Laser consolidation of Ni-base IN-738 superalloy for repairing gas turbine blades

Abstract

A feasibility study on laser consolidation of IN-738 has been completed. The results show that the laser consolidation (LC) process can successfully build IN-738 thin-wall shapes on the cast IN-738 substrate without preheating. Optical microscope and SEM analysis revealed that the bond between the LC IN-738 and cast IN-738 substrate is metallurgically sound. No cracks or porosity was observed in the bond area, either in the cast IN-738 substrate or in the LC IN-738. The consolidated IN-738 shows a directionally solidified microstructure: very fine columnar dendrites growing almost parallel to the build direction (vertical direction). After the standard solution and aging treatments, near cuboidal shaped γ’ particles were observed in the consolidated IN-738. Room temperature testing showed that the tensile strength of the consolidated IN-738 is about 1270 MPa, which is 15% higher than that of the cast IN-738 material. The bond strength of the consolidated and cast IN-738 is higher than 900 MPa. Preliminary stress rupture testing at 1010°C (1850°F) and 55 MPa (8 ksi) indicates that the average stress rupture life of LC IN-738 specimens is 423 hours, which is about 150% longer than that of cast IN-738 baseline samples. The stress rupture life of the bond area of LC IN-738/cast IN-738 specimens falls within the range of the cast IN-738 baseline data. This study demonstrates that the laser consolidation process has the potential for repairing cast IN-738 blades with commercially available IN-738 alloy powder.