Know-how

Absorber, thermical

On one hand, „thermical absorbers“ represent certain components in solarthermics and photovoltaics area. On the other hand, and this is how it is understood here, the term represents highly efficient heat sinks in electron beam technology, nuclear technology, energy technology, and drive engineering. Their purpose is to prevent heat accumulations by collecting and dispatching local heat inputs that would otherwise damage the facility. Thermical absorbers are counted among the so-called CT applications.

Adhering tendency

There is a tendency for electrical contact materials in the high voltage range to stick together with the contact partner when the contact closes due to flash over arcs. Therefore high adhesion tendency also reflects lower arc resistance.

Arc resistance

Resistance to damage of contact materials in the high voltage range by flash over arcs. Lack of arc resistance shows itself in an undesirable electric erosion ("burning down") or localised melting, leading to the adhesion of the contact partners (adhering tendency).

Brazing

Brazing is a bonding technique carried out at temperatures above 450 °C. Resulting material bonds are stronger than classical soldering bonds. Brazing will be applied when welding is impossible for material reasons.

CEP DISCUP®

PM material on the basis of pure copper, generated by using the RMMA process. Targeted additions of aluminium oxide and other dispersion agents will lead to an ultra-fine grain structure and a dispersion strengthening effect. CEP DISCUP® is a registered trademark of CEP Freiberg.

Conductivity, electrical

Ability of a material to conduct electric current. Often measured in Siemens per meter, but also in % IACS (Percentage of the conductivity compared with annealed pure copper). As for metals in general, a good electrical conductivity will be accompanied by a good thermal conductivity too.

Contact tip

Also called: welding tip, welding nozzle, or contact tube. The ball-pen-like tool of a MAG, MIG or SMA welding machine. The welding rod passes through and leaves the welder through it. The contact tip has to conduct both electricity and heat perfectly without being affected by them. Therefore it is a typical CT application.

CT applications

Abbreviation for „conductivity temperature applications“. Refers to parts and components providing a high electrical as well as thermal conductivity and, at the same time, a high thermal stability. As for conventinal metals, both features are in contradiction to each other. However, copper-based high temperature materials are of a high conductivity and thermal stability as well.

Dispersion strengthening

Increasing hardness, strength and toughness of materials on the basis of dispersions caused by dispersion agents. The effect of the dispersions is to block the movement of certain natural defects in the metallic grid, the so-called dislocations. Dislocation movement is the metal-physical prerequisite for every deformation. At the same time, a very fine grain structure ensures that no critical dislocations pile-ups may occur which would reduce the fracture resistance of the material.

Dispersions, non-metallic

Dispersions are foreign microscopic particles as e.g. metallic compounds (oxides, nitrides, carbides, carbonitrides) which are embedded in the metal's texture in fine distributions. They occur naturally as contaminations but can also purposefully be generated to gain dispersion strengthening effects by adding alloying elements to the molten metal. In powder metallurgy dispersions with a similar effect can also be achieved in a "cold" way by intense mechanical contact (RMMA).

Electrics bronze

General term for classic wrought alloys of copper and other metals (Ni, Be, Co, Cr, Zr) which are used as materials in electrical engineering (cables and contacts). They are of a slightly higher hardness, strength and thermal stability than pure copper.

Electrolytic copper

Also: pure copper. Refers to a copper of high purity gained by electrolysis. It is primarily utilised as a material in electrical engineering (cables and contacts) and is of low hardness, strength and thermal stability.

Extrusion, hydrostatic

Special method to form metallic materials. It enables the production of pipes and bars with a very high dimensional precision. The material block is not directly pressed by the punch into the die, but is surrounded by a fluid, for example oil, that transfers the compression force onto it very smoothly.

Therefore even materials can be processed by hydrostatic extrusion that would otherwise be difficult to form. These include e.g. copper, aluminium and magnesium alloys which are developed, for example, for aerospace engineering. Niobium alloys, tantalum alloys and superconductor materials may be processed, too. Hydrostatic extrusion is also the method used by CEP Freiberg to transform workpieces made of powder metallurgic materials into semi-finished products.

hydrostatic extrusion

GLIDCOP

A powder metallurgic material provided by Höganäs AB. The dispersion strengthened material is based on copper and will be generated through spraying and smouldering. Aluminium oxide is utilised as a dispersion agent. The characteristics of GLIDCOP are basically similar to those of CEP DISCUP®.

GLIDCOP

Hardness and electrical conductivity of GLIDCOP compared to CEP DISCUP®

Hardness

A material characteristic which is defined by the penetration depth of an indented test body in the material surface under standardised conditions. There are different hardness measurement scales. One of the most common is the Vickers Hardness (HV) which is measured with a pyramid-shaped diamond tip.

