temperature). Amalgams have been used since 200 BC in China for gilding objects such as armor and mirrors with precious metals. The ancient Romans often used mercury-tin amalgams for gilding their armor. The amalgam
1240-408: A high relative density and a small grain size. Therefore, being able to control these properties during processing is of high technical importance. Since densification of powders requires high temperatures, grain growth naturally occurs during sintering. Reduction of this process is key for many engineering ceramics. Under certain conditions of chemistry and orientation, some grains may grow rapidly at
1364-403: A large magnetostriction and magnetic flux when a magnetic field is applied to it. This case exists for a large range of compressive stresses , with a trend of decreasing magnetostriction as the compressive stress increases. There is also a relationship between the magnetic flux and compression in which when the compressive stress increases, the magnetic flux changes less drastically. Terfenol-D
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#17328588791941488-409: A lower affinity for water and a lower plasticity index than clay , requiring organic additives in the stages before sintering. Sintering begins when sufficient temperatures have been reached to mobilize the active elements in the ceramic material, which can start below their melting point (typically at 50–80% of their melting point ), e.g. as premelting . When sufficient sintering has taken place,
1612-432: A modified sintering method which combined electric current with pressure . The benefits of this method were proved for the sintering of refractory metals as well as conductive carbide or nitride powders. The starting boron – carbon or silicon –carbon powders were placed in an electrically insulating tube and compressed by two rods which also served as electrodes for the current. The estimated sintering temperature
1736-446: A molten metal is mixed with another substance, there are two mechanisms that can cause an alloy to form, called atom exchange and the interstitial mechanism . The relative size of each element in the mix plays a primary role in determining which mechanism will occur. When the atoms are relatively similar in size, the atom exchange method usually happens, where some of the atoms composing the metallic crystals are substituted with atoms of
1860-433: A molten metal may not always mix with another element. For example, pure iron is almost completely insoluble with copper. Even when the constituents are soluble, each will usually have a saturation point , beyond which no more of the constituent can be added. Iron, for example, can hold a maximum of 6.67% carbon. Although the elements of an alloy usually must be soluble in the liquid state, they may not always be soluble in
1984-455: A more concentrated form of iron carbide (Fe 3 C) in the spaces between the pure iron crystals. The steel then becomes heterogeneous, as it is formed of two phases, the iron-carbon phase called cementite (or carbide ), and pure iron ferrite . Such a heat treatment produces a steel that is rather soft. If the steel is cooled quickly, however, the carbon atoms will not have time to diffuse and precipitate out as carbide, but will be trapped within
2108-444: A particle size around the penetration depth of microwaves in the particular material. The sintering process and side-reactions run several times faster during microwave sintering at the same temperature, which results in different properties for the sintered product. This technique is acknowledged to be quite effective in maintaining fine grains/nano sized grains in sintered bioceramics . Magnesium phosphates and calcium phosphates are
2232-405: A pioneer in steel metallurgy, took an interest and produced a steel alloy containing around 12% manganese. Called mangalloy , it exhibited extreme hardness and toughness, becoming the first commercially viable alloy-steel. Afterward, he created silicon steel, launching the search for other possible alloys of steel. Robert Forester Mushet found that by adding tungsten to steel it could produce
2356-515: A relative density higher than 75% of theoretical sample density. This will remove supercritical pores from the body. The sample will then be cooled down and held at the second sintering temperature until densification is completed. Grains of cubic zirconia and cubic strontium titanate were significantly refined by TSS compared to CRH. However, the grain size changes in other ceramic materials, like tetragonal zirconia and hexagonal alumina, were not statistically significant. In microwave sintering, heat
2480-508: A rod larger than 8 mm in diameter due to the surface tension of the Terfenol-D and how the FSZM process has no container to restrict the material. The MB process offers a minimum of 10 mm diameter size and is only restricted due to the wall interfering with the crystal growth . Both methods create solid crystals that require later manufacturing if a geometry other than a right-angle cylinder
2604-429: A single melting point , but a melting range during which the material is a mixture of solid and liquid phases (a slush). The temperature at which melting begins is called the solidus , and the temperature when melting is just complete is called the liquidus . For many alloys there is a particular alloy proportion (in some cases more than one), called either a eutectic mixture or a peritectic composition, which gives
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#17328588791942728-424: A sinterisation cycle of a particular ceramic's formulation (i.e., tails and frits) can be easily obtained by observing the expansion-temperature curves during optical dilatometer thermal analysis. In fact, sinterisation is associated with a remarkable shrinkage of the material because glass phases flow once their transition temperature is reached, and start consolidating the powdery structure and considerably reducing
2852-453: A small amount of accuracy of around 1 dB. Due to its high temperature range, Terfenol-D is also useful in deep hole acoustic transducers where the environment may reach high pressure and temperatures like oil holes. Terfenol-D may also be used for hydraulic valve drivers due to its high strain and high force properties. Similarly, magnetostrictive actuators have also been considered for use in fuel injectors for diesel engines because of
2976-404: A solid piece. Since the sintering temperature does not have to reach the melting point of the material, sintering is often chosen as the shaping process for materials with extremely high melting points, such as tungsten and molybdenum . The study of sintering in metallurgical powder-related processes is known as powder metallurgy . An example of sintering can be observed when ice cubes in
