Microstructure and Microhardness of a Laser Additive Forming Repaired Steam Turbine Blade

The laser additive forming repair (LAFR) of a damaged turbine blade with pre-fabricated defects was carried out. The parameters were as follows: the laser power 800 W, the laser beam diameter 3 mm, the laser beam moving speed 6 mm/s, the 17-4PH powder feeding speed 0.4 L/min. The microstructure and the microhardness were examined along the positions from the 2Cr13 matrix to the 17-4PH LAFRed zone top. The results showed that the pre-fabricated defects were repaired successfully. Three distinguished zones can be recognized, i.e., the column grain zone, the heat affected zone (HAZ), and the 2Cr13 martensite matrix. Optical microscopy and scanning electron microscopy analysis indicated that the LAFRed zone was free of pores and contained very fine martensite variants. The microhardness test results showed that the 2Cr13 matrix possessed the minimum microhardness of about 320 HV. The microhardness profile showed an oscillation feature with the peak value of 440 HV, which is believed to be the result of microstructure modification induced by the cyclic heat input during the LAFR processing. This study confirmed that 17-4PH is a promising material for the laser additive forming repairing of the damaged 2Cr13 steam turbine blade.