Nickel alloys high-temperature corrosion


There are several types of slurry or powdered paint methods for coating high temperature processing equipment in the chemical and petroleum industry, and for turbine blades. These last are used for aircraft and power generation (qv) and are exposed to high temperature corrosive gases. The process consists of cleaning, sand blasting, and acid pickling parts, then applying a slurry by dipping or spraying. The parts are dried at 120°C and fired to 930—1200°C. The coating and blasting slurries are made of an aluminum source, eg, pure aluminum powder or 5—12% silicon—aluminum alloy a vehicle, water or an organic solvent a clay or gum binder and an inert material such as alumina or a ceramic oxide. The thickness of the coating depends mosdy on the substrate and the firing temperature, with a lesser effect from the time at temperature. For chromium stainless steels the thickness of the diffusion layer increases with the temperature. Nickel and cobalt alloys decrease the diffusion rate of aluminum in alloys owing to the stabiUty of the intermetaUic compounds NiAl, Ni Al, CoAl, and Co Al and the low soHd solubiUty of aluminum in nickel and cobalt. This limits the attainable thickness of the diffusion layer in nickel and cobalt alloy steels.  [c.138]

The contact ends of printed circuit boards are copper. Alloys of nickel and iron are used as substrates in hermetic connectors in which glass (qv) is the dielectric material. Terminals are fabricated from brass or copper from nickel, for high temperature appHcations from aluminum, when aluminum conductors are used and from steel when high strength is required. Because steel has poor corrosion resistance, it is always plated using a protective metal, such as tin (see Tin and tin alloys). Other substrates can be unplated when high contact normal forces, usually more than 5 N, are available to mechanically dismpt insulating oxide films on the surfaces and thereby assure metaUic contact (see Corrosion and corrosion control).  [c.30]

Stainless steel alloys show exceUent corrosion resistance to HCl gas up to a temperature of 400°C. However, these are normally not recommended for process equipment owing to stress corrosion cracking during periods of cooling and shut down. The corrosion rate of Monel is similar to that of mild steel. Pure (99.6%) nickel and high nickel alloys such as Inconel 600 can be used for operation at temperatures up to 525°C where the corrosion rate is reported to be about 0.08 cm/yr (see Nickel and nickel alloys).  [c.446]

Metals. Aircraft and space vehicles, turbine generators, and other such appHcations require high strength at high temperature along with exceUent oxidation resistance. Superalloys, ie, complex nickel and cobalt-based alloys, and refractory metals, eg, niobium, tungsten, molybdenum, tantalum, and their alloys, are used for appHcations at temperatures above 1000°C. In many cases the coatings must be resistant both to oxidation and to hot corrosion by sulfidation from sulfur-bearing gases. Testing must be done to assure compatibiHty between the coatings and the substrate and to avoid undesirable soHd-state reactions and interdiffusion, which can produce voids, cracks, and weak layers. Refractory metal coatings must be sufficiently ductile for the anticipated service and environmental pressures and stresses. AH coatings must resist thermal cycling and mechanical forces without cracking (see also Refractory coatings) (22,40).  [c.136]

Nickel—Copper. In the soHd state, nickel and copper form a continuous soHd solution. The nickel-rich, nickel—copper alloys are characterized by a good compromise of strength and ductihty and are resistant to corrosion and stress corrosion ia many environments, ia particular water and seawater, nonoxidizing acids, neutral and alkaline salts, and alkaUes. These alloys are weldable and are characterized by elevated and high temperature mechanical properties for certain appHcations. The copper content ia these alloys also easure improved thermal coaductivity for heat exchange. MONEL alloy 400 is a typical nickel-rich, nickel—copper alloy ia which the nickel content is ca 66 wt %. MONEL alloy K-500 is essentially alloy 400 with small additions of aluminum and titanium. Aging of alloy K-500 results in very fine y -precipitates and increased strength (see also Copper alloys).  [c.6]