3100-428: A stronger and more ductile material. Alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Most alloys are metallic and show good electrical conductivity , ductility , opacity , and luster , and may have properties that differ from those of
3224-420: A very hard edge that would resist losing its hardness at high temperatures. "R. Mushet's special steel" (RMS) became the first high-speed steel . Mushet's steel was quickly replaced by tungsten carbide steel, developed by Taylor and White in 1900, in which they doubled the tungsten content and added small amounts of chromium and vanadium, producing a superior steel for use in lathes and machining tools. In 1903,
3348-480: A way to harden aluminium alloys for use in machine-gun cartridge cases. Knowing that aluminium-copper alloys were heat-treatable to some degree, Wilm tried quenching a ternary alloy of aluminium, copper, and the addition of magnesium, but was initially disappointed with the results. However, when Wilm retested it the next day he discovered that the alloy increased in hardness when left to age at room temperature, and far exceeded his expectations. Although an explanation for
3472-448: A wicking structure in certain types of heat pipe construction, where the porosity allows a liquid agent to move through the porous material via capillary action . For materials that have high melting points such as molybdenum , tungsten , rhenium , tantalum , osmium and carbon , sintering is one of the few viable manufacturing processes. In these cases, very low porosity is desirable and can often be achieved. Sintered metal powder
3596-434: Is a determining factor for properties such as strength and electrical conductivity. To yield the desired bond area, temperature and initial grain size are precisely controlled over the sintering process. At steady state, the particle radius and the vapor pressure are proportional to (p 0 ) and to (p 0 ) , respectively. The source of power for solid-state processes is the change in free or chemical potential energy between
3720-576: Is a metal. This is usually called the primary metal or the base metal, and the name of this metal may also be the name of the alloy. The other constituents may or may not be metals but, when mixed with the molten base, they will be soluble and dissolve into the mixture. The mechanical properties of alloys will often be quite different from those of its individual constituents. A metal that is normally very soft ( malleable ), such as aluminium , can be altered by alloying it with another soft metal, such as copper . Although both metals are very soft and ductile ,
3844-456: Is affected by the change in pressure and differences in free energy across the curved surface. If the size of the particle is small (and its curvature is high), these effects become very large in magnitude. The change in energy is much higher when the radius of curvature is less than a few micrometers, which is one of the main reasons why much ceramic technology is based on the use of fine-particle materials. The ratio of bond area to particle size
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3968-425: Is an electric current assisted sintering (ECAS) technology originated from capacitor discharge sintering . It is used for the production of diamond metal matrix composites and is under evaluation for the production of hard metals, nitinol and other metals and intermetallics. It is characterized by a very low sintering time, allowing machines to sinter at the same speed as a compaction press. Pressureless sintering
4092-431: Is called hot isostatic pressing . To allow efficient stacking of product in the furnace during sintering and to prevent parts sticking together, many manufacturers separate ware using ceramic powder separator sheets. These sheets are available in various materials such as alumina, zirconia and magnesia. They are additionally categorized by fine, medium and coarse particle sizes. By matching the material and particle size to
4216-406: Is commonly used. Materials for which liquid phase sintering is common are Si 3 N 4 , WC , SiC , and more. Liquid phase sintering is the process of adding an additive to the powder which will melt before the matrix phase. The process of liquid phase sintering has three stages: For liquid phase sintering to be practical the major phase should be at least slightly soluble in the liquid phase and
4340-761: Is extremely slow thus the penetration was not very deep, so the alloy was not homogeneous. In 1740, Benjamin Huntsman began melting blister steel in a crucible to even out the carbon content, creating the first process for the mass production of tool steel . Huntsman's process was used for manufacturing tool steel until the early 1900s. The introduction of the blast furnace to Europe in the Middle Ages meant that people could produce pig iron in much higher volumes than wrought iron. Because pig iron could be melted, people began to develop processes to reduce carbon in liquid pig iron to create steel. Puddling had been used in China since
4464-482: Is generally considered successful when the process reduces porosity and enhances properties such as strength, electrical conductivity , translucency and thermal conductivity . In some special cases, sintering is carefully applied to enhance the strength of a material while preserving porosity (e.g. in filters or catalysts, where gas adsorption is a priority). During the sintering process, atomic diffusion drives powder surface elimination in different stages, starting at
4588-461: Is mostly used for its magnetostrictive properties, in which it changes shape when exposed to magnetic fields in a process called magnetization . Magnetic heat treatment is shown to improve the magnetostrictive properties of Terfenol-D at low compressive stress for certain ratios of Tb and Dy. Due to its material properties, Terfenol-D is excellent for use in the manufacturing of low frequency, high powered underwater acoustics . Its initial application
4712-399: Is needed. The solid crystals produced have a fine lamellar structure . The other two techniques, sintered powder compact and polymer matrix composites , are powder based. These techniques allow for intricate geometry and detail. However, the size is limited to 10mm in diameter and 100mm in length due to the molds used. The resulting microstructures of these powder based methods differ from
