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Abstract
The necessity to reduce time and maintenance costs in electrical energy generation turbines promotes the development of new materials and processes to recover cavitated areas. Nowadays, different automated welding process have been studied, mainly plasma-transferred arc welding (PTA) in substitution of fluxed core arc welding (FCAW). The PTA process presents as its main advantages: low dilution, a narrow heat-affected zone and excellent arc stability; however, few cavitation resistant alloys are developed for this process. This paper aims to compare three cobalt cavitation resistant alloys deposited with the PTA process. The first alloy is a cobalt stainless steel alloy developed for the FCAW process, the second is a cobalt stainless steel alloy developed for the PTA process and the third is a national developed stainless steel alloy with cobalt. The samples were analysed by optical and electronic microscopy, microhardness and accelerated cavitation testing, ASTM G32-95. Results show that a refined austenitic microstructure was observed in all samples. The commercial alloys, developed for PTA welding, presented a better arc stability and lower quantity of defects. The national alloy demonstrated good results during deposition while the FCAW alloy presented better cavitation resistance.
Acknowledgements
The authors thank Cleide Marquese Engineering of the Federal University of Santa Catarina for carrying out the accelerated cavitation tests. They thank Prof. Ireneu of the X-ray Lab of the Federal University of the State of Parana for loaning the equipment to perform the tests. They also thank the company Durum do Brasil for the supply and discussions on the development of the Durcavit alloy and the Eutetic-Castolin company for supplying the Cavitec alloy.