Improvement of grain structure and mechanical properties of a land based gas turbine blade directionally solidified with liquid metal cooling process

The manufacturing process of a directionally solidified (DS) IN738LC turbine blade, produced with the liquid metal cooling (LMC) process was improved based on process modelling. The improvement involved varying the system dimensions in the baffle area and optimising the mould thickness, design and the withdrawal parameters. The grain structure of the DS blades produced exhibits a well defined <001>. texture with a few stray grains near the blade top compared to the previous design. Some blades were given to a two stage heat treatment followed by tension tests at 25 and 650°C as well as creep tests at 152 MPa/982°C and 340 MPa/850°C. The yield and tensile strength of improved DS blades were comparable to conventionally cast (CC) IN738LC blades, while the creep properties and the tensile elongation of the DS blades were significantly improved using the optimised LMC process. The LMC system is under more modifications to produce defect free single crystal turbine blades.