4836-400: Is performed by heating the base metal beyond its melting point and then dissolving the solutes into the molten liquid, which may be possible even if the melting point of the solute is far greater than that of the base. For example, in its liquid state, titanium is a very strong solvent capable of dissolving most metals and elements. In addition, it readily absorbs gases like oxygen and burns in
4960-471: Is prevented (forming martensite), most heat-treatable alloys are precipitation hardening alloys, that depend on the diffusion of alloying elements to achieve their strength. When heated to form a solution and then cooled quickly, these alloys become much softer than normal, during the diffusionless transformation, but then harden as they age. The solutes in these alloys will precipitate over time, forming intermetallic phases, which are difficult to discern from
5084-429: Is sometimes generated internally within the material, rather than via surface radiative heat transfer from an external heat source. Some materials fail to couple and others exhibit run-away behavior, so it is restricted in usefulness. A benefit of microwave sintering is faster heating for small loads, meaning less time is needed to reach the sintering temperature, less heating energy is required and there are improvements in
Terfenol-D - Misplaced Pages Continue
5208-429: Is still considered part of powder metallurgy) is liquid-state sintering in which at least one but not all elements are in a liquid state. Liquid-state sintering is required for making cemented carbide and tungsten carbide . Sintered bronze in particular is frequently used as a material for bearings , since its porosity allows lubricants to flow through it or remain captured within it. Sintered copper may be used as
5332-437: Is the density, E is Young's modulus and d is the maximum density of iron. Sintering is static when a metal powder under certain external conditions may exhibit coalescence, and yet reverts to its normal behavior when such conditions are removed. In most cases, the density of a collection of grains increases as material flows into voids, causing a decrease in overall volume. Mass movements that occur during sintering consist of
5456-410: Is the latest advancement in this field. In spark plasma sintering (SPS), external pressure and an electric field are applied simultaneously to enhance the densification of the metallic/ceramic powder compacts. However, after commercialization it was determined there is no plasma, so the proper name is spark sintering as coined by Lenel. The electric field driven densification supplements sintering with
5580-400: Is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction . Sintering happens as part of a manufacturing process used with metals , ceramics , plastics , and other materials. The atoms/molecules in the sintered material diffuse across the boundaries of the particles, fusing the particles together and creating
5704-677: Is the sintering of a powder compact (sometimes at very high temperatures, depending on the powder) without applied pressure. This avoids density variations in the final component, which occurs with more traditional hot pressing methods. The powder compact (if a ceramic) can be created by slip casting , injection moulding , and cold isostatic pressing . After presintering, the final green compact can be machined to its final shape before being sintered. Three different heating schedules can be performed with pressureless sintering: constant-rate of heating (CRH), rate-controlled sintering (RCS), and two-step sintering (TSS). The microstructure and grain size of
5828-548: Is used to make frangible shotgun shells called breaching rounds , as used by military and SWAT teams to quickly force entry into a locked room. These shotgun shells are designed to destroy door deadbolts, locks and hinges without risking lives by ricocheting or by flying on at lethal speed through the door. They work by destroying the object they hit and then dispersing into a relatively harmless powder. Sintered bronze and stainless steel are used as filter materials in applications requiring high temperature resistance while retaining
5952-560: The Wright brothers used a chromium-nickel steel to make the crankshaft for their airplane engine, while in 1908 Henry Ford began using vanadium steels for parts like crankshafts and valves in his Model T Ford , due to their higher strength and resistance to high temperatures. In 1912, the Krupp Ironworks in Germany developed a rust-resistant steel by adding 21% chromium and 7% nickel, producing
6076-611: The bloomery process , it produced very soft but ductile wrought iron . By 800 BC, iron-making technology had spread to Europe, arriving in Japan around 700 AD. Pig iron , a very hard but brittle alloy of iron and carbon, was being produced in China as early as 1200 BC, but did not arrive in Europe until the Middle Ages. Pig iron has a lower melting point than iron, and was used for making cast-iron . However, these metals found little practical use until
6200-408: The solid state. If the metals remain soluble when solid, the alloy forms a solid solution , becoming a homogeneous structure consisting of identical crystals, called a phase . If as the mixture cools the constituents become insoluble, they may separate to form two or more different types of crystals, creating a heterogeneous microstructure of different phases, some with more of one constituent than
6324-670: The Mediterranean, so it was often valued higher than gold. To make jewellery, cutlery, or other objects from tin, workers usually alloyed it with other metals to increase strength and hardness. These metals were typically lead , antimony , bismuth or copper. These solutes were sometimes added individually in varying amounts, or added together, making a wide variety of objects, ranging from practical items such as dishes, surgical tools, candlesticks or funnels, to decorative items like ear rings and hair clips. The earliest examples of pewter come from ancient Egypt, around 1450 BC. The use of pewter
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#17328588791946448-565: The Middle East, people began alloying copper with zinc to form brass. Ancient civilizations took into account the mixture and the various properties it produced, such as hardness , toughness and melting point, under various conditions of temperature and work hardening , developing much of the information contained in modern alloy phase diagrams . For example, arrowheads from the Chinese Qin dynasty (around 200 BC) were often constructed with
