Laser surface alloying of copper with Ni-based hardfacing alloys for enhancing hardness and corrosion resistance by KAM WENG SENG Thesis Supervisor: Prof. KWOK CHI TAT Electromechanical Engineering Copper was successfully laser surface alloyed with Ni-Cr-Si-B alloys (Ni45 and Ni60) using a 2.3 kW high-power diode laser with beam diameter of 1 mm at powers of 1 to 2 kW and scanning speeds of 30 to 40 mm/s. The thickness of the alloyed layers are between 300 to 500 μm. Ni45 and Ni60 contain Nickel, Chromium, Boron and Carbon so various phases would be formed during laser surfacing. With BSE imaging, EDS and XRD analyses, Ni boride, Cr boride and Cr carbide were identified. The surface hardness was investigated along longitudinal and transverse directions. Generally, the hardness of the laser-alloyed specimens is 230 Hv. Hardness of the specimens which are processed with 1 kW and 40 mm/s is generally higher than the others because of the formation of NiCu matrix, the hardness is 800 Hv. However, the NiCu matrix do not continuously cover the whole layer, and it results in fluctuation of hardness. The hardness of different phases is measured. The hardness of NiCu matrix reaches 670 Hv, while the hardness of CuNi matrix is 250 Hv. Cr-rich phases performed high hardness as around 1400Hv. Laser-alloyed cooper with Ni45 and Ni60 performed similar corrosion behavior. Open circuit potential (OCP) measurement showed that all the specimens became nobler after laser surface alloying. On the other hand, based on the corrosion current density (Icorr), the corrosion resistance for the laser-alloyed specimens increased up to 24 times. Specimens which is laser-processed at 1 kW and 40 mm/s show the lowest Icorr, so those specimens have the lowest corrosion rate.