It is an unsung metal, yet plays many vital roles in modern materials applications. Peter Cutler raises the curtain on nickel. unique combination of properties. ickel is found in the first transition series of elements in the periodic table, and this position gives rise to it metallurgical make-up: • has a high melting point of 1453°C • forms an adherent oxide film • resists corrosion by alkalis • is face-centred cubic, conferring ductility • forms alloys readily, both as solute and solvent • is ferromagnetic at room temperature • is readily deposited by electroplating • exhibits catalytic behaviour. As this article shows, these properties mean that there are an enormous number of nickel- containing materials employed in a great variety of applications. Nickel's role as a catalyst in chemical process- es is perhaps the least-known of its uses. However, finely-divided nickel-based are key to several important reactions, including the hydrogenation of vegetable oils, reforming of hydrocarbons and the production of fertilisers, pesticides and fungicides. At the other end of the spectrum, nickel elec- troplating is extremely well-known and widely applied. The technique has long been used to provide both corrosion-resistant and decorative finishes, and i also used to create the substrate for the familiar chromium coatings. Plating on plasticS has enjoyed considerable growth recently. The success of the process depend on suitable etching of the plastic to pro- vide good adhesion to the first metallic deposit. Once this conducting layer is in place, the com- ponent can be electroplated in the normal way to produce a velY durable, lightweight item. Nickel provides the corrosion resistance and lustrous appearance. Automobile trim, bathroom fittings and electronic connectors are just three of the areas in which designers are now exploiting the opportunities this process offers. Nickel electroplating can also be used to make items by building up thick deposits on a sub- strate. The surface detail of the substrate is repro- duced very faithfully on the deposit when the materials are separated, figure 1. This process is known as electroforming and is widely used to produce items as diverse as moulds for pressing compact discs and security holograms, and screens for carpet printing. Nickel can also be deposited from solution without using electric current. These 'electroless' nickel deposits are very uniform in thickness and contain phosphorus, the level of which can be selected to provide good wear and corrosion resistance. The hardness can be increased by heat treatment, making these coatings well-suited to many pump and valve applications. Other mate- rials can be co-deposited - PTFE to increase lubricity and silicon carbide to increase wear resistance. A major application of electroless nickel today is in computer hard discs. It forms an extremely uniform, smooth, stable, non-magnetic substrate for the magnetic recording layer, as well as pro- viding corrosion protection for the underlying aluminium disc. kel ere • N ickel-containing materials make major contributions to many aspects of modern life, but often go unrecog- nised. The list is very long, and includes applications in buildings and infrastructure, chemical production, communica- tions, energy supply, environmental protection, food preparation, water treatment and travel. All these areas rely, to some degree, on nickel's Figure 2 Stainless steel roofing on the Thames Barrier Figure 1 Electroformed nickel microgear in the eye of a needle eve NiDI Nickel Development Institute Reprint Series No. 14048 reprinted from Materials World, September 1998
Transcript
It is an unsung metal, yet plays many vital roles in modernmaterials applications. Peter Cutler raises the curtain on nickel.
unique combination of properties.ickel is found in the first transition series of
elements in the periodic table, and this positiongives rise to it metallurgical make-up:• has a high melting point of 1453°C• forms an adherent oxide film• resists corrosion by alkalis• is face-centred cubic, conferring ductility• forms alloys readily, both as solute and solvent• is ferromagnetic at room temperature• is readily deposited by electroplating• exhibits catalytic behaviour.
As this article shows, these properties meanthat there are an enormous number of nickelcontaining materials employed in a great varietyof applications.
Nickel's role as a catalyst in chemical processes is perhaps the least-known of its uses.However, finely-divided nickel-based cat~lystsare key to several important reactions, includingthe hydrogenation of vegetable oils, reforming ofhydrocarbons and the production of fertilisers,pesticides and fungicides.
At the other end of the spectrum, nickel electroplating is extremely well-known and widelyapplied. The technique has long been used toprovide both corrosion-resistant and decorativefinishes, and i also used to create the substratefor the familiar chromium coatings.