6572-453: The Terfenol-D throughout the life of the material is increased by using ET-Ryma. Terfenol-D has some minor drawbacks which stem from its material properties. Terfenol-D has low ductility and low fracture resistance. To solve this, Terfenol-D has been added to polymers and other metals to create composites. When added to polymers, the stiffness of the resulting composite is low. When composites of Terfenol-D with ductile metal binders are created,
6696-431: The ability to regenerate the filter element. For example, sintered stainless steel elements are employed for filtering steam in food and pharmaceutical applications, and sintered bronze in aircraft hydraulic systems. Sintering of powders containing precious metals such as silver and gold is used to make small jewelry items. Evaporative self-assembly of colloidal silver nanocubes into supercrystals has been shown to allow
6820-409: The additive should melt before any major sintering of the solid particulate network occurs, otherwise rearrangement of grains will not occur. Liquid phase sintering was successfully applied to improve grain growth of thin semiconductor layers from nanoparticle precursor films. These techniques employ electric currents to drive or enhance sintering. English engineer A. G. Bloxam registered in 1906
6944-516: The aerospace industry, to beryllium-copper alloys for non-sparking tools. An alloy is a mixture of chemical elements , which forms an impure substance (admixture) that retains the characteristics of a metal. An alloy is distinct from an impure metal in that, with an alloy, the added elements are well controlled to produce desirable properties, while impure metals such as wrought iron are less controlled, but are often considered useful. Alloys are made by mixing two or more elements, at least one of which
7068-414: The air, readily combines with most metals to form metal oxides ; especially at higher temperatures encountered during alloying. Great care is often taken during the alloying process to remove excess impurities, using fluxes , chemical additives, or other methods of extractive metallurgy . Alloying a metal is done by combining it with one or more other elements. The most common and oldest alloying process
7192-420: The alloy a unique and low melting point, and no liquid/solid slush transition. Alloying elements are added to a base metal, to induce hardness , toughness , ductility, or other desired properties. Most metals and alloys can be work hardened by creating defects in their crystal structure. These defects are created during plastic deformation by hammering, bending, extruding, et cetera, and are permanent unless
7316-429: The alloy. However, most alloys were not created until the 1900s, such as various aluminium, titanium , nickel , and magnesium alloys . Some modern superalloys , such as incoloy , inconel, and hastelloy , may consist of a multitude of different elements. An alloy is technically an impure metal, but when referring to alloys, the term impurities usually denotes undesirable elements. Such impurities are introduced from
7440-444: The atomic arrangement that forms the alloy. They can be further classified as homogeneous (consisting of a single phase), or heterogeneous (consisting of two or more phases) or intermetallic . An alloy may be a solid solution of metal elements (a single phase, where all metallic grains (crystals) are of the same composition) or a mixture of metallic phases (two or more solutions, forming a microstructure of different crystals within
7564-635: The base metal. Unlike steel, in which the solid solution separates into different crystal phases (carbide and ferrite), precipitation hardening alloys form different phases within the same crystal. These intermetallic alloys appear homogeneous in crystal structure, but tend to behave heterogeneously, becoming hard and somewhat brittle. In 1906, precipitation hardening alloys were discovered by Alfred Wilm . Precipitation hardening alloys, such as certain alloys of aluminium, titanium, and copper, are heat-treatable alloys that soften when quenched (cooled quickly), and then harden over time. Wilm had been searching for
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#17328588791947688-554: The base metals and alloying elements, but are removed during processing. For instance, sulfur is a common impurity in steel. Sulfur combines readily with iron to form iron sulfide , which is very brittle, creating weak spots in the steel. Lithium , sodium and calcium are common impurities in aluminium alloys, which can have adverse effects on the structural integrity of castings. Conversely, otherwise pure-metals that contain unwanted impurities are often called "impure metals" and are not usually referred to as alloys. Oxygen, present in
7812-426: The carbon atoms are said to be in solution in the iron, forming a particular single, homogeneous, crystalline phase called austenite . If the steel is cooled slowly, the carbon can diffuse out of the iron and it will gradually revert to its low temperature allotrope. During slow cooling, the carbon atoms will no longer be as soluble with the iron, and will be forced to precipitate out of solution, nucleating into
7936-427: The ceramic body will no longer break down in water; additional sintering can reduce the porosity of the ceramic, increase the bond area between ceramic particles, and increase the material strength. Industrial procedures to create ceramic objects via sintering of powders generally include: All the characteristic temperatures associated with phase transformation, glass transitions, and melting points, occurring during
8060-413: The ceramics may vary depending on the material and method used. Constant-rate of heating (CRH), also known as temperature-controlled sintering, consists of heating the green compact at a constant rate up to the sintering temperature. Experiments with zirconia have been performed to optimize the sintering temperature and sintering rate for CRH method. Results showed that the grain sizes were identical when
8184-502: The crystals internally. Some alloys, such as electrum —an alloy of silver and gold —occur naturally. Meteorites are sometimes made of naturally occurring alloys of iron and nickel , but are not native to the Earth. One of the first alloys made by humans was bronze, which is a mixture of the metals tin and copper. Bronze was an extremely useful alloy to the ancients, because it is much stronger and harder than either of its components. Steel
8308-427: The elements via solid-state diffusion . By adding another element to a metal, differences in the size of the atoms create internal stresses in the lattice of the metallic crystals; stresses that often enhance its properties. For example, the combination of carbon with iron produces steel, which is stronger than iron, its primary element. The electrical and thermal conductivity of alloys is usually lower than that of
