2,808
edits
Changes
→5.2.1 Technical Grade Pure Nickel
Technical grade pure nickel commonly contains 99.0 to 99.8 wt% Ni and up to 1 wt% Co. Other ingredients are iron and manganese ''(Tables 5.21 and 5.22)''. Work hardening and softening behavior of nickel are shown in Figs. 5.45 and 5.46.
One of the significant properties of nickel is its modulus of elasticity which is almost twice as high as that of copper. At temperatures up to 345°C nickel is ferro-magnetic.
Nickel has a high corrosion resistance, is very ductile, and easy to weld and clad. It is of great importance as a backing material for multiple layer weld profiles. In addition nickel is used as an intermediate layers for thin claddings, acting as an effective diffusion barrier between copper containing carrier materials and goldand palladium-based contact materials.
Because of the always present thin oxide layer on its surface, nickel is not suitable as a contact material for switching contacts.
Fig. 5.45:
Strain hardening
of technical pure
nickel by
cold working
Fig. 5.46;
Softening of technical
grad nickel after annealing
for 3 hrs after 50% cold working
====5.2.2 Nickel Alloys====
Because of its low electrical conductivity NiCu30Fe is besides pure Ni and CuNi alloys the most widely used backing material for weldable contact components. With 1 – 2 wt% additives of Fe as well as 0.5 – 1 wt% Mn and Co the mechanical strength of the binary alloy NiCu30 can be increased.
The strength values of NiCu30Fe are significantly higher than those of the copper rich CuNi alloys ''(Figs. 5.47 and 5.48)''. The good spring properties and thermal stability of NiCu30Fe make it a suitable material for the use as thermally stressed contact springs.
Fig. 5.47:
Strain hardening
of NiCu30Fe by cold working
Fig. 5.48:
Softening of NiCu30Fe
after annealing
for 0.5 hrs and after 80%
cold working
Table 5.21: Physical Properties of Nickel and Nickel Alloys (2 Teile!)
Table 5.22: Mechanical Properties of Nickel and Nickel Alloys (2 Teile!)
====5.2.3 Nickel-Beryllium Alloys====
Because of decreasing solubility of beryllium in nickel with decreasing temperature NiBe can be precipitation hardened similar to CuBe ''(Fig. 5.49)''. The maximum soluble amount of Be in Ni is 2.7 wt% at the eutectic temperature of 1150°C. to achieve a high hardness by precipitation hardening NiBe, similar to CuBe, is annealed at 970 - 1030°C and rapidly quenched to room temperature. Soft annealed material is easily cold formed and after stamping and forming an hardening anneal is performed at 480 to 500°C for 1 to 2 hours.
Commercial nickel-beryllium alloys contain 2 wt% Be. Compared to CuBe2 the NiBe2 materials have a significantly higher modulus of elasticity but a much lower electrical conductivity. The mechanical strength is higher than that of CuBe2 ''(Fig. 5.40)'', the spring bending force limit can exceed values of over 1400 MPa and the fatigue strength reaches approximately 400 MPa.
A further advantage of NiBe2 is its high temperature stability. Cold worked and subsequently precipitation hardened NiBe2 can withstand sustained
temperatures of 400 - 650°C, depending on ist pre-treatment.
Similar to CuBe materials, NiBe alloys are available in mill hardened in various conditions or also already precipitation hardened at the manufacturer.
Nickel-beryllium alloys are recommended for mechanically and thermally highly stressed spring components. For some applications their ferro-magnetic properties can also be advantageous.
Fig. 5.49:
Phase diagram of nickel-beryllium
Fig. 5.50:
Precipitation
hardening of NiBe2
(soft) at 480°C