Plating on plasticS has enjoyed considerablegrowth recently. The success of the processdepend on suitable etching of the plastic to provide good adhesion to the first metallic deposit.Once this conducting layer is in place, the component can be electroplated in the normal way toproduce a velY durable, lightweight item. Nickelprovides the corrosion resistance and lustrousappearance. Automobile trim, bathroom fittingsand electronic connectors are just three of theareas in which designers are now exploiting theopportunities this process offers.
Nickel electroplating can also be used to makeitems by building up thick deposits on a substrate. The surface detail of the substrate is reproduced very faithfully on the deposit when thematerials are separated, figure 1. This process isknown as electroforming and is widely used toproduce items as diverse as moulds for pressingcompact discs and security holograms, andscreens for carpet printing.
Nickel can also be deposited from solutionwithout using electric current. These 'electroless'nickel deposits are very uniform in thickness andcontain phosphorus, the level of which can beselected to provide good wear and corrosionresistance. The hardness can be increased by heattreatment, making these coatings well-suited tomany pump and valve applications. Other materials can be co-deposited - PTFE to increaselubricity and silicon carbide to increase wearresistance.
A major application of electroless nickel todayis in computer hard discs. It forms an extremelyuniform, smooth, stable, non-magnetic substratefor the magnetic recording layer, as well as providing corrosion protection for the underlyingaluminium disc.
kelere
•
Nickel-containing materials make majorcontributions to many aspects ofmodern life, but often go unrecognised. The list is very long, andincludes applications in buildings and
infrastructure, chemical production, communications, energy supply, environmental protection,food preparation, water treatment and travel. Allthese areas rely, to some degree, on nickel's
Figure 2Stainless steel roofing on
the Thames Barrier
Figure 1Electroformed nickel
microgear in the eye of a
needle
evenic~
NiDI Nickel Development Institute Reprint Series No. 14048 reprinted from Materials World, September 1998
':'hckel's corrosion resistance is one of its mostvaluable properties. The e timated annual co t ofcorrosion in the USA alone i 300 billion equivalent to 4% of GNP. Far and away the largestuses of nickel alloys are in providing cost-effective ways of combating corrosion.
Two-thirds of all nickel produced goes intostainless steel, in which it promotes a stable, ductile, austenitic structure as well as contributing tothe corrosion resistance. The most commonaustenitic grades in use are Type 304, which contains 18% chromium and 8% nickel, and the morcorrosion-re istant Type 316 (l8%Cr, 10% i,2%Mo). The combination of corrosion resistance,cleanability, ease of fabrication, appearance andavailability means that these teels are the materials of choice for many hygienic applications infood proce sing, beverage production and themedical field. They are also increasingly popularfor domestic kitchen equipment and uten il .These stainless steels are commonly found inmany architectural applications, figure 2, and arewidely used in the transport, chemical processingand energy industries. The stability and toughness of the austenitic structure also allows thesestainless steels to be used for cryogenic applications.
Stainless steels are thought of as expensivematerials, but they often prove economicallysound materials when all costs, including maintenance and repair, are taken into considerationover the whole life of a product. This is partlywhy the use of stainless steels continues to grow.Some highway authorities are now consideringselective use of stainless steel reinforcing bars inconcrete bridges to avoid the corrosion problemscaused by de-icing salt.
Further additions of alloying elements to thestandard austenitic stainless steels, particularlynickel, chromium, molybdenum and nitrogen,result in a series of steel grades with higher resistance to general corrosion as well as pitting,crevice and stress corrosion. These grades are
suitable for the moreaggressive environments encountered incertain marine applications, and in the oil,gas, power and chemical industries. Theseindustries are al 0 making increa ing lise ofduplex stainless steels(which typically contains 5-7% nickel) inwhich the mixed ferrite/austenite structureprovides a combinationof high strength andresistance to corrosion,particularly tr S corrosion.
Copper-nickel alloyshave a long history ofcombating corro ion inmarine environments.Typical applicationsinclude large desalination plants, which providethe water es ential to developments in arid parts ofthe world.
The most economical way to use all these corrosion-resistant alloys is often as surface claddingson components. Claddings for pipe may be bonded to the backing steel before the pipe is formed.Alternatively, claddings on valves and similar components may be applied as an overlay by welding.Extensive use has also been made of a 'wallpapering' technique for applying high-nickel, corrosionresistant alloys to protect the inside of flue gasdesulphurisation units for coal-fired power stations, figure 3. AdheSively-bonded cladding materials, which are currently being developed, couldalso be used in these sorts of applications.