8432-455: The examples which have been processed through the microwave sintering technique. Sintering in practice is the control of both densification and grain growth . Densification is the act of reducing porosity in a sample, thereby making it denser. Grain growth is the process of grain boundary motion and Ostwald ripening to increase the average grain size. Many properties ( mechanical strength , electrical breakdown strength, etc.) benefit from both
8556-410: The expense of their neighbours during sintering. This phenomenon, known as abnormal grain growth (AGG), results in a bimodal grain size distribution that has consequences for the mechanical, dielectric and thermal performance of the sintered material. For densification to occur at a quick pace it is essential to have (1) an amount of liquid phase that is large in size, (2) a near complete solubility of
8680-415: The firing process used in the manufacture of pottery and other ceramic objects. Sintering and vitrification (which requires higher temperatures) are the two main mechanisms behind the strength and stability of ceramics. Sintered ceramic objects are made from substances such as glass , alumina , zirconia , silica , magnesia , lime , beryllium oxide , and ferric oxide . Some ceramic raw materials have
8804-405: The first patent on sintering powders using direct current in vacuum . The primary purpose of his inventions was the industrial scale production of filaments for incandescent lamps by compacting tungsten or molybdenum particles. The applied current was particularly effective in reducing surface oxides that increased the emissivity of the filaments. In 1913, Weintraub and Rush patented
8928-466: The first airplane engine in 1903. During the time between 1865 and 1910, processes for extracting many other metals were discovered, such as chromium, vanadium, tungsten, iridium , cobalt , and molybdenum, and various alloys were developed. Prior to 1910, research mainly consisted of private individuals tinkering in their own laboratories. However, as the aircraft and automotive industries began growing, research into alloys became an industrial effort in
9052-416: The first century, and was introduced in Europe during the 1700s, where molten pig iron was stirred while exposed to the air, to remove the carbon by oxidation . In 1858, Henry Bessemer developed a process of steel-making by blowing hot air through liquid pig iron to reduce the carbon content. The Bessemer process led to the first large scale manufacture of steel. Steel is an alloy of iron and carbon, but
9176-499: The first stainless steel. Due to their high reactivity, most metals were not discovered until the 19th century. A method for extracting aluminium from bauxite was proposed by Humphry Davy in 1807, using an electric arc . Although his attempts were unsuccessful, by 1855 the first sales of pure aluminium reached the market. However, as extractive metallurgy was still in its infancy, most aluminium extraction-processes produced unintended alloys contaminated with other elements found in
9300-400: The form of a high-manganese pig-iron called spiegeleisen ), which helped remove impurities such as phosphorus and oxygen; a process adopted by Bessemer and still used in modern steels (albeit in concentrations low enough to still be considered carbon steel). Afterward, many people began experimenting with various alloys of steel without much success. However, in 1882, Robert Hadfield , being
9424-427: The formation of necks between powders to final elimination of small pores at the end of the process. The driving force for densification is the change in free energy from the decrease in surface area and lowering of the surface free energy by the replacement of solid-vapor interfaces. It forms new but lower-energy solid-solid interfaces with a net decrease in total free energy. On a microscopic scale, material transfer
9548-618: The high stresses that can be produced. The increase in use of Terfenol-D in transducers required new production techniques that increased production rates and quality because the original methods were unreliable and small scale. There are four methods that are used to produce Terfenol-D, which are free stand zone melting, modified Bridgman, sintered powder compact, and polymer matrix composites. The first two methods, free stand zone melting (FSZM) and modified Bridgman (MB), are capable of producing Terfenol-D that has high magnetostrictive properties and energy densities. However, FSZM cannot produce
9672-474: The interstices, but some of the iron atoms are substituted by nickel and chromium atoms. The use of alloys by humans started with the use of meteoric iron , a naturally occurring alloy of nickel and iron. It is the main constituent of iron meteorites . As no metallurgic processes were used to separate iron from nickel, the alloy was used as it was. Meteoric iron could be forged from a red heat to make objects such as tools, weapons, and nails. In many cultures it
9796-551: The introduction of crucible steel around 300 BC. These steels were of poor quality, and the introduction of pattern welding , around the 1st century AD, sought to balance the extreme properties of the alloys by laminating them, to create a tougher metal. Around 700 AD, the Japanese began folding bloomery-steel and cast-iron in alternating layers to increase the strength of their swords, using clay fluxes to remove slag and impurities. This method of Japanese swordsmithing produced one of
9920-405: The iron crystals. When rapidly cooled, a diffusionless (martensite) transformation occurs, in which the carbon atoms become trapped in solution. This causes the iron crystals to deform as the crystal structure tries to change to its low temperature state, leaving those crystals very hard but much less ductile (more brittle). While the high strength of steel results when diffusion and precipitation
10044-403: The latter portions of the process, boundary and lattice diffusion from the boundary become important. Control of temperature is very important to the sintering process, since grain-boundary diffusion and volume diffusion rely heavily upon temperature, particle size, particle distribution, material composition, and often other properties of the sintering environment itself. Sintering is part of