Nickel-Base Superalloys. Superalloys, which are critical to gas-turbine engines because of their high temperature strength and superior creep and stress mpture-resistance, basically are nickel—chromium alloyed with a host of other elements. The alloying elements include the refractory metals tungsten, molybdenum, or niobium for additional soHd-solution strengthening, especially at higher temperatures and aluminum in appropriate amounts for the precipitation of for coherent particle strengthening (see Refractories). Titanium is added to provide stronger y, and niobium reacts with nickel in the sohd state to precipitate the y -phase y is the main strengthening precipitate in the 718-type alloys. Cobalt, generally present in many superalloys in large (>10 wt%) amounts, enhances strength, oxidation, and hot-corrosion resistance which is also provided by the chromium in the alloy. Small excess amounts of carbon usually are present in superalloys for intentional carbide precipitation at grain-boundaries which, as discrete and equiaxed particles, can provide obstacles for grain-boundary sliding and motion, thus suppressing creep at high temperatures. Small or trace amounts of elements, eg, zirconium, boron, and hafnium, may be present and these enhance grain-boundary strength and improve ductiUty. The strength and elevated-temperature properties of a superalloy are dependent on the volume fraction of the fine y -precipitates, which can be increased to ca 60 wt %, depending on the aluminum and titanium content. Besides precipitation control at the grain boundaries, improved heat resistance can result from either the elimination of grain boundaries or through the growth of aligned grains with minimum grain boundaries perpendicular to the principal appHed stress direction, eg, in turbine-blade apphcations.  [c.7]

Nickel sulfide, NiS, can be prepared by the fusion of nickel powder with molten sulfur or by precipitation usiag hydrogen sulfide treatment of a buffered solution of a nickel(II) salt. The behavior of nickel sulfides ia the pure state and ia mixtures with other sulfides is of iaterest ia the recovery of nickel from ores, ia the high temperature sulfide corrosion of nickel alloys, and ia the behavior of nickel-containing catalysts.  [c.11]

As for other tests that involve appHcation of Hquids or chemical tracers, such test materials must be removed from the test surfaces and discontinuities after use to avoid later corrosion or damage to the base materials. In aerospace and nuclear test appHcations involving sensitive materials such as austenitic stainless steels, the tracers and removers must be formulated with a minimum of halogen or sulfur impurities so that residues that might be retained within discontinuities or crevices in assembled components do not contribute to later stress corrosion cracking or other deterioration. This precaution is essential in the case of various high temperature and exotic alloys such as nickel-base alloys, austenitic stainless steels, and titanium and its alloys (see High temperature alloys Nickel and nickel alloys Steel). Oil-base tracers and other Hquids that might react with Hquid or gaseous oxygen (qv) should be avoided when testing stmctures to be used for oxygen storage.  [c.124]

Pipe materials are metaUic, nonmetaUic, or lined metallic. The most common material, carbon steel, is generally the least expensive. In many cases, however, it caimot be used because of the corrosivity or the temperature of the flowing medium. When temperature, rather than corrosivity, is the limiting factor, the lowest grade of steel (qv) that provides the required service life at the design temperature is used. Thus, as the design temperature increases, carbon steel is replaced progressively by carbon—molybdenum steels, chromium—molybdenum steels, and finally, higher alloyed chromium—nickel steels and other high temperature alloys (qv). When the design temperature and pressure require expensive alloy piping, the economics of a higher strength material having a thinner wall should be compared with that of a lower strength material having a thicker wall. When corrosivity of the fluid is of prime importance, because corrosion rate is usually temperature-dependent, perceptive process design and plant layout (qv) can result in significant cost savings hy minimizing the amount of expensive piping required.  [c.54]

Equipment Materials and Abrasion Resistance. Stainless steel, especially Type 316, is the constmction material of choice and can resist a variety of corrosive conditions and temperatures. Carbon steels are occasionally used. Rusting may, however, cause time-consuming maintenance and can damage mating locating surfaces, which increases the vibration and noise level. Titanium, HasteUoy, or high nickel alloys are used in special instances, at a considerable increase in capital cost.  [c.405]

