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Various requirements based on the enduse of the contact components have to be met by carrier materials. Copper materials have to exhibit high electrical and thermal conductivity, good mechanical strength even at elevated temperatures, and in addition a sufficient high resistance against corrosion. If used as springs the carrier materials also must have good elastic spring properties. Besides these, the materials must, depending on the manufacturing processes employed, also have good technological properties like ductility to allow warm and cold forming, suitability for cutting and stamping, and be capable to be welded, brazed or coated by electroplating.
==<!--5.1 -->Copper and Copper Alloys==
===Standards Overview===
|-
|ASTM B 534-07 || Sec. for CuCoBe-Alloy and CuNiBe-Alloy Plate, Sheet, Strip, and Rolled Bar
|-
|}
The above DIN EN standards replace in part or completely the older DIN standards DIN 1777,
DIN 17670, DIN 1751, DIN 1791.
===<!--5.1.2 -->Pure Copper===
Copper is used in electrical engineering mostly because of its high electrical conductivity<ref>As units for electrical conductivity MS/m and m/Ω.mm<sup>2</sup> are commonly used. Frequently – and mostly in North America – the % IACS value (International Annealed Copper Standard) is also used, where 100% is equivalent to 58 MS/m or m/Ωmm<sup>2</sup> .For the description of mechanical strength properties the units of N/mm<sup>2</sup> or MPa are most commonly used:
1 MS/m = 1 m/Ωmm<sup>2</sup>
1 MPa = 1 N/mm<sup>2</sup></ref> which with 58 MS/m (or m/Ωmm²) is only slightly below that of silver. Other advantages of copper are its high thermal conductivity, corrosion resistance, and its good ductility. The work hardening properties of ETP copper is illustrated in <xr id="fig:Strain hardening of Cu-ETP by cold working" />. The increase in strength achieved by cold working can be reversed easily by subsequent annealing. The softening properties are strongly dependent on the preceding cold working percentage ''(<xr id="fig:Softening of Cu-ETP after annealing for 3hrs after 25% cold working"/> and <xr id="fig:Softening of Cu-ETP after annealing for 3hrs after 50% cold working"/> <!--5.3)''-->.
The purity of technically pure and un-alloyed copper used for electrical applications depends on the type used and ranges between > 99.90 and 99.95
wt%. The copper types are designated mainly by their oxygen content as oxygen containing, oxygen-free, and de-oxidized with phosphorus as
described in DIN EN 1652 ''(<xr id="tab:MaterialDesignations"/> and <xr id="tab:tab5.2Composition of Some Pure Copper Types"/> <!--5.2)''-->. <xr id="tab:tab5.3Physical Properties of Some Copper Types"/> <!--Tables 5.3. --> and <xr id="tab:tab5.4Mechanical Properties of Some Copper Types"/> <!--5.4 --> show the physical and mechanical properties of these copper materials. According to these, Cu-ETP, Cu-OFE, and Cu-HCP are the types of copper for which minimum values for the electrical conductivity are guaranteed.
Cu-ETP is less suitable for welding or for brazing in reducing atmosphere because of the oxygen content (danger of hydrogen embrittlement).
<figtable id="tab:MaterialDesignations">
<caption>'''<!--Table 5.1: -->Material Designations of Some Copper Types'''</caption>
<table class="twocolortable" border="1" cellspacing="0" style="border-collapse:collapse">
<tr>
<th>WerkstMaterialEN-Designation</th><th>EN-Number</th><th>DIN-Designation</th><th>DIN-Number</th><th>UNS</th></tr>
<figtable id="tab:tab5.2Composition of Some Pure Copper Types"><caption>'''<!--Table 5.2: -->Composition of Some Pure Copper Types'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
<figtable id="tab:tab5.3Physical Properties of Some Copper Types"><caption>'''<!--Table 5.3: -->Physical Properties of Some Copper Types'''</caption>
<table class="twocolortable">
<figtable id="tab:tab5.4Mechanical Properties of Some Copper Types"><caption>'''<!--Table 5.4: -->Mechanical Properties of Some Copper Types'''</caption>
<table class="twocolortable" border="1" cellspacing="0" style="border-collapse:collapse">
</figtable>
<xr id="fig:Strain hardening of Cu-ETP by cold working"/> <!--Fig. 5.1: --> Strain hardening of Cu-ETP by cold working
<xr id="fig:Softening of Cu-ETP after annealing for 3hrs after 25% cold working"/> <!--Fig. 5.2: --> Softening of Cu-ETP after annealing for 3hrs after 25% cold working
<xr id="fig:Softening of Cu-ETP after annealing for 3hrs after 50% cold working"/> <!--Fig. 5.3: --> Softening of Cu-ETP after annealing for 3hrs after 50% cold working
<div class="clear"></div>
===<!--5.1.3 -->High Cu Content Copper Alloys===
The high Cu content alloy materials are closest in their properties to pure copper materials. By defined addition of small amounts of alloying elements it is possible to increase the mechanical strength and especially the softening temperature of copper and at the same time decrease the electrical conductivity only insignificantly <xr id="fig:Influence of small additions on the electrical conductivity of copper"/> <!--(Fig. 5.4)-->. Silver, iron, tin, zinc, nickel, chromium, zirconium, silicon, and titanium are used. Usually the additive amounts are significantly below 3 wt%. This group of materials consists of mixed crystal as well as precipitation hardening alloys. The precipiytion hardening copper-beryllium and copper-chromium-zirconium materials are decribed later in a separate section.