10168-415: The leftover powder is still pure, so it can be recycled. Particular disadvantages of the powder technology include: Plastic materials are formed by sintering for applications that require materials of specific porosity. Sintered plastic porous components are used in filtration and to control fluid and gas flows. Sintered plastics are used in applications requiring caustic fluid separation processes such as
10292-465: The liquid concentration must also create the required capillary pressure within range, else the process ceases. The vitrification rate is dependent upon the pore size, the viscosity and amount of liquid phase present leading to the viscosity of the overall composition, and the surface tension. Temperature dependence for densification controls the process because at higher temperatures viscosity decreases and increases liquid content. Therefore, when changes to
10416-450: The metal is recrystallized . Otherwise, some alloys can also have their properties altered by heat treatment . Nearly all metals can be softened by annealing , which recrystallizes the alloy and repairs the defects, but not as many can be hardened by controlled heating and cooling. Many alloys of aluminium, copper, magnesium , titanium, and nickel can be strengthened to some degree by some method of heat treatment, but few respond to this to
10540-485: The metal). Examples of alloys include red gold ( gold and copper ), white gold (gold and silver ), sterling silver (silver and copper), steel or silicon steel ( iron with non-metallic carbon or silicon respectively), solder , brass , pewter , duralumin , bronze , and amalgams . Alloys are used in a wide variety of applications, from the steel alloys, used in everything from buildings to automobiles to surgical tools, to exotic titanium alloys used in
10664-408: The neck and the surface of the particle. This energy creates a transfer of material through the fastest means possible; if transfer were to take place from the particle volume or the grain boundary between particles, particle count would decrease and pores would be destroyed. Pore elimination is fastest in samples with many pores of uniform size because the boundary diffusion distance is smallest. during
10788-429: The nibs in whiteboard markers, inhaler filters, and vents for caps and liners on packaging materials. Sintered ultra high molecular weight polyethylene materials are used as ski and snowboard base materials. The porous texture allows wax to be retained within the structure of the base material, thus providing a more durable wax coating. For materials that are difficult to sinter, a process called liquid phase sintering
10912-455: The ore; the most abundant of which was copper. These aluminium-copper alloys (at the time termed "aluminum bronze") preceded pure aluminium, offering greater strength and hardness over the soft, pure metal, and to a slight degree were found to be heat treatable. However, due to their softness and limited hardenability these alloys found little practical use, and were more of a novelty, until the Wright brothers used an aluminium alloy to construct
11036-418: The other constituent. This is called a substitutional alloy . Examples of substitutional alloys include bronze and brass, in which some of the copper atoms are substituted with either tin or zinc atoms respectively. In the case of the interstitial mechanism, one atom is usually much smaller than the other and can not successfully substitute for the other type of atom in the crystals of the base metal. Instead,
11160-416: The other. However, in other alloys, the insoluble elements may not separate until after crystallization occurs. If cooled very quickly, they first crystallize as a homogeneous phase, but they are supersaturated with the secondary constituents. As time passes, the atoms of these supersaturated alloys can separate from the crystal lattice, becoming more stable, and forming a second phase that serves to reinforce
11284-436: The particle undergoes grain-growth and grain-shape changes occurs. Shrinkage would result when the liquid slips between particles and increases pressure at points of contact causing the material to move away from the contact areas, forcing particle centers to draw near each other. The sintering of liquid-phase materials involves a fine-grained solid phase to create the needed capillary pressures proportional to its diameter, and
11408-400: The phenomenon was not provided until 1919, duralumin was one of the first "age hardening" alloys used, becoming the primary building material for the first Zeppelins , and was soon followed by many others. Because they often exhibit a combination of high strength and low weight, these alloys became widely used in many forms of industry, including the construction of modern aircraft . When
11532-464: The porosity of the material. Sintering is performed at high temperature. Additionally, a second and/or third external force (such as pressure, electric current) could be used. A commonly used second external force is pressure. Sintering performed by only heating is generally termed "pressureless sintering", which is possible with graded metal-ceramic composites, utilising a nanoparticle sintering aid and bulk molding technology. A variant used for 3D shapes
11656-441: The presence of nitrogen. This increases the chance of contamination from any contacting surface, and so must be melted in vacuum induction-heating and special, water-cooled, copper crucibles . However, some metals and solutes, such as iron and carbon, have very high melting-points and were impossible for ancient people to melt. Thus, alloying (in particular, interstitial alloying) may also be performed with one or more constituents in
11780-428: The product properties. A failing of microwave sintering is that it generally sinters only one compact at a time, so overall productivity turns out to be poor except for situations involving one of a kind sintering, such as for artists. As microwaves can only penetrate a short distance in materials with a high conductivity and a high permeability , microwave sintering requires the sample to be delivered in powders with
11904-636: The pure elements such as increased strength or hardness. In some cases, an alloy may reduce the overall cost of the material while preserving important properties. In other cases, the mixture imparts synergistic properties such as corrosion resistance or mechanical strength. In an alloy, the atoms are joined by metallic bonding rather than by covalent bonds typically found in chemical compounds. The alloy constituents are usually measured by mass percentage for practical applications, and in atomic fraction for basic science studies. Alloys are usually classified as substitutional or interstitial alloys , depending on