Because of its low capture cross section for fast neutrons as weU as its resistance to corrosion by liquid sodium and its good high temperature creep strength, vanadium alloys are receiving considerable attention as a fuel-element cladding for fast-breeder reactors. Vanadium is a component in several permanent-magnet alloys containing cobalt, iron, sometimes nickel, and vanadium. The vanadium content in the most common of these alloys is 2—13 wt % (see Magnetic materials). Vanadium and several vanadium compounds are also used as catalysts in certain chemical and petrochemical reactions.  [c.387]

Nickel Alloys. Nickel-based alloys have great technological importance in the development of high strength, high temperature alloys (qv), in part because of the occurrence of unique intermetallic phases (31). However, the precipitation of certain intermetallic phases can decrease the resistance to corrosion because this can deplete the matrix of alloying elements. For example, the nickel-base alloys containing chromium for passivity, which are of great importance to the chemical industry, can become sensitized in a manner similar to the austenitic stainless steels and thus become vulnerable to intergranular corrosion.  [c.280]

Type 316 (18-8-3 Cr-Ni-Mo) has, by far, the highest resistance to naphthenic acids of any of the 18-8 Cr-Ni alloys and provides adequate protection under most circumstances. It provides excellent protection against both high temperature sulfur corrosion and naphthenic acids whereas the 18-8 Cr-Ni alloys without molybdenum are not adequate for both. The high-nickel alloys, except those containing copper (such as monel) are also highly resistant but have little advantage in this respect over Type 316. Copper and all copper alloys, including aluminum-copper alloys such as Duralumin (5-Cu), are unsuitable.  [c.264]

Flexible metallic media are especially suitable for handling corrosive liquors and for high-temperature filtration. They have good durability and are inert to physical changes. Metallic media are fabricated in the form of screens, wire windings, or woven fabrics of steel, copper, bronze, nickel and different alloys. Perforated sheets and screens are used for coarse separation, as supports for filter cloths or as  [c.129]

Let us now consider the basic materials used in the fabrication of chemical equipment from the point of view of a designer. The principal construction materials for welded, forged and cast chemical vessels are cast irons, gray cast iron, white cast iron, malleable cast irons, nodular cast iron, austenitic cast iron, high-silicon cast iron, low-carbon steels (mild steel), high-carbon steels, low-carbon/low-alloy steels, high-carbon/low-alloy steels, high-alloy steels (corrosion-resistant, heat resistant and high-temperature), nickel and nickel alloys. Each of these is described below.  [c.53]

Nickel alloys have two main properties good resistance to corrosion and high-temperature strength. There are alloys for medium-and low-temperature applications and for high-temperature conditions in which creep resistance is of main importance [24].  [c.74]

Steel is the most common constructional material, and is used wherever corrosion rates are acceptable and product contamination by iron pick-up is not important. For processes at low or high pH, where iron pick-up must be avoided or where corrosive species such as dissolved gases are present, stainless steels are often employed. Stainless steels suffer various forms of corrosion, as described in Section 53.5.2. As the corrosivity of the environment increases, the more alloyed grades of stainless steel can be selected. At temperatures in excess of 60°C, in the presence of chloride ions, stress corrosion cracking presents the most serious threat to austenitic stainless steels. Duplex stainless steels, ferritic stainless steels and nickel alloys are very resistant to this form of attack. For more corrosive environments, titanium and ultimately nickel-molybdenum alloys are used.  [c.898]

Intergranular corrosion of nickel and its alloys is nearly always associated with grain boundary precipitates. In certain commercial grades of nickel, which contain carbon as an impurity, lengthy exposure to high temperatures may result in the formation of a grain boundary film of graphite which in some circumstances renders the material susceptible to intergranular corrosion on subsequent exposure in an environment to which the material is otherwise well suited, viz. caustic alkalis with nickel this form of corrosion may be intensified by stress in the metal. For these reasons, the low-carbon grade of commercial nickel. Nickel 201, is, in practice, preferred where this form of attack is a possibility. With material of higher carbon content the possibility of intergranular corrosion developing to a serious extent may be minimised by applying a stress-relieving heat treatment after fabrication. The presence of other elements in nickel, notably sulphur, may also render the metal liable to intergranular penetration and embrittlement.  [c.783]

