| Abstract: |
The deposition of cavitation resistant materials coatings in turbine blades is an important way to reduce the cavitation damage. The cobalt stainless steel is a class of cavitation resistant steel. These alloys exhibit a great cavitation resistance because a high induced strain hardening, phase transformartion and lower stacking fault energy. Fe-Cr-Mn-Si is other class of steel that exhibit lower stacking fault energy and high induced strain hardening. This class of steel has many desoxidation elements and this aspect can be important for arc spraying materials. The influence of air pressure, voltage and chemical composition on the microstructure, oxide volumetric fraction, porosity, microhardness and cavitation resistance of the Fe-Mn-Cr-Si coatings were studied. Microstructures and properties of the manganese steel coatings were investigated by X-ray diffraction, optical and electronic microscopy, microhardness and ultrasonic cavitation test, ASTM G32-93. The increase in air pressure, 280 to 550kPa, modified the oxide fraction from 7,9% to 12,9%, in the SMA_Mn1 samples. The mass loss rate were 31,8, 25,8 and 37,2mg/h, respectively, for the samples with 280, 410 and 550kPa of the air pressure. For the SMA3 samples the increase in the arc voltage, from 25 to 35V reduce the oxide fraction from 15,3% to 13,4%. These aspect promote changes in mass loss rate from 43,8, 32,4 to 29,4mg/h for 25, 30 and 35V, respectively. The SMA_Mn2 and SMA_Mn5 mass loss rate (180A, 30V, 410kPa) are 27,1mg/h,and 27,4mg/h. Phase transformations occurred in the arc thermal spray coatings after cavitation tests. The SEM analysis verified that the mass loss in arc thermal spray coatings occurred because of the interlamellae oxide fracture and the splats delamination. Phase transformation in the splats was observed after the cavitation test. The modifications in the process parameters modified the cavitation resistance and was observed that 410kPa and 35V result in better performance.
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