12028-415: The pure metals. The physical properties, such as density , reactivity , Young's modulus of an alloy may not differ greatly from those of its base element, but engineering properties such as tensile strength , ductility, and shear strength may be substantially different from those of the constituent materials. This is sometimes a result of the sizes of the atoms in the alloy, because larger atoms exert
12152-443: The purest steel-alloys of the ancient world. While the use of iron started to become more widespread around 1200 BC, mainly because of interruptions in the trade routes for tin, the metal was much softer than bronze. However, very small amounts of steel, (an alloy of iron and around 1% carbon), was always a byproduct of the bloomery process. The ability to modify the hardness of steel by heat treatment had been known since 1100 BC, and
12276-534: The range of 0.1 to 1 micrometres develop pressures in the range of 175 pounds per square inch (1,210 kPa) to 1,750 pounds per square inch (12,100 kPa) for silicate liquids and in the range of 975 pounds per square inch (6,720 kPa) to 9,750 pounds per square inch (67,200 kPa) for a metal such as liquid cobalt. Densification requires constant capillary pressure where just solution-precipitation material transfer would not produce densification. For further densification, additional particle movement while
12400-415: The rare material was valued for the manufacture of tools and weapons. Because the ancients could not produce temperatures high enough to melt iron fully, the production of steel in decent quantities did not occur until the introduction of blister steel during the Middle Ages. This method introduced carbon by heating wrought iron in charcoal for long periods of time, but the absorption of carbon in this manner
12524-407: The reduction of total porosity by repacking, followed by material transport due to evaporation and condensation from diffusion . In the final stages, metal atoms move along crystal boundaries to the walls of internal pores, redistributing mass from the internal bulk of the object and smoothing pore walls. Surface tension is the driving force for this movement. A special form of sintering (which
12648-612: The resulting aluminium alloy will have much greater strength . Adding a small amount of non-metallic carbon to iron trades its great ductility for the greater strength of an alloy called steel. Due to its very-high strength, but still substantial toughness , and its ability to be greatly altered by heat treatment , steel is one of the most useful and common alloys in modern use. By adding chromium to steel, its resistance to corrosion can be enhanced, creating stainless steel , while adding silicon will alter its electrical characteristics, producing silicon steel . Like oil and water,
12772-412: The resulting material has increased stiffness and ductility with reduced magnetostrictive properties. These metal composites may be formed by explosion compaction . In a study done on processing Terfenol-D alloys, the resulting alloys created using copper and Terfenol-D had increased strength and hardness values, which supports the theory that the composites of ductile metal binders and Terfenol-D result in
12896-428: The same degree as does steel. The base metal iron of the iron-carbon alloy known as steel, undergoes a change in the arrangement ( allotropy ) of the atoms of its crystal matrix at a certain temperature (usually between 820 °C (1,500 °F) and 870 °C (1,600 °F), depending on carbon content). This allows the smaller carbon atoms to enter the interstices of the iron crystal. When this diffusion happens,
13020-720: The samples were sintered to the same density, proving that grain size is a function of specimen density rather than CRH temperature mode. In rate-controlled sintering (RCS), the densification rate in the open-porosity phase is lower than in the CRH method. By definition, the relative density, ρ rel , in the open-porosity phase is lower than 90%. Although this should prevent separation of pores from grain boundaries, it has been proven statistically that RCS did not produce smaller grain sizes than CRH for alumina, zirconia, and ceria samples. Two-step sintering (TSS) uses two different sintering temperatures. The first sintering temperature should guarantee
13144-521: The sintering community. Using a direct current (DC) pulse as the electric current, spark plasma, spark impact pressure, joule heating, and an electrical field diffusion effect would be created. By modifying the graphite die design and its assembly, it is possible to perform pressureless sintering in spark plasma sintering facility. This modified die design setup is reported to synergize the advantages of both conventional pressureless sintering and spark plasma sintering techniques. Electro sinter forging
13268-502: The sintering of electrical joints at temperatures lower than 200 °C. Particular advantages of the powder technology include: The literature contains many references on sintering dissimilar materials to produce solid/solid-phase compounds or solid/melt mixtures at the processing stage. Almost any substance can be obtained in powder form, through either chemical, mechanical or physical processes, so basically any material can be obtained through sintering. When pure elements are sintered,
13392-400: The smaller atoms become trapped in the interstitial sites between the atoms of the crystal matrix. This is referred to as an interstitial alloy . Steel is an example of an interstitial alloy, because the very small carbon atoms fit into interstices of the iron matrix. Stainless steel is an example of a combination of interstitial and substitutional alloys, because the carbon atoms fit into
13516-476: The solid crystal ones because they do not have a lamellar structure and have a lower density . However, all methods have similar magnetostrictive properties. Due to size restriction, MB is the best process to produce Terfenol-D, however it is a labor-intensive method. A newer process like MB is ET-Ryma crystal growth (ECG) that results in larger diameter Terfenol-D crystals and increased magnetostrictive performance. The reliability of magnetostrictive properties of
13640-425: The solid in the liquid, and (3) wetting of the solid by the liquid. The power behind the densification is derived from the capillary pressure of the liquid phase located between the fine solid particles. When the liquid phase wets the solid particles, each space between the particles becomes a capillary in which a substantial capillary pressure is developed. For submicrometre particle sizes, capillaries with diameters in
