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UM E-Theses Collection (澳門大學電子學位論文庫)

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Title

Laser surface modification of copper for corrosion and electrical wear resistance

English Abstract

Commercial pure copper (cp Cu) is an excellent electric contact material due to its high electrical and thermal conductivities, high ductility, ease of fabrication and reasonable affordability. However, its major drawbacks are low hardness, low wear resistance, and susceptibility to corrosion in chloride-containing media. In order to improve its corrosion and wear resistance, laser surface modification of cp Cu with tungsten (W), titanium (Ti) and nitinol (NiTi) was attempted using a 2.3-kW CW high-power diode laser. The corrosion characteristics of the laser-modified samples in 3.5 wt.% NaCl solution and synthetic acid rain (SAR) at 25 oC were studied by means of potentiodynamic polarization and immersion test. Electrical wear tests in dry and wet conditions were conducted using a pin-on-disc tribometer at a normal load of 50 N, sliding speeds of 40 km/h and 60 km/h, with and without electric current. The microstructures, compositions, phases present and wear mechanisms before and after corrosion and electrical wear tests were investigated by SEM, EDX and XRD. Surface hardness and interfacial contact resistance were also examined. The corrosion and electrical wear resistance of all laser-modified samples are enhanced. In particular, the corrosion resistance of cp Cu laser-alloyed with Ti is the highest and is 160 times higher than that of cp Cu. The increase in corrosion resistance is due to the presence of protective oxide layer which acts as a barrier for corrosion attack. Whereas, cp Cu laser-alloyed with NiTi possesses superior electrical wear resistance which is enhanced by three orders of magnitude as compared with cp Cu. The improvement in electrical wear resistance is due to the presence of martensitic NiTi phase, reinforcement with intermetallic phases and the work hardening effect during electrical sliding wear tests. iii Among all the laser-modified samples, cp Cu laser-alloyed with NiTi has excellent corrosion and wear resistance but moderate hardness. Its interfacial contact resistance is close to that of cp Cu and suggesting that it is a good candidate for electrical contact applications.

Issue date

2016

Author

Wong, Po Kee

Faculty

Faculty of Science and Technology

Degree

Ph.D.

Subject

Copper -- Corrosion

Corrosion and anti-corrosives

Electromechanical Engineering -- Department of Electromechanical Engineering

Supervisor

Kwok, Chi Tat

Man, H. C.

Files In This Item

Full-text (Intranet)

Location
1/F Zone C
Library URL
991001890009706306