Microstructure Engineering to Optimize Hardness and Conductivity in Electrolytic Tough Pitch Copper
- PDF / 3,889,422 Bytes
- 12 Pages / 593.972 x 792 pts Page_size
- 21 Downloads / 179 Views
NTRODUCTION
ELECTROLYTIC tough pitch (ETP) copper is commercially pure, high-conductivity copper. It is used for motor and transformer windings, residential wiring, electrical cables, and bus bars. Among these, motor and transformer windings and residential wiring (called building wire) require high strength, along with conductivity higher than 100 pct IACS, preferably reaching 102 pct IACS.[1,2] If conductivity can be improved without loss in strength, it will improve efficiency and reduce losses. Hence, there exist several studies focusing on either conductivity or strength with specific reference to the effect of defects on these properties. Electrical conductivity of metals depends on electron mobility and the distance which electrons can cover without scattering off any obstacles present. The obstacles typically present in the path of the electrons are impurity atoms, vacancies, dislocations, and internal boundaries—such as grain or phase boundaries. They lead to a decrease in conductivity, or, a rise in the inverse of conductivity, called resistivity. Total M.P. GURURAJAN and PRITA PANT are with the Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai 400076 India. Contact e-mail: [email protected] N. HARSHAVARDHANA is with the Department of Mechanical Engineering, SRM Institute of Science and Technology, Kattankulathur, Kancheepuram, Tamil Nadu 603 203, India. Manuscript submitted July 24, 2018. Article published online June 11, 2019 3566—VOLUME 50A, AUGUST 2019
resistivity (q) can be expressed as a sum of resistivities, each accounting for a different type of obstacle. This relation is called Matthiessen’s law: q = qt + qI + qd + qb.[3] In the case of commercially pure metals, the contributions of dislocations (qd), temperature (qt), and internal boundaries (qb) are significant, while the impurity contribution (qI) is negligible. On the other hand, in general, the defects that reduce conductivity (by scattering electrons moving through the crystal) lead to enhanced mechanical strength by impeding the movement of dislocations. Specifically, impurity atoms, dislocations, and boundaries lead to solute, work, and boundary strengthening, respectively. Hence, reports of a combination of high mechanical strength and high electrical conductivity are rare—but they do exist. For example, a combination of 95 pct International Annealed Copper Standard (IACS) conductivity and 610 MPa yield strength is reported in Reference 4, while 96.9 ± 1.1 pct IACS conductivity and 900 MPa yield strength is observed in electrodeposited samples.[5] Typically, samples with both high strength and high conductivity require specialized processing, such as high strain rate deformation at liquid nitrogen temperatures[4] or electrodeposition.[5] Such high strength and high conductivity combination is attributed to either bimodal grain structures or to the combined effects of ultrafine grains and optimal size and spacing of twins in these reports. Other processes such as severe plastic d
Data Loading...
