With the growing importance of Electro Mobility (eMobility) and the use of electric powertrain technologies (in combination with an increase of electrical/digital equipment), the demand for effective shielding materials as well as sensors is on the increase. Nickel-containing materials are playing a crucial role in this growing field of application.
Nickel-based alloys are well known for their corrosion resistance and their high temperature strength. However, some of them have even more to offer.
Nickel-iron alloys form the group called soft-magnetic alloys. Soft-magnetic nickel-iron alloys can easily be magnetised and demagnetised. Their magnetic properties, coercive force, permeability and hysteresis losses are clearly superior to those of the iron materials.
Higher nickel content, higher shielding
One of the most important fields of application is magnetic shielding.
Electrical equipment generates electromagnetic and magnetic fields. These fields can disturb interference-sensitive devices. In order to reduce the unwanted fields, the generating and/or the sensitive devices have to be “shielded”. The shielding effect is the result of the undesired “magnetic flux” being redirected via the shielding material, reducing or eliminating the field inside the shielded volume. The shielding property of a material is described by the shielding factor and correlates with the so called “permeability”.
Generally speaking, the higher the nickel content (up to 85% Ni), the higher the shielding factor. The appropriate shielding material can be selected according to the strength of the undesired magnetic and electromagnetic field. Alloys with about 80% Ni provide the highest magnetic permeability. Soft magnetic nickel-based alloys, such as VDM® Magnifer 7904 (UNS N14080) with more than 75% Ni is a shielding material with the highest permeability.
Typical applications for shielding in nickel-iron alloys include sound recording heads, microphones, sensors and electron beam tubes. In some cases, these nickel materials are also used for cladding complete examination rooms in hospitals where highly sensitive measuring equipment is used.
The challenge is to transfer the know-how and experiences from other industries to the transportation sector.
Increased demand on sensors
With eMobility, the demand on sensors is increasing. For example, current measurement sensors for battery management systems are made from soft-magnetic nickel-based alloys due to their properties of saturation flux density, high permeability and low coercive force.
For both medical and transport applications alloys such as VDM® Magnifer 7904, VDM® Magnifer 36 (UNS K93600), and VDM® Magnifer 50 (UNS K94840) can be used.
Manufacturing for the desired properties
For good soft magnetic properties, very pure material has to be produced, starting with melting in air followed by vacuum treatment or vacuum melting. Soft-magnetic nickel-
iron alloys are available as solid parts—forgings, bars, sheet, plate, strip and sheet metal—and as thin films or wires. The Ni-Fe alloys must be subjected to a final annealing. Only after the final annealing do the extraordinary soft-magnetic properties become apparent for the first time in the manufacturing process.
The desired magnetic properties of the nickel-iron alloys can be adapted to specific applications by alloy modifications as well as by adjusting the annealing procedures.
Thus, the future of soft-magnetic nickel-iron-alloys is poised to play a key role in the implementation of a sustainable and climate-friendly transport systems.