Nickel and its alloys are usually resistant to dry gases, including NHj, SOj, Fj, CI2, HCl and HF even at high temperatures, and are often the preferred materials for handling such gases. Nickel and Alloy 600 are used in service at elevated temperatures with dry Clj, HCl, Fj and HF. Alloy 600 and certain other nickel alloys are resistant to dry SO2 and dry NHj. When moist or under dew-point conditions these gases are in many instances appreciably more corrosive towards nickel and most nickel alloys, with some exceptions. Ni-Cr-Mo alloys do, however, possess good resistance to condensates containing SO2 and Cl at temperatures well in excess of 100°C, and also to solutions containing NHj and its salts. Ni-Cr-Mo alloys are among the most resistant metallic materials to moist halogens.  [c.791]

Nickel and Ni-Cr alloys are among the most resistant metallic materials to corrosion and oxidation at high temperatures and are widely used to resist corrosion by gases and molten salts at elevated temperatures (see Sections 7.1 and 7.5).  [c.795]

Gold-copper alloys exhibit exceptional resistance to corrosion, and have very low vapour pressures. Gold-nickel alloys, with similar low vapour pressure, are somewhat stronger than gold-copper at high temperatures. Both series of alloys are widely employed in vacuum systems.  [c.937]

Stress This can be of importance in two ways. An effect analogous to aqueous stress corrosion, in which attack is accelerated at grain boundaries, may be produced this is particularly noticeable and very well known in cases of attack by other molten metals. Stress may also accelerate general attack when the metal is suffering progressive deformation, as in creep or fatigue the mechanical properties of the metal and of the scale may differ sufficiently from one another for the scale to crack periodically as deformation of the metal increases, and thus produce corresponding increases in the rate of corrosive attack. Gulbransen and Andrew have reported effects of this nature on the rate of oxidation of nickel-chromium alloys, although the test specimens were cooled to normal temperature for the strain to be imposed. It was shown that the magnitude of the change in the rate of oxidation depended critically on the silicon content of the alloy. Abnormal oxidation effects during high-temperature fatigue tests on Nimonic alloys have been described by Betteridge, accelerated oxidation occurring at the point of fatigue cracking.  [c.952]

Power sources for vehicles in space similarly must incorporate superalloys into their design. For example, high temperature alloys have been used extensively in the NASA space shutde main engine. A high pressure oxidizer turbopump, driven by a hot gas turbine having inlet temperature of up to 850°C, dehvers Hquid oxygen at a rate of over 450 kg/s. The turbine is constmcted primarily of nickel and cobalt-base alloys, with highly stressed parts cooled by hquid hydrogen. MarM-246 (Hf-modifted) nozzles, Waspaloy turbine disks and shaft, and Inconel 718 high pressure main pump impeller are typical superalloy parts. Nickel-base alloys of the HasteUoy series are utilized for their resistance to extreme corrosion environments such as nitric and hydrofluoric acids.  [c.123]

Cobalt-Base Superalloys. Cobalt-base superaHoys are used principally where operating metal temperatures range from 650 to 1000°C and stresses are relatively low. Strengthened primarily by carbide precipitation and soHd-solution effects, these alloys are widely used as forgings and castings for nozzle vanes in gas turbine engines, because of good thermal shock and hot corrosion resistance, and in sheet metal assembHes, such as combustion chamber liners, tail pipes, and afterburners. However, rotating parts such as turbine blades and disks, are more likely to be made from nickel-base alloys, because of the latter s superior strength at low and intermediate temperatures. Some of the industrial uses of cobalt-base alloys include grates for heat-treating furnaces, quenching baskets, pouring fuimels for molten copper, skids for slab reheating furnaces, and other foundry and metalworking operations where the prime requisites are resistance to oxidation at elevated temperatures, comparabiHty with slags, and resistance to thermal and mechanical shocks. In addition, the wrought grades are used for high temperature springs and fasteners. Cast alloys where carbon exceeds 1 wt % and chromium contents are in the range 26—32% are used for cutting tools and wear-resistant facings, where high hardness and abrasion resistance at elevated temperatures are the prime requirements (see Tool materials). Cobalt alloys also are used extensively in valves,pumps (qv), nozzles, and mixers for the chemical process industries. These alloys generally also contain significant amounts of tungsten, iron, nickel, and sometimes molybdenum. A prominent example is StelHte 6, which has 30% Cr, 2.5% Ni, 3% Fe, 1.5% Mo, 4% W, 1.4% Mn, and 1% C.  [c.124]