<figure id="fig:Influence of small additions on the electrical conductivity of copper">
</figure>
From the large number of high-Cu alloys only the properties of selected ones are covered here <xr id="tab:tab5.5Physical Properties of Selected High Cu Content Copper Alloys"/> <!--(Tab. 5.5) --> and <xr id="tab:tab5.6Mechanical Properties of Selected High Cu Content Copper Alloys"/> <!--(Tab. 5.6)-->. Some of these materials are not included in the EN standards system.
The low alloyed materials CuAg0.1 and CuCd1 are mostly used as overhead drive cables where they have to meet sustained loads at elevated temperatures without softening.
<figtable id="tab:tab5.5Physical Properties of Selected High Cu Content Copper Alloys"><caption>'''<!--Tab. 5.5 -->Physical Properties of Selected High Cu Content Copper Alloys'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
!Composition
!Density<br />[g/cm<sup>3</sup>]
!colspan="2" style="text-align:center"|Electrical<br />Conductivity<br />[MS/m] [% IACS]
!Electrical<br />Resistivity<br />[μΩ·cm]
!Thermal<br />Conductivity<br />[W/(m·K)]
!Softening Temperature<br />(approx. 10% loss in<br />strength)<br />[°C]
!Melting<br />Temp Range<br />[°C]
|-
!
!
!
![MS/m]
![% IACS]
!
!
!
!
!
!
|-
|CuAg 0,1<br />CW 013A
<figtable id="tab:tab5.6Mechanical Properties of Selected High Cu Content Copper Alloys"><caption>'''<!--Table 5.6; :-->Mechanical Properties of Selected High Cu Content Copper Alloys''' </caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
|-
|CuNi2Si
|R 430<sup>2)</sup><br />R 510<sup>2)</sup><br />R 600<sup>2)</sup>
|430 - 520<br />510 - 600<br />600 - 680
|> 350<br />> 450<br />> 550
These newer copper based materials optimize properties such as electrical conductivity, mechanical strength, and relaxation, which are custom tailored to specific applications. Typical uses include contact springs for relays, switches, and connectors.
===<!--5.1.4 -->Naturally Hard Copper Alloys===
Alloys like brasses (CuZn), tin bronzes (CuSN), and German silver (CuNiZn), for which the required hardness is achieved by cold working are defined as naturally hard alloys. Included in this group are also the silver bronzes (CuAg) with 2 – 6 wt% of Ag.
Main Articel: [[Naturally Hard Copper Alloys| Naturally Hard Copper Alloys]]
===<!--5.1.5 -->Other Naturally Hard Copper Alloys===
Main Articel: [[Other Naturally Hard Copper Alloys| Other Naturally Hard Copper Alloys]]
===<!--5.1.6 -->Precipitation Hardening Copper Alloys===
Besides the naturally hard copper materials precipitation hardening copper alloys play also an important role as carrier materials for electrical contacts. By means of a suitable heat treatment finely dispersed precipitations of a second phase can be achieved which increase the mechanical strength of these copper alloys significantly.
Main Articel: [[Precipitation Hardening Copper Alloys| Precipitation Hardening Copper Alloys]]
===<!--5.1.7 -->Application Properties for the Selection of Copper Alloys===
Important for the usage as spring contact components are besides mechanical strength and electrical conductivity mainly the typical spring properties such as the maximum spring bending limit and the fatigue strength as well as the bendability. During severe thermal stressing the behavior of spring materials is determined by their softening and relaxation. The following briefly describes these material properties.
