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Brazing (or hard brazing) is a joining process that takes place at temperatures above 450 °C. It creates joints between materials that are stronger than typical soft-soldered joints. Brazing is used where welding is not possible due to material-related constraints.


CEP DISCUP® is a powder-metallurgical, copper-based high-temperature material produced by means of the RMMA process. An ultra-fine microstructure and dispersion strengthening are achieved through the targeted addition of aluminium oxide and other dispersion formers to pure copper powder. The materials are thus classified as ODS coppers (oxide dispersion strengthened coppers). CEP DISCUP® is a registered trademark of CEP Freiberg.

Conductivity, electrical

The ability of a material to conduct electric current. Often measured in Siemens per metre, but also in % IACS (the percentage of conductivity compared to that of pure annealed copper). Good electrical conductivity in metals is usually associated with good thermal conductivity.

Hardness and electrical conductivity: CEP DISCUP® in comparison to other conductor materials.

GLIDCOP is an ODS copper from Höganäs AB.

Dispersion strengthening

Increasing the hardness, strength and toughness of materials by means of precipitates (dispersions) through the addition of dispersion formers. The effect of the precipitates is to increase the deformation resistance of the material by hindering the movement of natural defects in the metal’s atomic lattice – so-called ‘dislocations’. Dislocation movement is the metallo-physical prerequisite for any deformation. At the same time, a very fine microstructure ensures that barriers to critical dislocation cannot form – a phenomenon that would lower the fracture resistance of the material.

Electric arc resistance

Resistance to the damage caused to contact materials in the high-voltage range due to arcing. A lack of arc resistance manifests itself in undesirable electro-erosion (“flashing loss”) or local melting, which leads to the contact partners sticking together (sticking tendency).


An umbrella term for typical wrought alloys made of copper and other metals (Ni, Be, Co, Cr, Zr), which are used as a material in electrical engineering (wires and contacts) and which exhibit a slightly higher hardness, strength and heat resistance than pure copper.

Electrolytic copper

Another term for pure copper. Copper with a high degree of purity as produced by electrolysis. Primarily used as a material in electrical engineering (wires and contacts), and which exhibits low hardness, strength and heat resistance

Extrusion, hydrostatic

In hydrostatic extrusion, a preformed billet of material is heated to the forming temperature. A ram then presses the billet through a die into a cavity, called the recipient. During this process, the billet is surrounded by a pressurised fluid (usually oil), such that the compressive force is transmitted in a finely distributed manner. This allows the processing of materials that are sensitive or otherwise difficult to form. Hydrostatic extrusion is a discontinuous extrusion process that produces short bars or tubes – one press at a time. CEP Freiberg uses the process to produce composite tubes made of CEP DISCUP®+Cu. To create the tube, a mandrel is fed inside the container during the extrusion process, with the mandrel used to create different internal cross-sections as well as different internal geometries.

Hydrostatic extrusion, functional diagram

Extrusion, indirect

With indirect extrusion, a preformed block of raw material (the green compact or “green body”) is heated to the forming temperature and placed in a recipient. In contrast to the typical direct extrusion process, a ram then presses the recipient against a die, which is mounted on a fixed hollow stem. This results in lower frictional forces and, thus, higher efficiency. It is a discontinuous extrusion process in which each extrusion procedure produces bars in the diameter range of from 8 mm to 30 mm.

Indirect extrusion, functional diagram


This material property is defined by the penetration depth of a reference indenter pressed into the surface of the material under standard conditions. There are a number of different hardness measurement scales. One of the most common is Vickers hardness (HV), which is measured using a pyramid-shaped diamond-tipped indenter.

Hardness and electrical conductivity: CEP DISCUP® in comparison to other conductor materials.

GLIDCOP is an ODS copper from Höganäs AB.

Heat resistance

Heat resistance describes the resistance of a material to softening through recrystallisation. It serves as an umbrella term describing the preservation of certain material properties – primarily hardness and strength, but also wear resistance – after the material has been temporarily exposed to high temperatures. Temperatures above the recrystallisation temperature – which would normally change the material’s structure – are of particular importance.