Nickel—Iron—Chromium. A large number of industrially important materials are derived from nickel—iron—chromium alloys. These alloys are within the broad austenitic, gamma-phase field of the ternary Ni—Fe—Cr phase diagram and are noted for good resistance to corrosion and oxidation and good elevated temperature strength (see High temperature alloys). Examples are the INCONEL alloys, which are based on the INCONEL alloy 600 composition. AHoy 600 is a soHd solution alloy with good strength and toughness from cryogenic to elevated temperatures and good oxidation and corrosion resistance in many media. In addition, the alloy is easily fabricated and joined. Many modifications of alloy 600 have been made to produce other alloys with different characteristics. Eor example, INCONEL alloy 601 [12631 -43-5] (UNS N06601) contains aluminum for improved high temperature oxidation resistance, INCONEL alloy 625 contains molybdenum and niobium in soHd solution for better strength, and INCONEL alloy 690 [54385-90-9] (UNS N06690) with further additions of chromium was developed for use in the nuclear industry and is particularly noted for its resistance to corrosion by high purity water (see Nuclear reactors).  [c.7]

The INCOLOY alloys exemplify another class of nickel—iron—chromium alloys. INCOLOY alloy 800 is resistant to hot corrosion, oxidation, and carburization and has good elevated-temperature strength. Modifications of alloy 800 impart different strength or corrosion-resistance characteristics. Eor example, INCOLOY alloy 801 [12605-97-9] (UNS N08801) contains more titanium, which, with appropriate heat treatments, can age-harden the alloy and provide increased resistance to intergranular corrosion INCOLOY alloy 802 [51836-04-5] (UNS N08802) contains more carbon which provides improved high temperature strength through carbide strengthening. INCOLOY alloy 825 [12766-43-7] (UNS N08825) and HASTELLOY alloy G-3 contain molybdenum, copper, and other additions and are exceptionally resistant to attack by aggressive corrosive environments.  [c.7]

The corrosion- and heat-resistant alloys, eg, alloys 600 and 800, are used extensively in heat-treating equipment, nuclear and fossil-fuel steam generators, heater-element sheathing and thermocouple tubes, and in chemical and food-processing equipment. Alloys 625 and 825 are used in chemical processing, pollution control, marine and pickling equipment, ash-pit seals, aircraft turbines and thmst reversers, and radiation waste-handling systems. The age-hardened INCONEL and INCOLOY alloys are used in gas turbines, high temperature springs and bolts, nuclear reactors, rocket motors, spacecraft, and hot-forming tools. There are also nickel—iron—chromium alloys used as welding electrode and filler metals.  [c.7]

Oxide-Dispersion-Strengthened Alloys. Through mechanical alloying and other powder-metaHurgical techniques, highly hot-oxidation and corrosion-resistant nickel—chromium matrices are strengthened by very fine dispersions of somewhat chemically inert oxide particles to produce alloys such as INCONEL alloy MA754. These oxide dispersions replace y as the main strengthening agent and provide strength benefits close to the melting temperature. Gamma-prime precipitation strengthening usually begins to decline above 800°C. The oxide-dispersion-strengthened (ODS) nickel-, iron-, and cobalt-base alloys are used mainly in bar and sheet forms in gas turbine vanes in combustion chambers and as exhaust hardware in very high temperature apphcations.  [c.7]

