Nickel base alloy
Nickel-based alloys are materials whose main component is nickel and which are usually produced using a melting process with at least one other chemical element.
Properties and composition
These alloys have good corrosion and / or high temperature resistance ( creep resistance ). Some have special physical properties such as electrical resistance, controlled thermal expansion, special magnetic properties, etc. Nickel-copper, nickel-iron, nickel-iron-chromium, nickel-chromium, nickel-molybdenum are used. Chromium, nickel-chromium-cobalt, low-alloy nickel alloys (with a nickel content of up to 99.9%) and other multi-component alloys. Most nickel alloys are classified according to international standards.
application areas
The nickel materials are used in many ways:
- chemical industry (e.g. boilers, heat exchangers , valves and pumps, chemical reactors)
- Aviation (e.g. engines , turbines , fasteners)
- Automotive industry (e.g. valve technology, catalysts )
- Energy generation (e.g. power plant generators )
- Oil and gas production (e.g. drilling tools )
- Environmental protection and waste management (e.g. flue gas desulphurisation plants , waste incineration plants , seawater desalination plants )
- Electronic and household applications ( heating conductor alloys , electronic circuits, computer manufacture, kitchen machines, kitchen stoves)
Nickel-copper alloys are used for embossing, for industrial pipelines and valves, in seaworthy components, condenser tubes, heat exchangers, thermocouples, desalination plants, ship propellers, etc. Nickel-chrome alloys are used for many high temperature applications such as furnaces, jet engine parts, and reaction vessels. Nickel alloys containing molybdenum are distinguished by their corrosion resistance and thermal stability and, like nickel-iron-chromium alloys, are used in nuclear and fossil steam generators, food processing plants and chemical processing plants for heat treatment. The majority of permanent magnets are made of nickel-cast iron alloys (Mastromatteo, 1986). The other groups of nickel alloys are used according to their specific properties for acid-resistant equipment, heating elements for furnaces, low elongation alloys, cryogenic applications, storage of liquefied gases, alloys with high magnetic permeability and surgical implants and prostheses.
Manufacturing
Nickel alloys are preferably melted openly (in air) in an electric arc furnace , sometimes also using the induction melting process , openly or in a vacuum. It usually closes a AOD treatment ( English Argon Oxygen Decarburization ) or a remelting according to the electroslag remelting (ESR) on.
Another possibility for production is what is known as mechanical alloying. A mixture of alloy powder with oxides is mixed with high energy input in order to obtain a particularly homogeneous and highly heat-resistant structure.
From the slabs cast in this way, sheets and strips are produced in hot and possibly subsequent cold rolling steps and bars are forged or rolled. Pipes are in particular Rohrreduzierwerken of blocks or in pilgrim tube rolling mills of blooms produced wires in wire rolling - or -ziehwerken.
Superalloys
Nickel- based superalloys are alloys with a special composition that are specially produced for high-temperature applications (e.g. in engine construction).
The main advantage of nickel-based superalloys is their creep and fatigue strength at high temperatures. From around 550 ° C they are superior to hot work steels in this regard . The hardening through intermetallic phases means that nickel-based superalloys can be used up to their melting point and even outperform refractory metals in this temperature range . The strength is usually achieved by adding aluminum and / or titanium . The resulting Ni 3 [Al, Ti] precipitations take on a characteristic block-shaped structure at higher alloy contents. In the commercially most widespread alloy IN718, hardening takes place through Ni 3 Nb precipitations. The creep is prevented by grain boundary networks of M 23 C 6 carbides.
Since their corrosion resistance is also very high due to the formation of an impermeable oxide layer, they are the first choice for construction materials in gas turbines in power plants and in aircraft turbines. Simple forged components are used for the turbine disks and more highly alloyed cast components are used for the turbine blades, which are usually straightened and manufactured as single crystals . With the help of coatings and internal air cooling, such turbine blades can even be used at ambient temperatures beyond the melting point of their alloy (around 1200 ° C).
Examples
Alloy 718
| Manufacturer | Special Metals Corporation , VDM Metals |
|---|---|
| Material number / UNS number | 2.4668 / N07718 |
| Short name | NiCr19NbMo |
| density | 8.19 g / cm³ |
Chemical composition: 0.04% C; 19% Cr; 3.0% Mo; 52.5% Ni; 0.9% Al; ≤0.1% Cu; 5.1% Nb; 0.9% Ti; 19% Fe.
This superalloy, reinforced with Ni 3 [Nb, V] precipitates , still accounts for 60–70% of the volume of all nickel-based alloys.
Alloy 600
| Manufacturer | Special Metals Corporation , VDM Metals , BGH Edelstahl Freital |
|---|---|
| Material number / UNS number | 2.4816 / N06600 |
| Short name | NiCr15Fe |
Good resistance to general corrosion and stress corrosion cracking. Excellent resistance to oxidation up to approx. 1150 ° C. Cannot be used above 550 ° C in a sulphurous atmosphere. In carbon dioxide , the limit of use is 500 ° C, as strong corrosion sets in from 650 ° C. In sodium , Alloy 600 should not be used above 750 ° C, as material degradation occurs from this temperature. In chlorine-free usable water to 590 ° C.
Well weldable with all known welding processes . It should be annealed before welding. Good soldering and brazed. Very good ductility . As an alloy with a high nickel content, Alloy 600 has very good mechanical properties at high temperatures. Since it is a soft, tough material, machining is made easier if the material is not machined in the annealed but in the as-rolled condition.
Alloy 600 is the standard material for the construction of pressurized water reactors, furnace construction, synthetic fiber production, glass tub fume cupboards, plastics industry, paper production, food processing, steam boilers, distillation columns and aircraft engines.
Individual evidence
- ↑ iarc.fr: IArc Monograph Nickel and Nickelcompounds , accessed June 29, 2016
- ^ A b c Joseph R. Davis: Nickel, Cobalt, and Their Alloys . ASM International, 2000, ISBN 978-0-87170-685-0 , pp. 200 ( limited preview in Google Book Search).
- ↑ Alloy 718 data sheet.Retrieved August 10, 2017 .
- ↑ Alloy 600 data sheet.Retrieved July 27, 2017 .