Microstructural evaluation of welded joints of ASTM Mar-M247 superalloy using ERNiCrMo-3 filler alloy

ABSTRACT

ASTM Mar-M247 is one of the superalloys used to manufacture gas turbine blades in power stations. This paper studies the microstructure across welded joints of a turbine blade made of a high-strength material (Mar-M247 alloy) employing AWS ERNiCrMo-3 as a filler alloy. This process was carried out using gas tungsten arc welding (GTAW). The dendritic and interdendritic structures were observed in the fusion zone. The results also showed the presence of epitaxial growth at the interface between the weld metal and the base alloy without solidification cracks. Al and Co concentrations gradually decrease towards the weld metal zone during the solidification process, while Cr content increases towards the fusion zone. Vickers hardness revealed that the hardness in the heat-affected zone (HAZ) is higher than that of the base metal and the weld metal zone, the average in the HAZ is 340HV, while in the base metal and the fusion zone is 322HV, 284HV respectively. Coarse grains in the HAZ were found with an agglomeration of carbides at the grain boundaries due to the input heat of the welding process.

Keywords
Gas turbine blade; Mar-M247; GTAW; Filler alloy; Microstructure; Hardness