Nickel and nickel alloys are non-ferrous metals with high strength and toughness, excellent corrosion resistance, and superior elevated temperature properties. Products differ in terms of composition, grade, shape, dimensions, and features. Commercially pure, unalloyed or very low alloy nickel does not contain or contains only very small amounts of alloying elements. By contrast, nickel alloys contain significant amounts of added elements or constituents. Clad or bimetal stock consists of two different alloys that are bonded integrally together. Metal matrix composites have a composite or reinforced metal or alloy matrix filled with a second component, which may be in particulate, chopped fiber, continuous filament, or fabric form. Other unlisted, specialty or proprietary nickel and nickel alloys are also available. These materials are often based on a unique alloy system, use a novel processing technology, or have properties tailored for specific applications.
Many nickel and nickel alloys meet the compositional standards of the Unified Numbering System (UNS), a specification established by the American Society for Testing and Materials (ASTM), the Society of Automotive Engineers (SAE), and metal trade associations such as the American Iron and Steel Institute (AISI). The UNS assigns metals and alloys a lettered prefix and a five-digit number. Nickel and nickel alloys belong to the UNS N category and have designations such as UNS N02200. Other standards for nickel and nickel alloys include casting grades, European Norm (EN), American Society of Mechanical Engineers (ASME) standards, and U.S. military specifications (MIL-SPEC). QQ and QQS prefixes are used to designate specific MIL-SPEC metals.
Suppliers provide nickel and nickel alloys in many stock shapes and forms. Semi-finished stock shapes are suitable for part fabrication by machining, assembly, or other processes. They are also used as feedstock for casting, forging, and spinning. Common stock shapes and forms for nickel and nickel alloys include bars, rods, tubes, plates, profiles, sheets, strips, shims, spheres, foil, wire, billets, slabs, and blooms. Materials are also supplied as billets, ingots, powders, fillers, and reinforcements. Round, hexagonal, coil, and hollow stock are also available. There are two basic types of anodes. Plating anodes are in used in plating or electroplating processes. Sacrificial anodes are used to protect stainless steel or other metal structures from corrosion.
Selecting nickel and aluminum alloys requires an analysis of dimensions, production processes, and performance features. Outer diameter (OD), inner diameter (ID), overall length, and overall thickness are important dimensions. Most materials are cast, wrought, extruded, forged, cold-finished, hot-rolled, or formed by compacting powdered metals or alloys. Performance features for nickel and nickel alloys include resistance to corrosion, heat, and wear.
--->Nickel-Titanium alloy :
It is a Shape-Memory Alloy that, after being strained, at a certain temperature revert back to its original shape.
Nickel-Titanium (NiTi) alloy is the most used Shape Memory Alloy. It is an equiatomic compound of NiTi, whose transformation temperature can range between -100 and +110 C.
It has great shape-memory strain (up to 8%), is thermally stable, and has excellent corrosion resistance. Because of the reactivity of titanium, all melting of it must be done in a vacuum. Forging, bar rolling and extrusion are also used.
--->An improved tungsten alloy having a tungsten content of approximately 95 weight percent, a nickel content of about 3 weight percent, and the balance being cobalt of about 2 weight percent is described. A method for producing said tungsten-nickel-cobalt alloy is further described and comprises (a) coating the tungsten particles with a nickel-cobalt alloy, (b) pressing the coated particles into a compact shape, (c) heating said compact in hydrogen to a temperature in the range of 1400° C and holding at this elevated temperature for a period of about 2 hours, (d) increasing this elevated temperature to about 1500° C and holding for 1 hour at this temperature, (e) cooling to about 1200° C and replacing the hydrogen atmosphere with an inert argon atmosphere while maintaining this elevated temperature for a period of about 1/2 hour, and (f) cooling the resulting alloy to room temperature in this argon atmosphere.
--->copper nickel alloy
Dr. Agnes Sagal wrote :
Background
Sometimes called cupro-nickels, there exists a range of different copper nickel alloys that possess different properties and hence are suited to a range of different applications. Some of the better known copper nickel alloys include:
· Copper with 10% nickel
· Copper with 30% nickel
· Copper with 25% nickel with 0.05-0.4% manganese
· Copper with 45% nickel (also known as constantan)
All copper nickel alloys consist of only one phase as the copper nickel binary system exhibits complete solid solubility.
Key Properties
Properties vary with composition, however, some properties are outlined below.
Copper 90/10 and Copper 70/30
· Outstanding resistance to corrosion, particularly sea water
· 70/30 is stronger and has superior resistance to impingement corrosion
· Good resistance to biofouling, with the 90/10 alloy being slightly superior compared to the 70/30 alloy
Copper rich alloys are:
· Ductile
· Can be hardened only by cold working
· Good corrosion resistance
· Good strength
· Low temperature co-efficient of electrical resistance
The nickel content in these alloys also enables them to retain their strength at elevated temperatures compared to copper alloys without nickel.
Applications
Sea Water Condensor Systems And Desalination Plants
Due to the good resistance to sea water corrosion, the 90/10 and 70/30 alloys are employed for sea water condenser systems and in desalination plants, as well as pipe work in chemical plants.
Automotive Applications
Due to the fact that the 90/10 alloy requires no surface protection and hence gives extra safety, this alloy is being increasingly employed for brake and hydraulic suspension systems and cooling systems in cars and commercial vehicles.
Marine Applications
The good resistance to biofouling and sea water corrosion resistance of the 90/10 and 70/30 alloys have lead to its use in applications such as cladding for ships’ hulls, legs of oil rig platforms and sea water intake screens.
Coins
The copper with 25% nickel with 0.05-0.4% manganese is commonly used for the
manufacture of coins, medals and other semi valuable applications.
Resistance Wire
Due to the very low temperature co-efficient of electrical resistivity, the copper with 45% nickel alloy is used for resistance wire in high precision resistors. This property allows the resistor to operate at almost exactly the same resistance regardless of temperature.
Thermocouples
The copper-45% nickel alloy is also used for thermocouples as it develops a high and uniform EMF when coupled with other metals such as copper and iron.
Other Applications
Cooling circuits, ammunition, sea water corrosion-resistant assemblies, condenser tubes.
----> The nickel-chromium alloysThe nickel-chromium system shows that chromium is quite soluble in nickel. This is a maximum at 47% at the eutectic temperature and drops off to about 30% at room temperature. A range of commercial alloys is based on this solid solution. Such alloys have excellent resistance to high temperature oxidation and corrosion and good wear resistance.
Oxidation Resistance
The introduction of small amounts (<7%) of chromium to nickel increase the sensitivity of the alloy to oxidation. This is because the diffusion rate of oxygen in the scale is increased. This trend reverses after addition levels increase above 7% chromium and increases up to an addition level of approximately 30%. Above this level, there is little change.
Oxidation resistance can be attributed to the formation of a highly adherent protective scale. The adherence and coherence of the scale can be improved by the addition of small amounts of other reactive elements such as zirconium, silicon, cerium, calcium or similar. The scale thus formed is a mixture of nickel and chrome oxides (NiO and Cr2O3). These combine to form nickel chromite (NiCr2O4), which has a spinel-type structure.