The highest melting refractory metals are tungsten, tantalum, molybdenum, and niobium, although titanium, hafnium, zirconium, chromium, vanadium, platinum, rhodium, mthenium, iridium, osmium, and rhenium may be included (see Refractories). Many of these metals do not resist air oxidation. Hence, very few, if any, are used in elemental form for high temperature protection. However, bulk alloys based on nickel, iron, and cobalt and alloying elements such as chromium, titanium, aluminum, vanadium, tantalum, molybdenum, siHcon, and tungsten are used extensively in high temperature service. Some modem high temperature oxidation- and corrosion-resistant coatings have compositions similar to the high temperature bulk alloys (see High TEMPERATURE alloys) and are appHed by thermal spraying, evaporation, or sputtering. The protection mechanism for these high temperature alloy coatings is based on adherent impervious surface films of AI2O2, Si02, Cr02, or a spinel-type material that grow upon high temperature exposure to air.  [c.40]

Use of metals in hot steam is limited by oxidation rate, mechanical strength, and creep resistance (see CORROSION AND CORROSION CONTROL). Temperature and stress limits and corrosion allowances are specified in national standards and pressure vessel codes (42,43). General corrosion rates in pure steam (Table 7) are about the same as in high purity deoxygenated water, except for gray iron, nickel, lead, and zirconium, which corrode faster in steam. Iron-base alloys, including the austenitic and ferritic stainless steels, are used extensively in contact with steam. These oxidize to form a protective film of the spinel oxide, Ee O (magnetite), or, in the case of stainless steels, M O, where M is iron, chromium, or nickel. Gamma-Ee202 has also been found on ferrous alloys in degassed high temperature water and steam. Its physical properties are very similar to those of Ee O. It is magnetic and has an almost identical crystal stmcture.  [c.370]

Materials and Scaling Issues. Two aspects of the basically simple desalination process require special attention. One is the high corrosivity of seawater, especially pronounced ia the higher temperature distillatioa processes, which requires the use of corrosioa-resistant, and therefore expensive, materials. Typical materials ia use are copper—nickel alloys, stainless steel, titanium, and, at lower temperatures, fiber-reiaforced polymers and special concrete compositions (39). It is noteworthy that ia quest of a lower initial cost, the use of iaadequate materials of coastmctioa ia many locatioas combiaed with poor operatioa by virtually uatraiaed hands led to rapid deterioration and failure of plants long before their estimated design life. Adequate experience suggests by now how to avoid such failures. The other aspect is scale formation (40,41), discussed ia more detail below.  [c.241]

Nonferrous alloys account for only about 2 wt % of the total chromium used ia the United States. Nonetheless, some of these appHcations are unique and constitute a vital role for chromium. Eor example, ia high temperature materials, chromium ia amounts of 15—30 wt % confers corrosion and oxidation resistance on the nickel-base and cobalt-base superaHoys used ia jet engines the familiar electrical resistance heating elements are made of Ni-Cr alloy and a variety of Ee-Ni and Ni-based alloys used ia a diverse array of appHcations, especially for nuclear reactors, depend on chromium for oxidation and corrosion resistance. Evaporated, amorphous, thin-film resistors based on Ni-Cr with A1 additions have the advantageous property of a near-2ero temperature coefficient of resistance (58).  [c.129]

With cobalt historically being approximately twice the cost of nickel, cobalt-base alloys for both high temperature and corrosion service tend to be much more expensive than competitive alloys. In some cases of severe service their performance iacrease is, however, commensurate with the cost iacrease and they are a cost-effective choice. For hardfaciag or wear apphcations, cobalt alloys typically compete with iron-base alloys and are at a significant cost disadvantage.  [c.376]

Stainless Steels (Iron-Based Alloys). The great abundance of iron and the numerous corrosion resistant iron-based alloys, such as stainless steels, have limited uses as restorative dental materials. Dental restorative alloys evolved from gold casting alloys, entrenching the gold casting technology as a preferred method of fabrication of prostheses. The strength and performance requirements for cast alloy prostheses led to the use of alloys, other than stainless steels, from the 1930s—1970s as more desirable, functional replacements for more expensive gold alloys. The iron-based casting alloys of that time did not provide the needed corrosion resistance, especially against pitting and crevice corrosion, casting ease, compatibiHty with dental porcelains, high temperature oxidation resistance, and surface appearance as did the cobalt— chromium and nickel—chromium alloys.  [c.486]

