Development and Turbine Engine Performance of Three Advanced Rhenium Containing Superalloys for Single Crystal and Directionally Solidified Blades and Vanes

Abstract

Turbine inlet temperatures over the next few years will approach 1650°C (3000°F) at maximum power for the latest large commercial turbofan engines, resulting in high fuel efficiency and thrust levels approaching 445 KN (100,000 lbs.). High reliability and durability must be intrinsically designed into these turbine engines to meet operating economic targets and ETOPS certification requirements. This level of performance has been brought about by a combination of advances in air cooling for turbine blades and vanes, design technology for stresses and airflow, single crystal and directionally solidified casting process improvements, and the development and use of rhenium (Re) containing high γ′ volume fraction nickel-base superalloys with advanced coatings, including full-airfoil ceramic thermal barrier coatings. Re additions to cast airfoil superalloys not only improves creep and thermo-mechanical fatigue strength, but also environmental properties including coating performance. Re dramatically slows down diffusion in these alloys at high operating temperatures. A team approach has been used to develop a family of two nickel-base single crystal alloys (CMSX-4® containing 3 percent Re and CMSX®-10 containing 6 percent Re) and a directionally solidified, columnar grain nickel-base alloy (CM 186 LC® containing 3 percent Re) for a variety of turbine engine applications. A range of critical properties of these alloys is reviewed in relation to turbine component engineering performance through engine certification testing and service experience. Industrial turbines are now commencing to use this aero developed turbine technology in both small and large frame units in addition to aero-derivative industrial engines. These applications are demanding, with high reliability required for turbine airfoils out to 25,000 hours, with perhaps greater than 50 percent of the time spent at maximum power. Combined cycle efficiencies of large frame industrial engines are scheduled to reach 60 percent in the U. S. ATS programme. Application experience to a total 1.3 million engine hours and 28,000 hours individual blade set service for CMSX-4 first stage turbine blades is reviewed for a small frame industrial engine.

Formation of an Intermediate Layer Between Grains in Nickel-Based Superalloy Turbine Blades

“…[3] This slow ramp is due to the proximity of the c¢ solvus to the melting point. [12] To identify any grain defects which could be observed on the surface of the component, the blades were etched to allow visual inspection. The preferential attack into the boundary by the etchant enabled the inspection for secondary grains on the surface of the blades.…”

High Resolution Experimental and Computational Methods for Modelling Multiple Row Effusion Cooling Performance

“…As a consequence, the last fifty years have seen temperatures at entry to the high pressure (HP) turbine rise by over 500 K with turbine blade operating temperatures now in excess of the material's engineering limits [1]. This has necessitated increasingly complex methods of internal convective cooling on the inside of the blade surface and external film cooling, which acts to shield the blade from the hotter core gas.…”

New Single Crystal Superalloys, CMSX®-7 and CMSX®-8

“…Rhenium has been widely used in advanced single crystal superalloys for turbine blade, vane and seal segments due to its potent effect in slowing diffusion and hence creep deformation and fatigue crack initiation under high temperature operating conditions [3]. High temperature creep resistance and fatigue properties are directly related to the useful service life of gas turbine components and turbine engine performance such as power output, fuel burn and carbon dioxide emissions.…”