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→5.2 Nickel and Nickel Alloys
The increasing requirements on spring components in connectors, especially for use in automotive applications, such as higher surrounding temperatures, increased reliability, and the trend towards miniaturization led to a change of materials from traditionally CuZn30 and CuSn4 to CuNiSi alloys, for example. These CuNiSi alloys and the newer heavy duty copper alloys like CuNi1Co1 are significantly improved with regards to mechanical strength, relaxation behavior, and electrical conductivity.
==<!--5.2 -->Nickel and Nickel Alloys==
===<!--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 <xr id="tab:Physical Properties of Nickel and Nickel Alloys"/> <!--(Tab. 5.21) --> and <xr id="tab:Mechanical Properties of Nickel and Nickel Alloys"/> <!--(Tab. 5.22)-->. Work hardening and softening behavior of nickel are shown in [[#figures11|(Figs. 5 – 6)]] <!--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.
<div id="figures11">
<xr id="fig:Strain hardening of technical pure nickel by cold working"/> <!--Fig. 5.45: --> Strain hardening of technical pure nickel by cold working
<xr id="fig:Softening of technical grad nickel after annealing for 3 hrs"/> <!--Fig. 5.46; --> Softening of technical grad nickel after annealing for 3 hrs after 50% cold working
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===<!--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 [[#figures12|(Figs. 7 – 8)]] <!--(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.
<div id="figures12">
<xr id="fig:Strain hardening of NiCu30Fe by cold working"/> <!--Fig. 5.47: --> Strain hardening of NiCu30Fe by cold working
<xr id="fig:Softening of NiCu30Fe after annealing for 0.5 hrs"/> <!--Fig. 5.48: --> Softening of NiCu30Fe after annealing for 0.5 hrs and after 80% cold working
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<figtable id="tab:Physical Properties of Nickel and Nickel Alloys">
<caption>'''<!--Table 5.21: -->Physical Properties of Nickel and Nickel Alloys'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
<figtable id="tab:Mechanical Properties of Nickel and Nickel Alloys">
<caption>'''<!--Table 5.22: -->Mechanical Properties of Nickel and Nickel Alloys'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
<sup>c</sup>solution annealed, cold rolled, and precipitation hardened at mill (mill hardened)
===<!--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 <xr id="fig:Phase diagram of nickel beryllium"/> <!--(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.
<figure id="fig:Phase diagram of nickel beryllium">
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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 <xr id="fig:Precipitation hardening of NiBe2 soft at 480C"/> <!--(Fig. 5.50)-->, the spring bending force limit can exceed values of over 1400 MPa and the fatigue strength reaches approximately 400 MPa.
<figure id="fig:Precipitation hardening of NiBe2 soft at 480C">