Nickel and its alloys are also very resistant toheat. The combination of a high melting point, aface-centred cubic crystal structure, an adherent
Figure 3Installing a high alloy
stainless steel and nickel
alloy liner in a flue gas
desulphurisation duct
COURTESY OF MANNESMANN
ANLAGENBAU
Figure 4Cast high nickel-base alloy
blades and vanes in an
industrial gas turbine
COURTESY OF:
ASEA BROWN BOVERt (ABB)
Figure 5Liquid natural gas storage
tank lined with low
expansion 36%Ni-Fe alloy
- COURTESY OF
GAZ- TRANSPORT
oxide and good alloying ability has allowed nickel to form the basis of a wide range of heat-andcreep-resistant alloys that are essential materials inthe chemical and aerospace industries.
For many years, 800/0Ni-200/0Cr alloys have beenused as heating elements. Additional alloying elements such as cobalt, molybdenum and tungstenprovide solid solution strengthening; aluminiumand titanium additions give precipitation hardening; additional chromium improves the corrosionresistance; small amounts of carbon, zirconiumand boron are important for developing strengthand ductility; oxide dispersion can provide additional trengthening; and single crystal components can offer improved creep resistance.
With all these variables, the composition mustbe carefully balanced and processing tightly controlled to develop the optimum properties. Thi istrue whether the materials are for ethylenereformer tubes or for the ga turbine blades thatmake cheap air travel possible and that areincreasingly being used for electricity generation,figure 4. Remarkably, some of these materials canbe stronger at their operating temperatures thanmild steel at room temperature. Yet new materialscontinue to achieve still higher operating temperatures - for example, intermetallics such asnickel aluminide.
Nickel-based materials have a number of specialpropelties that open up additional applications.
ickel-iron alloys have low expansion characteristicsas a result of a balance between thermal expansionand magnetostrictive changes with temperature.Originally used in clock pendulums, these alloys arenow widely employed as lead-frames in packagingelectronic chips and for the shadow-masks in colourtelevision tubes. On a much larger scale, they provide one solution to coping with the thermal expansion requirements of storage and transportationtanks for the growing liquid natural gas industry,figure 5.
The soft magnetic properties of nickel and itsalloys are employed in electronic devices and forelectromagnetic shielding of computers and com-
munication equipment. Coins and tokens can beproduced with a tailored electromagnetic response,which aid identification in vending machines.
Equiatomic nickel-titanium shape memory alloyshave gone from being interesting curiosities tohaving real applications. Components are formedinto shape at an elevated temperature.Deformation at the lower service temperaturecauses a martensitic transformation - this can bereversed by reheating so that the componentsregain their original shape. The transformationtemperatures are determined by composition andprocessing. Current applications include actuatorhydraulic connectors and spectacle frame.Superelastic alloys are closely related materials thatcan undergo large elastic strains without plasticdeformation. Medical devices and mobile telephone aerials are two applications currentlyexploiting this property.
ickel also plays a part in portable power pro-vision. ickel-cadmium rechargeable batteriecontaining nickel plates and nickel hydroxide havebeen in use for everal years. Nickel metal-hydridebatteries have been introduced more recently,employing some nickel rare-earth alloys to absorblarge amounts of hydrogen. These higher-performance rechargeable batteries have, in turn, led toimproved performance from cordless power tools,portable computers and other mobile electronicequipment. The hydrogen storage alloys may findwider application if greater use is made of hydrogen as a fuel in the future.
The future looks bright for nickel. Recent developments are expected to bring significant new nickelsupplies to world markets within the next four to fiveyears, and so the ready availability of the materialsseems set to continue. The next century will posemany technological challenges. However they aretackled, nickel and nickel-containing materials arewell placed - being cost-effective, long-lasting materials - to be chosen for critical applications in toughenvironments and for enabling future technologicalinnovations to be exploited. ickel will be contributing to our live for many years to come. •
Dr Peter Cutler CEng MIM isTechnical Director (Europe),Nickel Development Institute,Technical Information Centre,The Holloway, Alvechurch,Birmingham B48 7QB.Tel:+44 (0)1527 584777Fax:+44 (0)1527 585562E-mail: [email protected] site: www.nidi.org
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