Beryllium copper

Beryllium copper, also known as copper beryllium, CuBe or beryllium bronze, is a metal alloy of copper and 0.5 to 3% beryllium, and sometimes with other alloying elements, and has significant metalworking and operating performance qualities.

Properties
Beryllium copper is a ductile, weldable, and machinable alloy. It is resistant to non-oxidizing acids (for example, hydrochloric acid, or carbonic acid), to plastic decomposition products, to abrasive wear and to galling. Furthermore, it can be heat-treated to improve its strength, durability, and electrical conductivity.

As beryllium is toxic there are some safety concerns for handling its alloys. In solid form and as finished parts, beryllium copper presents no particular health hazard. However, breathing its dust, as formed when machining or welding may cause serious lung damage. Beryllium compounds are known human carcinogens when inhaled. As a result, beryllium copper is sometimes replaced by safer copper alloys such as Cu-Ni-Sn bronze.

Uses
Beryllium copper is used in springs and other parts that must retain their shapes during periods in which they are subjected to repeated strain. Due to its electrical conductivity, it is used in low-current contacts for batteries and electrical connectors. And because it is non-sparking but physically tough and non-magnetic, it is used to make tools that can be used in explosive environments.

Beryllium copper is also frequently used in the manufacture of professional-quality percussion instruments, especially tambourine and triangle, where it is prized for its clear tone and strong resonance. Unlike most other materials, an instrument composed of beryllium copper will maintain a consistent tone and timbre for as long as the material resonates. The "feel" of such instruments is rich and melodious to the point that they seem out of place when used in darker, more rhythmic pieces of classical music.

Beryllium copper has also found use in ultra-low temperature cryogenic equipment, such as dilution refrigerators, because of its combination of mechanical strength and relatively high thermal conductivity in this temperature range.

Alloys
High strength beryllium copper alloys contain up to 2.7% of beryllium (cast), or 1.6-2% of beryllium with about 0.3% cobalt (wrought). The high mechanical strength is achieved by precipitation hardening or age hardening. The thermal conductivity of these alloys lies between steels and aluminium. The cast alloys are frequently used as material for injection molds. The wrought alloys are designated by UNS as C172000 to C17400, the cast alloys are C82000 to C82800. The hardening process requires rapid cooling of the annealed metal, resulting in a solid state solution of beryllium in copper, which is then kept at 200-460 °C for at least an hour, facilitating precipitation of metastable beryllide crystals in the copper matrix. Overaging is avoided, as an equilibrium phase forms that depletes the beryllide crystals and reduces the strength enhancement. The beryllides are similar in both cast and wrought alloys.

High conductivity beryllium copper alloys contain up to 0.7% beryllium, together with some nickel and cobalt. Their thermal conductivity is better than of aluminium, only a bit less than pure copper. They are usually used as electric contacts in connectors.