Nickel and Nickel Alloys A wide range of ferrous and nonfer-rous nickel and nickel-bearing alloys are available. They are usually selected because of their improved resistance to chemical attack or their superior resistance to the effects of high temperature. In general terms their cost and corrosion resistance are somewhat a func tion of their nickel content. The 300 Series stainless steels are the most generally used. Some other frequently used alloys are hsted in Table 10-35 together with their nominal compositions. For metallurgical and corrosion resistance data, see Sec. 28.  [c.973]

A nucleated cryst hne ceramic-metal composite form of glass has superior mechanical properties compared with conventional glassed steel. Controlled high-temperature firings chemically and physically bond the ceramic to steel, nickel-based alloys, and refractory metals. These materials resist corrosive hydrogen chloride gas, chlorine, or sulfur dioxide at 650°C (1,200°F). They resist all acids except HF up to 180°C (350°F). Their impact streuffth is 18 times that of safety glass abrasion resistance is superior to that of porcelain enamel. They have 3 to 4 times the thermal-shock resistance of glassed steel.  [c.2452]

The ability of Be to age-harden Cu was discovered by M. G. Corson in 1926 and it i.s now known that of Be increases the strength of Cu sixfold. In addition, the alloys (which also usually contain 0.25% Co) have good electrical conductivity, high strength, unusual wear resistance, and resistance to anelastic behaviour (hysteresis, damping, etc.) they are non-magnetic and corrosion resistant, and find numerous applications in critical moving parts of aero-engines, key components in precision instruments, control relays and electronics. They are also non-.sparking and are thus of great use for hand tools in the petroleum industry. A nickel alloy containing 2% Be is used for high-temperature springs, clips, bellows and electrical connections. Another major use for Be is in nuclear reactors since it is one of the most effective neutron moderators and reflectors known. A small, but important, use of Be i.s as a window material in X-ray tubes it transmits X-rays 17 times better than Al and 8 times better than Lindemann glass. A mixture of compounds of radium and beryllium has long been used as a eonvenient laboratory. source of neutrons and. indeed, led to the di.scovery of the neutron by J. Chadwick in 1932 Bc(a,n) -C.  [c.110]

Selective attack Corrosion of alloys at high temperatures is complicated by effects due to diffusion, particularly where the alloy components have different affinities for the environment, and corrosion of an alloy in a fused salt at high temperature often exhibits features similar to those of internal oxidation. Selective removal of the less noble component occurs, and as it diffuses outwards, vacancies move inwards and segregate to form visible voids (Kirkendall effect). Since diffusion rates are faster at grain boundaries than in the grains, voids tend to form at the grain boundaries and specimens often have the appearance of having undergone ordinary intercrystalline corrosion. More careful examination has shown, however, that in the case of Fe-18Cr-8Ni corroding in a fused 50-50 NaCl/KCl melt at 800°C in the presence of air, the attack is not continuous at the boundaries, and the voids formed are not in communication with each other In high-nickel alloys, a greater proportion of voids are formed within the grains and the appearance of intercrystalline attack is less markedWhen Inconel is exposed to fused sodium hydroxide, a two-phase corrosion-product layer is formed, resulting from growth of the reaction product —a mixture of oxides and oxysalts—into the network of channels.  [c.440]

Nickel and nickel alloys are normally resistant to fresh water and natural waters at temperatures up to normal boiling point there may, however, sometimes be a risk of pitting in waters of high acidity or high salinity in stagnant conditions. In flowing conditions, oxygen dissolved in the water is normally suflicient to maintain passivity. Aerobic bacteria appear to have little influence, but corrosion may become severe in the presence of bacteria-induced decay products. Steam condensates containing O2 and COj may, however, be aggressive towards nickel and Ni-Cu alloys, in which circumstances Ni-Cr-Fe alloys are more resistant.  [c.787]


See pages that mention the term Nickel alloys high-temperature corrosion : [c.131]    [c.134]    [c.165]    [c.2449]    [c.194]    [c.237]    [c.697]    [c.761]   
Corrosion, Volume 2 (2000) -- [ c.4 , c.7 , c.91 , c.152 ]