Purpose: To investigate the effect of addition of nickel on the microstructure, hardness and tribological properties of cobalt-based hardfacing alloy (Stellite 12) deposited by plasma transferred arc (PTA) welding technique. Design/methodology/approach: Microstructural characterization was carried out on deposited layers by utilising X-ray diffractometer and energy dispersive X-ray (EDX) equipped scanning electron microscope (SEM). Mechanical properties of the coatings were determined by hardness measurements and sliding wear tests. Hardness of the deposited layers was evaluated in HV scale. Wear tests were conducted under normal load of 3 N at room temperature (RT), 300 and 500ºC. Findings: Microstructural studies revealed that addition of nickel into Stellite 12 alloy dominated FCC crystal structure in the cobalt rich solid solution matrix rather than HCP crystal structure. Furthermore, nickel addition reduced the hardness and wear resistance of the deposited layer at room temperature. Nickel containing Stellite12 deposited layers demonstrated better wear resistance as compared to a Stellite12 deposited layer at high temperatures (300 and 500°C) owing to the formation of stable oxide layer on the worn surface. Practical implications: Determining the sliding wear performance of Stellite 12 alloy deposited layer which nickel is added to enhance the corrosion resistance in harsh environments. Originality/value: The investigation of high temperature wear performance of Stellite 12 alloy deposited layer upon addition of nickel.