Main Articel: [[Application Properties for the Selection of Copper Alloys| Application Properties for the Selection of Copper Alloys]]
===<!--5.1.8-->Selection Criteria for Copper-Based Materials===
If current carrying capability is the key requirement, mechanical strength may have to be sacrificed as for example in carrier parts for stationary contacts. In this case, depending on the current level, pure copper or low alloyed copper materials such as CuSn0.15, or for economic reasons CuZn30, may be suitable.
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:tab5.21Physical Properties of Nickel and Nickel Alloys"/> <!--(Tab. 5.21) --> and <xr id="tab:tab5.22Mechanical 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
</div>
<div class="clear"></div>
===<!--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
</div>
<figtable id="tab:tab5.21Physical 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"
|-
!Material<br />Designation<br />WST-Nr.<br />EN UNS
!Composition<br />[wt%]
!Density<br />[g/cm<sup>3</sup>]
!colspan="2" style="text-align:center"|Electrical<br />Conductivity<br />[MS/m] [% IACS]
!Electrical<br />Resistivity<br />[μΩ·cm]
!Thermal<br />Conductivity<br />[W/(m·K)]
!Melting<br />Temp Range<br />[°C]
|-
|-
|CuBe2Ni 99,2<br />CW101C2.4066<br />C17200|Be 1.8 - 2.117740<br />Co 0.3N02200<br />Ni 0.3<br />Cu Rest|8Mn < 0.3|8 - 935<supbr />aCu </sup>0.25<br />12 - 13Si <sup>b</sup>0.25<br />11Fe <sup>c</sup>|14 - 160.4<br />21 - 22C <br />19|11 - 120.5<sup>a01<br /sup><br /Ni >799.7 - 2|8.3<sup>b</sup><br />9|11|19|9.1<sup>c</sup>0|11070,5|1713.0|125<sup>a</sup><br />135<sup>b</sup>207|ca. 380450|870 - 9801140
|-
|CuCo2BeNiCu30Fe<br />CW104C2.4360<br />17743<br />C17500N04400|Co 2.0 Cu 28 - 2.834<br />Be 0.4 Fe 1 - 02.75<br />Ni 0.3Rest<br />Cu RestBe 1.85 - 2.05
|8.8
|11 - 2.1|3.6|48.0|22|14<sup>a</sup><br />25 .0|185|ca. 420|1300 - 27<sup>b</sup><br />27 1350|- 34<sup>c</sup>|19 - 24NiBe2<br />43 - 47<br />47 - 59N03360|7Ti 0.1 4 - 90.1<sup>a</sup>6<br />Ni Rest|8.3.7 - 4|5.0<sup>ba</sup><br />|8.6|0.2.9<sup>ca</sup>|48|14.4
|210
|18|1311380|}</figtable> <sup>a</sup>solution annealed, and hardened <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"|-!Material!Hardness<br />Condition!Tensile Strength R<sub>m</sub><br />[MPa]!0,2% Yield Strength<br />R<sub>p02</sub><br />[MPa]!Elongation<br />138A<sub>50<sup/sub><br />[%]!Vickers<br />Hardness<br />HV!Spring Bending<br />Limit σ<sub>FB</sub><br />[MPa]!Fatigue<br />Strength σ<sub>BW</sub><br />[MPa]|-|Ni99,2|R 380|≥ 380|≥ 100|≥ 40|≥ 100|||-|NiCu30Fe|R 400<br />R 700|400 - 600<br />b700 - 850|≥ 160<br /sup>≥ 600|ca. 450≥ 30<br />≥ 4|1030 95 - 125<br />200 - 1070240||
|-
|CuNi2BeNiBe2|R 700<br /sup>CW110Ca<br /sup>C17510|Ni 1.4 - 2.2<br />Be 0.2 - 0.6R 1300<sup>a<br /sup>Co 0.3<br />Cu Rest|8.8|11 - 14R 1500<sup>ab</sup><br />25 - 27R 1900<sup>b</sup><br />27 - 34R 1800<sup>c</sup>|19 - 24≥ 700<br />≥ 1300<br />43 - 47≥ 1500<br />47 - 59≥ 1900<br />≥ 1800|7.1 - 9.1≥ 300<supbr />a≥ 1200<br /sup>≥ 1100<br />3.7 - 4.0≥ 1750<supbr />b≥ 1700|≥ 30<br /sup>≥ 1<br />2.9≥ 12<supbr />c≥ 1<br /sup>≥ 5|230≥ 170<br />≥ 370<br />≥ 450<br />≥ 520<br />≥ 500|18<br /> <br /> <br /> <br />≥ 1400|131<supbr />a<br /sup><br />138<sup>b<br /sup>|ca. 480|1060 - 1100≥ 400
|}
</figtable>
<sup>c</sup>solution annealed, cold rolled, and precipitation hardened at mill (mill hardened)
<figure id="fig:Phase diagram of nickel beryllium">
</figure>
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">
Nickel-beryllium alloys are recommended for mechanically and thermally highly stressed spring components. For some applications their ferro-magnetic properties can also be advantageous.