The recrystallisation temperature can be exceeded during production as well as during the use of the material, thus negating previous measures to increase the material’s strength. While the recrystallisation temperature of steels, for example, ranges from 550 °C to 700 °C, CEP DISCUP® can recover its properties even after operation at temperatures of up to 900 °C.

Comparison of the hardness of CEP DISCUP®, pure copper and CuCr1Zr at room temperature after annealing

Machinability, mechanical

Machinability refers to the suitability of a material for machining, i.e., for drilling, milling, turning, grinding or polishing. It is influenced by the hardness and the microstructure of the material. It is not only very hard materials that are difficult to machine: Very soft materials, such as electrolytic copper, pose a problem too – they tend to “smear”. Dispersion-hardened powder-metallurgical materials, on the other hand, are easy to machine.

Powder metallurgy

Powder metallurgy is a subdomain of metallurgy, in which materials are processed from powdered metallic raw materials by means of pressing or sintering and additional processes into metallic semi-finished products or finished components. Such products exhibit different property profiles than typical materials produced by melting metallurgy (i.e., wrought alloys).

Precipitates, non-metallic

Precipitates (dispersions) are microscopic particles in the form of chemical compounds (oxides, nitrides, carbides, carbonitrides) that are finely distributed and embedded in the microstructure of metals. While they can occur as a result of impurities, they can also be produced intentionally by alloying – with the aim of dispersion strengthening. Alloying is carried out by adding the materials (i.e., alloying elements & compounds) to the molten metal.

In powder metallurgy, precipitations can also be achieved with the same effect through intense mechanical contact with the metal in a “cold” process (e.g., the RMMA process).

RMMA Process

RMMA is the abbreviation for “Reaction Milling/Mechanical Alloying”. RMMA is a “cold” manufacturing processes for powder-metallurgical materials used at CEP Freiberg. A mixture of pure copper powder, alloying additives and dispersion formers is ground intensively in a ball mill according to a very specific grinding regime. Through repetitive pulverisation and cold-welding processes, ultrafine, thermally stable oxides and carbides are formed as precipitates and finely dispersed in the copper matrix. A so-called ODS copper (oxide dispersion strengthened copper) is produced – initially in granulate form. This is then further processed into semi-finished or finished products by forming processes such as extrusion.

CEP DISCUP®-type copper-based high-temperature materials manufacturing process

Sticking tendency

This term refers to the tendency of electrical contact materials in the high-voltage range to stick to their contact partner when the contact is closed due to arcing between the contacts. In this respect, a high sticking tendency is also an expression of low electric arc resistance.


Strength and ‘strength properties’ are umbrella terms for those properties of a material that are defined, essentially, in terms of the parameters of the static tensile test. One of the most important is the 0.2 % yield strength (Rp0.2), the stress that results in precisely 0.2 % plastic elongation. For copper and copper materials, the value lies between 160 and 340 MPa, with high-strength structural steels having values of between 340 and 960 MPa. The second important parameter is the ultimate tensile strength (i.e., the stress at fracture). The value for copper and copper materials lies between 200 and 400 MPa, and for high-strength structural steels between 520 and 1,150 MPa.

Strength-memory property

Strength memory is a special property of CEP DISCUP® material, and it results from the dispersion strengthening mechanism. If the material is heated above its recrystallisation temperature, it does not lose its strength permanently – unlike typical metals. The strength of the material restores itself after cooling; softening due to overheating is reversed by the strength-memory property.

Comparison of the microstructures of CEP DISCUP®, pure copper and CuCr1Zr before and after heat treatment


Toughness is the resistance of a material to crack initiation and sudden fracture under mechanical stress. It is determined in special tests, e.g., the notched bar impact test, or in fracture mechanics testing. Especially at low temperatures and under the influence of ionising radiation, many typical metallic materials lose their toughness – they become brittle. Dispersion-strengthened powder-metallurgical materials, on the other hand, are often tougher and more resistant.

Wear resistance

An umbrella term for the resistance of materials to various types of frictional wear, e.g., adhesive or abrasive wear. This refers to damage to the surface of a material, often caused by friction between materials that have been paired together. The influences of oxidation and temperature are usually also involved, so that it becomes a question of resistance to complex wear stresses, e.g., high-temperature wear and spark erosion. Dispersion-hardened powder-metallurgical materials often achieve better values in this respect than typical metals.