Hot forming

Forming method carried out at temperatures above recrystallisation temperature of the material structure. Therefore, hot forming will not lead to cold work hardening. By purposeful conducting the temperature, especially at deceeding the recrystallisation temperature in the final stage of forming, nevertheless special microstructure effects may be generated in order to improve strength properties. Hydrostatic extrusion as well as isostatic extrusion are hot forming methods applied by CEP Freiberg.

Machinability

Machining properties or „machinability“ refer to the suitability of a material for chipping technology, therefore for drilling, milling, turning, grinding or polishing. It will be influenced by the hardness and the texture of the material. Not only very hard, but also very soft materials such as e.g. electrolytic copper are very difficult to process mechanically – they "smear". Dispersion strengthened PM materials are of a very good machinability.

ODS coppers

Abbreviation for "oxide dispersion strengthened copper". Material-related technical term for dispersion strengthened PM copper alloys such as CEP DISCUP® or GLIDCOP. They combine characteristics of different conventional metals in one PM material – characteristics that normally could not be combined.

Powder metallurgy

Powder metallurgy (PM) is a branch of metallurgy in which materials made of granular metallic raw materials are processed by pressing or sintering and additional procedures into semi-finished metal or finished parts. They indicate other characteristic profiles compared to traditional melting metallurgic materials (wrought alloys).

RMMA

Abbreviation for "reaction milling and mechanical alloying" and, in this combination, the term of a special "cold" forming method for PM materials which is applied by CEP Freiberg. Pure copper powder is milled intensively together with alloying additives and dispersion agents in a ball mill passing through a specific milling regime. By repeated crushing and cold welding processes, oxides and carbides will be transformed into segregations and finely dispersed into the copper matrix.

The result is a copper composite material with a homogeneous structure. The raw material consists of granules. They will be pressed to workpieces ("green bodies") then. These workpieces will subsequently be processed to semi-finished or finished products by hydrostatic extrusion or other forming processes.

RMMA

Production process of CEP DISCUP®

Stability, thermal

Refers to the resistance of a material to softening by recrystallisation. General term to describe the retention of certain material characteristics, usually the hardness and strength but also the wear resistance after the material has been exposed to high temperatures temporarily. In particular, temperatures above the recrystallisation temperature will cause modifications of the grain structure that deteriorate the above mentioned material properties. Recrystallisation temperature may be exceeded in both, manufacturing and application of a component, which counteracts previous measures to improve material properties. For example, while the recrystallisation temperature of steel is 550 °C to 700 °C, CEP DISCUP® achieves more than 900 °C.

thermal stability

Thermal stability of CEP DISCUP® compared with other copper materials

Strength

Strength and strength properties are general terms for material characteristics which are essentially defined through the parameters of the static tensile test. One of the most important is the 0.2% yield strength (Rp0.2), the tension that leads straight to 0.2% plastic strain. For copper and copper materials, this value is between 160 and 340 MPa, for higher-strength structural steels it is between 340 and 960 MPa. The second most important parameter is the tensile strength (failure stress). It lies between 200 and 400 MPa for copper and copper-based materials, for higher-strength structural steels it is between 520 and 1,150 MPa.

Strength memory

A special material property of CEP DISCUP®, resulting from dispersion strengthening. Unlike conventional metals this material will not lose its strength permanently when heated to temperatures above recrystallisation temperature. It will instead recover spontaneously after cooling.

strength memory

Toughness

Means a material´s resistance against crack initiation and brittle fracture under mechanical stress. Will be determined in special tests such as the notched-bar impact test or fracture mechanical testing. Especially at low temperatures and under the influence of ionising radiation, many conventional metals lose their toughness – they become brittle. Dispersion strengthened PM materials are however often more resistant.

Wear resistance

General term for the resistance of materials against various types of wear, for example, adhesive or abrasive wear. This deals with surface area material damage which often occurs caused by friction between material combinations. These influences are superimposed by oxidation and thermic effects, so that it comes to resistance against a complex wear stress e.g. high temperature wear and spark erosion. PM materials often perform better than conventional metals under such conditions.

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Literature

The following publications are thematically related to the work of CEP Freiberg:

  • Oxiddispersionsgehärtete Kupferlegierungen mit nanoskaligem Gefüge (Kudashov, D.; Diss. TU Bergakademie Freiberg, 2003);
  • Anwendungsoptimierte Cu-Werkstoffe durch PM-Technologie (Hofmockel, M., Forschungsarbeit 2008);
  • Erweiterung der Prozessgrenzen beim Strangpressen von Mg-Knetlegierungen (Swiostek, J., Diss. TU Hamburg-Harburg, 2008);
  • Large Hadron Collider – the guide. CERN FAQ. CERN Communication Group, February 2009
  • Scheuerlein, Chr. et al.: Mechanical Properties of the HL-LHC 11 T Nb3Sn Magnet Constituent Materials. In: IEEE Transactions On The Applied Superconductivity 27(2017)4