C14500 is the UNS designation for tellurium copper, usually shortened to TeCu. It is a high-conductivity copper to which a small, closely controlled amount of tellurium has been added so that the material can be machined at high speed on automatic lathes without the lead addition used in conventional free-cutting copper grades. The combination of machinability and conductivity makes it the workhorse material for machined electrical components.
Chemistry and How Tellurium Works
Tellurium is almost insoluble in solid copper. During solidification it forms a fine dispersion of copper telluride particles that interrupt the continuous chip, so swarf breaks into short pieces instead of forming long stringy turnings that wrap around the tool and damage the surface finish. The result is a machinability rating of roughly 90% of that of free-cutting brass, achieved while electrical conductivity remains above 90% IACS, which is far beyond what leaded or heavily alloyed coppers can offer.
Phosphorus is added at the same time in the range 0.004-0.012% to deoxidise the melt. Deoxidation matters because residual oxygen would otherwise form cuprous oxide at the grain boundaries and cause cracking during hot working and welding.
Specified Composition and Typical Properties
| Item | Value | Comment |
|---|---|---|
| Tellurium | 0.40-0.70% | Chip-breaking addition |
| Phosphorus | 0.004-0.012% | Deoxidiser |
| Copper incl. Te | 99.90% min | Balance of the composition |
| Density | about 8.94 g/cm³ | Little changed from pure copper |
| Electrical conductivity | about 93% IACS | Annealed condition, high-conductivity class |
| Thermal conductivity | of the order of 360 W/(m·K) | Tracks the electrical value |
| Machinability rating | about 90% of free-cutting brass | Reference rating 100 for free-cutting brass |
Mechanical values for commercial rod and bar are typically in the following bands; the applicable product standard sets the guaranteed minimum for the ordered temper.
| Temper | Tensile strength | Elongation | Typical use |
|---|---|---|---|
| O60 annealed | 200-260 MPa | 40% min | Heavy forming, busbar, general machining |
| H02 half-hard | 260-330 MPa | 15% min | Connectors, machined contacts |
| H04 hard drawn | 330-400 MPa | 8-12% | High-strength machined hardware |
Why Tellurium Is Used Instead of Lead
Historically, machinability in copper was obtained by adding lead, which forms a soft insoluble phase that lubricates the chip. Lead-bearing coppers are now restricted in electrical and electronic equipment and in automotive applications, and many buyers simply refuse to specify leaded grades. Tellurium delivers a similar chip-breaking effect through a hard, finely distributed telluride rather than a soft metallic phase, so components can be turned, drilled and tapped at production speeds while remaining fully lead-free.
Tellurium is handled as a controlled alloying addition. Melting and casting are carried out with extraction and ventilation because tellurium fume and dust must not be inhaled, and finished material is supplied in the deoxidised, oxide-free condition that reduces airborne dust during subsequent machining.
Fabrication and Processing Guidance
Machining: use sharp, positive-rake carbide tooling at high cutting speed and moderate feed; the telluride dispersion gives short chips and good surface finish with minimal built-up edge.
Cold working: C14500 cold forms acceptably in the annealed condition but has less ductility than C11000; severe bending and deep drawing should be planned around a fully annealed temper with intermediate stress relief.
Annealing: recrystallisation annealing is carried out in the 400-650 deg C range, and low-temperature stress relief at approximately 200-300 deg C removes forming stresses without destroying the temper.
Joining: soldering and brazing are straightforward and are the normal production methods. Fusion welding is not recommended, because the alloying dispersion that provides machinability is lost in the weld pool and the joint can crack; where welded assemblies are unavoidable, a weldable copper grade should be used for the welded portion.
Finishing: parts are usually supplied bright, with a light protective oil film or in a tinned condition when long-term tarnish resistance is required.
Applications
C14500 is specified wherever a component must be machined to tight tolerance and still carry current or conduct heat at high efficiency. Typical parts include high-current electrical connectors and terminals, contact tips and switchgear components, commutator segments, semiconductor lead frames, heat sinks and cold plates, welding fixtures and shunts, machined busbar fittings and general precision electrical hardware.
Inspection and Purchasing Points
Chemistry: verify tellurium and phosphorus by optical emission spectrometry on each heat, since both control machinability and conductivity respectively.
Electrical performance: confirm conductivity by eddy-current or four-terminal measurement rather than assuming it from the grade designation.
Oxygen content: a fully deoxidised structure is a prerequisite for hot working and for leak-tight machined parts.
Dimensions and surface: bar straightness, diameter tolerance and freedom from laps, seams and scale all affect tool life in high-speed machining.
Documentation: for restricted-market supply, the material certificate should state that no lead has been intentionally added to the analysis.
FAQ
Q: Is C14500 tellurium copper lead-free?
Yes. Tellurium, not lead, provides the chip-breaking behaviour, so the alloy contains no intentionally added lead and can be used where lead restrictions apply to copper alloys.
Q: How does C14500 compare with C11000 for conductivity?
C11000 reaches about 100% IACS while C14500 is normally quoted at about 93% IACS in the annealed condition. The small loss is the price paid for machinability that is roughly three times that of ordinary ETP copper.
Q: Which standards cover C14500 rod and bar?
Free-cutting copper rod, bar and shapes are covered by ASTM B301/B301M, and the Chinese designation for tellurium copper is listed in GB/T 5231. Mill certificates should state the Te and P analysis against these limits.
Q: Can C14500 be welded?
Brazing and soldering are commonly used and are reliable. Fusion welding is not recommended because the telluride dispersion is destroyed in the weld pool. Where a welded joint is essential, the design should use a weldable copper grade for that joint.
Q: What tempers are supplied?
Annealed, half-hard and hard-drawn rod and bar are standard, and special tempers are rolled or drawn to suit the machining and forming operations of the customer.
Q: How should C14500 be stored?
Keep bars in dry, sealed packing away from sulphur-bearing atmospheres, which cause rapid tarnishing. Tinned or oiled surfaces are recommended for long storage or sea freight.
