DEVELOPMENT OF A CORROSION-RESISTANT DIRECTIONALLY SOLIDIFIED MATERIAL FOR LAND-BASED TURBINE-BLADES

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 s uperalloys. However, results of earlier work on IN-738 reveal that the DS process does not significantly improve temperature capability of t his alloy. A research program was initiated to develop a corrosion res istant Ni-based DS blade material for land based turbines. In this pro gram, eight heats with varied Cr, Al, Ti, Ta, and W contents were sele cted for evaluation. Screening tests performed on these heats in the D S condition include tensile, creep, and corrosion. The results of expe rimental heats were compared with those of IN-738 in the equiaxed cond ition. From these results, two chemistries offering approximately 100 degrees F temperature advantage at typical row 1 turbine blade operati ng stress were selected for castability and further mechanical propert y evaluation. Several row 1 solid and cored turbine blades were succes sfully cast. The blades were evaluated for grain structure and mechani cal properties. Tests were also conducted to evaluate the effects of w ithdrawal rates on properties. These results are summarized in this pa per.