Development of a Corrosion Resistant Directionally Solidified Material for Land Based Turbine Blades

Abstract

Advanced turbines with improved efficiency require materials that can operate at higher temperatures. Availability of these materials would minimize cooling flow requirements, and, thus, improve the efficiency of a turbine. Advanced processing. such as directional solidification (DS), can improve temperature capability of the majority of Ni based superalloys. However, results of earlier work on IN-738 reveal that the DS process does not significantly improve temperature capability of this alloy. A research program was initiated to develop a corrosion resistant Ni-based DS blade material for land based turbines. In this program, eight heats with varied Cr, Al, Ti, Ta, and W contents were selected for evaluation. Screening tests performed on these heats in the DS condition include tensile, creep, and corrosion. The Results of experimental heats were compared with those of IN-738 in the equiaxed condition. From these results, two chemistries offering approximately 100°F temperature advantage at typical row I turbine blade operating stress were selected for castability and further mechanical property evaluation. Several row 1 solid and cored turbine blades were successfully cast. The blades were evaluated for grain structure and mechanical properties. Tests were also conducted to evaluate the effects of withdrawal rates on properties. These results are summarized in this paper.