Copper (Cu) is widely used as electrical contact materials because of its relatively low electrical wear and low cost compared to metallic materials such as silver (Ag), platinum (Pt), palladium (Pd) and cadmium (Cd). However, the electrical and mechanical properties of copper are not good compared to other metal contacts.
The working conditions of contact materials require thermal, electrical, mechanical and chemical properties to be excellent. It is because when capacitive and inductive loads are switched on and off, the temperature of contact generated at the contact surface is high, with a large number of switches and high contact pressure, and they work under the conditions of electrical wear and mechanical wear caused by arc discharges. The electrical and mechanical properties are not negligible in contact materials.
Several methods have been applied to improve the properties of contact materials. Recently, worldwide research on carbon nanotubes (CNT) has been active and the range of their application has been extended. CNTs have been widely used as reinforcement materials for metal matrix composites because of their good mechanical, physicochemical and electrical properties.
The tensile strength of CNT is 50-200GPa and its modulus of elasticity is about 1TPa. When carbon nanotubes are added to copper matrix, the tensile and flexural strength of carbon nanotube reinforced copper matrix composites increases by over 20% compared to pure copper. In addition, carbon nanotubes can be either conductors or semiconductors depending on what angle the hexagonal ring takes on the tube wall. In the case of conductors, the electrical transport capacity of carbon nanotubes is 1×109A/cm2, which is 1 000 times higher than that of copper wires.
This indicates that carbon nanotubes can be incorporated into metal matrix to enhance the mechanical and electrical properties of metal matrix composites. The addition of carbon nanotubes, excellent carbon nanomaterial, is the best way to realize the refinement of the matrix microstructure. Carbon nanotubes are placed at the boundary of the matrix microstructure and hinder grain growth, and thus grain refinement has a positive effect on both strength and toughness.
Nevertheless, the content of carbon nanotubes should not be too high. Because of the large surface area of carbon nanotubes, carbon nanotubes with relatively large surface activation energy are easily aggregated and negatively affect the microstructure and properties of metal matrix.
Jon Song Won, a researcher at the Faculty of Material Science and Technology, investigated the effect of carbon nanotubes on the properties and texture of contact carbon nanotube reinforced copper matrix composites prepared by direct addition of carbon nanotubes by blocking them in molten state.
When the CNT content was 2.0vol.%, the grain size of the CNT-reinforced Cu matrix composites was 21-23μm, and grain refinement was observed in their microstructure. However, no change in size, distribution and shape of inclusions was observed. The electrical and mechanical properties of carbon nanotube reinforced copper matrix composites are as follows: Tensile strength is 315MPa, elongation is 12%, hardness is HB 80 and electrical resistivity is 0.017 3μΩ·m.