13764-456: The term alloy steel usually only refers to steels that contain other elements— like vanadium , molybdenum , or cobalt —in amounts sufficient to alter the properties of the base steel. Since ancient times, when steel was used primarily for tools and weapons, the methods of producing and working the metal were often closely guarded secrets. Even long after the Age of Enlightenment , the steel industry
13888-404: The ware being sintered, surface damage and contamination can be reduced while maximizing furnace loading. Most, if not all, metals can be sintered. This applies especially to pure metals produced in vacuum which suffer no surface contamination. Sintering under atmospheric pressure requires the use of a protective gas, quite often endothermic gas . Sintering, with subsequent reworking, can produce
14012-410: The years following 1910, as new magnesium alloys were developed for pistons and wheels in cars, and pot metal for levers and knobs, and aluminium alloys developed for airframes and aircraft skins were put into use. The Doehler Die Casting Co. of Toledo, Ohio were known for the production of Brastil , a high tensile corrosion resistant bronze alloy. Sintered Sintering or frittage
14136-517: Was 2000 °C. In the United States, sintering was first patented by Duval d'Adrian in 1922. His three-step process aimed at producing heat-resistant blocks from such oxide materials as zirconia , thoria or tantalia . The steps were: (i) molding the powder; (ii) annealing it at about 2500 °C to make it conducting; (iii) applying current-pressure sintering as in the method by Weintraub and Rush. Sintering that uses an arc produced via
14260-824: Was another common alloy. However, in ancient times, it could only be created as an accidental byproduct from the heating of iron ore in fires ( smelting ) during the manufacture of iron. Other ancient alloys include pewter , brass and pig iron . In the modern age, steel can be created in many forms. Carbon steel can be made by varying only the carbon content, producing soft alloys like mild steel or hard alloys like spring steel . Alloy steels can be made by adding other elements, such as chromium , molybdenum , vanadium or nickel , resulting in alloys such as high-speed steel or tool steel . Small amounts of manganese are usually alloyed with most modern steels because of its ability to remove unwanted impurities, like phosphorus , sulfur and oxygen , which can have detrimental effects on
14384-422: Was applied as a paste and then heated until the mercury vaporized, leaving the gold, silver, or tin behind. Mercury was often used in mining, to extract precious metals like gold and silver from their ores. Many ancient civilizations alloyed metals for purely aesthetic purposes. In ancient Egypt and Mycenae , gold was often alloyed with copper to produce red-gold, or iron to produce a bright burgundy-gold. Gold
14508-535: Was commissioned by the King of Syracuse to find a way to check the purity of the gold in a crown, leading to the famous bath-house shouting of "Eureka!" upon the discovery of Archimedes' principle . The term pewter covers a variety of alloys consisting primarily of tin. As a pure metal, tin is much too soft to use for most practical purposes. However, during the Bronze Age , tin was a rare metal in many parts of Europe and
14632-695: Was in naval sonar systems. It sees application in magnetomechanical sensors, actuators , and acoustic and ultrasonic transducers due to its high energy density and large bandwidth capabilities, e.g. in the SoundBug device (its first commercial application by FeONIC ). Its strain is also larger than that of another normally used material ( PZT8 ), which allows Terfenol-D transducers to reach greater depths for ocean explorations than past transducers. Its low Young's modulus brings some complications due to compression at large depths, which are overcome in transducer designs that may reach 1000 ft in depth and only lose
14756-416: Was not generally considered an alloy until the decades between 1930 and 1970 (primarily due to the work of scientists like William Chandler Roberts-Austen , Adolf Martens , and Edgar Bain ), so "alloy steel" became the popular term for ternary and quaternary steel-alloys. After Benjamin Huntsman developed his crucible steel in 1740, he began experimenting with the addition of elements like manganese (in
14880-450: Was often found alloyed with silver or other metals to produce various types of colored gold . These metals were also used to strengthen each other, for more practical purposes. Copper was often added to silver to make sterling silver , increasing its strength for use in dishes, silverware, and other practical items. Quite often, precious metals were alloyed with less valuable substances as a means to deceive buyers. Around 250 BC, Archimedes
15004-588: Was shaped by cold hammering into knives and arrowheads. They were often used as anvils. Meteoric iron was very rare and valuable, and difficult for ancient people to work . Iron is usually found as iron ore on Earth, except for one deposit of native iron in Greenland , which was used by the Inuit . Native copper, however, was found worldwide, along with silver, gold, and platinum , which were also used to make tools, jewelry, and other objects since Neolithic times. Copper
15128-492: Was the hardest of these metals, and the most widely distributed. It became one of the most important metals to the ancients. Around 10,000 years ago in the highlands of Anatolia (Turkey), humans learned to smelt metals such as copper and tin from ore . Around 2500 BC, people began alloying the two metals to form bronze, which was much harder than its ingredients. Tin was rare, however, being found mostly in Great Britain. In
15252-557: Was very competitive and manufacturers went through great lengths to keep their processes confidential, resisting any attempts to scientifically analyze the material for fear it would reveal their methods. For example, the people of Sheffield , a center of steel production in England, were known to routinely bar visitors and tourists from entering town to deter industrial espionage . Thus, almost no metallurgical information existed about steel until 1860. Because of this lack of understanding, steel
15376-556: Was widespread across Europe, from France to Norway and Britain (where most of the ancient tin was mined) to the Near East. The alloy was also used in China and the Far East, arriving in Japan around 800 AD, where it was used for making objects like ceremonial vessels, tea canisters, or chalices used in shinto shrines. The first known smelting of iron began in Anatolia , around 1800 BC. Called
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