Interesting Properties of Nickel Aluminium Bronze (NAB) Alloys
What are Aluminium Bronze or NAB Alloys ?
Aluminium Bronze are a family of copper based alloys including aluminium, nickel and iron ; Each individual component is adjusted to improve strength, corrosion resistance and/or machinability and is then identified by a different grade.
Aluminium bronze have properties which are usefull in many pump, valve, heat exchanger and ship propulsion application, in particular because of resistance to sea water corrosion, but not only :
- High mechanical strength
- Density (5 % lighter than steel)
- Non sparking
- Low magnetic permeability (of <1.03µ in selected grades)
- High Corrosion resistance (in particular marine based corrosions)
- Good stress corrosion properties
- Good cryogenic properties
- High resistance to cavitation
- High resistance to biofouling
- Lower cost than Titanium
With a main property coming from its protective oxide surface film which has the ability to self-repair thus outstanding any coated steel application in the long run.
In case standard mechanical properties are not sufficient, special proprietary alloys such as Inoxyda 154 are available
Rm in MPa
0.2 Rm in M pa
And which can further be increased by additional forging .
Especially important in pump, turbine and propulsion applications, this results from small water vapour bubbles formed at low pressure points causing erosion at the point of contact which in some extreme cases damages the blade. Nickel Aluminium Bronze provides an excellet resistance to this phenomenon explaining why in addition to corrosion resistance it is widely used for propellers in the shipbuilding industry.
Cryogenic applications requires the use of alloys which resist low temperatures. Unlike most steels, copper based alloys do not embrittle and have a good dimensional stability at low temperatures down to -190°C . For those very specific alloys, Inoxyda has improved the standard alloy by giving its Inoxyda 3 Cryo alloy better performances at low temperatures for use in valve and pump applications.
Biofouling can be a serious problem with any systems handling sea water, particularly at elevated temperatures with warm climates.
High copper alloys have considerable resistance to the growth of crustaceans, sea weeds and other marine organisms. The slow dissolution of copper ions inhibits their growth and prevents mass population.
NAB alloys have 2 main advantages compared to Titanium, Duplex or Super Duplex alloys regularly used in similar applications :
- Machining of Nickel Aluminium Bronze is easier and more cost effective ,
- Nickel Aluminium Bronze can easily be repaired by qualified welders (using matching welding electrodes to minimise corrosion issues)
More detailed technical informations are available in the Guide to Nickel Aluminium Bronze for Engineers , published by Ivan Richardson and the Copper Developement Association (see download area)Download
Today most aluminium bronze alloys are documented in various standards either :
International : EN 1982 / BS 1400 / ASTM B 148 / ASTM B171 / ASTM B 505
Military specifications : DEF STAN / STF / GAMM MM11 / GAMM MM12 / MIL-STD
Proprietary alloys :
such as the INOXYDA aluminium bronze including following specific grades
- Inoxyda 90 : for plates and heat exchangers
- Inoxyda 3 Cryo : for cryogenic applications
- Inoxyda 72 : for wear applications
- Inoxyda 53 AMA : for low magnetic applications
- Inoxyda 154 : for high mechanical characteristics