==<!--5.3 -->Triple-Layer Carrier Materials==
Manufacturing of triple-layer carrier materials is usually performed by cold rollcladding. The three materials cover each other completely. The advantage of this composite material group is that the different mechanical and physical properties of the individual components can be combined with each other.
The thickness ratios of the components can be selected according to the application requirements. The two outer layers usually have the same thickness.
==<!--5.4 -->Thermostatic Bimetals==
Thermostatic bimetals are composite materials consisting of two or three layers of materials with different coefficients of thermal expansion. They are usually bonded together by cladding. If such a material part is heated either directly through current flow or indirectly through heat conduction or radiation, the different expansion between the active (strong expansion) and passive (low expansion) layer causes bending of the component part.
*'''Stamped and formed parts''' for special designs and applications
The wide variety of thermostatic bimetal types is specified mostly through DIN 1715 and/or applicable ASTM standards <xr id="tab:tab5.23Partial Selection from the Wide Range of Available Thermo-Bimetals"/> <!--(Table 5.23)-->. The different types have varying material compositions for the active and passive side of the materials. The mostly used alloys are iron-nickel and manganese-copper-nickel. Mainly used in circuit protection switches (i.e. circuit breakers) some thermo-bimetals include an intermediate layer of copper or nickel which allows to design parts with a closely controlled electrical resistance.
<figtable id="tab:tab5.23Partial Selection from the Wide Range of Available Thermo-Bimetals"><caption>'''<!--Table 5.23: -->Partial Selection from the Wide Range of Available Thermo-Bimetals'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
</figtable>
===<!--5.4.1 -->Design Formulas=== For the design and calculation of the most important thermostatic-bimetal parts formulas are given in <xr id="tab:Design Formulas for Thermostatic Bimetal Components"/><!--Table 5.24-->. The necessary properties can be extracted for the most common materials from <xr id="tab:Partial Selection from the Wide Range of Available Thermo-Bimetals"/><!--Table 5.23-->. The values given are valid only for a temperature range up to approximately 150°C. For higher temperatures data can be obtained from the materials manufacturer.
<figtable id="tab:tab5.24Design Formulas for Thermostatic Bimetal Components"><caption>'''<!--Table 5.24: -->Design Formulas for Thermostatic Bimetal Components'''</caption>
{| class="twocolortable" style="font-size:1em;"
|}
===<!--5.4.2 -->Stress Force Limitations===
For all calculations according to the formulas in <xr id="tab:tab5.24Design Formulas for Thermostatic Bimetal Components"/> <!--Table 5.24 --> one should check if the thermally or mechanically induced stress forces stay below the allowed bending force limit. The following formulas are applicable for calculating the allowable load (Force P<sub>max</sub> or momentum M<sub>max</sub>):
<table class="twocolortable" style="text-align: left; font-size:12px;width:60%">
<tr>
<td>Single side fixed strip</td>
<td><math>P_{max} <
\frac {\sigma Bs^2}{6L} </math> </td>
</tr><tr>
<td>Both sides fixed strip</td>
<td><math>P_{max} <
\frac {\sigma Bs^2}{1,5L} </math></td>
</tr><tr>
<td>Spiral or filament </td>
<td><math>M_{max} <
\frac {\sigma Bs^2}{6} </math></td>
</tr><tr>
<td>Disc </td>
<td><math>P_{max} <
\frac {2 \sigma s^2}{3} </math></td>
</tr>
</table>
<math>\sigma</math> = bending stress
Kreye, H.; Nöcker, H.; Terlinde, G.: Schrumpfung und Verzug beim Aushärten von Kupfer-Beryllium-Legierungen. Metall 29 (1975) 1118-1121
[[de:Trägerwerkstoffe]]
